Microbiology – Study of Microorganisms
Microorganisms studied in Microbiology:
- Virus → Virology
- Bacteria → Bacteriology
- Fungi → Mycology
- Parasites → Parasitology
Virology (Study of Viruses)
General Rules
- DNA Viruses
- All are dsDNA, except Parvovirus → ssDNA
- All are linear, except:
- Papillomavirus → spiral / projection shape
- Hepadnavirus (HBV) → circular
- Envelope: Herpes virus acquires nuclear membrane, others from cell membrane
- RNA Viruses
- All are ssRNA, except Reovirus → dsRNA
1. DNA Viruses
| Virus Family | Genome | Shape | Envelope |
|---|---|---|---|
| Herpes virus | dsDNA | Linear | Enveloped (from nuclear membrane) |
| Parvovirus | ssDNA | Linear | Non-enveloped |
| Papillomavirus | dsDNA | Circular / Spiral-like projection | Non-enveloped |
| Hepadnavirus (HBV) | dsDNA (partially ds) | Circular | Enveloped |
| Others (Adeno, Pox, etc.) | dsDNA | Linear | Variable |
2. Herpesviridae Family (HSV–HHV Subtypes)
| Subtype | Name | Transmission | Clinical Features | Latency Site |
|---|---|---|---|---|
| HSV-1 | Herpes simplex virus type 1 | Respiratory route, Saliva | – Gingivostomatitis – Conjunctivitis – Meningitis | Trigeminal ganglia |
| HSV-2 | Herpes simplex virus type 2 | Sexual intercourse Vaginal delivery (→ need C-section) | – Painful genital ulcers | Sacral ganglia |
| HSV-3 | Varicella-zoster virus (VZV) | Respiratory route | – Chickenpox (rash, cough, vesicles) – Reactivation → Shingles – CN V1 involvement → Herpes zoster ophthalmicus | Dorsal root ganglia |
| HSV-4 | Epstein–Barr virus (EBV) | Respiratory route, Saliva | – Infectious mononucleosis (pharyngitis → splenomegaly → fever) – Burkitt’s lymphoma (t(8:14)) – Nasopharyngeal carcinoma | B lymphocytes |
| HSV-5 | Cytomegalovirus (CMV) | Saliva, Placenta, Sexual intercourse, Transplant | – Retinitis in HIV patients – Opportunistic infection in transplant pts – Owl’s eye inclusions | Latent in monocytes/macrophages |
| HSV-6/7 | (not in your notes, optional) | Saliva | Roseola infantum (exanthem subitum, fever + rash in infants) | T-cells |
| HSV-8 | Kaposi’s sarcoma virus | Sexual route (esp. in HIV pts) | – Cancer of endothelial cells → Kaposi sarcoma (AIDS defining) | B-cells & endothelial cells |
3. Genital Ulcers
| Type | Cause | Features | Notes / Diagnosis |
|---|---|---|---|
| Painless ulcer | Syphilis | – Single, indurated ulcer (chancre) – Painless – Clean base | Test: Dark-field microscopy (gold standard) |
| Painful ulcer (shallow) | HSV-2 (Herpes genitalis) | – Multiple small ulcers/vesicles – Painful, burning – Often recurrent | Test: Tzanck smear (multinucleated giant cells), PCR |
| Painful ulcer (deep) | Chancroid | – Soft, ragged edges – Painful ulcer – Tender suppurative inguinal lymphadenitis (“bubo”) | Test: Gram stain (“school of fish” pattern), culture |
| Virus | Genome | Shape | Diseases / Associations |
|---|---|---|---|
| Parvovirus | ssDNA | Linear | – Aplastic crisis in Thalassemia, Sickle cell disease, Hereditary spherocytosis |
| Papillomavirus (HPV) | dsDNA | Spiral | – HPV 6, 11 → Warts / Verrucae – HPV 16, 18 → Cervical cancer |
| Adenovirus | dsDNA | Linear | – Sore throat – Acute hemorrhagic cystitis (bladder bleed) – Pneumonia – Myocarditis – Conjunctivitis |
4. Acute Hemorrhagic Cystitis (AHC):
- Viral cause → Adenovirus
- Drug-induced cause → Cyclophosphamide (toxic metabolite: acrolein)
- Antidote / Prevention → Mesna (binds acrolein, protects bladder)
5. RNA Viruses
Reoviridae
- Non-enveloped, dsRNA, linear
- Example: Rotavirus → diarrhea in children (can be fatal)
Picornaviridae (PERCH) – non-enveloped, ssRNA, linear
- P → Polio virus (vaccine available)
- E → Echovirus
- R → Rhinovirus → common cold
- C → Coxsackie virus → myocarditis
