Cellular micro 2

Gram positive bacteria features:

Stains purple (retains crystal violet dye)

thick peptidoglycan layer

contains lipoteichoic acid

cell wall contains teichoic acids

no outer membrane

periplasmic space has granular layer

produces exotoxins only

susceptible to penicillin and sulfonamide

Gram negative bacteria features:

Stains pink (acceps counterstain safranin)

thin peptidoglycan layer

has outer membrane which contains lipopolysaccharides, lipoproteins and phospholipids

no teichoic acid

periplasmic space has periplasm

produces endo and exotoxins

susceptible to streptomycin, chloramphenicol and tetracycline

3 domains of life

Archaea, bacteria and eukarya

phylogenetics is based on

16S ribosomal RNA gene sequences

Gram negative bacteria phyla:

Proteobacteria

Chlamydiae

Spirochaetes

Gram positive bacteria phyla:

Firmicutes

Tenericutes

Actinobacteria

Which are Low GC gram-positive bacteria, non-spore forming (firmicutes)

streptococcus

lactobacillus

Listeria

Mycoplasma

Lactic acid bacteria:

streptococcus

lactobacillus

Which are Low GC gram-positive bacteria,spore forming (firmicutes)

Clostridium

Bacillus

High GC gram positive bacteria

Streptomyces

Corynebacteria

Mycobacteria

Alphaproteobacteria:

Rickettsia

Can grow with low nutrients

Unusual morphology

Agriculturally significant - nitrogen fixation in symbiosis with plants

Also human and plant pathogen

Betaproteobacteria:

Bulkholderia

Bordatella

Gammaproteobacteria:

Enterobacteriaceae (Salmonella, Escherichia, Shigella)

Vibrionales

Epsilonproteobacteria

Campylobacterales (Campylobacter, Helicobacter)

Proteobacteria characteristics:

gram-negative

chemoheterotrophic

Rickettsia:

Alphaproteobacterium

obligate intracellular parasites

gram-negative, rod shaped bactria or coccobacilli

TRANSMITTED TO HUMANS VIA INSECT AND TICK BITES

induce phagocytosis and binary fission inside host cell

Spotted fever diseases

Epidemic typhus: Rickettsia prowazekii via lice

Endemic murine typhus: R.typhii via rat fleas

Rocky mountain spotted fever: R.rickettsii via ticks

Characterised by a spotted rash as it increases permeability of capillaries due to damage.

Burkholderia:

Betaproteobaceterium

Motile by a single polar flagellum or tuft of flagella

Burkholderia cepacia - aerobic gram-negative rod

Burkholderia psuedomallei - humans and farm animals in tropics/subtropics

Burkholderia mallei - glanders in horses

May grow in disinfectant

Burkholderia cepacia

Opportunistic infection in CF lung infections - metabolises respiratory secretions and chronic granulomatous disease patients

Resistant saprophyte in soil and water

Causes: rapidly fatal necrotising pneumonia and bacteraemia

Burkholderia pseudomallei

Melioidosis in humans and farm animals – tropics/ subtropics

Occurs in Africa/Asia

Found in soil, water and rice paddies

Long term environmental survival

Clinically similar to Glanders: localised infection which may progress into blood stream

Pulmonary infection – mild bronchitis to severe pneumonia

Difference to B.mallei – geographical distribution and habitat

Burkholderia mallei

Glanders in horses – rarely in humans

Occurrence – Solipeds (horses & donkeys)

Endemic in parts of Africa, Asia and middle east

Rare in humans – vets, groomers etc.

Symptoms: ulcerations and cutaneous lesions. Pulmonary abscesses, septicaemia. Chronic: multiple abscesses

Bordatella pertussis

Betaproteobacterium

non-motile

aerobic

gram-negative rod

Colonises respiratory tract to cause whooping cough

Tranmission via droplets/inhalation

Colonisation of upper respiratory tract, production of toxins

Incubation period: 5-10 days

Catarrhal stage: ~ 1-2 weeks rhinorrhoea and mild cough

Paroxysmal stage: ~1-6 weeks , can go on for 6 months, 5-20 forceful, hacking successive coughs, title time for breathing, whoop when air rushes back into the lungs

Vomiting and frequent coughing exhausts child

Complications - pneumonia, otitis media, asthma

Psuedomonas:

gammaproteobacterium

Aerobic - some capable of subsitutuing nitrate for oxygen

gram-negative rods

motile by polar flagella (either single or tuft)

Common in soil and natural environments

Many secrete extracellular, water-soluble pigments.

Psuedomonas aeruginosa - blue-green

Grow on unusual carbon sources such as soap residue

Can grow in some antiseptics

Inefficient heterotroph

Resistant to some antibiotics due to cell wall porins - control entry into cell

Adhesions/pilli/EPS/LPS

Capsule

Phycocyanin - impairs ciliary function, stimulates inflammatory response

Exotoxins: inhibit protein synthesis; tissue damage

Cytotoxic: leukocyte damage; pulmonary injury

Enzyme: elastase; protease; haemolysins. Variety of cell and tissue damage

Infection Mechanisms:
No single mechanism - multifactorial

Opportunistic

P.aeruginosa - can infect urinary tract, burns, wounds, blood infections, abscesses and meningitis.

