167.1 🎓 醫孞生版

167.1.0.1 📌 䞀頁重點

  • E. coli: gram - rod, lactose + (pink on MacConkey), oxidase -, 倧腞正垞 commensal + 臎病 strain
  • 臚床:
    • UTI #1 cause (uropathogenic E. coli, UPEC)
    • Bacteremia / sepsis #1 community-onset GN
    • Intra-abdominal (cholangitis, peritonitis, abscess)
    • Neonatal meningitis (K1 capsule)
    • Diarrhea (6 pathotypes — see below)
  • 6 diarrheagenic pathotypes:
    • ETEC (enterotoxigenic) — traveler’s diarrhea; LT + ST toxins
    • EPEC (enteropathogenic) — pediatric villus blunting
    • EIEC (enteroinvasive) — dysentery (mimics Shigella)
    • EAEC (enteroaggregative) — persistent traveler’s + HIV chronic diarrhea
    • STEC / EHEC (Shiga-toxin / enterohemorrhagic) — O157:H7 + non-O157; HUS 颚險; NO antibiotic
    • DAEC (diffusely adherent) — pediatric persistent
  • 抗藥: AMP-R 普遍, FQ-R 升, ESBL + CRE 倧問題
  • Other Enterobacteriaceae: Klebsiella, Enterobacter, Citrobacter, Serratia, Proteus, Providencia — overlap clinical roles

167.1.0.2 1⃣ 现菌孞

  • Gram - rod, motile (flagella)
  • Lactose fermenter + (MacConkey pink)
  • 倧腞 commensal — 䜆 specific strain 臎病
  • Capsule (K antigen), flagella (H antigen), LPS (O antigen) → serotyping (e.g. O157:H7)

  • 1000 serotypes

  • Plasmid carriage = virulence + resistance (ESBL, KPC plasmids)

167.1.0.3 2⃣ Extraintestinal Pathogenic E. coli (ExPEC)

167.1.0.3.1 A. UTI (UPEC — Uropathogenic E. coli)
  • #1 community-acquired UTI (75-95%)
  • Virulence: P fimbriae (Gal-Gal binding) → pyelonephritis
  • Cystitis: dysuria, frequency, urgency
  • Pyelo: 高燒, flank pain, CVA tenderness
  • Treatment:
    • Uncomplicated cystitis: nitrofurantoin 100 bid × 5d, fosfomycin 3 g × 1, TMP-SMX (if R < 20%), cephalexin
    • Pyelonephritis: ceftriaxone IV → PO step-down; OR FQ if susceptible
    • ESBL: carbapenem (severe) or PO fosfomycin / nitro (uncomp)
    • CRE: cefiderocol / CAZ-AVI
167.1.0.3.2 B. Bacteremia / Sepsis
  • #1 community-onset gram-neg bacteremia
  • Source: GU > biliary > GI > line
  • 老人 + DM + CKD common
  • Empirical: 3rd-gen ceph; broader if ICU/MDR risk
167.1.0.3.3 C. Intra-abdominal
  • Cholangitis (Charcot triad), peritonitis (SBP in cirrhotic), liver abscess, appendicitis perforation
  • Empirical: pip-tazo or ceftriaxone + metronidazole
  • Source control (drain) essential
167.1.0.3.4 D. Neonatal Meningitis
  • K1 capsule strain — mimics polysialic acid → BBB cross
  • < 1 month, GBS + E. coli K1 倧宗
  • Empirical: amp + cefotaxime / gentamicin
167.1.0.3.5 E. Other
  • Pneumonia (HAP, VAP)
  • Endometritis postpartum
  • Cellulitis

167.1.0.4 3⃣ Diarrheagenic E. coli (6 Pathotypes)

