MSE-2019 gram negative bacteria

3 morphological types of gram negative bact.

Cocci, bacilli, coccobacilli

Lipid A in gram negative bacterial infections

• Endotoxin

• Induces fever, vasodilation, inflammation, shock and disseminated intravascular coagulation

Gram negative bacteria

• Constitute largest of human bacterial pathogens

• Part of gut flora (e. coli production of 1/8th K needed in humans)

Neisseria sp.

• gram negative cocci

• responsible for gonorrhoeea and meningitis

Enterobacteriae and pasteurellacae

• facultative anaerobic bacteria

• Accounts for almost half of all gram negative bacteria

Pseudomonas sp.

• gram negative aerobic bacilli

• Ubiquitous, requires water chlorination in bodies of water (swimming pools)

Bacteroides sp.

Anaerobic gram negative bacilli

Enterobacteriaceae

• Enteric - part of intestinal microbiotica

• Uniquitous in water soil and decaying vegetation

• Can be pathogenic or opportunistic

• Accounts for most nosocomial infections (hospital setting)

e.g. of enterobacteriaceae

• E.coli

• Causes 80% of UTIs in women

7 features of Enterobacteria structure/physiology

• Coccobacilli or bacilli

• 1um x 1.2-3um

• Presence of peritrichous flagella if motile

• Nitrate reduction to nitrite

• Can have prominent capsule or loose slime

• Facultative anaerobic (glucose fermentation)

• Oxidase negative

enterobacteria testing

• all share similar staining properties and microscopic appearance

• Biochemical tests, motility and colonies used to distinguish (MacConkey/blood agar)

E.

E. coli in MacConkey agar

Turns pink, E.coli ferments lactose in MacConkey

3 antigenic components making up outer membrane lipopolysaccharides (COL)

• Core polysaccharide

• O polysaccharide

• Lipid A

Core polysaccharide

Shared by all enteric bacteria, common antigen

O polysaccharide

• Contributes to immune system evasion

• Various antigenic varieties among and species

Enterobacteria immune system evasion

Controls genetic expression and alternatively producing/inhibiting K and H antigens

K antigens

Formation of protein and polysaccharide capsule around enterobacteria

H antigens

Flagellar proteins

Enterobacteriae species recognition

Serological identification of antigens used to distinguish strain and species

6 virulence factors of enterobacteria (LCFEIHT)

• Lipid A-induced disease

• Capsules evading immune system

• Fimbriae attachment to host surface

• Exotoxin release

• Iron binding compound-induced antibiotic dilution

• Haemolysins

• Type 3 secretion system

6 opportunistic coliforms (KESHEC)

• E. coli

• Klebsiella sp.

• Serratia sp.

• Enterobacter sp.

• Hafnai sp.

• Citrobacter sp.

Klebsiella sp.

Travels from gut, can spread to respiratory system during prolonged periods of bedrestCi

Citrobacter sp.

Opportunistic multi-resistance species

4 opportunistic noncoliforms

• Proteus sp.

• Morganella sp.

• Proveidencia sp.

• Edwardsiella sp.

Proteus sp.

• medically important

• Very motile

• Induces UTI

• Increases urine ph (~13), extremely alkaline

• Causes bladder stones

Coliforms vs noncoliforms

determined by ability to ferment lactose into acid and gas

3 truly pathogenic enterobacteria

• salmonella sp.

• Shigella sp.

• Yersinia sp.

E. coli

• most common and important coliform

• Has many O, H and K antigens - used in strain identification

• O157 antigen secretion - associated with virulence

• Transferable virulence plasmids

• Part of normal flora, can become pathogenic

2 types of noninvasive e.coli

• Enteropathogenic (EHEC, EPEC)

• Enterotoxigenic (LT, ST)

2 variants of enteropathogenic e.coli

EHEC - infection of human reservoir, VT toxin release

EPEC - zoonotic disease

2 types of invasive E.coli

• Nontoxigenic

• Toxigenic (STEC)

Nontoxigenic vs toxigenic e.coli

• harmless/mild disease vs severe illness

• shiga-like cytotoxins production in toxigenic leads to protein synthesis inhibitiion

4 diseases induced by E.coli

• UTIs

• Neonatal meningitis

• Gastroenteritis

• severe/ fatal hemorrhagic colitis

e. coli-induced neonatal meningitis

Mother’s water breaking and stress on baby leads to uptake of more bacteria

E.coli-induced gastroenteritis

• exotoxin (enterotoxin) release

• binds to proteins on intestinal tract cell lining

• Toxin enters cell and triggers series of chemical reactions

• Loss of electrolytes, diarrhoea and vomiting

• Common cause of paediatric infections in developing countries

E. coli-induced haemorrphagic colitis

• EHEC (O157:H7) produce large amounts of bacteriophage-mediated shiga-like toxin

• VT alter cytotoxic effect on cultured vero cells

• second cytotoxin production (shiga-like toxin 2/vero toxin 2)

E. coli treatment

Antimicrobials

E. coli disease prevention

Prevent faecal contamination in food and water

Truly pathogenic enterobacteria

• Noncoliform

• Not considered members of normal human microbiotia - almost always pathognic due to virulence factors

• Type 3 secretion system synthesis

Salmonella sp.