- H → HAV → acute hepatitis
Hepevirus
- HEV → acute hepatitis, lethal in pregnancy
Flaviviridae
- Hepatitis C virus → cirrhosis → liver CA
- Dengue virus → hemorrhagic fever
- (Also included under flavivirus in your notes)
Togaviridae
- Rubella
- Adult → post-auricular lymphadenopathy, fever, rash
- Congenital → cataract, hearing loss, PDA
Retrovirus
- HIV → CD4 destruction → AIDS
Paramyxoviridae
- Measles
- Mumps
- Respiratory syncytial virus (RSV) → bronchiolitis in < 2 yr
- Parainfluenza → Croup
Rhabdoviridae
- Rabies virus
- Bullet-shaped
- 100% mortality
- Autopsy → Negri bodies
Deltavirus
- Hepatitis D virus → defective virus (needs HBV)
Orthomyxoviridae (Influenza virus)
- Antigenic shift → major, abrupt mutation → pandemic
- Antigenic drift → minor, gradual mutation → epidemic
- Treatment → Oseltamivir (neuraminidase inhibitor)
DNA Viruses (selected from your notes)
- Herpes viruses
- HSV-1 → DOC: Acyclovir
- EBV
- CMV → DOC: Ganciclovir
- HHV-8 → Kaposi sarcoma
- Other points
- HAV → Councilman bodies (acute hepatitis)
- HAV in pregnancy → common
- HEV in pregnancy → lethal, common
- HBsAg → antigen
- Anti-HBs → antibody
- HBeAg → envelope antigen
- Anti-HBe → antibody
- IgM → acute response
- IgG → chronic
Other Key Associations
- Dengue → bleeding
- Chikungunya → joint pain
- Pseudomonas → green pus
- Actinomyces israelii → sulfur granules in pus (after IUD)
- Serratia marcescens → red pigment
Here are other materials for NLE NRE step 1
6. Gram-negative vs Gram-positive Bacteria
| Feature | Gram-negative (-ve) | Gram-positive (+ve) |
|---|---|---|
| Cell wall | Thin peptidoglycan | Thick peptidoglycan |
| LPS | Present (+), contains Lipid A | Absent (–) |
| Toxin type | Endotoxin (Lipid A of LPS) | Exotoxin (protein) |
| Antigen release | Antigen released when LPS destroyed | Antigen secreted out directly |
| Vaccine | No toxoid vaccine (endotoxin unstable for vaccine use) | Toxoid vaccine possible |
| Heat stability | Stable at 100 °C | Destroyed at 60 °C |
7. Gram-Positive Bacteria
| Organism | Key Feature / Disease | Notes / Treatment |
|---|---|---|
| Staphylococcus epidermidis | Prosthetic valve infection | |
| Streptococcus viridans | Dental infection | |
| Staphylococcus aureus | Skin infections, IV drug users → most common valve = Tricuspid | |
| Streptococcus bovis (gallolyticus) | Colon cancer association | |
| Bacillus cereus | Food poisoning from reheated rice | Toxin = Cereulide, onset 2–5 hr, Tx = supportive |
| Clostridium tetani | Releases tetanospasmin, blocks GABA release in spinal cord → spastic paralysis | |
| Clostridium botulinum | Blocks Ach release → diplopia, dysarthria, dyspnea, dysphagia → flaccid paralysis | |
| Clostridium difficile | Pseudomembranous colitis (esp. after Clindamycin) | Tx: 1. Metronidazole 2. Vancomycin (SE: Red man syndrome) |
8. Gram-Negative Bacteria
| Organism | Key Feature / Disease | Notes / Treatment |
|---|---|---|
| E. coli | Diarrhea; DM patient → foot ulcer | |
| Pasteurella multocida (dog bite) | DM + otitis media after bite | Tx: Co-amoxiclav |
| Bartonella henselae | Cat scratch disease | |
| Bacillus anthracis (actually Gram + but you wrote here in sheet contact) | Respiratory anthrax (wool/sheet contact) → pulmonary disease | Tx: Ciprofloxacin |
| Cutaneous anthrax → black eschar |
9. Spirochetes
| Organism | Key Feature / Disease | Notes / Treatment |
|---|---|---|
| Borrelia burgdorferi (Lyme disease) | Facial nerve palsy (Bell’s), arthritis, heart block, erythema migrans (target rash) | Tx: Doxycycline |
| Leptospira interrogans | Animal pee in river | Weil disease = bleeding + jaundice + nonspecific symptoms |
| Treponema pallidum | Syphilis | (you wrote “palledra” = corrected spelling pallidum) |