Multisystem, Nutrition & Genetics

Staphylococcus aureus. Coagulase-positive (distinguishes it from other staph); produces protein A (binds Fc of IgG), TSST-1 superantigen, exfoliatin (scalded skin), and a preformed heat-stable enterotoxin causing rapid-onset food poisoning. Treat with anti-staph penicillins (nafcillin/oxacillin) or vancomycin for MRSA.

Staphylococcus epidermidis. Coagulase-negative and novobiocin-sensitive; adheres via biofilm/polysaccharide capsule to prosthetic valves, joints, and catheters. A common blood-culture contaminant. Treat device infections with vancomycin (often methicillin-resistant).

Staphylococcus saprophyticus — the second most common cause of uncomplicated UTI in young women (after E. coli). Coagulase-negative and novobiocin-resistant (vs novobiocin-sensitive S. epidermidis).

Streptococcus pyogenes (Group A Strep). β-hemolytic, bacitracin-sensitive, PYR-positive. Causes pharyngitis, cellulitis/erysipelas, impetigo, scarlet fever, necrotizing fasciitis, and toxic shock (via exotoxin A superantigen). Sequelae: rheumatic fever (M-protein molecular mimicry) and post-streptococcal glomerulonephritis. Treat with penicillin.

Streptococcus agalactiae (Group B Strep). β-hemolytic, bacitracin-resistant, CAMP-test positive, hydrolyzes hippurate. Colonizes the vagina → neonatal sepsis, pneumonia, and meningitis. Screen pregnant women at 35–37 weeks; give intrapartum penicillin prophylaxis.

Streptococcus pneumoniae. α-hemolytic (green), optochin-sensitive, bile-soluble; IgA protease and a polysaccharide capsule (the main virulence factor — basis of vaccines). 'MOPS': Meningitis, Otitis media (children), Pneumonia, Sinusitis. Asplenic patients are at high risk. Treat with ceftriaxone ± vancomycin.