What is coagulase-negative (Coag neg) staph?

Coagulase-Negative Staphylococci (CoNS)

Coagulase-negative staphylococci are a group of staphylococcal species distinguished from Staphylococcus aureus by their inability to produce free coagulase, and they are the most common cause of catheter-related infections while typically residing as normal flora on human skin and mucous membranes. 1

Definition and Classification

Coagulase-negative staphylococci (CoNS) include:

• Staphylococcus epidermidis (most common)
• Staphylococcus lugdunensis
• Staphylococcus saprophyticus
• Staphylococcus haemolyticus
• Staphylococcus hominis
• Staphylococcus capitis
• Staphylococcus auricularis
• Staphylococcus simulans

Clinical Significance

CoNS have evolved from being considered mere contaminants to recognized pathogens, particularly in:

• Catheter-related bloodstream infections (CRBSIs) - CoNS are the most common pathogens in CRBSIs 1
• Prosthetic valve endocarditis - Leading cause 1
• Native valve endocarditis - Particularly in patients with underlying valvular abnormalities 1
• Central nervous system shunt infections
• Surgical site infections
• Peritonitis in patients with continuous ambulatory peritoneal dialysis

Pathogenicity Mechanisms

CoNS possess several virulence factors that contribute to their pathogenicity:

1. Biofilm formation - Many strains produce an extracellular polysaccharide "slime" that:

   • Protects against host defense mechanisms
   • Reduces susceptibility to antimicrobial agents
   • Enhances adherence to polymer surfaces and medical devices 1

2. Surface adherence - CoNS adhere to polymer surfaces more readily than other pathogens 1

3. Antimicrobial resistance - Approximately 55-75% of nosocomial isolates are methicillin-resistant 1

Special Consideration: Staphylococcus lugdunensis

S. lugdunensis deserves special mention as it:

• Causes a substantially more virulent form of infection than other CoNS
• Can cause endocarditis and metastatic infections similar to S. aureus
• Has a high rate of perivalvular extension of infection
• Should be managed similarly to S. aureus infections 1

Treatment Recommendations

For uncomplicated CoNS catheter-related bloodstream infections:

1. If catheter is removed:

   • Treat with antibiotics for 5-7 days 1
   • Some patients may be observed without antibiotics if they have no intravascular or orthopedic hardware and follow-up blood cultures confirm absence of bacteremia 1

2. If catheter is retained:

   • Treat with systemic antibiotics for 10-14 days in combination with antibiotic lock therapy 1
   • For tunneled catheters or implanted devices, systemic antibiotics for 7 days plus antibiotic lock therapy for 14 days 1

3. Antibiotic selection:

   • Vancomycin is commonly used due to high prevalence of methicillin resistance
   • Change to a semisynthetic penicillin if the isolate is susceptible 1
   • Combination therapy with vancomycin plus gentamicin or rifampin is not recommended for routine therapy 1

Clinical Pitfalls and Caveats

1. Distinguishing contamination from true infection:

   • CoNS are the most common contaminants in blood cultures
   • Multiple positive blood cultures from different sites strongly suggest true infection 1

2. Treatment failure indicators:

   • Persistent fever
   • Persistent positive blood cultures
   • Relapse of infection after antibiotics discontinuation These require catheter removal 1

3. Biofilm considerations:

   • Antibiotic lock therapy is crucial for intraluminal infections
   • Catheters in place <2 weeks are most often infected extraluminally, making antibiotic lock therapy less effective 1

4. Hospital transmission:

   • Evidence suggests clonal spread of S. epidermidis strains within and between hospitals
   • Infection control measures may be necessary for multiresistant CoNS isolates 2

5. S. lugdunensis identification:

   • Microbiological differentiation from other CoNS may be difficult
   • Many laboratories lack capability to assign species identification to CoNS isolates 1
   • Should be treated more aggressively, similar to S. aureus infections

By understanding the clinical significance of CoNS and implementing appropriate treatment strategies, clinicians can effectively manage these increasingly important pathogens that were once dismissed as mere contaminants.