• gram negative

• Facultative anaerobe

• Motile - petrichous flagella

• numerous strains, induced infections more than once

• all species are pathognic to humans and animals

• Complex transmission cycle

Salmonella in poultry

• Cattle given antibiotics to prevent zoonotic spread

• Frequent resistance of cehalosporins observed

• Chicken/hens vaccinated against salmonella

Salmonella Enteridis on XLD agar

• Xylase lactose deficient agar - black colonies of salmonella

• Hydrogen sulphide production

5 main reservoirs of salmonella (GSFAH)

• GI of birds and animals

• Sewage

• Fertilisers/slurry

• Animmal feeds

• Human carriers

7 Foods susceptible to salmonella contamination (MDFCMWPb)

• meat products

• dairy products

• fish

• confectionery

• miscellaneous foods - dried yeast, frog legs

• Marijuana

• peanut butter

3 Salmonella enteritis infection symptoms (WAE)

• watery D&V

• abdominal pain

• Enteric fevers

salmonella enteritis clinical features

• 5-72 hrs incubation period

• Disease last 2-5 days

• Infective dose varies in food

2 salmonella enteritis species that induce serious infections

S. typhi, S. paratyphi

salmonella pathogenicity

• salmonella adhere to epithelial lining of ileum by fimbriae

• Invasion and proliferation

• Endotoxin production

• Self limiting disease (apart from immunocompromised and infants)

self limiting disease

condition that resolves on its own, typically no long-term harm

Prevention of salmonella contamination in food

• joint action by agriculture and food sectors industries and consumers

• Control starts on farm, continues through supply chain

S. typhi

• human-only hosts

• Infection via ingestion of contaminated food/water

• Bacteria pass through intestinal wall to bloodstream

• Phagocytised but not killed, carried to liver, spleen, bone marrow, gallbladder

3 types of S. typhi symptoms

• self-limiting symptoms - fever, headache, muscle pain

• gastroenteritis abdominal pain, recurring bacteremia

• Peritonitis in adbominal cavity

S. typhi recurring bacteremia

bacteria released from gallbladder re-infect intestines

S. typhi peritonitis

Bacteria ulcerate and perforate intestinal wall, abdominal space fills with bacteria and matter from GI tract

Mary Mallon

Typhoid mary, known for healthy carrier of typhoid fever

Shigella

• gram negative

• Non-spore forming

• rod-shaped

• closely related to e. coli and salmonella

• cause disease in primates

• Causative agent of human shigellosis

shigella serotype A

• S. dysenteriae

• typical cause of dysentry epidemic in confined ppopuations (refugee camps)

shigella serotype B

• S. flexneri

• most frequently isolated species worldwide

• accounts for 60% of cases in developing countries

shigella serotype C

s. boydil

shigella serotype D

• s. sonnei

• causes 77% of cases in developing countries (vs 15% in 1st world)

Shigella pathogenesis

• via ingestion of faecal contaminated food/water (very low infective dose)

• causes dysentry, result in destruction of epithelial cells of intestinal mucosa @ cecum and rectum

• some produce enterotoxin and shiga toxin (similar to VT O157:H7)

shiga and verotoxin

associated with causing haemolytic uremic syndrome

shigella action mechanism

• invades host through epithelial cells @ large intestine

• Uses Type 3 secretion system

• Includes virulence plasmid, enocdes conserved primary virulence determinants

Shigella chromosomes

share most genes with E. coli K12 strain MG1655

shigella treatment

• self-limiting

• replace fluid and electrolytes

• oral antibiotics (ciprofloxacin and cephalosporins)

• Vaccine - some success for flexneri

yerisinia

• typical pathogens of animals (zoonotic)

• contain virulence plasmids that code for adhesins and Type 3 secretion systems

3 notable yresinia species

• y. enterocolitica

• y. psuedotuberculosis

• y. pestis

Y. enterocolitca and psuedoTB

• enteric pathogens acquired via faecal-oral contamination

• enterocolitica occurs most often in young children

• may be confused for appendicitis in older children/adults - due to inflammation of mesenteric lymph nodes

Y. pestis

• plague - infectious disease of animal/humans

• infected by bite/handling of rodent flea carrying plague bacterium

• responsible for millions of deaths in middle ages, flea-infested rat infestations

Y. pestis treatment

• modern antibiotics effective against plague

• untimely treatment can cause illness or death

oriental rat flea

• male xenosylla cheopis

• main vector of y. pestis

2 types of plague

bubonic and pneumonie plague

Bubonic plague

• painful, swollen lymph nodes

• bacteremia results in DIC, subcutaneous hemorrhaging and tissue death (black death)

DIC

disseminated intravascular coagulopathy, abnormal blood clotting throughout blood vessels

Pneumonic plague

• pulmonary distress within a day

• Can spread person-person via aerosols and sputum

Pasteurellaceae

• Oxidase positive

• multocida carried in oral flora of cats and dogs - bite-induced infection

• only gram negative bacteria treated with penicillin

Haemophilus sp.

• requires growth factors

• influenza - common, carried as throat flora

• X factor (haemin) growth

• Needs blood agar to be heated (80oC) to grow colonies

bartonella and brucella

• gram negative bacteria

• rare organisms

• brucella spread from goat milk

Bordetella

pertussis - whooping cough

Burkholderia

• inherent/acquired multi-antibiotic resistance

• susceptible in cystic fibrosis patient, highly lethal