Microbiology — 30-Min Notes

1. Bacteriology

• Gram-positive cocci: Staphylococcus aureus → skin infections, abscess, MRSA; Streptococcus pyogenes → pharyngitis, rheumatic fever.

• Gram-negative cocci: Neisseria meningitidis → meningitis; Neisseria gonorrhoeae → STD, PID.

• High-yield: Oral pathogens → Streptococcus mutans → dental caries; Porphyromonas gingivalis → periodontitis

• Tip: Gram stain differentiates bacteria by cell wall composition; key for initial antibiotic selection.

• Bacilli: Clostridium tetani → tetanus; Clostridium perfringens → gas gangrene; Bacillus anthracis → anthrax.

2. Virology

• DNA viruses: Herpes simplex → vesicular lesions; Varicella-zoster → chickenpox, shingles.

• RNA viruses: Influenza, Hepatitis C, HIV → important systemic infections.

• High-yield: HIV → oral manifestations: candidiasis, hairy leukoplakia

• Tip: Vaccines available for HBV, HPV, and influenza; critical for prevention.

• Transmission routes: airborne, fecal-oral, sexual, parenteral; knowing route aids prevention strategies.

3. Mycology

• Candida albicans → oral thrush, denture stomatitis; opportunistic in immunocompromised.

• Aspergillus → pulmonary infections; can cause sinus involvement.

• High-yield: Oral fungal infections common in diabetes, immunocompromised patients

• Tip: KOH prep and culture for diagnosis; antifungals: nystatin, fluconazole.

• Histoplasma, Cryptococcus → systemic mycoses; rare in healthy adults.

4. Parasitology

• Plasmodium spp. → malaria; transmitted by Anopheles mosquito.

• Entamoeba histolytica → amoebic dysentery; Giardia lamblia → diarrhea.

• High-yield: Oral protozoa: Entamoeba gingivalis → associated with periodontal disease

• Tip: Stool examination, antigen tests, or PCR for diagnosis.

• Toxoplasma gondii → congenital infections; immunocompromised risk of encephalitis.

5. Immunology

• Innate immunity → first line: neutrophils, macrophages, complement system.

• Adaptive immunity → B cells (humoral), T cells (cell-mediated).

• High-yield: IgG → most abundant, crosses placenta; IgA → mucosal immunity

• Tip: Vaccines stimulate adaptive immunity; memory cells prevent reinfection.

• Hypersensitivity types: I (allergy), II (cytotoxic), III (immune complex), IV (delayed type).

6. Antibiotics & Resistance

• Beta-lactams → inhibit cell wall synthesis (penicillin, cephalosporins).

• Aminoglycosides → inhibit protein synthesis; nephrotoxic risk.

• High-yield: MRSA resistant to methicillin; VRE resistant to vancomycin

• Tip: Use culture and sensitivity to select appropriate antibiotic.

• Mechanisms of resistance: enzyme production (beta-lactamase), efflux pumps, target modification.

7. High-Yield Repeated Points (NEET MDS)

• Streptococcus mutans → dental caries

• Porphyromonas gingivalis → periodontitis

• HIV → oral candidiasis, hairy leukoplakia

• Candida albicans → opportunistic oral infections

• MRSA → resistant to methicillin; VRE → resistant to vancomycin

• Innate vs adaptive immunity → neutrophils/macrophages vs B/T cells

• Gram stain → differentiates bacteria; guides initial antibiotics

• Vaccine-preventable diseases → HBV, HPV, influenza