Gram-Positive Bacteria
Stains Violet
💡 Key Rule
Catalase ⊕ → Staph | Catalase ∅ → Strep
Coagulase ⊕ = S. aureus · Optochin sensitive = S. pneumo · Novobiocin resistant = S. saprophyticus
S. aureus
MCC: Osteomyelitis · Acute endocarditis · Post-influenza pneumonia · Toxic Shock
Reservoir
Nasal mucosa & skin
Virulence
Protein A (blocks opsonization) · TSST-1 (superantigen) · Coagulase · Exfoliatins · Enterotoxins (heat-stable)
Diseases
- Scalded Skin — exfoliatins destroy stratum granulosum
- Toxic Shock — fever, hypotension, scarlatiniform rash (palms/soles)
- Gastroenteritis — preformed toxin, 2–6 hr (custard, potato salad)
- Post-influenza pneumonia — rapid 2–3 day necrosis
- IVDA Endocarditis — tricuspid regurgitation
Nafcillin/OxacillinVancomycin (MRSA)Linezolid (VRSA)
S. epidermidis
MCC endocarditis — prosthetic valves. Biofilm on IV catheters & implants. Must remove infected implant.
Normal flora
Skin
Key feature
Biofilm makes antibiotics ineffective
Vancomycin + Aminoglycoside
⚠ Must remove or replace infected implant
S. saprophyticus
2nd MCC UTI in sexually active females age 17–27. "Honeymoon cystitis."
Normal flora
Female genital tract
Virulence
Adhesins → adhere to urothelium
TMP-SMX or Quinolones
S. pyogenes (Group A)
Jones criteria for RF: Joints · ♥ Carditis · Nodules · Erythema marginatum · Sydenham Chorea
Virulence
M protein (antiphagocytic) · Streptolysin O (→ ASO titer) · Exotoxins A–C (scarlet fever superantigens)
Diseases
- Scarlet fever — sandpaper rash, strawberry tongue, circumoral pallor
- Rheumatic fever — Type II HS, 2 weeks post-pharyngitis
- AGN — M12 serotype, Type III HS, smoky urine
- Necrotizing fasciitis — rapid, high mortality
Penicillin G/V
ASO titer >200 = significant for Rheumatic Fever. Prophylaxis × 5 years post-acute RF.
S. pneumoniae
MOPS: Meningitis (MCC adults) · Otitis media (MCC children) · Pneumonia (MCC typical — rusty sputum) · Sinusitis
Morphology
Lancet-shaped diplococci · Quellung reaction ⊕ (capsule swelling)
Predisposed
Asplenia, Sickle cell (MCC death = septicemia), COPD, Alcoholism, HIV
Virulence
Polysaccharide capsule (major) · IgA protease · Pneumolysin O (rusty sputum)
Pneumonia: MacrolidesMeningitis: Ceftriaxone
Vaccine: PCV13 (pediatric) · PPSV23 (>65 yr, asplenia, AIDS, sickle cell)
S. agalactiae (Group B)
MCC neonatal meningitis & septicemia. Top 3: #1 GBS · #2 E. coli (K1) · #3 Listeria
Reservoir
Vagina (25% of women), GI tract
Risk
Prolonged labor after rupture of membranes
Ampicillin + AminoglycosideIV Ampicillin (intrapartum prophylaxis)
Viridans Streptococci
MCC Subacute Infective Endocarditis (overall). S. sanguis on damaged valves. S. mutans → dental caries via dextran biofilm.
Pearl
Give prophylactic antibiotics before dental work if patient has damaged heart valve
Penicillin G + Aminoglycosides
Enterococcus
Subacute endocarditis in elderly during GI/GU procedures. Strep bovis endocarditis → always rule out colon cancer!