P.syringae - plant pathogen

CF patients especially prone

Pseudomonas aeruginosa Human Infections

Gastrointestinal: any part (oropharynx to rectum) in immunocompromised

Skin and soft tissue: after breakdown of integumentary (burns, trauma, dermatitis, high moisture conditions)

Endocarditis: mostly heart valves of IV drug users

Respiratory infections: 80% of CF patients colonised in lungs, cats and dogs with chronic illness

Bacteraemia and septicaemia: in immunocompromised patients (AIDS, diabetes mellitus and severe burns)

Central Nervous system infections: meningitis and brain abscesses after invasion from contiguous structure (e.g. inner ear or paranasal sinus)

Ear infections including external otitis: a predominant bacterial pathogen in external otitis, chronic in cats and dogs

Eye infections: causes devastating infections in the human eye

Bone and joint infections: most often seen in IV drug users, and in conjunction with urinary tract or pelvic infections

Urinary tract infections: usually hospital-acquired after catheterization 

Gastrointestinal: any part (oropharynx to rectum) in immunocompromised

Skin and soft tissue: After breakdown of integument (burns, trauma, dermatitis, high moisture conditions (swimmers; toe webs of athletes and troops; divers; perineal region; under nappies of infants)

Pseudomonas fluorescens  & Pseudomonas putida

Poor pathogens.

Can grow at 4o C – rare cases of endotoxic shock from contaminated blood products

Pseudomonas aeruginosa Other infections

Also found in:

•API 20NE assimilation tests 

•Aviation fuel 

•Distilled water 

•Photographic chemicals 

•Cosmetics 

•Plasticisers

Faecal carriage rates are between 15 – 25% (higher in vegetarians)

P. aeruginosa survives in hospital environments: 

•Mops 

•Sinks / Toilets 

•Dialysis equipments 

•Respiratory tubing 

•Cut flowers

Pseudomonas syringae

Ice nucleation

•Cell surface ice nucleating proteins

•Ice damage to plants, promoting bacterial uptake

•precipitation/snow making

chlorosis and necrotic regions on leaves

Pseudomonas marginalis

pectinolytic, soft rots

Legionella

gammaproteobacterium

Fastidious gram-negative rods

Non-spore forming

Vary from short, thin forms to longer filamentous

Motile via single polar flagella

aerobic

Common in streams and warm-water supplies, air conditioning systems

Able to survive and reproduce within aquatic ameoba

Legionnaires disease

L.pneumophilia

Legionnaires disease

•Incubation periods of 2-10 days (16 days max)

•Death occurs through progressive pneumonia with respiratory failure and/or shock and multi-organ failure

•Untreated disease usually worsens during the 1^st week

•75-80% are <50 years and 60-70% male

•Community, travel or hospital acquired

•Acute pneumonia, bacterium multiplies in alveolar macrophages

•Produces cytokines that elicit an influx of monocytes and polymorphonuclear cells

•Obliteration of air spaces compromises respiratory functions

•Fevers, coughs, breathlessness

In enviornment

•Only documented source of Legionella species is water

•Found naturally in the freshwater of streams, lakes, warm springs, rivers, and riverbanks

•Intracellular parasite of amoeba and other protozoa: protects against chlorine, drying and heat

•Modifying our environment to suit ourselves has unexpectedly created ideal conditions for Legionella growth

•Many artificial water systems are an ideal environment for its growth (temperature and stagnation)

Vibrionales

gammaproteobacteria

facultatively anaerobic gram-negative rods

Mostly in aquatic habitats

rods that are curved

Vibrio cholerae - cholera and diarrhorea

V. parahaemolyticus - less intense form of gastroenteritis

inhabiting coastalsalt waters, it’s transmitted to humans mostly by raw or under-cooked shellfish.

V.cholerae

2 strains:

O1 and O139 - pan/epidemic cholera, Cholera toxin +, waterborne/ person-to-person

Non-O1 and Non-O139 - sporadic cases, gastroenteritis, may be CT-, water/shellfish

V.cholerae O1 - acute secretory diarrhoeal disease

• short incubation period (< 12 hours)

• early vomiting

• painless loss of copious amounts of watery diarrhea (up to 1L per hour) known as “rice-water stool”

• severe and rapidly progressing dehydration and hypovolemic shock

• without treatment, severe cholera kills about half of infected individuals

1. Ingestion and passage through acidic stomach

2. Colonisation of small intestine (distal region).; organism remains extracellular

3. Production of CT to induce secretory diarrhoea and mucin release

4. Exit from host in mucusassociated aggregrates

V. parahaemolyticus

A. Enteritis (shellfish-borne infections)

Main clinical symptoms is watery diarrhoea, often accompanied with abdominal pain, nausea and vomiting

Typically a self-limiting illness, with rare severe morbidity and mortality

Sporadic cases in UK

Most common pathogen in Japan & other parts of Asia where raw seafood consumption is high

B. Soft tissue infections / septicaemia

entry via wounds or skin lesions, often linked to injury due to handling contaminated shellfish

symptoms of skin infection (swelling, pain, erythema, bullae (blister), necrosis and gangrene)

symptoms of septicaemia (fever, hypotension, bullae, pain in lower extremities, tachycardia, shock, multiorgan dysfunction)

infections may be life-threatening

hemolysins (e.g. thermostable direct haemolysin (TDH) and related variant TRH); lysis of red blood cells

Type 3 secretion system (T3SS) Two systems in organism; T3SS1 causes cytotoxicity (cell death) and T3SS2 is associated with diarrhoea (enterotoxicity)

V. vulnificus

Wound infection / septicaemia from exposure to organism in sea water

Can be fatal; rapidly spreading systemic disease → septicaemia

Foodborne illnesses

Raw oysters

Can be fatal (septicaemia)

Healthy individuals rarely susceptible (liver damage, high serum iron)

Hemolysin - Encoded by genes vvhA and vvhB; only secreted toxin; member of the cholesteroldependent cytolysin (CDC) family of pore-forming toxins; capable of dissolving red blood cells

Proteases e.g. VVP – an elastase that increases vascular permeability of host cells; other functions in promoting clotting, which prevents effective host immune response e.g. RtxA - MARTX toxin with multiple functions including interfering with actin cytoskeleton rearrangements and promoting necrotic cell death

Capsule Required for infection, provides CPS provides resistance to opsonization by complement and subsequent phagocytosis by macrophages

Enterobacteriales

gammaproteobacterium

facultatively anaerobic

gram-negative rods

if motile, peritrichously flagellated

straight tods

Inhabit intestinal tracts of humans and animals - enterics

Most are active fermentors of glucose.

catalase positive

oxidase negative

Have fimbrae which allow them to adhere to surfaces or mucous membrane

Specialised sex pilli aid exchange of genetic information

produce bacteriocins that cause the lysis of closely related species of bacteria

Bacteriocins may help maintain the ecological balance of various enterics in the intestines

Important genera of the order include Escherichia, Salmonella, Shigella, Yersinia, Enterobacter

Escherichia

inhabitant of the human intestinal tract

5 Species: E. albertii, E. coli, E. fergusonii, E. hermannii, E. vulneris

E.coli - not usually pathogenic but can be a cause of UTI or certain strains cause travelers diarrhorea and foodborne disease.

