Coagulase negative staphylococci

An overview of coagulase-negative staphylococci, their characteristics, clinical significance, and treatment.

Coagulase-negative staphylococci (CoNS) are a group of Staphylococcus species that do not produce the enzyme coagulase. Unlike their coagulase-positive counterpart, Staphylococcus aureus, CoNS are generally less virulent but are significant as opportunistic pathogens, particularly in nosocomial infections.

Characteristics

Coagulase-negative staphylococci are Gram-positive bacteria that appear as clusters under a microscope. They are facultative anaerobes, meaning they can grow in both the presence and absence of oxygen. CoNS are part of the normal microbiota of human skin and mucous membranes, which makes them frequent contaminants in clinical specimens.

Species

There are over 40 species of CoNS, but the most clinically significant include:

• Staphylococcus epidermidis - Commonly associated with infections related to indwelling medical devices such as catheters and prosthetic joints.
• Staphylococcus saprophyticus - Known for causing urinary tract infections in young women.
• Staphylococcus lugdunensis - Can cause more severe infections similar to those caused by S. aureus.

Clinical Significance

CoNS are a major cause of hospital-acquired infections, particularly in patients with compromised immune systems or those with implanted medical devices. They are known for their ability to form biofilms on surfaces, which protects them from the host immune response and antibiotic treatment.

Infections

• Bacteremia - CoNS are a common cause of bloodstream infections, especially in patients with central venous catheters.
• Endocarditis - Particularly in patients with prosthetic heart valves.
• Peritonitis - In patients undergoing peritoneal dialysis.

Diagnosis

Diagnosis of CoNS infections involves isolating the bacteria from clinical specimens and differentiating them from contaminants. This often requires multiple positive cultures and clinical correlation.

Treatment

Treatment of CoNS infections can be challenging due to their intrinsic resistance to many antibiotics and their ability to acquire resistance genes. Vancomycin is often used for serious infections, but susceptibility testing is crucial to guide therapy.

Prevention

Preventive measures include strict adherence to aseptic techniques during the insertion and maintenance of indwelling devices, as well as the use of antibiotic-impregnated catheters.

Also see

• Staphylococcus aureus
• Biofilm
• Antibiotic resistance
• Nosocomial infection