Gram-positive — Flashcards

Flashcard 1: Gas gangrene

Answer: Clostridium perfringens

Extra: alpha toxin causes myonecrosis and hemolysis

Flashcard 2: Gram stain status of Clostridium perfringens

Answer: Gram-positive (+)

Extra: Characteristics: - Morphology: Large, box-car shaped Gram-positive bacilli - Oxygen requirement: Anaerobe - Pathogenesis: Alpha toxin (lecithinase) - Clinical: Gas gangrene (myonecrosis), food poisoning

Flashcard 3: Characteristics of Clostridium botulinum:

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

Extra: Clinical features: Botulism (descending paralysis), Floppy baby syndrome (infant botulism from honey). Toxin: Botulinum toxin (protease that cleaves SNARE proteins, preventing ACh release).

Flashcard 4: What are the key microbiological characteristics and toxins of Clostridium tetani?

Answer: Gram-positive, anaerobic, spore-forming bacilli (drumstick appearance)

Extra: - Tetanospasmin: Neurotoxin that blocks release of inhibitory neurotransmitters (GABA and glycine) from Renshaw cells in spinal cord. - Clinical features: Trismus (lockjaw), Risus sardonicus (raised brows, open grin), Opisthotonus (back arching). - Spores are found in soil; enter via penetrating wounds.

Flashcard 5: _____, _____, and _____ are important spore-forming Gram-positive bacteria found in soil.

Answer: Bacillus anthracis

Flashcard 6: What is the causative agent of Diphtheria?

Answer: Corynebacterium diphtheriae

Extra: Exotoxin inhibits protein synthesis via ADP-ribosylation of EF-2. Presentation: Pseudomembranous pharyngitis (grayish-white membrane), cervical lymphadenopathy ("bull neck"), myocarditis, arrhythmias, and cranial nerve palsies.

Flashcard 7: Gram stain and morphology of Corynebacterium diphtheriae:

Answer: Gram-positive bacilli (non-spore forming)

Extra: - Morphologically described as club-shaped, V or L shaped (Chinese letter appearance). - Culture: Black colonies on Cystine-Tellurite agar (Tinsdale medium). - Biochemical: Catalase positive. - Key pathogen: Causes Diphtheria (pseudomembranous pharyngitis).

Flashcard 8: What is the clinical significance of Streptococcus bovis bacteremia?

Answer: Bacteremia and subacute endocarditis associated with colon cancer.

Extra: Streptococcus bovis (Group D streptococci) can grow in bile but not in 6.5% NaCl (unlike Enterococci). Presence in blood is a classic herald for underlying colorectal malignancy.

Flashcard 9: Gram stain and key biochemical characteristics of Enterococcus (E. faecalis/faecium)?

Answer: Gram-positive cocci; Catalase-negative; Grows in 6.5% NaCl and Bile Esculin.

Extra: Part of normal colonic flora; penicillin G resistant. Causes: UTI, biliary tract infections, and subacute endocarditis (following GI/GU procedures). VRE (vancomycin-resistant enterococci) are an important cause of nosocomial infections.

Flashcard 10: What are the primary clinical conditions caused by Streptococcus agalactiae (Group B Strep) and its key biochemical identification test?

Answer: CAMP test positive; Neonatal sepsis, meningitis, and pneumonia.

Extra: - Gram-positive cocci in chains. - Beta-hemolytic. - Bacitracin resistant (distinguishes from S. pyogenes). - Colonizes the maternal vagina; screened at 35-37 weeks gestation.