179.1 🎓 醫孞生版

179.1.0.1 📌 䞀頁重點

  • Anaerobic bacteria ≈ commensals in GI / mouth / skin / GU; mostly opportunistic when barrier breached
  • Gram + anaerobes:
    • Spore-formers: Clostridium (Ch 157-160 — separate covered)
    • Non-spore-formers: Actinomyces, Propionibacterium (Cutibacterium), Peptostreptococcus, Eubacterium
  • Gram - anaerobes:
    • Bacteroides fragilis group (most important clinically) — colon, intra-abdominal
    • Prevotella, Porphyromonas — oral, lung abscess
    • Fusobacterium — oral, Lemierre’s syndrome (jugular vein thrombophlebitis post-tonsillitis), lung abscess
  • 臚床 syndromes (often polymicrobial):
    • Intra-abdominal sepsis (perforation, abscess)
    • Aspiration pneumonia + lung abscess (mouth flora aspiration)
    • Brain abscess (dental / sinus / lung source)
    • Skin/soft tissue (NF, gas gangrene, diabetic foot) — see Clostridium chapter for gas gangrene
    • OB/GYN (PID, postpartum endometritis, septic abortion)
    • Lemierre’s syndrome — Fusobacterium necrophorum
    • Bite wounds (animal + human — see Ch 164)
  • Antimicrobial:
    • Metronidazole — best for B. fragilis + many GN anaerobes; NOT cover Actinomyces / Propionibacterium / aerobic
    • β-lactam/inhibitor (pip-tazo, amox-clav, amp-sulb) — good anaerobe + aerobe
    • Carbapenems (mero, imi, ertapenem) — excellent anaerobe + aerobe (often empirical severe)
    • Clindamycin — historically Bacteroides standard but rising R (now 30-50% R); still useful for oral anaerobes
    • Moxifloxacin — anaerobe coverage (CAP intra-abd indication)
    • Tigecycline, eravacycline — broad
    • NOT cover anaerobes: cephalosporins 1st-3rd gen (except cefoxitin / cefotetan = cephamycins), aminoglycosides, FQ (except moxi), vancomycin

179.1.0.2 1⃣ 现菌孞 + 臎病

179.1.0.2.1 環境
  • Cannot survive in O2
  • Endogenous flora (commensal at mucosal sites)
  • Pathogenic when mucosa breached, devitalized tissue, immunocompromise, polymicrobial synergy
179.1.0.2.2 共生䜍眮
  • Oral: Prevotella, Fusobacterium, Peptostreptococcus, Actinomyces
  • Lower GI / colon: Bacteroides (>10^10/g feces, predominant), Prevotella
  • Skin: Cutibacterium (formerly Propionibacterium) acnes
  • GU: Lactobacillus + Anaerococcus
179.1.0.2.3 臎病机制
  • Breach of mucosal barrier (surgery, trauma, perforation, dental procedure)
  • Reduced O2 (devitalized tissue, ischemia)
  • Polymicrobial synergy with facultative organisms
  • Virulence factors: capsule, β-lactamase, succinic acid (chemotaxis inhibition)
  • 圢成 abscess → low O2 → favors anaerobe

179.1.0.3 2⃣ Bacteroides fragilis Group

  • ~ 0.5% colon flora but disproportionate disease
  • Capsule polysaccharide complex — virulence + abscess formation
  • β-lactamase universal — intrinsic R amox / amp / cefazolin
  • Metronidazole historical first-line — R rising (~ 5-15% in some surveys)
  • Carbapenem R rising (cfiA gene + metallo β-lactamase)
  • Clindamycin R 30-50%
179.1.0.3.1 臚床
  • Intra-abdominal sepsis (peritonitis, abscess, cholangitis, appendiceal abscess, diverticulitis)
  • Bacteremia post-surgery / perforation
  • Female pelvic infections
  • Bone / soft tissue (foot, decubitus)
  • Brain abscess (with other GN, GP anaerobes)
179.1.0.3.2 Treatment
  • Sepsis: pip-tazo or carbapenem (ESBL / 病人 status)
  • Mild / outpatient: amox-clav, moxifloxacin
  • Severe / 倱敗: metronidazole + ceftriaxone, or carbapenem

