Microbiology

Gram + Bacteria

Streptococcus
Staphylcoccus
Bacillus
Clostridium
Corynebacterium
Listeria

Group A Strep
Hemolytic status, virulence factor

Beta hemolytic; Major virulence factor = M protein

What is ASO?

Anti-streptolysin O. Following strep infection, these antibodies develop and can be measured in pt's blood to confirm recent infection. O stands for oxygen labile.

4 diseases caused by Group A strep that are due to local invasion and/or exotoxin release

Streptococcal pharyngitis
Strep skin infections
Scarlet fever
Strep TSS

2 diseases caused by strep that are delayed antibody mediated

Rheumatic fever
Post-strep glomerulonephritis

Scarlet fever

Group A betahemolytic strep
Exotoxin releasee
Fever and rash that spares the face

Rheumatic fever
6 manifestations

Follows untreated strep throat
Fever, myocarditis, arthritis, chorea, subQ nodules, Rash - erythema marginatum

How does Rheumatic fever cause heart disease?

Antibody-mediated. Heart has antigens similar to strep, which causes an immunological attack on heart tissue.
Pts complain of chest pain and may develop arrhythmias or heart failure.
Mitral valve most often damaged.

Acute post-strep GN pathophysiology

Occurs ~ 1 week following throat OR skin strep infection.
Only a few stains can cause it
Ag-Ab complexes travel to and deposit in glomerular BM
Leads to glomerular destruction

Acute post-strep GN symptoms

Fluid retention
Tea-colored urine (hematuria)
HTN caused by hypervolemia
Hx of sore throat or skin infection one week ago.

Group B Strep
-diseases?
-presenting symptoms

Cause neonatal infections: meningitis, pneumonia, sepsis.
Infants present with nonspecific signs such as fever, vomiting, poor feeding, etc.

Viridans Group Strep
-? hemolytic
-Types of infections
-Optochin sensitivity?

-Alpha hemolytic
-Causes dental infections, endocarditis (SBE!) and abscesses
-Optochin RESISTANT

Group D Strep
-subtypes

Enterococcus
Non-enterococcus

Enterococcus

Alpha hemolytic
Normal bowel flora - grow well in bile or NaCL
Common infecting agents in UTIs, biliary tract infections, bacteremia, and SBE
Common nosocomial infection sources
Resistant to most drugs used for Gram +

Streptococcus pneumoniae
-microscopic appearance
-Virulence factor
-Diseases
-Optochin sensitivity?

Lancet shaped diplococci
Major virulence factor = polysaccharide capsule
Optochin sensitive!
Most common cause of OM in kids and bacterial meningitis and pneumonia in adults

Staphylococci
-Most are resistant to what Abx?
-Catalase?
-Coagulase?

* Most resistant to Penicillin G
* Staph are catalase +
* S. Aureus is coagulase +

Staph Aureus virulence factors

Protein A (prevent opsonization)
Coagulase
Hemolysins (destroys blood cells)
Leukocidins
Penicillinase (beta-lactamase)

Staph aureus diseases caused by exotoxin release (3)

1. Gastroenteritis
2. Toxic Shock Syndrome (TSST-1 toxin)
3. Scalded skin syndrome (exfoliatin toxin)

S. Aureus diseases caused by direct organic invasion by the bacteria

Pneumonia, meningitis, osteomyelitis, Acute bacterial endocarditis, Septic arthritis, Skin infections, Bacteremia, UTI

Treatment for MRSA

Vancomycin

Staph epidermidis

Normal flora
Coag-
Infects prosthetic devices and catheters
Contaminates blood cultures

Spore-forming Gram + rods

Bacillus
Clostridium

Bacillus anthracis

G+ rod
Virulence factor = protein capsule (only bacteria with this)
Causes cutaneous, respiratory, and intestinal anthrax disease
Releases exotoxin

Bacillus cereus

Motile, non-capsulated, resistant to PCN.
Causes food poisoning (2 types) via preformed enterotoxins
-Heat labile toxin causes nausea, abd. pain and diarrhea
-Heat-stable toxin causes severe N/V without much diarrhea.

Clostridium

G+ spore-forming ANAEROBE
Secrete very powerful exotoxins and enzymes.

Clostridium botulinum
-mechanism
-what it causes

-produces a lethal neurotoxin that blocks the release of ACh at NMJ
-Causes flaccid paralysis from ingesting preformed toxin (adults) or spores in honey (babies)

Clostridium tetani
-mechanism

*produces an exotoxin which acts on Renshaw cell interneurons in SC, preventing release of GABA/Glycine (inhibitory NTs)
-Results in sustained muscle contractions

How should you treat the following people with skin wounds about which you are worried about tetanus:
1. Immunized as a child but more than 10 years since last booster
2. Never been immunized
3. Already developed tetanus

1. Give a booster
2. Give a booster AND human tetanus Igs
3. Give human Ig, booster and penicillin, as well as supportive therapy

Clostridium perfringens

-Spores can be found in soil and infect wounds.
-Produces an alpha toxin (lecithinase) that causes myonecrosis and hemolysis

Clostridium difficile
-mechanism of disease
-what it causes
-how to treat it

-Produces a cytotoxin (exotoxin) that kills enterocytes. Often d/t antibiotic use, esp. clindamycin or ampicillin
-Treat with metro or vanco
-causes pseudomembranous colitis

Corynebacterium Diphtheriae
-Disease it causes
-Exotoxin

-Causes diphtheria - sx are pseudomembranous pharyngitis and lymphadenopathy
-Exotoxin is encoded by ß-prophage and inhibits protein synthesis via ADP ribosylation of EF-2

The only Gram + organism that has an endotoxin

Listeria monocytogenes

Listeria monocytogenes
-How is it acquired?
-What disease does it cause?

-Acquired by ingesting unpasteurized dairy or by vaginal transmission at birth
-Causes amnionitis, septicemia, and SA in pregnant women
-Also causes granulomatosis infantiseptica, neonatal meningitis, meningitis in immunocompromised pts, mild gastroenteri