E.albertii - associated with sporadic infections in humans, birds and calves

E.coli

•colonises mammalian GI tract a few hours after birth and maintains regular presence over lifetime

•Of >700 different serotypes (O,H,K), most are harmless

Strains: ETEC, EIEC, EAggEC, EPEC, EHEC/STEC, UPEC:UTIs, MNEC: Meningitis associated E.coli

Intestinal pathogenic strains of E.oli

ETEC

EIEC

EAggEC

EPEC

EHEC/STEC

Extra-intestinal infections of E.coli

UPEC

SEPEC

MNEC

ETEC

Intestinal Pathogenic strain of E.coli

•watery diahorrea,

•High infectious dose 10^6 organisms

•Site of damage - small intestine; extracellular

•Toxins: LT and ST Colonisation factor e.g. fimbriae

•Treatment: Self-limiting; oral rehydration; antibiotics (e.g. fluoroquinolones)

EIEC

Intestinal Pathogenic strain of E.coli

•Dysentery, bloody diarrhoea

•High infectious dose 10^6 – 10^10 organisms

•Site of damage – colon; intracellular

•Toxins: none Colonisation factor e.g. pINV (T3SS)

•Treatment: Oral rehydration; Antibiotics (e.g. azithromycin)

EAggEC

Intestinal Pathogenic strain of E.coli

•Diarrhoea (persistent)

•High infectious dose 10^10 organisms

•Site of damage – colon; extracellular

•Toxins: SPATEs (proteases), enterotoxins

•Colonisation factor e.g. fimbrial & afimbrial adhesins

Treatment: Self-limiting; oral rehydration; antibiotics (e.g. rarely)

EPEC

Intestinal Pathogenic strain of E.coli

Attatching and Effacing E.coli

•Diarrhoea

•High infectious dose 10^8 -10^10 organisms

•Site of damage - colon; extracellular

•Toxins: proteases

•Colonisation factor e.g. A/E lesion (LEE pathogenicity island)

•Treatment: Self-limiting, oral rehydration; antibiotics (rarely)

EHEC/STEC

Intestinal Pathogenic strain of E.coli

Attatching and Effacing E.coli

•Bloody diarrhoea, kidney disease

•Low infectious dose 50-500 organisms

•Site of damage - colon; extracellular

•Toxins: Shiga toxin (Stx)

•Colonisation factor e.g. A/E lesion (LEE pathogenicity island)

•Treatment: None at present

•LEE contains genes coding for type 3 secretion system (T3SS)

•T3SS enables bacterium to export proteins directly into host cell

•EPEC/EHEC export their own receptor called Tir, which interacts with outer membrane protein called

UPEC

uropathogenic E. coli

•Types of UTI include: asymptomatic bacteriuria (1% normally, 20% elderly)

•cystitis (bladder infection)

•pyelonephritis (upper ureter infection, kidney infection)

•Found in intestines of healthy individuals

•Periurethral contamination can occur after bowel mocement or during sexual intercourse

•Infection caused by P.fimbrae binding to P blood antigen in 99% of people (D-galactose-D-galactose)

MNEC

meningitis-associated E. coli

•Major cause of CNS infections in infants <1 month old

•Primary bloodstream infection with secondary distribution to CNS – mechanism of infection

•80% E.coli strains involved synthesise K-1 capsular antigens, major virulence factor

•K-1 common in GI tract of pregnant women and newborns

SEPEC

septicaemic E. coli

Salmonella

Almost all members of Salmonella are pathogenic

Common inhabitant of intestines of animals

Only 2 species of Salmonella: S. enterica and S. bongori

S.bongori resident of cold-blooded animals and rarely found in humans

S.enterica is infectious to warm-blooded animals

Includes many serovars (serological varieties) e.g. Salmonella Typhimurium is not a species

•Non-lactose fermenter

•Indole test negative

•Selective media (Salmonella from Shigella/E.coli): H2S and Acid production (XLD, SS media)

Different antibodies can be used to differentiate Salmonella serovars by Kauffman-white scheme.

Serology

when salmonellae are injected into appropriate animals, their flagella, capsules, and cell walls serve as antigens that cause the animals to form antibodies in their blood that are specific foreach of these structures. Thus, serological means are used to differentiate the microorganisms.

Salmonella Typhimurium is not a species - more properly written as Salmonella enterica serovar Typhimurium

Typhoid fever

caused by Salmonella Typhi

caused by any member of the genus Salmonella

less severe gastrointestinal disease caused by other S. enterica serovars is called salmonellosis.

Salmonellosis is one of the most common forms of foodborne illness.

