2 - BACTERIOLOGY (GRAM-POSITIVE)

Gram positive cocci in clusters, catalase positive, coagulase positive

Staphylococcus aureus

Most common infection in open fractures?

Staphylococcus aureus

Gram positive cocci in clusters, catalase positive, coagulase negative, Novobiocin resistant

Staphylococcus saprophyticus

Gram positive cocci in clusters, catalase positive, coagulase negative, Novobiocin sensitive

Staphylococcus epidermidis

IV drug user with endocarditis affecting tricuspid valve

Staphylococcus aureus

Prosthetic heart valve develops endocarditis

Staphylococcus epidermidis

A patient who underwent dental surgery develops endocarditis. What is the causative agent?

Viridans Streptococci

Toxic Shock Syndrome caused by S. aureus (vs S. pyogenes)

S. aureus has no site of pyogenic inflammation and blood/CSF cultures negative

Toxin causing skin necrosis and hemolysis in Staphylococcus

Alpha toxin

mecA gene mediates what resistance in S. aureus

Methicillin resistance

Gram positive cocci in chains, catalase negative, beta hemolytic, bacitracin resistant, CAMP positive

Streptococcus agalactiae (Group B)

Gram positive cocci in chains, catalase negative, beta hemolytic, bacitracin sensitive, PYR test positive

Streptococcus pyogenes

(Group A)

Jones criteria for acute rheumatic fever includes:

Polyarthritis

Carditis

Subcutaneous nodules

Erythema marginatum

Sydenham chorea

Elevated Anti-Streptolysin O titers suggest

Antecedent streptococcal pharyngitis

Elevated Anti-DNAse B titers suggest

Antecedent streptococcal skin infection

Most common cause of neonatal pneumonia, sepsis, and meningitis

Streptococcus agalactiae

Pregnant women screened for Group B Strep at

35-37 weeks

Most common cause of CAP across all ages

Streptococcus pneumoniae

Rusty colored sputum characteristic of:

Streptococcus pneumoniae

Patient with migrating arthritis, serpiginous rash, fever, and Aschoff bodies/Anitschkow cells

Streptococcus pyogenes (Acute Rheumatic Fever)

Superficial infection extending into dermal lymphatics

Erysipelas (S. pyogenes)

Exotoxin B causes necrotizing fasciitis (flesh-eating disease)

Streptococcus pyogenes

Gram positive bacilli, spore-forming, aerobic, non-motile with malignant pustule

Bacillus anthracis

Most common form of anthrax

Cutaneous anthrax

Most deadly form of anthrax

Inhalational Anthrax

Drug of choice for cutaneous anthrax

Ciprofloxacin

Food poisoning after reheated fried rice (Gram +, spore-forming, aerobic, motile)

Bacillus cereus

Puncture wound, muscle rigidity (tetanus), toxin inhibits GABA release by cleaving synaptobrevin 2

Clostridium tetani

Mode of action of botulinum toxin

Blocking the release of acetylcholine

Most common source of infection in Floppy Baby Syndrome

Ingestion of spores in household dust or honey

Motorcycle accident with swollen arm, dark serous fluid, crepitus (gas gangrene)

Clostridium perfringes

Toxin responsible for gas gangrene

Lecithinase

Agar used for C. perfringens

Egg yolk agar

A 68-year-old woman was admitted for community-acquired pneumonia and started on clindamycin. One week later, she developed profuse watery diarrhea, lower abdominal cramping, and a low-grade fever. Her WBC count was elevated, and a stool toxin assay came back positive. Colonoscopy revealed pseudomembranes on the colonic mucosa.

Pseudomembranous colitis due to C. difficile

Antibiotics that can cause pseudomembranous colitis

Clindamycin, 2nd and 3rd Cephalosporins and Ampicillin

Disruption of actin cytoskeleton and tight junctions by toxin A (enterotoxin) and B (cytotoxin), leading to colonic

epithelial cell death and inflammation

1st step in treating C. difficile infection

Stop the antibiotic responsible for the infection

Antibiotic of choice for treatment of C. difficile

Oral vancomycin or fidaxomicin

Exotoxin mechanism of C. diphtheriae

Inhibits protein synthesis by adding ADP-ribose to elongation factor 2

Culture media of C. diphtheria

Loeffler’s medium or Potassium tellurite

Antibiotic choice for C. diphtheria

Erythromycin

Facultative intracellular rod, cold enhancement, narrow beta hemolysis

Listeria monocytogenes

Mode of listeria transmission

unpasteurized milk, across placenta, or contact during delivery

Escapes phagosome via toxin

Listeriolysin

Molar tooth colonies, jaw abscess after trauma

Actinomyces israelii

Treatment of choice for Actinomyces israelii

Penicillin

Weakly acid-fast, orange colonies, chronic cough, HIV patient

Nocardia asteroides

Drug of choice for Nocardia infection

Co-trimoxazole

Prosthetic valve

Staphylococcus epidermidis

Dental procedure

Viridans streptococci

GI/GU surgery

Enterococcus faecalis

Marantic endocarditis with S. bovis growth

Perform colonoscopy for colon cancer screening

Sequestered focus of osteomyelitis in metaphysis caused by S. aureus

Brodie abscess

Ritter disease: epidermal separation layer

Stratum granulosum