Microbiology

Bacteriology, virology, mycology and parasitology paired with antimicrobial mechanisms — the highest-volume memorization block.

Exam weight 10–15% · 2 QBank items · 4 flashcards

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Gram-positive bacteria

S aureus: catalase +, coagulase +; causes abscess, endocarditis in IV drug use, toxic shock via TSST-1 superantigen.
S pneumoniae: lancet-shaped diplococci, optochin sensitive; MOPS — meningitis, otitis, pneumonia, sinusitis.
Group B strep colonises the vagina — screen at 35–37 weeks and give intrapartum penicillin.
Clostridioides difficile follows antibiotics; toxins A and B cause pseudomembranous colitis — treat with oral vancomycin or fidaxomicin.

Neisseria meningitidis: maltose fermenter, ferments both maltose and glucose; N gonorrhoeae ferments glucose only.
Pseudomonas: oxidase +, non-lactose fermenter, grape-like odour, blue-green pigment; classic in burns, cystic fibrosis, hot-tub folliculitis.
H pylori: urease +, causes duodenal ulcer and MALT lymphoma; triple therapy with PPI + clarithromycin + amoxicillin.
Legionella: silver stain, charcoal yeast extract with cysteine and iron, hyponatremia and diarrhea with pneumonia; urine antigen test.

DNA viruses are double-stranded except parvovirus; RNA viruses are single-stranded except reovirus.
HBV serology: anti-HBs alone = vaccinated; anti-HBc IgM with negative HBsAg and anti-HBs = window period.
HIV enters via gp120 binding CD4 plus CCR5 (early) or CXCR4 (late); CCR5-Δ32 homozygotes are resistant.
Herpes latency sites: HSV-1 trigeminal ganglion, HSV-2 sacral ganglion, VZV dorsal root ganglia.

Cryptococcus: India ink halo, latex agglutination, soap-bubble brain lesions in AIDS.
Aspergillus: acute-angle branching septate hyphae; allergic bronchopulmonary aspergillosis in asthma and cystic fibrosis.
Mucor/Rhizopus: wide-angle non-septate hyphae in diabetic ketoacidosis with black eschar — surgical emergency.
Plasmodium falciparum: irregular fever, parasitized RBC rosetting causes cerebral malaria; treat with artemisinin combination therapy.

Cell wall: penicillins and cephalosporins (transpeptidase), vancomycin (D-Ala-D-Ala).
30S: aminoglycosides (bactericidal) and tetracyclines (bacteriostatic); 50S: macrolides, clindamycin, linezolid, chloramphenicol.
Fluoroquinolones inhibit DNA gyrase — tendon rupture, avoid in children and pregnancy.
Anti-TB: RIPE — rifampin (orange fluids, CYP inducer), isoniazid (B6-responsive neuropathy), pyrazinamide (hyperuricemia), ethambutol (optic neuritis).