Typhoid Fever (S.typhi)

•1st phase: slow fever, rose spots, mild, bacteraemia

•2nd phase: organism reaches gallbladder, formation of ulcers, haemorrhage, death (20%)

•Typhoid state “muttering delirium” or “coma vigil” (picking at bedclothes and imaginary objects)

Enteric fever (S. Paratyphi)

→ similar to typhoid fever but less severe; rare

Non-typhoid Salmonella (NTS)

Predominant Serovars: Salmonella Enteritidis, Salmonella Typhimurium, Salmonella Heidelberg, Salmonella Newport

•Causes self-limiting enteritis in healthy individuals

•Can be invasive with immunocompromised/malnourished individuals

Vehicles of NTS:

Route: faecal-oral transmission

Predominantly poultry and poultry products but many foods have been associated with infection

Salmonella pathogenesis

•Must cross epithelial barrier to colonise the host

1)Cross epithelium via phagocytic cells or direct uptake

2)Targets macrophages or re-invades epithelial cells from basolateral site

3)May evade killing by inducing macrophage apoptosis/manipulate for bacterial replication

4)Severe disease results from systemic spread and bacteraemia

Main Salmonella Virulence factors:

Main Salmonella Virulence factor:

Type 3 secretion systems (T3SSs) – encoded on Salmonella pathogenicity island (SPI)

•T3SS = molecular ‘syringe’ that transfers proteins (effectors) from bacterial cytoplasm to host cell

•SPI1 – encodes genes necessary for invasion of intestinal epithelial cells and induction of intestinal secretory and inflammatory responses

•SPI2 – encodes genes essential for intracellular replication and necessary for establishment of systemic infection beyond the intestinal epithelium

Shigella

Responsible for bacillary systentery or shigellosis.

Only found in humans

•able to induce sustained transmissions in close contact communities e.g. MSM and Jewish communities

•Treatment: increasingly resistant, first-line treatment – fluroquinolones (ciprofloxacin)

•Transmitted by faecal-oral route and person-person spread

•aggressive watery or mucoid/bloody diarrhoea, fever and stomach cramps

•begins 1-2 days after ingestion of organism and in immunocompetent individuals will resolve in 5-7 days;

•affects mostly children < 5 years

Low infectious dose (10-100 organisms)

Pathogenesis:

•Crosses epithelium via Microfold cells and induces uptake via macrophages

•Kills macrophages & escapes to reach basolateral surface

•Bacterium induces lysis of phagosome and disseminates intracellularly

Virulence factors:

Plasmid-borne factors (Pinv):

•Entry region: codes for type 3 secretion system (T3SS), which allows bacterium to inject proteins into host cell

Chromosomal factors:

•SHI-1 – enterotoxins (SigA, Pic, Set1A,1bB)

•SHI-2 – siderophores (IucA-D, IutA)

•SHI-3 – siderophores (IucA-D, IutA)

•SHI-O – serotype conversion/O-antigen

•Stx-phage p27 – shiga toxin

Species:

A: S. dysenteriae – most severe, (ancient) cause of epidemics

B: S. flexneri – most frequent, 60% cases in developed world

C: S. boydii – confined to Indian sub-continent

D: S. sonnei – mildest infection, developed world (main species)

Yersinia

caused the plague

•7 genera including type genus Yersinia

•Optimum temperature 28-29°C

• Some lack nitrate reductase

•G+C content ~47%; genome size 4.6 Mbp

•Non-motile at 37°C (with all but Y. pestis motile by peritrichous flagella below 30°C)

•17 Yersinia species → 3 species are pathogenic to humans or animals

Y. enterocolitica - self-limiting gastroenteritis and mesenteric lymphadenitis that mimics acute appendicitis

Y. pseudotuberculosis - self-limiting gastroenteritis usually without diarrhoea, rare but more likely to become systemic

Y. pestis - pneumonic and bubonic plague

Host entry:

•All pathogenic Yersinia cross epithelial barrier via microfold cells

•Goes to Lymph nodes or tissues

•Spreads systematically by bloodstream and colonising deep tissue sites such as liver or spleen

Virulence factors:

•T3SS found in all pathogenic Yersinia

•Y. pestis has acquired additional plasmid DNA that encodes for factors that enable colonization and transmission via the flea vector and survival in blood but has lost motility and cell adhesive properties to enable colonisation of mammalian host.

Y.enterocolitica

•self-limiting gastroenteritis and mesenteric lymphadenitis that mimics acute appendicitis

•Fever, vomiting, abdominal pain, diarrhoea

•Most common < 7 yr old

•Rare systemic or rheumatology complications

•Low mortality rate

Treatment:

•Supportive care as self-limiting

•Antibiotics on occasion of sepsis

Y. pestis

pneumonic and bubonic plague

•Enzootic cycle – wild rodent reservoir little host mortality

•Epizootic cycle (amplifying hosts disease)

•Transmitted directly via inhalation, ingestion, wounds and bites to humans (bubonic plague)

•Then spreads to lungs via blood – primary plague pneumonia

•Droplet aerosols – secondary plague pneumonia

Clinical aspects of plague:

Bubonic plague:

•Transported to regional lymph nodes but survives in normal inactivated macrophages, massive proliferation in LN causes bubo (inflammatory response). Death 60%, disease may stop.

Septicaemic plague (black death):

•Escapes LN and spreads to bloodstream, lysis of bacteria releases LPS, causing septic shock. Death 100%, disease progression

Pneumonic plague:

•Invades lung macrophages, organism is now transmitted in aerosols (highly contagious)

Epsilonproteobacteria

Slender, gram-negative rods that are helical or curved.

Motile by means of flagella

Microaerophilic

Campylobacter and Helicobacter

microaerophilic

an organism requiring very little free oxygen.

Campylobacter

Epsilonproteobacteria

Family: campylobacterales

• Oxidase positive

• Catalase positive

• Nitrate reductase positive

• G+C%: 30-40%; genome size 1.5 – 1.7 Mbp

• Optimum growth (30 - 42˚C)

microaerophilic vibrio

Each cell has 1 polar flagellum

very sensitive to a variety of external conditions (UV light, heat, salt etc).

They are unable to multiply and thrive outside the host's body meaning that they cannot reproduce on samples such as meat etc.

