🩺 Skin, mucosa & underlying tissues

Follicular & superficial

  • Furuncles / carbuncles – S. aureus (face, neck, axillae).
  • Hot tub folliculitis – Pseudomonas aeruginosa.
  • Acne – Propionibacterium acnes (anaerobic diphtheroid).
  • Impetigo – honey‑crusted: S. pyogenes; bullous: S. aureus.
  • Herpetic vesicles – HSV (neurologic prodrome).

Granulomatous & deep

  • Fish‑tank granuloma – M. marinum (tropical fish).
  • Vibrio vulnificus – saltwater / oyster exposure → cellulitis.
  • Sporotrichosis – Sporothrix schenckii (rose gardeners).
  • Mycetoma – Actinomyces, Nocardia, fungi.
  • Lumpy jaw – Actinomyces israelii (dental trauma).
⚡ Malignant pustule – Bacillus anthracis (black eschar).
Ecthyma gangrenosum – Pseudomonas sepsis.

Cellulitis & wounds

  • Erysipelas – S. pyogenes (raised, butterfly face).
  • Pseudomonas – blue‑green pus, grape odor, burns.
  • Surgical wounds – clean: S. aureus; dirty: mixed enterics + anaerobes.
  • Tennis‑shoe puncture – Pseudomonas.
  • Animal bites – Pasteurella (dog/cat), Eikenella (human), Capnocytophaga (dog).
  • Cat scratch – Bartonella henselae (stellate granulomas).

👂 Ear, nose & throat

Otitis media (acute)

  • S. pneumoniae, H. influenzae (non‑typeable), M. catarrhalis, RSV, rhinovirus.

Otitis externa

  • Mixed: S. aureus, Candida, Proteus, Pseudomonas.

Malignant otitis externa

  • Pseudomonas aeruginosa (diabetic, life‑threatening).

Pharyngitis & oral

  • Strep throat – S. pyogenes (erythrogenic toxin → rash).
  • Herpangina – Coxsackie A (papules on posterior palate).
  • Infectious mononucleosis – EBV (heterophile+, Downey cells).
  • Diphtheria – Corynebacterium diphtheriae (membrane bleeds).
  • Thrush – Candida (immunocompromised, antibiotics).
❄ Common cold – rhinoviruses (summer–fall), coronaviruses (winter–spring), metapneumovirus, adenovirus.

👁️ Eye infections

  • Neonatal conjunctivitis – 2‑5 d: N. gonorrhoeae; 5‑10 d: C. trachomatis (D‑K).
  • Adult conjunctivitis – viral (adenovirus) > bacterial; bacterial: S. aureus, S. pneumoniae, H. influenzae.
  • Trachoma – C. trachomatis serotypes A‑C (corneal scarring, blindness).
  • Chorioretinitis – Toxoplasma, CMV (neonates / AIDS).
  • Congenital syphilis – T. pallidum (retinopathy).
Unilateral peri‑orbital bite + travel to Mexico/Central America → Trypanosoma cruzi (Chagas).

❤️ Cardiac infections

  • Acute endocarditis – S. aureus (IVDU, rapid valve destruction).
  • Subacute endocarditis – Viridans streptococci (dental / poor hygiene).
  • HACEK (oral flora) – Haemophilus, Actinobacillus, Cardiobacterium, Eikenella, Kingella.
  • Enterococcal endocarditis – biliary/GU manipulation (elderly).
  • Fungal endocarditis – Candida, Aspergillus (IVDU, immunocompromised).
  • Dilated cardiomyopathy – T. cruzi (rural South America).

🫁 Middle & lower respiratory

Typical pneumonia

  • #1 adult – S. pneumoniae (rusty sputum).
  • Klebsiella – alcoholic, aspiration, currant‑jelly sputum.
  • Pseudomonas – neutropenia, burns, CF.
  • Staph aureus – post‑influenza, abscess, salmon‑colored.

Atypical pneumonia

  • Mycoplasma – teens/young adults (hacking cough).
  • Legionella – AC exposure, smokers, older adults.
  • Psittacosis – bird exposure (C. psittaci).
  • Pneumocystis – AIDS, ground‑glass, silver stain cysts.

Granulomatous / chronic

  • TB – HIV+, immigrants, calcified lesions.
  • Histoplasma – bird/bat droppings (Ohio/Mississippi).
  • Coccidioides – desert SW (valley fever).
  • Blastomyces – rotting wood (southeastern US).
Epiglottitis (2‑3 yr, unvaccinated) – H. influenzae type B. Croup – parainfluenza.