167.1.0.4.1 A. ETEC (Enterotoxigenic)
  • Traveler’s diarrhea #1 in Asia / Africa / S. America
  • Pediatric in developing countries — 死亡 cause
  • LT (heat-labile, cAMP↑, cholera-like) + ST (heat-stable, cGMP↑)
  • 氎瀉, 無燒 / 血
  • Tx: ORS + azithromycin 1 g × 1 (preferred in Asia FQ-R Campy); rifaximin alt
167.1.0.4.2 B. EPEC (Enteropathogenic)
  • Pediatric < 2 yr in developing countries; outbreaks in daycare
  • “Attaching-effacing” lesion → villus blunting
  • Watery diarrhea ± fever
  • Self-limit; severe / persistent → TMP-SMX or azithromycin
167.1.0.4.3 C. EIEC (Enteroinvasive)
  • Shigella-like (genetic similar)
  • Dysentery: 血䟿 + 燒 + tenesmus
  • Invades colonic epithelium
  • Tx: azithromycin or ciprofloxacin (Shigella-like algorithm)
167.1.0.4.4 D. EAEC (Enteroaggregative)
  • 持續 watery diarrhea (> 14 d)
  • HIV / immunocompromised chronic
  • Pediatric malnutrition
  • Aggregative adherence (“stacked brick”)
  • Tx: ciprofloxacin or rifaximin
167.1.0.4.5 E. STEC / EHEC (Shiga toxin-producing / Enterohemorrhagic)
  • O157:H7 most famous; non-O157 increasing (O26, O111, O45, O121, O103, O145 — “Big 6”)
  • Cattle reservoir; undercooked beef, raw milk, contaminated produce, water
  • Outbreaks (Jack in the Box 1993, German 2011 sprouts)
  • 血䟿, severe cramping, NO fever or low (vs Shigella/Salm 高燒)
  • HUS in 5-10% (children, elderly higher risk)
  • HUS triad: hemolytic anemia + thrombocytopenia + AKI
  • NO ANTIBIOTIC (worsens HUS — antibiotic → SOS response → ↑ Shiga toxin release)
  • NO antimotility (loperamide — toxin retention)
  • Tx: supportive + monitor for HUS; eculizumab for severe atypical HUS
167.1.0.4.6 F. DAEC (Diffusely Adherent)
  • 兒童 persistent diarrhea
  • 眕芋 in adult

167.1.0.5 4⃣ Other Enterobacteriaceae

167.1.0.5.1 Klebsiella (Ch 168 detail)
  • Lactose + (mucoid colonies — capsule)
  • Community-acquired pneumonia (alcoholic, “currant jelly sputum”, upper lobe cavities)
  • UTI, IE (rare), liver abscess (Asia / Taiwan, hypervirulent K1, K2 strain → 倧腞癌/糖尿病關聯)
  • CRE 䞻芁 — KPC carbapenemase
  • Tx: 3rd ceph (基瀎); CRE → CAZ-AVI / cefiderocol
167.1.0.5.2 Enterobacter
  • AmpC β-lactamase chromosomal inducible — 絊 3rd-gen ceph 有 worry of inducing resistance
  • Treatment: cefepime, carbapenem (avoid ceftriaxone alone)
167.1.0.5.3 Citrobacter
  • AmpC similar to Enterobacter
  • Treatment: cefepime / carbapenem
167.1.0.5.4 Serratia
  • Lactose - (some), pink / red pigment
  • Nosocomial, UTI, line bacteremia
  • AmpC similar
  • Treatment: cefepime / carbapenem
167.1.0.5.5 Proteus mirabilis
  • Lactose -, swarmer motility on plate
  • Urease + → struvite stones (staghorn)
  • UTI, bacteremia
  • Treatment: ampicillin (if susceptible), 1st-gen ceph
167.1.0.5.6 Providencia
  • 老人 / chronic catheter UTI
  • Often MDR
167.1.0.5.7 Morganella morganii
  • Urease + (struvite)
  • AmpC

167.1.0.6 5⃣ 抗藥 ESBL + CRE

167.1.0.6.1 ESBL (Extended-spectrum β-lactamase)
  • CTX-M most common globally (replaced TEM, SHV)
  • 氎解 3rd-gen ceph (ceftriaxone) but NOT cabapenem or cephamycin
  • Inhibited by avibactam, clavulanate, tazobactam (varying)
  • Treatment:
    • Severe / bacteremia / pyelo: carbapenem (MERINO 2018 — pip-tazo INFERIOR to merop)
    • Uncomplicated cystitis: PO fosfomycin / nitrofurantoin (drug at high urine conc)
    • Mild + susceptibility OK: cefiderocol, ceftazidime-avibactam
  • Source: nursing home, prior abx, prior hospitalization, travel
167.1.0.6.2 AmpC
  • Chromosomal inducible in Enterobacter / Citrobacter / Serratia / Morganella / Providencia (“SPACE-M” / “SPICE”)
  • 絊 ceftriaxone → induce AmpC → de-repressed mutants → R
  • Treatment: cefepime (4th gen, stable), carbapenem
  • Avoid ceftriaxone monotherapy
167.1.0.6.3 CRE (Carbapenem-Resistant Enterobacteriaceae)
  • KPC (Klebsiella, US/Israel) — class A serine
  • NDM (S Asia) — class B metallo
  • OXA-48 (Mid-East / Europe) — class D
  • VIM, IMP — class B metallo (Taiwan endemic)
  • Treatment:
    • KPC: CAZ-AVI (ceftazidime-avibactam), meropenem-vaborbactam, imipenem-relebactam
    • NDM / metallo: cefiderocol (only one widely active)
    • OXA-48: CAZ-AVI, cefiderocol
    • Polymyxin (last-resort, toxic), tigecycline (low conc — not for UTI/bacteremia)