Diseases
UTI, biliary tract infections, subacute endocarditis
Resistance
Intrinsic resistance; VRE strains = D-ala D-lac mutation (no vancomycin binding)
Penicillin + Gentamicin (prophylaxis)
Gram-Negative Bacteria
Stains Pink
💡 ShYPS — Non-Lactose Fermenters
Shigella · Yersinia · Proteus · Salmonella
Lactose fermenters turn PINK on MacConkey · Oxidase ⊕ = Pseudomonas, Neisseria, Campylobacter, Vibrio, Legionella
N. meningitidis
MCC meningitis children/young adults. Petechial rash on palms/soles → DIC → Waterhouse-Friderichsen syndrome (adrenal hemorrhage)
Risk
C5–C9 deficiency → recurrent bacteremia · Dormitories/military recruits
Vaccine
Covers A, C, Y, W-135 — NO type B vaccine (poor immunogen, ~50% of cases)
CeftriaxoneRifampin (close contacts)
N. gonorrhoeae
MC bacterial STD · PID · Septic arthritis (knee MCC). Fitz-Hugh-Curtis = perihepatitis (RUQ pain). Always test/treat for Chlamydia.
Virulence
Pili (most important — antigenic variation) · Opa proteins · IgA protease
Neonatal
Ophthalmia neonatorum at day 2 → blindness if untreated
CeftriaxoneErythromycin eye drops (neonates)
Pseudomonas aeruginosa
Blue-green pus, grape-like odor. Recurrent pneumonia in CF · Ecthyma gangrenosum (neutropenic) · Hot tub folliculitis · Swimmer's ear
Virulence
Exotoxin A (ADP-ribosylates eEF-2 — same mechanism as diphtheria) · Biofilm (slime layer in CF)
Associated
CF, Neutropenic, CGD, Burns, IVDA, Diabetics
Pip-TazoAminoglycosidesTobramycin inhaled (CF)
Escherichia coli
MCC: UTI · Gram-neg sepsis · 2nd MCC neonatal meningitis (K1 capsule)
| Strain | Mechanism | Disease / Key Fact |
|---|---|---|
| ETEC | LT (↑cAMP) / ST (↑cGMP) | Traveler's diarrhea — watery, non-inflammatory |
| EPEC | Actin rearrangement | 2nd MCC infantile diarrhea (after rotavirus) |
| EIEC | Invades large bowel | Bloody diarrhea, fever (like Shigella) |
| EHEC | O157:H7; Verotoxin (↓60S) | Bloody diarrhea → HUS in children. NO ANTIBIOTICS! |
Salmonella
Typhi: Constipation first → rose spots (25%) → alternating C/D. Necrosis of Peyer patches.
MCC osteomyelitis in sickle cell disease
MCC osteomyelitis in sickle cell disease
Source
Raw chicken, eggs, reptiles · Humans only (typhi)
Key rule
Gastroenteritis → NO antibiotics (prolongs fecal excretion). Typhoid → Ceftriaxone.
Ceftriaxone (typhoid)
Shigella
Bloody diarrhea, NO septicemia (shallow ulcers, no blood vessel invasion). S. sonnei = MCC US. S. dysenteriae = most severe. S. flexneri → Reiter's syndrome.
Toxin
Shiga toxin (A-B) — clips 60S ribosomal subunit → ↓protein synthesis (same as EHEC verotoxin)
Mechanism
Invades M cells → actin jet trails → shallow ulcers. Extremely acid-resistant.
Fluoroquinolones (severe)
NO antidiarrheals (worsen disease)
H. influenzae
Epiglottitis in unvaccinated toddlers — "catcher's stance" with drooling. Pre-vaccine: MCC meningitis 1–5 yr olds. Type b capsule = polyribitol phosphate.
Nontypable
Otitis media (2nd MCC), sinusitis, COPD exacerbations in smokers
Vaccine
Conjugate polysaccharide-protein (diphtheria toxoid) — T-cell dependent. Given 2, 4, 6 months + booster 15 months.
CeftriaxoneRifampin (prophylaxis)
Legionella pneumophila
Atypical pneumonia + mental confusion + diarrhea + hyponatremia. Air conditioning systems. Smokers >55 yr + high ETOH intake.
Culture
Buffered Charcoal Yeast Extract (BCYE) agar
Diagnosis
Urinary antigen test (most useful) · DFA on biopsy · Silver stain
FluoroquinolonesAzithromycin
Bordetella pertussis
Stages: Incubation → Catarrhal (best culture!) → Paroxysmal (whoops + vomiting) → Convalescent. Immunity wanes 5–7 yrs.
