Microbiology Lecture Final: New Content

Basic characteristics of staphylococcus

• Grape-like clusters

• Common microbiota of the skin and mucous membranes

• Characteristics:

  •  Catalase positive 

    • 2H₂O₂ →      2H₂0 + O₂

  • Some form capsules or slime layer 

  • Facultative anaerobes

  • Salt tolerant

Streptococcus disease manifestations

• S. aureus

• Capsule/slime layer

  • Inhibits phagocytosis

  • Increases adherence to artificial surfaces and forms biofilms

• Protein A

  •   Surface protein

  •  Bind Fe portion of antibodies

Staphylococcus exoenzymes

• Coagulase

• Staphylokinase

• Hyaluronidase

• Lipase

• Beta-lactamase

Staphylococcus exotoxins

• Hemolysins

• Enterotoxin (interstitial) 

• Exfoliative toxin

• Toxic shock syndrome toxin (TSST)

Coagulase

•  Clot blood

•  Helps S. aureus establish infection 

Staphylokinase

S. Aureus:  Dissolves clot to invade deeper into tissues

S. Pyogenes:  Lyses blood clots 

•  Aids spread of infection

Hyaluronidase

•  Break down matrix between cells 

Lipase

•  Hydrolyzes bonds in lipids

Beta-lactamase

• – some strains

  • Alters beta-lactam ring of some antibiotics

Hemolysins

•   Lyse RBCs

Enterotoxin (interstitial)

• Heat stable

• Induces nausea, diarrhea

Exfoliative toxin

•   Skin cells to separate and pull apart 

Toxic Shock Syndrome Toxin (TSST)

• Superantigen

  Massive T-cell activation and lots of inflammation

common skin infections caused by S. aureus

1. Impetigo

2. Folliculitis

3. Furuncle

4. Carbuncle

5. MRSA (methicillin resistant S. aureus)

Impetigo

-Pus-filled sores

• Spreads easily

• Treat with antibiotics

• May scar if not treated

Folliculitis

• Infection of a hair follicle

  •  Lipase to break down sebum 

Furuncle

• Also called boils

• When infection from folliculitis progresses into deeper tissue

Carbuncle

Multiple furuncles spreading under the tissue

MRSA (methicillin resistant S. aureus)

• Usually present as skin infections

• Hospital acquired MRSA

• Community acquired MRSA

• Incidence of serious infections has decreased

Systemic Staph Aureus Infections

1. Osteomyelitis

2. Pneumonia

   1. S. aureus fatality rate 50%

3. Endocarditis

4. Meningitis

5. Bacteremia -> sepsis (50% mortality) 

Osteomyelitis

•  invasion of bone (high fever)

Staphylococcus Toxigenic Infections

• Scalded skin syndrome -> high fevers 

  • Exfoliative toxin

• Food poisoning 

  • Enterotoxin

• Toxic Shock Syndrome

  •  Toxic shock syndrome toxin

  • Sudden onset of high temperature

  • Vomiting

  • Diarrhea

  • Rash

  • Confusion

Basic characteristics of streptococcus

• G+ cocci in chains

• Non-motile, usually 

• Non-spore forming

• Facultative anaerobes

  •  Some capnophiles 

    •  Grow best at high CO2 concentrations (candle jar) 

• Catalase negative

  • Peroxidase positive

H₂O₂ + NADH + H⁺ -------🡪 2H₂O + NAD⁺

Streptococcus classification

• Hemolysis patterns on blood agar

  • Alpha ( α )

    • Partial hemolysis, greenish

  • Beta ( β )

    • Total hemolysis of RBC

  • Gamma ( γ )

    • No hemolysis of RBC

• Lancefield groups

  • Named for Rebecca Lancefield (1930s)

  •  Based on carbohydrate on surface of cell

Streptococcus pyogenes virulence factors

• Surface

  • Hyaluronic acid capsule -> adhere

    • Evades phagocytosis

  • M protein

  • C Carbohydrate

  • C5a protease

M protein

• less C3b, less phagocytosis

  • Function

    • Inhibits activation by alternative complement pathway

C carbohydrates

• Basis for Lancefield Groups

• Function

  •  Protects cell from lysozyme -> cleaves NAM-NAG bonds 

S. pyogenes exoenzymes

• Streptokinase

• Hyaluronidase- digest connective tissue 

• Streptodornase (DNase)

