Staphylococci are a group of bacteria that are part of the normal flora of the skin and mucous membranes. While
Staphylococcus aureus is well-known for causing a range of infections, the non-aureus staphylococci, also known as
Coagulase-negative staphylococci (CoNS), are increasingly recognized for their role in infectious diseases, particularly in healthcare settings.
What are Non-Aureus Staphylococci?
Non-aureus staphylococci are a group of staphylococcal species that do not produce coagulase, an enzyme that allows S. aureus to clot plasma. These bacteria are ubiquitously found on the skin and mucosal surfaces of humans and animals. Some of the most common species include
Staphylococcus epidermidis, Staphylococcus saprophyticus, and Staphylococcus lugdunensis.
Why are they Clinically Significant?
Although traditionally considered to be non-pathogenic or contaminants, CoNS have emerged as significant pathogens, particularly in immunocompromised patients and those with medical devices. Their ability to form
biofilms on the surfaces of medical devices such as catheters, prosthetic valves, and joint replacements is a major factor contributing to their pathogenicity. This biofilm formation protects the bacteria from host immune responses and increases resistance to antibiotics.
What Infections do they Cause?
CoNS are primarily associated with hospital-acquired infections. They are a leading cause of
catheter-related bloodstream infections and are also implicated in endocarditis, prosthetic joint infections, and surgical site infections.
Staphylococcus saprophyticus is an exception among CoNS, being a common cause of urinary tract infections, especially in young women.
How are These Infections Diagnosed?
The diagnosis of CoNS infections requires careful interpretation of microbiological findings. Since these bacteria are part of the normal skin flora, their presence in cultures can often be due to contamination. Clinical correlation is essential, and diagnosis often depends on repeated isolation of the organism from sterile sites, along with clinical signs of infection.
What Challenges Exist in Treating These Infections?
Treatment of CoNS infections is challenging due to their inherent and acquired resistance to multiple antibiotics. Methicillin-resistant CoNS (MR-CoNS) are common, similar to
Methicillin-resistant Staphylococcus aureus (MRSA). Their ability to form biofilms further complicates treatment by reducing the efficacy of antimicrobial agents. Removal of the infected device is often necessary to achieve a cure.
What are the Implications for Antibiotic Stewardship?
Given the increasing incidence of CoNS infections and their resistance patterns, antibiotic stewardship is crucial. Judicious use of antibiotics, guided by susceptibility testing, is essential to prevent the development of further resistance. Understanding the specific resistance mechanisms, such as the presence of the mecA gene in MR-CoNS, can help in selecting appropriate antimicrobial therapy.
How Can These Infections be Prevented?
Preventive measures are vital in reducing the incidence of CoNS infections. These include strict adherence to
infection control practices such as hand hygiene, aseptic techniques during insertion of medical devices, and timely removal of unnecessary catheters and devices. In healthcare settings, monitoring and surveillance of CoNS infections can help in understanding and controlling their spread.
What is the Prognosis for Patients with CoNS Infections?
The prognosis for patients with CoNS infections depends on several factors, including the patient's underlying health condition, the site of infection, and timely initiation of appropriate treatment. While these infections can be severe, especially in vulnerable populations, prompt and adequate treatment can lead to successful outcomes.
In conclusion, while non-aureus staphylococci were once considered benign, their role in infectious diseases, particularly in hospital settings, cannot be overlooked. Understanding their clinical significance, resistance patterns, and the challenges they pose is essential for effective management and prevention of these infections.