C.fetus - causes spontaneous abortion in domestic animals

C.jejuni - causes outbreaks of foodborne intestinal disease

Helicobacter

Epsilonproteobacteria

Family: campylobacterales

• Oxidase positive

• Catalase positive

• Nitrate reductase positive

• G+C%: 30-40%; genome size 1.5 – 1.7 Mbp

• Optimum growth (30 - 42˚C)

microaerophilic curvedrods with multiple flagella

fastidious microorganisms (require complex growth media (e.g. blood, serum) with additional amino acids)

Helicobacter pylori - most common cause of peptic ulcers in humans and a cause of stomach cancer

C.jejuni

Clinical symptoms:

day 1 → 3 ; fever, vomiting, headaches

day 3 → watery/bloody diarrhoea with abdominal pain; stools contain inflammatory cells and colonic biopsies show diffuse inflammatory colitis

Steps in infection:

1. ingestion of bacteria

2. reaches small intestine

3. (mucosal damage)

4. invades via transcellular and paracellular routes

5. provokes an immune response

6. virulence gene expression

7. eventually cleared from host

• Motility (e.g. major flagella protein (FlaA), structural/export apparatus protein (FlhA) CdtABC

• Lipooligosaccharide (LOS) and capsule (e.g. LOS resembles human neuronal gangliosides → molecular mimicry thought to lead to autoimmune disorders) (e.g. capsule provides protection from host immune system, aids adhesion)

• Colonization and invasion (e.g. outer membrane adhesins: CadF, DocA, VirB11 etc)

• Toxin production (e.g. cytolethal distending toxin (CdtABC) causes doublestranded breaks in DNA → cell death)

Helicobacter pylori

Humans is predominant reservior

Disease is 80% asymptomatic, 10-20% gastric hyperacidicty & ulcers, 0.5% gastric cancer

Infection via oral, mainly spread by intrafamilial transmission

Infection and Pathogenesis:

1. enters host and survival

2. motility and chemotaxis

3. adhesion-receptor interaction, establish colonisation

4. toxins release, damage to host, intracellular replication

Virulence factors:

• Urease production 7 gene cluster including ureA/B, which enables organism to cope with low pH of stomach. Mechanism: at low pH, urea entry across periplasm results in production of ammonium, which is believed to neutralise excess protons

• Flagella / motility 40 gene cluster including structural components FlaA, FlaB. The sheathed flagellum may help ‘hide’ the apparatus from detection by immune system

• Adhesins e.g. Blood-antigen binding protein A (BabA), sialic acid-binding adhesin (SabA)

• Toxins e.g. Cytotoxin-associated gene A (CadA) located on cag pathogenicity island; alters host cell signalling leading to disruptions in host cytoskeleton, inflammatory mediators etc

Spirochaetes

Gram negative bacteria

Coiled morphology

cells motility uses two or more axial filaments (endoflagella) (within the outer sheath and body of cell) allow motility through highly viscous media

Differing numbers of periplasmic flagella (endoflagella) according to genus & species

Treponemes are not culturable using artificial media

Borrellia and Leptospira spp. have been grown on complex media – liquid media is most successful

Disease caused: syphillis (venereal), pinta, yaws, bejel (non-venereal)

Species: Treponema, Borrelia, Leptospira

Treponema

Spirochaete

includes Treponema pallidum which causes syphilis

Fragile cells, no survival outside host

Transmission:

Contact between infectious lesions / abraded skin/mucous membranes

Most cases transmitted via sexual contact

Rarely skin to skin

Mother-to-child transmission

CANNOT be spread via swimming pools etc.

Treatment: Treponemal diseases respond well to penicillin. Secondary syphilis (weekly injections) are treated with penicillin injections IM

Borrelia

Spirochaete

causes relapsing fever and lyme disease transmitted by ticks or lice

Transmitted by Ixodus ticks.

Borrelia burgdorferi sensu lato species complex:

– Borellia burgdorferi sensu stricto only in North America

– Borrelia harinii and Borrelia afzelii also in Europe

Occupational risk groups: foresters, game keepers, rangers, farmers, deer handlers

Stages of disease:

Stage 1

• Tick must have been feeding for at least 24h

• Acute, localized disease at site of inoculation

• Non-specific flu-like symptoms

• Erythema migrans 1 to 4 weeks after bite (70-80% people)

• Without treatment rash clears within 3 to 4 weeks

Stage 2

• 80% patients get subacute, disseminated disease cardiac, neurological, skin lesions, CNS, musculoskeletal systems

Stage 3

• Latent period of up to 1yr

• Arthritis, neurological impairment

• Even with treatment a subset of patients continue to have arthritic symptoms (post infectious antibiotic refractory arthritis)

Erythema migrans meaning migrating redness (Bulls eye rash). Very low levels of spirochaetes may be detected in the blood of some patients

Treated with either doxycycline, amoxicillin or cefuroxime for 2-4 weeks. 10-20% Lyme patients continue to suffer persistent symptoms including fatigue, muscle and joint aches, and brain fog that can six months or longer.

Leptospira

Spirochaete

usually spread to humans via water contamination from urine of dogs etc.

Leptospira interrogans

Most common zoonotic infection in the world

It can cause a self-limiting influenza like illness or a much more serious Weil disease with multi-organ failure and death.

Weils disease:

• Mild virus-like syndrome

• Anicteric leptospirosis systemic with aseptic meningitis

• Icteric leptospirosis/Weil’s Disease

• jaundice (5-15% mortality)

– Vascular collapse

– Thrombocytopenia

– Haemorrhage

– Hepatic and renal dysfunction

Treatment: no antibiotics in mild cases just fluids and pain and fever control.

Antibiotics may include doxycycline, amoxicillin, or ampicillin.

Severe cases are treated with IV penicillin G, third-generation cephalosporins, or erythromycin.