Hyaluronidase

• digest connective tissue 

Streptodornase (DNase)

• Protects bacteria from becoming trapped in neutrophil extracellular traps (NETS) by digesting the NET’s web of DNA

S. pyogenes exotoxins

1. Streptolysin

2. Erythrogenic toxin

Streptolysin

• (a kind of hemolysin)

  • Acts on RBC’s, WBC’s, platelets

  • Role:

    • Growth and nutrient acquisition

    • Causes lysosomes to release their contents after phagocytosis kill WBCs

Erythrogenic Toxin

• (considered a pyrogenic (heat fever) toxin)

  • Superantigen carried on a lysogenic phage

  • Produces a bright red rash all over body

    • Followed by high fever (scarlet fever)

S. pyogenes infections

1. Impetigo → similar to S. aureus

2. Erysipelas

3. Cellulitis

4. Necrotizing fasciitis

5. Streptococcal pharyngitis (strep throat)

6. Secondary infections

   • Bronchitis, pneumonia

   • Scarlet fever

Erysipelas

• Raised red lesions

  • “Orange peel” consistency

• Usually begins after a mild trauma or burn

• High fever, 

• Many possible complications

Cellulitis

• Usually occurs on hands, face, or legs

• GAS commonly enters through a break in the skin

• Localized inflammation 

  • Swelling, redness, pain

  • Can involve deeper tissues

• Can spread to bloodstream and become life threatening

Necrotizing fasciitis

• Exoenzymes allow digestion of connective tissue

• Treatable if caught early on

• Mortality 50%

Streptococcal pharyngitis (strep throat)

• Transmission through droplets

• Signs/symptoms:

  • pus pockets on tonsils due to production of pyogenic toxin  

  • Fever

  • Sore throat

  • Abdominal pain

  • May have nausea, vomiting

  • Swollen lymph nodes

Complications of Strep Throat

Scarlet Fever

Rheumatic Fever

Acute glomerulonephritis

Rheumatic Fever

• 3-4 weeks after an untreated/ partially treated Gr. A strept infection

• Most common in children ages 5-15

• Nodules under skin

• Abnormal electrocardiogram

• Painful, swollen joints, fever, rash

• Our antibodies to Group A antigens cross react with proteins found in our body, most commonly heart valves

Scarlet Fever

Erythrogenic toxin produced by some strains, causing symptoms of

• Red rash

• Strawberry tongue

• Rare but serious complications

Acute glomerulonephritis

• Antibodies target kidneys

  • Blood flow obstructed

    • High blood pressure

    • Low urine output

• Damage can be permanent

S. agalactiae

• β-hemolytic

• Group B

• Forms capsules

• Normal microbiota in humans and mammals

  • Pharynx, large intestine, vagina

• Neonatal infections

  • Pneumonia

  • Sepsis

  • Meningitis

Streptococcus pneumoniae

• Forms capsules

• Disease

  1. Pneumonia

  2. Otitis media

     • Common in young children

     • Often follows viral infections

  3. Meningitis

S. Pneumoniae Pneumonia

• 85% of bacterial pneumonia

• Abnormal breathing sounds (crackles, pops, etc.)

• Cyanosis

• Treatable

Meningitis

• Crosses the blood-brain barrier

• Inflammation, permanent damage like retardation, blindness, deafness

• Less common now due to pneumococcal vaccine:

  • Conjugate vaccine: combines a weak antigen with a strong antigen as a carrier

S. pneumoniae vaccine

• Pneumococcal conjugate vaccines (PCVs) and pneumococcal polysaccharide vaccines (PPVs) are available.

• PCVs have significantly reduced invasive diseases caused by the serotypes they target.