Key toxins
Pertussis toxin (ADP-ribosylates Gi → ↑cAMP → lymphocytosis) · Adenylate cyclase toxin (impairs phagocytosis) · Tracheal cytotoxin (kills ciliated cells)
Erythromycin × 14 days (all household contacts)
Helicobacter pylori
Causes: Chronic gastritis · Duodenal ulcers · Gastric adenocarcinoma · Gastric MALT-oma · B-cell lymphoma
Virulence
Urease (ammonia cloud neutralizes acid) · Mucinase (penetrates mucous layer)
Diagnosis
Biopsy + culture (gold standard) · Urea breath test (13C)
PPI + Amoxicillin + Clarithromycin (triple therapy)
Campylobacter jejuni
MCC infectious diarrhea in US. Bloody diarrhea, 10+ stools/day. Complication: Guillain-Barré (30% of US GBS) via molecular mimicry with gangliosides.
Source
Contaminated poultry (MCC), handling puppies · Low dose = 500 organisms
Also causes
Reactive arthritis (Reiter's syndrome)
Erythromycin (severe)
Vibrio cholerae
Rice water diarrhea — up to 20L/day. Cholera toxin = ADP-ribosylates Gs-α → ↑cAMP → Cl⁻ and H₂O efflux. Same MOA as ETEC LT. DDx: ETEC is Oxidase negative.
IV Fluid ReplacementDoxycycline
Mycobacteria
Acid-Fast Rods
💡 Anti-TB Regimen
RIPE × 2 months → RI × 4 months
Rifampin · Isoniazid · Pyrazinamide · Ethambutol · Must do PPD BEFORE anti-TNF therapy!
M. tuberculosis
Damage by CMI (immune system), not organism directly. MC organ in dissemination = Kidney (sterile pyuria). Vertebral = Pott's disease.
Virulence
Sulfatides (block phagolysosome fusion) · Cord factor (trehalose dimycolate) · Mycolic acid (waxy wall)
PPD
≥5mm: HIV+, recent exposure | ≥10mm: IVDA, immigrants | ≥15mm: low risk
Side effects
Rifampin: P450 inducer, orange secretions · INH: peripheral neuritis (give B6), SLE · Ethambutol: retrobulbar neuritis (↓red-green vision) · Pyrazinamide: hyperuricemia
2 mo: RIPE4 mo: RI
Must do PPD BEFORE starting anti-TNF therapy (Infliximab, Adalimumab, Etanercept)
M. leprae (Leprosy)
Tuberculoid (TH1)
Lepromin ⊕ · Few lesions (macular) · Nerve granulomas · Strong CMI
Lepromatous (TH2)
Lepromin ∅ · Numerous nodular lesions · Leonine facies · Saddle nose · Foam cells · Weak CMI
Reservoir
Armadillos (TX/LA), human mucosa/skin/nerves
Dapsone + Rifampin+ Clofazimine (lepromatous)
M. avium complex (MAC)
CD4 <50: Fevers, diarrhea, malabsorption, bone marrow suppression. Resembles TB on imaging. Not contagious.
Prophylaxis
Azithromycin or Clarithromycin when CD4 <50
Clarithromycin + Ethambutol + Rifampin
Special & Atypical Bacteria
Obligate Intracellular & Others
Chlamydia trachomatis
MC bacterial STD in US. EB = infectious (extracellular) · RB = replicating (intracellular). Serotypes: D-K (STD) · A-C (Trachoma) · L1-3 (LGV)
Diseases
NGU · Cervicitis · PID · Inclusion conjunctivitis · Neonatal pneumonia (staccato cough)
Complications
Sterility · Reiter's syndrome · Fitz-Hugh-Curtis
DoxycyclineAzithromycinErythromycin (neonates)
NOT covered by cephalosporins (no peptidoglycan cell wall)
Rickettsia rickettsii (RMSF)
Rash starts WRISTS & ANKLES → spreads centripetally to trunk, palms, soles. East Coast (NC area). 2–12 day incubation.