Patients with icteric leptospirosis need intensive care unit admission

Firmicutes

Low G+C gram-positive bacteria

Includes:

• Endospore forming bacteria such as Clostridum and Bacillus (Clostridium is anaerobe only, Bacillus is aerobic or facultative anaerobes)

• Medically important - Staphylococcus, Enterococcus, Streptococcus

• Industrially important - Lactobacillus

• Mycoplasmas - do not possess cell wall

Clostridiales - Clostridium

Natural habitat is soil and the intestinal tract of man and animals. Invasive capability of pathogenic clostridia varies considerably.

Obligate anaerobes

Rod-shaped cells contain endospores that distend the cell

Diseases:

C.tetani - Tetanus

C.bolulinum - Botulism

C.perfrigens- Gas gangrene and foodborne

C.difficle - serious diarrhorea caused by antibiotic therapy altering the normal intestinal microbiota, allowing overgrowth

Endospore forming bacteria

Endospore:

•Usually formed when a population reaches conditions of nutrient limitation.

•Highly resistant to heat, uv, toxic chemicals, ionising radiation.

•Heat resistance is used for selection.

•Typical habitat is soil

Main genera:

Bacillus - aerobic or facultative anaerobes Clostridium - anaerobic

Spore structure:

Exosporium – thin delicate layer of mostly protein

Spore coat(s) – multiple layers of spore specific proteins

Cortex – loosely packed peptidoglycan

Spore protoplast or core – normal cell wall plasma membrane cytoplasm and nucleoid

Properties of core:

• Dipicolinate – protects DNA

• Dehydrated – only 10-30% of the water content of the vegetative cell –gives heat and stress resistance

• pH is more acidic than vegetative cell

• Abundant small acid-soluble spore proteins, SASPs – give resistance to dry heat, dessication, UV – protecting DNA Carbon source during outgrowth

• Low metabolic activity (low O2 uptake)

• No macromolecular synthesis

• Low enzymatic activity

• Low or absent mRNA synthesis

Germination:

Spores will remain dormant for decades, even if placed in optimal conditions.

State of dormancy can be broken by a variety of treatments - activation. heat shock. eg. several hours at 65C storage at low temperature (4C) When activated spores are placed in favourable conditions - germination.

C. Botulinum - Botulism

found in soil, water and decaying vegetation

Fatal food poisoning that follows ingestion of preformed toxin from growth of organism in food.

Animals are frequently affected from feeds.

Endospores are very resistant to heat and may withstand boiling for several minutes

Anaerobic conditions (incompletely sterilised canning) may germinate spores - grow into vegetative cells and eventually produce the deadly toxin.

Toxin acts by inhibiting release of acetylcholine from motorneurons causing flaccid paralysis. Toxin (Botox) can be used clinically to relieve muscle contractions or cosmetically.

C.botulinum may occasionally infect wounds.

Also, infant botulism can result from ingestion of spores in soil and dust - germinate in intestine (anaerobic).

Diagnosis of botulism

Clinical picture. ELISA for the toxin in suspect food or injection into mice. Culture may be attempted.

Prevention

Antitoxin is given to suspected cases. In contrast to spores, toxin is heat labile therefore cooking inactivates

C. tetani - Tetanus

Spores are introduced into the body through wound.

Wounding producing necrotic (dead) cells allows anaerobic conditions to develop and spores to germinate leading to formation of the toxin.

2 types of tetanus

• Generalised tetanus •

Neonatal tetanus occurs if umbilical stump becomes infected - from soil or bindings containing spores. High fatality rate >200,000 deaths each year

Pathogenesis

• Toxin migrates along peripheral nerve axons to the CNS (site of action)

• Symptoms take 3-21 days to develop.

• Toxin blocks glycine release from inhibitory interneurons leading to uncontrolled release of acetylcholine from motorneurons and spastic paralysis.

• Since spasms often involve neck and jaws disease is referred to as lockjaw (teeth have to be knocked out).

• Death results from muscular spasms affecting respiration. 50% mortality.

• Symptoms last 3-4 weeks, complete recovery not for months (if at all!)

Diagnosis

usually by clinical picture, although organism can be isolated - G+, drumstick shaped due to terminal spore.

Haemolytic toxin production can be demonstrated by growth on agar plates half spread with antitoxin - prevents haemolysis.

Prevention and treatment

by immunity produced by vaccination with formalin-inactivated toxin (in DPT triple vaccine). Tetanus toxoid vaccine has 100% efficacy!!! Following injury, non-immunised persons are given human tetanus immunoglobulins.

C. perfringens - Gas Gangrene

Normal flora in GI and vagina

Caused by C. perfringens usually although several other species of clostridia may also cause gangrene.

Results from contamination of wounds with spores of clostridia.

Able to grow in anaerobic conditions in deep necrotic wounds with reduced blood supply.

After germination organisms secrete exotoxins causing more tissue damage, resulting in rapid spread of the organisms.

Carbohydrate may be fermented resulting in the production of large quantities of gas (unpleasant odour) in tissue - constrict blood vessels. Diagnosis and Identification:

Usually on clinical picture (smell from protein digestion is characteristic).

X-ray for gas.

Since other organisms (eg. bacteroides) can produce similar infections, definitive diagnosis requires isolation and identification so culture attempted.

Organisms producing alpha toxin (phospholipase or lecithinase) will hydrolyse lecithin in egg yolk medium -> opaque area around colony.

This can be neutralised by presence of antitoxin antibody in media - Nagler reaction.

Prevention and Treatment

Cleansing of wounds.

Antibiotics have limited effect in necrotic areas.

Surgery may be necessary to remove affected parts.

C.perfringens is also a significant cause of food poisoning in man and animals.

C.difficile - Pseudomembranous Colitis

Severe colitis following antibiotic therapy leading to overgrowth of Clostridium difficile which may be normal flora of many people.

Produces toxins. 20% of cases of antibiotic-associated diarrhoea are caused by Clostridium difficile

C difficile is recognized as the most common nosocomial gastrointestinal infection.

Two major enterotoxins have been identified: toxin A, and toxin B.