Neisseria

• Nonmotile

• Aerobes

• Fastidious

  • N. gonorrhoeae-  

  • N. meningitidis-

N. gonorrhoeae

• Causative agent of gonorrhea

• Transmission

  •  sexual intercourse

    • Carried by sperm and vaginal fluid

  • mother to child

    • All babies treated with antibiotic eyedrops to prevent

         gonococcal ophthalmia neonatorum

  
  

N. gonorrhoeae infections symptoms

• Males:

  • Burning while urinating

  • Pus-filled discharge

  • Painful

  • Infertility, potential for dissemination

• Females

  • Painful urination

  • Vaginal discharge 

  • More serious complications

    • PID (pelvic inflammatory disease)

    • Infertility

    • Dissemination to other parts of body

N. gonorrhoeae virulence factors

• Fimbriae (pili)

  • Attachment to epithelial cells

    • Property of fimbriae that makes vaccine development difficult:

      • Composition of fimbriae proteins changes

• Exoenzyme: protease

  • Cleaves IgA

• LOS (lipooligosaccharide)

  •  A form of LPS

N. gonorrhoeae treatment

• Ceftriaxone (a cephalosporin) 

  • by injection

• Resistance a growing concern:

  • Gonorrhea “superbugs” resistant to ceftriaxone, azithromycin, penicillin, sulfonamides, tetracycline, fluoroquinolones, and macrolides. 

• Vaccine?

  • no licensed vaccine

  • Producing effective antibodies against N. gonorrhoeae is challenging because the bacterium uses antigenic and phase variation to rapidly change its surface molecules, like pili and Opa proteins. This prevents the immune system from developing lasting protective immunity after an infection and makes vaccine development difficult, as a vaccine must target a conserved antigen that the bacteria can't change. A vaccine that targets variable antigens will not be effective against new strains, and the bacteria's ability to switch antigens also means that a prior infection doesn't confer protection against future reinfections. 

Neisseria meningitidis

• Reservoir: humans 

• Transmission: droplet spread

  • Close contact: sneezing, coughing

• Disease

  • Meningococcal meningitis

    • Early symptoms:

      • fever

      •  headache

      •  stiff neck

      •  photophobia

      •  nausea and vomiting

      • confusion

• As infection quickly progresses:

  Release of outer membrane (endotoxin) called blebbing 

  •  100-100x more toxic -> more is released 

  • Petechiae

    • Black spots on skin caused by broken capillaries

  • Septic shock

  • High fever

  • Delirium, cardiac arrest

  • 10-20% mortality

virulence factors of Neisseria meningitidis

• ame as N. gonorrhoeae:

  • LOS, endotoxin

  • IgA protease

  • Fimbriae/Pili -> attachment 

    •  have protein adhesins specific for meninges

• Capsule 

  •  Antiphagocytic, helps avoid complement 

  •  5 main serotypes 

    • BA, B, C, Y, W -> 90% of disease 

Individuals most at risk for Neisseria meningitidis

• Infants less than 1 years old (capsule is T independent antigen)

• Adolescents and adults 10-20 yrs. old

• Individuals with complement deficiencies

• Individuals without spleens

• Individuals that are immunosuppressed

Neisseria meningitidis treatment

• Cephalosporin

• Anti-inflammatories to counteract endotoxin release

• Prophylactic antibiotics if exposed

Neisseria meningitidis vaccine

•  Meningococcal conjugate 

  •  MenACWY

  • Age 11-12, booster at 16

  • Sep. vaccine B serotype

Basic characteristics of Bacillus

• Environmental, also normal microbiota

• Aerobic

• Saprophytic

  •  Live on dead and dying organic material 

• Some are a source of antibiotics

• Form endospores

  •   In environment 

•   Some form capsules 

  •  In host, not environment 

• Examples

  • B. subtilis

  • B. cereus -> food poisoning 

  • B. anthracis -> anthrax

B. anthracis epidemiology

• Soil reservoir

• Zoonotic

  • A disease of livestock

  •  People don’t spread to other people -> not contagious 

B. anthracis virulence factors

• Capsule

  • Poly-D-glutamic acid (unique) -> amino acid 

  • Resists complement

    • Blocks phagocytosis

• Exotoxins

  • Edema toxin

    •  Causing swelling of tissues

  • Lethal toxin

    •  Causes cell death

Methods of anthrax transmission

1.Cutaneous anthrax

2. Pulmonary (Inhalation) Anthrax
“Woolsorter’s disease

3. Gastrointestinal anthrax

4. Injection Anthrax

Cutaneous anthrax

• Most common form, least likely to kill host

• Endospores enter through break in skin

  • Nodule formation

    •  Abnormal aggregate of tissue 

  • Eschar forms (black scab)

    •  Painless 

    •  20% mortality rate if left untreated -> 1%

• Who is at risk?