Mechanism
Invade endothelial cells → vasculitis in brain, liver, skin, lungs, kidneys
Diagnosis
Clinical — start doxycycline BEFORE lab confirmation. 4× ↑ titer diagnostic.
| Species | Vector | Disease |
|---|---|---|
| R. prowazekii | Human louse | Epidemic Typhus (NO palms/soles) |
| Coxiella burnetii | Inhalation | Q Fever — NO rash, Weil-Felix ∅ |
Doxycycline
Mycoplasma pneumoniae
MCC atypical (walking) pneumonia in young adults. Dry hacking cough. Cold agglutinins (IgM) ⊕ in 65%.
Risk
Military recruits, college dorms, children/teens
Erythromycin/MacrolidesTetracyclines
Penicillins & Cephalosporins DO NOT WORK — no cell wall!
Treponema pallidum
1° Painless indurated chancre → 2° Copper rash on palms/soles + condyloma lata → 3° Gummas + tabes dorsalis + "tree bark" aortic aneurysm
Serology
VDRL/RPR (screening, nontreponemal) → FTA-ABS (confirmatory, remains ⊕ for life)
False + VDRL
Viruses · Drugs · Rheumatic fever · Lupus/Leprosy
Congenital
Hutchinson's teeth · Saddle nose · Saber shin · CN VIII deafness
IM Penicillin G Benzathine (1°, 2°)IV Pen G (congenital, late)
Jarisch-Herxheimer: Shock in first 24hr of treatment (LPS release from killed organisms)
Viruses
DNA & RNA
💡 DNA Virus Mnemonic
"Her Po He Pa Par Ade"
Herpes · Pox · Hepadna · Papova · Parvo · Adeno — all dsDNA except Parvo (ssDNA) & Hepadna (partial). All replicate in nucleus except Pox.
HSV-1 & HSV-2
HSV-1 (Trigeminal ganglia)
Cold sores · Keratoconjunctivitis (dendritic ulcers) · MCC sporadic encephalitis US (temporal lobe) · Herpetic whitlow
HSV-2 (Sacral ganglia)
Painful genital vesicles · Neonatal herpes at birth (encephalitis)
Diagnosis
Tzanck smear → intranuclear Cowdry type A inclusions (HSV-1, HSV-2, VZV)
Acyclovir (HSV)Famciclovir (VZV)
Acyclovir resistance → Foscarnet (no phosphorylation required)
EBV (Epstein-Barr)
Mono: Fever + exudative sore throat + lymphadenopathy + splenomegaly. Downey cells = atypical reactive T-cells. Avoid contact sports!
Malignancies
Burkitt lymphoma · Hodgkin's · Nasopharyngeal carcinoma · Primary CNS lymphoma (AIDS) · Hairy oral leukoplakia (AIDS)
CMV (Cytomegalovirus)
MCC in utero infection in US. "Blueberry muffin baby" — thrombocytic purpura + periventricular calcifications + sensorineural hearing loss. AIDS → retinitis.
DDx
Heterophile NEGATIVE mono (vs EBV = positive)
GanciclovirFoscarnet (resistant cases)
HIV / AIDS
gp120 binds CD4 + CCR5 (macrophages) or CXCR4 (T-cells). MCC death in AIDS = P. jiroveci pneumonia. p24 = early marker.
| CD4 Count | Prophylaxis / Risk |
|---|---|
| <200 | P. jiroveci → TMP-SMX |
| <100 | Toxoplasma → Pyrimethamine-Sulfadiazine |
| <50 | MAC → Azithromycin · CMV retinitis → Ganciclovir |
Diagnosis
Screening: ELISA → Confirmation: Western Blot · Viral load: RT-PCR · Newborns: PCR
Influenza
Drift (A&B) = mutations → epidemics. Shift (A only) = reassortment → pandemics. MCC fatal superinfection: S. aureus pneumonia (2–3 days).
Complications
Reye syndrome (aspirin) · Guillain-Barré · Fatal S. aureus pneumonia
Oseltamivir (Tamiflu)Zanamivir (inhibit neuraminidase)
Measles & Mumps
Measles: 3 C's (Cough, Coryza, Conjunctivitis) + Koplik spots + Descending maculopapular rash (from ears down). Sequela: SSPE.