🫀 Genitourinary

  • Urethritis – N. gonorrhoeae (PMN diplococci), C. trachomatis, Ureaplasma, Trichomonas.
  • Cystitis – #1 E. coli; young sexually active: S. saprophyticus.
  • Pyelonephritis – E. coli, Staphylococcus.
  • Vaginal discharge – bacterial vaginosis (clue cells, fishy amine), Candida (cottage cheese), Trichomonas (motile).
  • Genital lesions – HSV (painful vesicles), syphilis (indurated ulcer), chancroid (H. ducreyi), granuloma inguinale (Klebsiella).
  • PID – N. gonorrhoeae / C. trachomatis (post‑menses).

🧫 Diarrhea & dysentery

Non‑inflammatory (watery)

  • S. aureus – ham/potato salad, 1‑6h, vomiting.
  • B. cereus – emetic (rice, <6h) / diarrheal (meat, >6h).

Inflammatory (dysentery)

  • Campylobacter – poultry, bloody, self‑limited.
  • Salmonella – poultry, water, fever, osteomyelitis (sickle cell).
  • Shigella – watery → dysentery (shallow ulcers).
  • Yersinia – terminal ileitis, mimics appendicitis.
  • C. difficile – antibiotic‑associated (pseudomembranes).
  • Entamoeba histolytica – flask‑shaped ulcers, extra‑intestinal abscess.
🔬 EIEC – enteroinvasive E. coli, similar to Shigella.

🧬 GI & liver

  • Hepatitis A – food/water (oysters), naked RNA, no chronic.
  • Hepatitis B – blood/body fluids, DNA, chronic → cirrhosis/HCC.
  • Hepatitis C – transfusion/IVDU, high chronicity (60%).
  • Hepatitis E – enteric, high mortality in pregnancy.
  • Peritonitis – mixed anaerobes (B. fragilis) + facultative (E. coli).
  • Schistosomiasis – S. mansoni (egg granulomas → fibrosis).
  • Pancreatitis – mumps virus (salivary swelling).

🧪 Hematologic changes

  • Megaloblastic anemia – Diphyllobothrium latum (B12 deficiency).
  • Microcytic anemia – hookworm (Ancylostoma, Necator), Trichuris.
  • Malaria – Plasmodium (rings/schizonts, cyclic fever).
  • Babesiosis – Babesia microti (splenectomized, NE, multiple rings).
  • Mononucleosis – EBV (heterophile+, Downey cells).
  • Lymphocytosis with cough – Bordetella pertussis.

🧠 CNS infections

Meningitis (by age)

  • Neonate – GBS (S. agalactiae), E. coli, Listeria.
  • 3 mo – 2 yr – H. influenzae (unvaccinated).
  • Adolescent – N. meningitidis (maltose+).
  • Elderly – S. pneumoniae.
  • Immunocompromised – Cryptococcus (urease+, encapsulated).

Encephalitis & other

  • Arboviruses – WNV, EEE (high morbidity), St. Louis.
  • HSV encephalitis – temporal lobe, RBCs in CSF.
  • Brain abscess – mixed (streptococci + Bacteroides).
  • Neurocysticercosis – Taenia solium (seizures, Mexico).
  • Guillain‑Barré – Campylobacter (GI) or influenza (resp).
CSF in bacterial: opaque, PMN, low glucose, high protein. Viral: clear, lymphocytes, normal glucose.

🌡️ Selected rashes

  • Scarlet fever – sandpaper rash, S. pyogenes exotoxin.
  • Toxic shock – sunburn‑like, desquamation, TSST‑1 (S. aureus).
  • Scalded skin – exfoliative toxin (S. aureus), bullae.
  • Rocky Mountain spotted fever – R. rickettsii (palms/soles).
  • Epidemic typhus – R. prowazekii (trunk → extremities).
  • Secondary syphilis – copper/bronze maculopapular, palms/soles.
  • Measles – maculopapular head→body, Koplik spots.
  • Lyme disease – erythema migrans (bull's‑eye).

🦴 Bone & joint

  • Osteomyelitis – #1 S. aureus; neonates: GBS, gram‑neg; sickle cell: Salmonella; trauma: Pseudomonas.
  • Septic arthritis – S. aureus (all ages); 15‑40: N. gonorrhoeae.
  • Prosthetic joint – coagulase‑negative staphylococci.
  • Reactive arthritis – post‑enteric (Salmonella, Shigella, Campylobacter, Yersinia) or post‑chlamydial.
  • Lyme arthritis – B. burgdorferi (large joint).
END