  •  People working with animals

Pulmonary (Inhalation) Anthrax
“Woolsorter’s disease”

• Endospores inhaled

  • Incubation period typically 1-6 days

• Prodromal phase

  •  Flu-like symptoms 

• Invasive phase (illness phase)

  • Extremely high fever

  • Pulmonary edema

  • Shock                         Mediastinal widening 

  • Lethal toxin acts on macrophage

  • 99.9% fatal without treatment

Gastrointestinal anthrax

• Spores ingested

• Necrosis, hemorrhaging of intestines

• Severe ascites

  •  Abdominal swelling 

• Near 100% mortality without treatment

Injection Anthrax

• IV drug users

  • Drugs contaminated with spores

  • Soft tissue infections, more deadly than cutaneous

Anthrax treatment

• antibiotics – also given prophylactically

• monoclonal antibody to neutralize toxins -> 2012

Anthrax transmission

• Effective in animals

• Human vaccine protects 1 yr. –only given to high risk individuals

Clostridium

-Gram + rods

-Endospore producers

•  Anaerobes, catalase (-) w

• Found in soil, sewage, vegetative debris

  • Saprobes (decomposers) 

  • Some species commensals with humans

  •  Many species produce neurotoxins 

Examples:

• C. botulinum

• C. tetani

• C. difficile (Now known as Clostridioides difficile)

• C. perfringens

  • Food poisoning 

  • Gas gangrene

C. botulinum virulence factor

Botulinum Neurotoxin

• Targets neuromuscular junctions

• Prevent acetylcholine release

• Leads to

  •  Flaccid paralysis “limp” 

  •  Lead to eventual suffocation

C. botulinum

• Foodborne botulism

  •  caused by  

  •   Ingesting toxin, typically caused by consuming improperly 

canned food 

• Early symptoms appear after 12-72 hours:

  •  Blurred vision or double vision 

  •  Ptosis (drooping eyelids) 

  •  Difficulty swallowing 

  • Abdominal cramps

  • Nausea, vomiting

  • Constipation or diarrhea

• Followed by

  • Gradual weakening and loss of control over muscles

  • Progressive flaccid paralysis and death by asphyxiation (without treatment)

Infant botulism

Caused by ingestion of spores

• Immature normal microbiota 

• Often in honey 

• “Floppy baby syndrome”

  • Difficulty in feeding, fussiness, weak and altered cry, ptosis

Wound botulism

• Spores germinate in wounds

  • After traumatic injury, deep puncture wound, or IV drug users

• Symptoms mimic foodborne

Wound botulism treatment

• Passive immunization with antitoxin

• Respiration and cardiac support

• Antibiotics for infant botulism

Avian botulism

a paralytic disease in birds caused by the ingestion of a toxin from the bacterium Clostridium botulinum

C. tetani  - tetanus “lockjaw”

• Spores contaminate a wound 

• Virulence factor

  • Tetanus neurotoxin 

  • Similar action as botulinum toxin, but effect is different

    • Muscles lose the ability to relax

      • First symptom: inability to relax the jaw 

        • Progresses to back 

        • Opisthotonus -> extreme arching 

• Death due to respiratory failure – fatality rate 10-70%

C. tetani  - treatment

• Treatment (50% mortality without)

  • Penicillin or another antibiotic 

  • Passive  immunotherapy with immunoglobulin

    • Human tetanus immune globulin (TIG)

  • Assisted breathing with use of ventilator

• Vaccine

  • tetanus toxoid

    • DTaP, Tdap, or Td

    •  Lasts about 10 years

Clostridioides difficile

•  Persistent diarrhea 

•  15,000 deaths in US annually 

• Normal microbiota of large intestine

  • Opportunistic pathogen

  • When normal microbiota altered by antibiotics

• Transmission – spores spread in feces

• Diarrhea ranges from mild to severe

  • Pseudomembranous colitis

  • Can potentially perforate the colon

Clostridioides difficile virulence factors

• Toxin A - an enterotoxin

• Toxin B- a cytotoxin

•  Exotoxins causes death of epithelial cells

Clostridioides difficile treatment

• Vancomycin (orally)

