Question
Coagulase negative staphylococci
Answer
Coagulase-negative staphylococci (CoNS) are staphylococcal species that lack the enzyme coagulase (unlike Staphylococcus aureus), previously regarded largely as harmless skin commensals, but now well-recognized as important opportunistic pathogens, especially in hospitalized and immunocompromised patients and in association with implanted medical devices.
Important species and clinical associations:
- Staphylococcus epidermidis — the most clinically significant CoNS; a leading cause of infections associated with indwelling medical devices (intravascular catheters, prosthetic joints, cardiac valves, cerebrospinal fluid shunts, peritoneal dialysis catheters), owing to its strong ability to form biofilm on synthetic/foreign surfaces, which protects it from host defences and antibiotics; also an important cause of neonatal sepsis (particularly in preterm infants with central lines) and a very common blood culture contaminant from skin flora, making clinical interpretation of a positive culture important (repeated isolation, or isolation from multiple sites, supports true infection over contamination).
- Staphylococcus saprophyticus — a distinct clinical entity, causing urinary tract infection in young, sexually active women; unusual among CoNS in being novobiocin-resistant (novobiocin susceptibility is used to distinguish it from S. epidermidis, which is novobiocin-sensitive).
Laboratory identification: catalase-positive, coagulase-negative (both slide and tube test); species-level identification relies on additional biochemical tests (e.g., novobiocin susceptibility) or automated/molecular methods.
Treatment: many hospital-acquired CoNS strains (especially S. epidermidis) are methicillin-resistant, often requiring vancomycin; device removal is frequently necessary for definitive cure of device-associated biofilm infections, since antibiotics alone often cannot eradicate biofilm-embedded organisms.