Mumps: Parotitis + Orchitis (→ sterility) + Meningoencephalitis
Mumps: Parotitis + Orchitis (→ sterility) + Meningoencephalitis
Vaccine
MMR — live attenuated
SSPE
Subacute Sclerosing Panencephalitis — progressive CNS degeneration years later
Hepatitis Viruses A–E
Hep E: High mortality in pregnancy · Window phase (HBV): Only HBcAb (IgG) ⊕ · HBeAg: Active replication = highly infectious
| Virus | Transmission | Chronicity | Key Fact |
|---|---|---|---|
| Hep A | Fecal-oral | Never | +ssRNA (Picorna); self-limiting |
| Hep B | Blood/sexual/vertical | Yes (5–10%) | Partial dsDNA; reverse transcriptase; HBsAg = infected |
| Hep C | Blood (MCC) | Yes (70–85%) | +ssRNA (Flavi); MCC post-transfusion hepatitis |
| Hep D | Requires HBV coat | Worse if superinfection | Defective; −ssRNA circular |
| Hep E | Fecal-oral | Never | +ssRNA; HIGH mortality in pregnancy! |
Rotavirus & Parvovirus B19
Rotavirus: MCC diarrhea in infants (winter, daycare). Villous destruction → ↓Na⁺ absorption.
B19: Slapped cheek rash (erythema infectiosum) in children. Aplastic crisis in sickle cell. Hydrops fetalis.
B19: Slapped cheek rash (erythema infectiosum) in children. Aplastic crisis in sickle cell. Hydrops fetalis.
Rotavirus
Only dsRNA virus · Reo family · "Right Out The Anus" · Vaccine available
B19
Infects erythroid progenitor cells · Adults: arthritis (hands/feet) · Sickle cell: aplastic crisis
Fungi
Systemic & Opportunistic
💡 Dimorphic Rule
Mold in the Cold (25°C) → Yeast in the Beast (37°C)
Histoplasma · Blastomyces · Coccidiodes · Paracoccidiodes · Sporothrix — No person-to-person spread
Systemic Dimorphic Fungi
All cause pneumonia-like illness; no person-to-person; biopsy = best diagnosis
| Organism | Geography | Clue | DOC |
|---|---|---|---|
| Histoplasma | Ohio/Mississippi valleys | Bird/bat droppings; yeast INSIDE macrophages; lesions CALCIFY | Itraconazole; Amp B (severe) |
| Blastomyces | Same + Great Lakes, SE US | Rotting wood; BROAD-BASED budding; lesions DO NOT calcify; skin | Itraconazole; Amp B (severe) |
| Coccidiodes | SW US (AZ, San Joaquin Valley) | Desert sand; spherules with endospores; erythema nodosum = good sign | Fluconazole; Amp B (severe) |
Candida albicans
Normal flora → disease in immunocompromised, IVDA, antibiotic overuse, diabetes. Oral thrush (white patches, easily scraped off). Yeast vaginitis (↓pH; cottage cheese).
IVDA
Endocarditis (Candida species)
Nystatin (topical/oral thrush)Fluconazole (systemic)Amphotericin B (disseminated)
Cryptococcus neoformans
Dominant meningitis in AIDS (CD4 <50). Pigeon droppings. Soap bubble lesions in brain. CSF: latex agglutination for capsular antigen (more sensitive than India ink).
Amphotericin B + Flucytosine (min 10 wks) → Fluconazole
Pneumocystis jirovecii
Diffuse interstitial pneumonia: Fever + dry cough + SOB + ground glass appearance on CXR. Silver-stained cysts. Foamy honeycomb on H&E.
Mechanism
Destroys Type I pneumocytes → ↑ Type II → alveolar exudate
TMP-SMX (DOC + prophylaxis)IV Pentamidine (severe)Dapsone
Aspergillus fumigatus
ABPA (Asthma/CF; Type I HS; eosinophilia) · Fungus ball (pre-formed cavities; cough; surgical) · Invasive (severe neutropenia; tissue infarcts)
Aflatoxins
Some Aspergillus species → hepatocellular carcinoma
ABPA: ItraconazoleInvasive: Voriconazole ± Caspofungin
Parasites
Protozoa & Helminths
Plasmodium (Malaria)
Fever spikes when merozoites rupture RBCs. Vivax/Ovale = hypnozoites → RELAPSE (Primaquine needed). Falciparum = most dangerous (cerebral malaria, irregular fever, no persistent liver form).