• FMT for recurring cases

  • Fecal Microbiota Transplantation

    • Repopulates normal microbiota

    • 80-95% success rate

Mycobacterium  characteristics

• Acid Fast bacilli

• Strict aerobes

•  Non-spore formers 

• No capsule

• No flagella

• About 75 species known

  • M. leprae - leprosy

  • M. bovis – bovine TB

  • M. tuberculosis

    • 1 in 4 infected worldwide with tuberculosis

    • Killed 1.25 million globally 2023

M. tuberculosis

Epidemiology

• Reservoir:  humans only 

• Transmission

  •   Droplet nuclei -> airborne 

  • Risk factors

    • HIV+

    • Inadequate nutrition

    • People living in congregate settings

M. tuberculosis virulence factors

Acid Fast cell walls

• Composed of  mycolic acid (fatty acid)

• Cell walls also contain cord factor (glycolipid)

• Mechanisms that

  • Cause the phagosome to fail to acidify

•  A mechanism to survive the nutrient deprivation inside the macrophage:

  •  Glyoxylate cycle:

Cord factor

• Cells remain attached

• Inhibits migration of neutrophils

• Inhibits fusion of phagosome with lysosome

Glyoxylate cycle

• a variant of Krebs cycle that allows organism to survive on 2C compounds like acetate

Mycolic acid (fatty acid)

• Resistance to digestion in the phagolysosome

• Resistance to drying and germicides

• Resistant to many antibiotics

• Also contributes to slow growth rate

Primary TB

• Inhalation

• Targets alveolar macrophages

  • bacilli replicate freely in the macrophages

    • Causes mild flu-like symptoms -> 80-80% fight off

• Tubercle formation in lungs

  • Specialized granuloma (mass of tissue)

  • Stalemate between bacteria and host

  • Collagen deposited

  •  Tubercules can be described as

    •  Ghon complexes-  little more calcified

    •  Caseous necrosis-  cheese-like consistency 

  •  Patient not contagious - latent

Secondary TB (reactivated)

• Infection progresses in 10% of individuals to this stage

•  Now infectious 

• Early symptoms

  • Productive cough

  • Chest pain

  • Bloody sputum

• Late symptoms

  • Fever, chills, night sweats

  • Appetite loss, weight loss

  • Paleness

  • Easily tired

3^rd stage disseminated (or miliary) TB

• Loss of kidney function

• Bones easily bent and fractured

• Meningitis

TB diagnosis

• Tuberculin skin test, mantoux 

  • Injection of TB protein derivative under skin

  • Positive for vaccination, primary TB, 

    active TB

• TB blood tests

  • Interferon gamma release assays (IGRA)

  • Prior vaccination does not cause positive

• Chest x-rays

  • tubercles

• Microscopy of Sputum

  • Acid fast staining

  • Fluorescent staining

TB Treatment

• Streptomycin – 1^st drug to treat (1946)

• Isoniazid, rifampicin, 2 others

  •  6 months 

  •  Side effects common: nausea, tiredness, rash, headache 

• Resistant forms

  • MDR (multiple drug resistant)   - 10% of new cases 

    • Resistant to first line drugs - 9 months 

    • Treat with kanamycin, fluoroquinolones, streptomycin

  • XDR (extensively drug resistant )   1-37% of new cases

    • Bedaquiline (new 2012) 

      • Interferes with mycobacterial ATP synthase

    • Pretomanid (new 2019)

      • Interferes with cells wall synthesis: lots of serious side effects

TB vaccines

• Bacille Calmette-Guerin (BCG)

  • Attenuated vaccine

    • Derived from Mycobacterium bovis

  • Effectiveness

    • Up to 80% in children

    • Less effective in adults (20-50%)

    • Protection lasts 5-15 years

  • Individuals test positive for tuberculin skin test -> complicates skin test