Diagnosis.

Most common test is an ELISA test for toxins A and B in the stools

Treatment. Stop the causative antibiotic therapy. Anti diarrhoea drugs and administer antibiotics effective against the C.difficile like metronidazole, vancomycin.

Bacillales

The order Bacillales includes several important genera of gram-positive rods and cocci

Includes:

Bacillus

Staphylococcus

Bacillus

rods which produce endospores

Common in soil, only few pathogenic to humans

Several species produce antibiotics

Bacillus anthracis - causes anthrax

Bacillus thuringiensis - insect pathogen

Bacillus cereus - food poisoning

Bacillus anthracis

Disease of sheep, goats & cattle that is also transmissable to humans

Survive in soil for 30 years or more.

Three general manifestations/routes of infection of human disease:

1. Cutaneous Anthrax

Most common form (2000ish cases per year)

Animal workers mostly

Spores germinate in skin abrasions

Skin ulcer – black eschar – can become systemic

Untreated 20% mortality, responds well to antibiotic

2. Gastrointestinal Anthrax

Caused by ingestion of undercooked contaminated meat.

2 types

- oral-pharyngeal (most rare) and abdominal (rare)

Abdominal Spores germinate in lower gastrointestinal tract primary intestinal lesion forms

Symptoms - nausea, severe abdominal pain, vomiting, bloody diarrhoea Intestinal perforation or anthrax toxemia are the usual causes of death

Mortality very high

3. Pulmonary anthrax

Inhalation of spores

Spores are mopped up by macrophages and trafficked to the draining lymph nodes

Germination in the lymph nodes may take up to 60 days

Anthrax bacilli replicate in the lymph nodes and disease immediately follows.

Capsule inhibits phagocytosis.

Hemorrhage, edema, and necrosis are the results of bacterial exotoxins released during replication.

Symptoms- flu-like with fever, myalgia, cough, headache, vomiting, chills, abdominal pain, and chest pain.

Cyanosis and hypotension result in death 80% mortality in 2 to 4 days whether antibiotics given or not.

Inhalational anthrax is 99% lethal in unvaccinated individuals. An ideal agent for biological warfare!

Virulence mechanisms

Capsule made of poly-D-glutamate polypeptide. Smooth mucoid colonies.

pX02 plasmid.

Toxin encoded on plasmid pX01.

3 parts

- PA (binding domain)

- EF (Edema factor)

- LF (Lethal factor)

Diagnosis

-G+ rod.

Central (non-staining spore) occurs in soil and in culture, but not in clinical samples.

Sometimes occur in chains.

Identified in blood, skin lesions, or respiratory secretions or by measuring specific antibodies in the blood or masuring DNA in samples by PCR

Treatment - penicillin, doxycycline, and fluoroquinolones (such as ciprofloxacin).

Prevention

Pasteur demonstrated efficacy of vaccine.

Several modern vccines based on an avirulent strain of B. anthracis which lacks the plasmid pX02 plasmid.

Control also relies on sterilisation of wool etc. from areas where anthrax is endemic.

Bacillus cereus

cause of food poisoning

Two types of poisoning:

Short-incubation or emetic , occurs between 1 and 6 hours after eating

Symptoms – nausea, vomiting and abdominal pain

Caused by heat stable enterotoxin which cannot be destroyed by cooking

Long-incubation or diarrheal, ocurrs 6-18 hours after eating

Symptoms – diarrhoea

Caused by an enterotoxin that can be destroyed by cooking.

Toxin activates intestinal adenylate cyclase and causes intestinal fluid secretion.

Staphylococci

Bacillales order

grape-like clusters

Species most important: S.aureus

S.epidermis - Major cause of nosocomial infections

facultative anaerobes

Many forms of pathogenicity:

Grow well under high osmotic pressure and low moisture (grow in nostrils and food)

Catalase positive (also distinguishes from Streptococcus)

Gram+ non-motile cocci (>30 species) often occurring in clusters like bunches of grapes (contrast to chains for streptococcus)

S.aureus

B-hemolytic and coagulase positive

Diseases

Pneumonia and septicaemia in new-born and immunocompromised patients (e.g. burns units).

Skin infections Organism invades subcutaneous tissue with the aid of lipases - inflammation

-> white blood cells -> organisms releases leucocidins that kill white blood cells forming pus

- > organisms releases coagulase - > fibrin barrier -> boils, carbuncles. Also impetigo.

Septic arthritis- joint infection

Osteomyelitis – bone infection

Endocarditis – heart tissue,valves

Wound infections, absesses.

Common hospital acquired infection - can be transmitted by hospital personnel, but usually patient.

Major cause of nosocomial infections.

Scalded skin syndrome (SSSS) – caused by S.aureus carrying a phage encoded exfoliatin toxin. Occurs after initial infection in the mouth, nasal cavities, throat, or umbilicus

Toxic shock syndrome due to infection and production of a super-antigen that stimulates T cells en masse.

Aside leucocidins, coagulase, exfoliatins and toxic shock syndrome superantigen, S.aureus produces protein A which binds to immunoglobulins contributing to both adherance and antiphagocytic activity.

S.aureus is also a major cause of food poisoning. -caused by ingestion of preformed toxin

- food contaminated from humans allowing bacterial growth and enterotoxin production.

-onset and recovery both occur within few hours Very rapid

- acts on emitic receptor site -> vomiting and inhibits water absorption → ‘explosive’ diarrhoea.

Treatment

S.aureus naturally produces penicillinase (B-lactamases).

Usually sensitive to synthetic (beta-lactamase resistant) penicillins such as oxacillin, methicillin.

In UK and other countries, many hospitals have been colonised with methicillin drug resistance S. aureus (MRSA) due to production of altered penicillin binding proteins and penicilinase - plasmid mediated.

Rates of MRSA infection in hospitals increased greatly in the 1990’s but have since stabilised.

