Gram-positive — Flashcards

Flashcard 11: scarlet fever

Answer: S. pyogenes infection

Extra: erythematous rash sparing face, strawberry tongue, erythematous throat

Flashcard 12: Group A strep are _____ to bacitracin.

Answer: sensitive

Flashcard 13: Group B strep are _____ to bacitracin.

Answer: resistant

Flashcard 14: Strep pyogenes is a Group _____ streptococcus.

Answer: A

Flashcard 15: Gram stain and morphology of Staphylococcus aureus?

Answer: Gram-positive cocci in clusters, Catalase (+), Coagulase (+)

Extra: Clinical presentations: Skin infections, abscesses, pneumonia, endocarditis, osteomyelitis, toxic shock syndrome (TSST-1), scalded skin syndrome (exfoliatin), food poisoning (enterotoxin).

Flashcard 16: Staphylococcal Toxic Shock Syndrome Toxin (TSST) is a superantigen that binds to _____ and _____.

Answer: MHC II

Flashcard 17: Toxin responsible for Toxic Shock Syndrome (TSS) in Staphylococcus aureus infection?

Answer: TSST-1 (Toxic Shock Syndrome Toxin-1), which acts as a superantigen.

Extra: Clinical presentation: Fever, vomiting, rash, desquamation, shock, and multisystem organ failure. Typically associated with prolonged tampon use or wound infections.

Flashcard 18: Identify the Gram-positive, catalase-positive, coagulase-negative cocci that is Novobiocin sensitive and a common cause of prosthetic valve endocarditis.

Answer: Staphylococcus epidermidis

Extra: Catalase (+), Coagulase (-), Novobiocin Sensitive. Frequently infects prosthetic devices and IV catheters due to biofilm production (extracellular polysaccharide matrix).

Flashcard 19: What are the key microbiological characteristics and common infections caused by Streptococcus pneumoniae?

Answer: Lancet-shaped Gram-positive diplococci, Optochin sensitive, Quellung reaction positive.

Extra: Streptococcus pneumoniae is a leading cause of: - Meningitis - Otitis media - Pneumonia (rust-colored sputum) - Sinusitis (Mnemonic: MOPS)

Flashcard 20: Gram stain and morphology of Clostridium difficile?

Answer: Gram-positive, anaerobic, spore-forming bacilli

Extra: Disease: Pseudomembranous colitis (often secondary to antibiotic use). Pathogenesis: Toxin A (enterotoxin) and Toxin B (cytotoxin). Both toxins act by inactivating Rho GTPases, leading to actin depolymerization and mucosal damage. Treatment: Oral vancomycin or fidaxomicin. Metronidazole is no longer the first-line treatment for non-severe cases in many updated guidelines.