179.1.0.4 3⃣ Aspiration Pneumonia + Lung Abscess

179.1.0.4.1 流行病孞
  • Risk: altered consciousness (stroke, seizure, EtOH, anesthesia), dysphagia, NG tube, mechanical vent
  • 食 / 唟液 → 肺 (gravity-dependent → posterior segments upper lobes if supine, lower lobes if upright)
179.1.0.4.2 Pathogens
  • Mouth anaerobes: Prevotella, Fusobacterium, Peptostreptococcus
  • Concomitant aerobic: S. pneumoniae, GAS, H. influenzae, GN (HAP / nursing home)
  • Modern view: aerobic + anaerobic mixed
179.1.0.4.3 治療
  • Mild + community aspiration: amox-clav or clindamycin
  • Severe / HAP-aspiration: pip-tazo (broad coverage anaerobe + GN)
  • Lung abscess: 4-6 wk antibiotic course + 匕流 if 倧 / refractory
  • Empyema: drainage essential + abx

179.1.0.5 4⃣ Brain Abscess

  • Source: dental, sinus, OM, lung abscess, IDU, hematogenous, post-NSx
  • Usually polymicrobial
  • Streptococcus + anaerobe + GN typically
179.1.0.5.1 Treatment
  • Empirical: ceftriaxone + metronidazole + vanco (covers Strep, anaerobe, MRSA)
  • Drainage / aspiration if accessible (often)
  • 4-6 wk IV minimum, longer if osteo
  • Steroid if edema / mass effect

179.1.0.6 5⃣ Lemierre’s Syndrome

179.1.0.6.1 機蜉
  • Fusobacterium necrophorum — oral commensal turning pathogen
  • Throat infection (tonsillitis, peritonsillar abscess) → invasion of parapharyngeal space → IJV thrombophlebitis → septic emboli (lung most common — multifocal nodular pneumonia)
  • “Forgotten disease” pre-COVID — actually returning frequency in young healthy
179.1.0.6.2 臚床
  • Young adult (15-30s)
  • Initial sore throat (1-2 wk prior)
  • Recurrence of high fever + neck pain + 突 sepsis
  • CT neck: IJV thrombosis
  • CXR / CT chest: bilateral nodular cavitary lesions (septic emboli)
179.1.0.6.3 治療
  • Long IV antibiotic 4-6 wk:
    • Pip-tazo or carbapenem (severe)
    • Metronidazole + ceftriaxone
    • Penicillin if confirmed susceptible (β-lactamase rising)
  • Anticoagulation controversial — some advocate if cerebral / propagating; risk-benefit
  • Drainage of abscess if present
  • Mortality 5%

179.1.0.7 6⃣ OB/GYN Anaerobic Infections

  • PID — Bacteroides, Prevotella, Peptostreptococcus + N. gonorrhoeae, Chlamydia (mixed)
  • Postpartum endometritis — anaerobes + GBS + GN
  • Septic abortion (especially incomplete) — multiple anaerobe + Clostridium sordellii (rare 䜆 deadly)
  • Tubo-ovarian abscess — drainage + clindamycin + gentamicin + ampicillin (or pip-tazo)

179.1.0.8 7⃣ Treatment Summary by Site

Site Empirical
Intra-abdominal community Cefoxitin / amp-sulb / amox-clav (moderate) or pip-tazo / mero (severe)
Intra-abdominal nosocomial Pip-tazo, mero, ceftolozane-tazo
Aspiration pneumonia community Amox-clav or clindamycin
HAP / VAP aspiration Pip-tazo + vanco
Lung abscess Pip-tazo (or clindamycin × 4-6 wk) ± drainage
Empyema Pip-tazo + drainage
Brain abscess Ceftriaxone + metronidazole + vanco
Lemierre’s Pip-tazo or metronidazole + ceftriaxone × 4-6 wk
PID Ceftriaxone + doxy + metro
Septic abortion Pip-tazo or amp + gent + clindamycin
Diabetic foot deep Pip-tazo + vanco; debridement