Staphylococcus epidermidis strains isolated from nosocomial infections represent a serious problem worldwide. In various Mexican states several reports have shown isolates from hospitals with antibiotic resistance to methicillin. In Mexico City, there is scarce information on staphylococcal infections in hospitals. Here, our research findings are shown in a four-year period study (2006–2010) for Staphylococcus epidermidis strains. Susceptibility and/or resistance to antibiotics in SE strains were assessed by phenotypic and molecular methods as mecA gene by PCR, as well as the correlation with biofilm production for these isolates and the relationship to the infection site. Out of a total of 161 (66%) negative biofilm SE strains, just 103 (64%) SE strains were confirmed as MRSE by PCR to mecA gene. From 84 (34%) positive biofilm SE strains, 76 (91%) were confirmed as MRSE by PCR to mecA gene. Higher percentages of resistance to antibiotics and higher number of resistance markers were found in biofilm-forming clinical strains (9 to 14) than non-biofilm-forming SE strains (3 to 8). These research findings represent a guide to establish infection control programs for this hospital. 1. Introduction Staphylococcus epidermidis (SE) is a saprophyte which is part of the normal human skin and mucous membranes microflora. Furthermore, SE is one of the most common etiologic agents of nosocomial infections (NIs) worldwide. Moreover, SE is the most prevalent etiology of NI in pediatric intensive care units (ICUs) in Mexican hospitals [1, 2]. However, SE is primarily associated with infections in patients implanted with medical devices, such as prosthetic heart valves and orthopedic prostheses, mainly in immunocompromised children. Furthermore, SE was isolated with higher incidence to catheter-related bacteremia in a report from secondary care Hospital in Durango, México [3, 4]. Biofilm is mainly made of polysaccharide component; it seems to be the most important factor by which SE adheres to and colonizes artificial materials (catheters) commonly implanted in patients with NI. Biofilm is believed to make clinical SE strains more resistant to administered antibiotics and to host defense mechanisms and highly contributed to cause NI in patients [2, 5–9]. In clinical practice, SE has become one of the most significant species among methicillin-resistant coagulase negative staphylococci (CoNS). There are various scientific world reports that stated that approximately between 80% and 90% of SE strains isolated from patients with NI carried the mecA gene [10–13]. The
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