152.1 🎓 醫孞生版

152.1.0.1 📌 䞀頁重點

  • 菌皮: Gram + cocci in clusters (像葡萄䞲)、catalase + (vs Strep -)、coagulase + (S. aureus) / - (CoNS)
  • S. aureus 臎病: TSST-1, exfoliative toxin, enterotoxin, PVL (Panton-Valentine Leukocidin), α-hemolysin
  • 臚床: SSTI、菌血症、心內膜炎、骚髓炎、肺炎、TSS、food poisoning
  • MRSA: mecA (→ PBP2a)、HA-MRSA vs CA-MRSA (USA300, PVL)
  • CoNS (S. epidermidis): prosthetic device infection (biofilm)
  • S. lugdunensis: aggressive endocarditis (像 S. aureus 衚珟)
  • MSSA 驖遾: nafcillin / cefazolin / oxacillin
  • MRSA 驖遾: vancomycin / daptomycin / linezolid / ceftaroline

152.1.0.2 1⃣ 现菌孞

  • Gram + cocci in clusters (vs Strep in chains)
  • Catalase + (vs Strep catalase -)
  • Coagulase + = S. aureus; Coagulase - = CoNS (S. epidermidis, S. saprophyticus, S. lugdunensis)
  • S. aureus: yellow (“aureus”) pigment on culture
  • Mannitol fermentation + on MSA plate
152.1.0.2.1 Carriage
  • 20-30% 健康成人 錻腔垶 S. aureus (持續或間歇)
  • Decolonization: mupirocin + chlorhexidine bath (pre-op)
152.1.0.2.2 Virulence Factors
  • Capsule (5+8 䞻芁)
  • Protein A: bind IgG Fc → 免疫躲避
  • Coagulase: 圢成 fibrin clot 保護菌體
  • TSST-1: 超抗原, 月經期 TSS
  • Exfoliative toxin (ETA, ETB): SSSS (Staphylococcal Scalded Skin Syndrome)
  • Enterotoxin A-E: food poisoning (heat-stable)
  • PVL (Panton-Valentine Leukocidin): CA-MRSA, necrotizing pneumonia, abscess
  • α-hemolysin: 现胞溶解

152.1.0.3 2⃣ 臚床衚珟

152.1.0.3.1 A. Skin & Soft Tissue (SSTI)
  • Folliculitis, furuncle, carbuncle (毛囊炎、癀、癰)
  • Impetigo: bullous (S. aureus) vs non-bullous (S. aureus or GAS)
  • Cellulitis (often + Strep)
  • Abscess — Inc & Drain 䞻治
  • SSSS (小孩 < 6 æ­², scalded skin appearance, Nikolsky +): exfoliative toxin
  • CA-MRSA SSTI 倧流行 (USA300)
152.1.0.3.2 B. Bacteremia / Endocarditis
  • S. aureus bacteremia (SAB) — 高死亡 (15-30%)
  • Endocarditis (IE):
    • Native: TV (IDU) 或 LV
    • Prosthetic: PVE (CoNS within 1 yr, S. aureus later)
  • TEE 匷制: 扟莅生物、abscess
  • Source 匷制: 抜血 × 2 sets q48-72h until clear
152.1.0.3.3 C. 骚髓炎 / 化膿性關節炎
  • S. aureus #1 cause (成人, 小孩)
  • 血流播散或盎接接皮 (穿刺、術埌)
  • MRI + bone biopsy (埮生物 + 病理)
  • Course: 4-6 weeks (IV → PO)
  • POET / OVIVA 2018: oral switch 等效 for stable
152.1.0.3.4 D. 肺炎
  • HAP / VAP 重芁 cause
  • Post-influenza secondary pneumonia (necrotizing)
  • CA-MRSA pneumonia (PVL +): necrotizing, severe, young healthy
152.1.0.3.5 E. TSS (Toxic Shock Syndrome)
  • 高燒 + 玅斑疹 + 䜎血壓 + 倚噚官衰竭
  • Menstrual (1980s tampon): TSST-1
  • Non-menstrual: post-op, post-partum, abscess, burn
  • Treatment: IV fluid + 抗生玠 (clinda for toxin suppression + vanco) + IVIG (severe)
152.1.0.3.6 F. Food Poisoning
  • 2-6 hr after ingestion (toxin preformed in food)
  • 噁吐 + 腹瀉 (沒燒, 沒長期沿甚)
  • Self-limited (24 hr)
152.1.0.3.7 G. CoNS
  • Prosthetic valve / vascular catheter / orthopedic device — biofilm
  • S. saprophyticus: UTI in young female
  • S. lugdunensis: virulence 像 S. aureus, 嚎重 IE

152.1.0.4 3⃣ MRSA

152.1.0.4.1 機蜉
  • mecA gene → PBP2a (low affinity for β-lactams)
  • SCCmec cassette (I-V): I-III = HA-MRSA, IV-V = CA-MRSA
152.1.0.4.2 HA-MRSA vs CA-MRSA
特埵 HA-MRSA CA-MRSA (USA300)
Setting 醫院, NH 瀟區 (幎茕、健康)
SCCmec I-III (倧) IV-V (小)
PVL 通垞無 有 (匕癌 necrotizing)
Resistance 倚重 (FQ, macrolide, etc.) β-lactam only (陀倖 mecA)
臚床 bacteremia, pneumonia SSTI, necrotizing pneumonia
治療 vanco IV TMP-SMX, doxy, clinda (oral)
152.1.0.4.3 MRSA Decolonization (Pre-op cardiac/ortho)
  • Mupirocin nares × 5d + chlorhexidine bath × 5d
  • 降 SSI

152.1.0.5 4⃣ 治療

152.1.0.5.1 MSSA (Methicillin-Sensitive)
  • Nafcillin / Oxacillin 2 g IV q4h (驖遾)
  • Cefazolin 2 g IV q8h (等效, 范少 hepatic / interstitial nephritis)
  • 侍甹 vancomycin for MSSA (worse outcome vs nafcillin/cefazolin)
152.1.0.5.2 MRSA
  • Vancomycin (trough 15-20 µg/mL or AUC 400-600)
  • Daptomycin 6-10 mg/kg/d (bacteremia, IE — NOT lung, surfactant inactivates)
  • Linezolid / Tedizolid (good for pneumonia, lung penetration)
  • Ceftaroline (5th gen ceph, anti-MRSA β-lactam)
  • Newer: dalbavancin (1-2 dose), oritavancin (1 dose) — long half-life for OPAT
152.1.0.5.3 Combination
  • Vanco + ceftaroline for persistent MRSA bacteremia (Geriak 2019)
  • Vanco + daptomycin in refractory IE (controversial but some use)
152.1.0.5.4 Bacteremia Management
  • Infectious Disease consult mandatory (降 mortality 30-50%)
  • Repeat blood cultures q48-72h until clear
  • TEE (TTE 䞍倠 sensitive)
  • Source control: line removal, abscess drainage
  • 2 weeks IV for uncomplicated; 4-6 weeks for IE, complicated