Coagulase-negative staphylococci

CoNS ID - The Usual Suspects

• Catalase-positive, coagulase-negative Gram-positive cocci in clusters.
• Often part of normal skin flora; opportunistic pathogens.

S. epidermidis - The Biofilm King

• Normal flora of the skin; a major opportunistic pathogen, especially in hospital settings (nosocomial).
• Primary Virulence Factor: Production of a polysaccharide slime layer (biofilm). This allows adherence to foreign materials and protects from antibiotics and host defenses.
• Associated Infections:
  • Prosthetic devices: Joints, heart valves (endocarditis).
  • Intravascular catheters & IV lines → bacteremia/sepsis.
  • Cerebrospinal fluid (CSF) shunts.
• Treatment: Vancomycin is the drug of choice due to widespread methicillin resistance (MRSE).

⭐ The most common cause of endocarditis on prosthetic heart valves, especially within the first 1 year post-surgery.

Biofilm Formation:

S. saprophyticus - UTI Specialist

• Clinical Role: A leading cause of community-acquired UTIs (cystitis), ranking second only to E. coli in its primary demographic.
• Classic Vignette: Presents as acute cystitis in young, sexually active women, often termed "honeymoon cystitis."
• Pathogenesis: Colonizes the urinary tract by adhering strongly to urothelial cells.
• Lab Diagnosis: Catalase (+), Coagulase (-).
• Treatment: Responds well to standard UTI antibiotics like TMP-SMX.

⭐ Key Distinguisher: Unlike most other coagulase-negative staphylococci, S. saprophyticus is innately resistant to novobiocin.

📌 Mnemonic: No StRESs: Novobiocin Resistant, Epidermidis is Sensitive.

Treatment Strategy - Attack & Remove

• Two-Pronged Approach: Success hinges on combining antimicrobial therapy with aggressive source control, especially removing colonized hardware.
• Primary Challenge: High prevalence of methicillin resistance and robust biofilm formation on foreign materials.

⭐ Biofilm is the Fortress: CoNS biofilms can increase antibiotic resistance up to 1000-fold, making device removal, not just drug therapy, the cornerstone of successful treatment.

High‑Yield Points - ⚡ Biggest Takeaways

• Coagulase-negative staphylococci (CoNS) are gram-positive, catalase-positive cocci.
• S. epidermidis is notorious for biofilm formation on prosthetic devices and catheters, leading to nosocomial infections.
• It is frequently methicillin-resistant (MRSE), often requiring vancomycin.
• S. saprophyticus is a common cause of UTIs in sexually active young women.
• Key differentiator: S. saprophyticus is novobiocin-resistant, whereas other CoNS are novobiocin-sensitive.