| Species | Cycle | Smear | Treatment |
|---|---|---|---|
| P. vivax | 48h (tertian) | Schüffner's dots; ameboid | Chloroquine → Primaquine |
| P. ovale | 48h (tertian) | Oval RBCs; Schüffner's dots | Chloroquine → Primaquine |
| P. malariae | 72h (quartan) | Rosette schizonts | Chloroquine |
| P. falciparum | Irregular (malignant) | Multiple rings; crescent gametes | Quinine + Pyrimethamine-Sulfadoxine (if resistant) |
Check G6PD before Primaquine — risk of hemolysis!
Toxoplasma gondii
AIDS: Ring-enhancing brain lesions. Congenital: Chorioretinitis + hydrocephalus + intracerebral calcifications → blindness in teens. Source: Raw pork (MCC) or cat feces.
Prophylaxis
CD4 <100 in AIDS patients
Pyrimethamine + Sulfadiazine (+ folinic acid)
Pregnant women: No deli meats (Listeria), no cat litter (Toxoplasma)
GI Protozoa
Giardia: Fatty, foul-smelling diarrhea · "Falling leaf motility" · Campers/stream water
Entamoeba: Bloody diarrhea · Liver abscess ("anchovy paste") · Travel history
Entamoeba: Bloody diarrhea · Liver abscess ("anchovy paste") · Travel history
| Organism | Source | Disease | TX |
|---|---|---|---|
| Giardia lamblia | Stream water | Fatty diarrhea; duodenum malabsorption | Metronidazole |
| Entamoeba histolytica | Contaminated water/travel | Bloody diarrhea; liver abscess | Metro → Iodoquinol |
| Cryptosporidium | Not killed by chlorination | Severe diarrhea in AIDS | Nitrazoxanide (AIDS) |
| Trichomonas vaginalis | Sexual | Frothy green discharge (↑pH) | Metronidazole |
High-Yield Helminths
Treatment: -Bendazoles for nematodes · Praziquantel for trematodes & cestodes
| Organism | Clue | Disease |
|---|---|---|
| Enterobius (pinworm) | MC helminth US; scotch tape test | Perianal itching — treat entire family |
| Trichinella spiralis | Wild game/raw bacon; encysted larvae | Myalgia + splinter hemorrhages + periorbital edema |
| Necator (hookworm) | Bare feet; filariform larvae | Microcytic anemia (bloodsucking) |
| Taenia solium | Cysticercosis = brain cysts | "Immigrant with new-onset seizures" |
| Schistosoma mansoni | Fresh water skin penetration | Portal hypertension (egg granulomas) |
| Schistosoma haematobium | Egypt/Africa; bladder veins | Hematuria → SCC of bladder |
| Diphyllobothrium latum | Raw fish; competes for B12 | Megaloblastic anemia |
Antibiotics & Antifungals
Mechanisms & Pearls
Cell Wall Synthesis Inhibitors
NOT covered by cephalosporins = LAME: Listeria · Atypicals (Chlamydia, Mycoplasma) · MRSA · Enterococci
| Drug | Spectrum | Key Pearl |
|---|---|---|
| Pen G/V | Narrow | Neurosyphilis, Strep, Viridans |
| Nafcillin/Oxacillin | Penicillinase-resistant | MSSA (not MRSA). Oxacillin excreted in bile. |
| Ampicillin/Amox | Broad (penicillinase-susceptible) | Listeria, H. pylori, ear infections, Borrelia |
| Pip-Tazo | Extended + β-lactamase inhibitor | Pseudomonas + Bacteroides |
| Vancomycin | MRSA, Enterococci, C. diff | A/E: Red Man Syndrome (slow infusion); Oto/Nephrotoxicity |
| Imipenem + Cilastatin | Empiric severe infections | Cilastatin prevents toxic metabolite; risk seizures |
Protein Synthesis Inhibitors
30S: Aminoglycosides (bactericidal) · Tetracyclines (bacteriostatic)
50S: Chloramphenicol · Macrolides · Clindamycin · Linezolid · Streptogramins