Many MRSA strains are resistant to multiple antibiotics – can presently be treated with the glycopeptide antibiotic, vancomycin. However, vancomycin-resistant MRSA have been identified which represents a future problem for treatment.

Staphylococcus epidermidis

Non-hemolytic, coagulase negative staphylococcus

major component skin flora, also in gut and respiratory tract but can cause opportunistic infections.

Major cause of nosocomial infections e.g. infection in catheters, shunts and prosthetic heart valves

Lactobacillales

representative of the industrially important lactic acid–producing bacteria

Most lack a cytochrome system and are unable to use oxygen as an electron acceptor

Unlike most obligate anaerobes, though, they are aerotolerant and capable of growth in the presence of oxygen.

They grow poorly compared to oxygen-utilizing microbes

Production of lactic acid from simple carbohydrates inhibits the growth of competing organisms and allows them to grow competitively in spite of their inefficient metabolism

Genus: Streptococcus, Lactobacillus, Enterococcus, listeria

Both latter are facultative anaerobes,and several species are important pathogen

Streptococcus

spherical, gram-positive bacteria that typically appear in chains

Spherical cells divide only in one plain and so form chains

Require complex media for growth

Unable to make haem group of cytochromes or catalase Grown on blood agar (good source of catalase)

several extraceullar substainces that contribute to pathogenicity:

• products that destroy phagocytic cells that ingest them

• Enzymes that spread infections to host connective tissye, which results in extensive tissue destruction

• Enzymes that digest fibrin of blood clots, allowing spread

Grouping of Streptococci II: Antigenically/Serologically

Lancefield Groups of ß-hemolytic Streps

Named after Rebecca Lancefield

A, B, C, D… based on the specific carbohydrate antigen extracted by heating cells to 150°C

Group A - S.pyogenes

Group B - Cattle and humans eg S. agalactiae

Group D - Intestinal tract of man and animals Enterococcus Etc etc

Grouping of Streptococci I: Hemolysis

B - complete hemolysis -> clear zone

α- incomplete hemolysis of red blood cells to produce a greenish-brown zone

γ- hemolytic - no hemolysis

Streptococcus pyogens

B haemolytic

Group A strep

Sensitive to bacitracin

Antigenicity of M-proteins in the cell wall provides sub-classification of group A into over 100 sub-serotypes.

Habitat: 5 - 30% of healthy people may be carriers of group A, beta hemolytic Streps in their throat and nasopharynx; however numbers usually low

Causes: strep throat, impetigo, cellulitis and necrotizing faciitis, scarlet fever

Scarlet fever: usually result of Strep sore throat caused by a pyrogenic toxin-producing organism - toxin (A, B and C) encoded by a phage.

Symptoms- Fever, susceptibility to endotoxic shock, erythematous rash.

Non-supporative diseases may also include:

Rheumatic fever.

It occurs in a small percentage of individuals, 2 - 3 weeks after an untreated pharyngeal infection that was caused by a B hemolytic group A Strep.

Joints and heart affected.

May be an immunological reaction - antibody to Strep also binding to heart/joint tissue.

Glomerulonephritis.

Most cases of glomerulonephritis occur about a week after group A Strep infection (skin or throat).

Also thought to be an immunolgical reaction in which a Strep-directed antibody reacts with the glomerular basement membrane; or antibody-antigen complexes are deposited onto basement membrane.

Leads to loss of protein (blood initially in urine) through kidneys and hypertension.

Can lead to kidney failure.

B-haemolytic streptococci

Group B Streptococci: S. agalactiae

Group D Streptococci - faecal flora - enterococci.

Group A - S.pyogenes

S. agalactiae

B-haemolytic

Group B

predominant species in this Lancefield group

Present in vaginal flora of up to 25% of woman.

May cause serious infections in newborn - septicaemia, pneumonia, meningitis with high fatality rates

Diagnostic tests include the hippurate test and the CAMP test

Group D Streptococci -

faecal flora - enterococci.

Urinary and wound infections.

Major problem of vancomycin-resistance.

α-hemolytic Streptococci

Viridans group:

Strep. Viridans is not a species but a large group of bacteria include many species that are normal inhabitants of throat and nasopharynx of humans

One example of a viridans species is S..mutans

Streptococcus pneumoniae

Viridans group:

a-haemolytic strep

Strep. Viridans is not a species but a large group of bacteria include many species that are normal inhabitants of throat and nasopharynx of humans.

One example of a viridans species is S..mutans which causes dental caries

Viridans Strep are a significant cause of bacterial endocarditis - infection of heart valve - invariably fatal if not treated.

Streptococcus pneumoniae

a-haemolytic strep

Lancet shaped organism - usually arranged in pairs (Diplococcus).

Virulent organisms are encapsulated. -resist phagocytosis.

Subdivided into 90 types on the basis of antigenicity of capsular polysaccaride.

Habitat: normal commensal of the upper respiratory tract.

Causes: acute lung inflammation. Chills, fever and pleural pain. Alveoli fill with exudate. Bacteremia occurs in 25%. Pneumococci may invade other tissues, eg. sinuses, middle ear and meninges.

10-20% mortality

Diagnosis

• direct smears of sputum examined for G+ encapsulated cocci

• Quellung test - encapsulated bacteria + type-specific antibody -> capsular swelling - capsule becomes more visible and refractile due to antiboby attachment.

• Growth of organism on blood agar – a-hemolytic mucoid colonies, sunken in center - (autolytic enzymes).

• Colonies are soluble in bile (10% deoxycholate drop onto colony - colony dissolves) and sensitive to optochin.

Treatment and vaccination

Can be treated with penicillin. However, strains of multiple-resistant pneumococci have appeared and are becoming increasingly common in some parts of the world.

These are presently treated with vancomycin but there are fears that resistance will spread from enterococci.

Vaccine has been made containing polysaccharide from 23 of the most prevalent types.

Gives 75 - 95% protection