Coagulase-Negative Staphylococcus, Species, Treatment, Antibiotics, UTI, and Gram Stain Findings

Coagulase-Negative Staphylococcus:

• What is Coagulase-Negative Staphylococcus?
• Species
• Treatment
• Antibiotics
• UTI
• Gram Stain Findings

What is Coagulase-Negative Staphylococcus?

Coagulase-Negative Staphylococcus (CoNS) refers to a group of Staphylococcus bacteria that do not produce the enzyme coagulase, which distinguishes them from Staphylococcus aureus. Coagulase-negative staphylococci are part of the normal flora on human skin and mucous membranes but can become opportunistic pathogens, especially in hospitalized or immunocompromised patients. They are one of the most common causes of bloodstream infections related to indwelling medical devices such as catheters and prosthetic implants.

Although CoNS are often dismissed as contaminants in blood cultures, they should not be overlooked in symptomatic patients with fever, sepsis, or indwelling devices. Their ability to form biofilms on artificial surfaces contributes to persistent infections and resistance to antibiotics, making them clinically significant despite being part of the normal microbiota.

Species

There are several species of Coagulase-Negative Staphylococcus, each with different clinical relevance. The most common pathogenic species include:

• Staphylococcus epidermidis – the most frequent cause of device-related infections and prosthetic valve endocarditis.
• Staphylococcus saprophyticus – a common cause of urinary tract infections, particularly in sexually active young women.
• Staphylococcus haemolyticus – associated with bloodstream and wound infections, often multidrug-resistant.
• Staphylococcus lugdunensis – an aggressive CoNS species that can cause infections similar to S. aureus, including skin abscesses and endocarditis.

Less common species such as S. capitis and S. hominis are occasionally implicated in neonatal sepsis and prosthetic joint infections. Accurate species identification is important for determining clinical relevance and guiding therapy, as antibiotic resistance patterns can vary.

Treatment

Treatment of CoNS infections depends on the infection site, species involved, and antibiotic susceptibility profile. Since CoNS often form biofilms, they are difficult to eradicate without removing the infected device or catheter. For bloodstream or prosthetic infections, removal of the contaminated hardware combined with antibiotic therapy yields the best outcomes.

Empirical therapy typically includes antibiotics effective against methicillin-resistant CoNS strains, such as vancomycin. Once culture and sensitivity results are available, therapy can be adjusted accordingly. Mild or localized infections may respond to oral antibiotics, whereas deep-seated or systemic infections require intravenous treatment. Supportive care and infection control measures are essential to prevent recurrence.

Antibiotics

Coagulase-Negative Staphylococcus species often exhibit resistance to multiple antibiotics, particularly beta-lactams, due to the presence of the mecA gene, which encodes an altered penicillin-binding protein. This makes them resistant to methicillin, oxacillin, and most cephalosporins.

The main antibiotics used for CoNS infections include:

• Vancomycin – first-line for methicillin-resistant strains (MR-CoNS).
• Linezolid or daptomycin – alternatives for resistant or vancomycin-intolerant patients.
• Rifampin – used in combination for biofilm-related infections.
• Clindamycin or trimethoprim-sulfamethoxazole – possible options for susceptible strains.

Antibiotic stewardship and susceptibility testing are essential to minimize resistance and ensure effective treatment.

UTI

Among CoNS, Staphylococcus saprophyticus is a well-known cause of urinary tract infections (UTIs), particularly in young, sexually active women. It accounts for 10–20% of community-acquired UTIs, second only to Escherichia coli. The infection presents with typical symptoms such as dysuria, urinary frequency, and suprapubic discomfort.

Treatment typically involves short courses of antibiotics such as nitrofurantoin or trimethoprim-sulfamethoxazole. Unlike other CoNS species, S. saprophyticus is usually sensitive to commonly used oral antibiotics. However, accurate identification is important to distinguish it from other pathogens and to prevent recurrent infections, especially in patients with risk factors like urinary obstruction or catheterization.

Gram Stain Findings

On Gram stain, Coagulase-Negative Staphylococcus appears as Gram-positive cocci in clusters, resembling Staphylococcus aureus. They are catalase-positive but coagulase-negative, which is the main test distinguishing them from S. aureus. Colonies on agar are typically white to gray, small, and non-hemolytic.

Microscopic examination shows round, clustered cells, often found in skin flora samples or from catheter tips. While a single positive culture may represent contamination, multiple positive cultures from separate blood draws suggest true infection. Gram stain results combined with culture data help confirm the clinical significance and guide appropriate antibiotic therapy.