50S: Chloramphenicol · Macrolides · Clindamycin · Linezolid · Streptogramins
| Drug | MOA | Key A/E |
|---|---|---|
| Aminoglycosides | Block initiation complex (30S) — bactericidal | Nephrotoxicity, Ototoxicity, NM blockade (avoid myasthenia gravis) |
| Macrolides | Inhibit aminoacyl translocation (50S) | P450 inhibitors (erythro strongest); prolongs QT; GI motility |
| Tetracyclines | Block tRNA attachment (30S) | Teeth discoloration (children); photosensitivity; contraindicated pregnancy; no milk/antacids |
| Clindamycin | Same as macrolide (50S) | Pseudomembranous colitis (C. diff); concentrates in bone |
| Chloramphenicol | Blocks peptidyl transferase (50S) | Gray baby syndrome; BM suppression; P450 inhibitor |
| Linezolid | Blocks initiation complex (23S) | BM suppression; inhibits MAO → serotonin syndrome risk |
Fluoroquinolones & Folate Inhibitors
FQ: Inhibit topoisomerase II (DNA gyrase) + IV — CANNOT use for anaerobes
TMP-SMX: Sequential folate blockade → DOC Nocardia, PCP, UTIs
TMP-SMX: Sequential folate blockade → DOC Nocardia, PCP, UTIs
FQ A/E
Tendonitis/rupture (Achilles) · QT prolongation · CNS effects (inhibits GABA) · Phototoxicity · Contraindicated pregnancy/children
Sulfonamide A/E
Stevens-Johnson · Kernicterus (neonates) · Hemolysis (G6PD)
Anti-Mycobacterial Drugs
All 4 can cause hepatitis. RIPE × 2 months → RI × 4 months.
| Drug | MOA | Key Side Effect |
|---|---|---|
| Isoniazid (INH) | Inhibits mycolic acid synthesis (prodrug) | Hepatitis · Peripheral neuritis (→ give B6) · SLE in slow acetylators |
| Rifampin | Inhibits RNA polymerase | Hepatitis · P450 INDUCER (OCP failure) · Orange body secretions |
| Ethambutol | Inhibits arabinogalactan | Retrobulbar neuritis → ↓ red-green color discrimination |
| Pyrazinamide | ↓ pH in tubercle cavity | Hepatitis · Hyperuricemia (gout) |
Antifungal Drugs
Amp B: Binds ergosterol → pores (gold standard, serious mycoses) · Azoles: Inhibit 14-α demethylase
| Drug | Use | Key A/E |
|---|---|---|
| Amphotericin B | Serious systemic mycoses; safe in pregnancy | Nephrotoxicity, arrhythmias, ↓K⁺; liposomal form ↓ nephrotox |
| Fluconazole | DOC Candida, Coccidiodes; penetrates CNS | Hepatotoxicity; NOT safe in pregnancy (teratogenic) |
| Itraconazole | DOC Blastomyces, Histoplasma, Sporothrix, ABPA | P450 inhibitor; testosterone inhibition (gynecomastia) |
| Voriconazole | DOC invasive aspergillosis | Visual disturbances; hepatotoxic |
| Caspofungin | β-glucan synthesis inhibitor; invasive aspergillosis | GI upset; flushing |
| Griseofulvin | Oral dermatophytes (tinea) | P450 INDUCER (↑warfarin); teratogenic; disulfiram-like |
Toxin Comparison Chart
Most tested toxin mechanisms side-by-side for rapid Step 1 review
| Mechanism | Organisms |
|---|---|
| ADP-ribosylates eEF-2 → ↓ protein synthesis | C. diphtheriae · Pseudomonas (Exotoxin A) |
| Inactivate 60S ribosome → ↓ protein synthesis | EHEC (verotoxin) · Shigella (Shiga toxin) |
| ADP-ribosylates Gs-α → ↑ cAMP | ETEC (heat-labile toxin) · Vibrio cholerae |
| ADP-ribosylates Gi → ↑ cAMP | Bordetella pertussis toxin |
| Acts as adenylate cyclase → ↑ cAMP | B. anthracis (edema factor) · B. pertussis (AC toxin) |
| Blocks ACh release (NMJ) → flaccid paralysis | C. botulinum |
| Blocks glycine/GABA → spastic paralysis | C. tetani (tetanospasmin) |