Isolation, vancomycin resistance and biofilm production of Staphylococcus epidermidis from patients with conjunctivitis, corneal ulcers, and endophthalmitis

Abstract

The infection frequency associated to bacterial conjunctivitis, corneal ulcers (CU), and endophthalmitis was studied along a five years period. The isolation and identification of microorganisms were performed by culture-based methods and biochemical test respectively. Also, a nested PCR to detect gram-negative and gram-positive bacteria in the clinical samples was assayed. Nested PCR was a more efficient method than culture to detect bacteria in the samples. The most frequently isolated species was Staphylococcus epidermidis, a bacterium commonly considered as a human saprophyte. The S. epidermidis strains from conjunctivitis, CU, and endophthalmitis exhibited 46, 33.9, and 34.1% of oxacilin-resistance respectively. A total of 28% of intermediate-vancomycin resistance (MIC = 8-16 microg/ml) was observed among S. epidermidis strain collection. The UPGMA cluster analysis of the multiresistance profile data of intermediate vancomycin-resistant S. epidermidis strains showed a high phenotypic diversity and no relationship between each group and their clinical origin. The biofilm formation capacity was broadly distributed (66%), particularly among intermediate-vancomycin strains (> 75%). In brief, S. epidermidis displayed a high diversity of antibiotic resistance profiles and biofilm formation capacity. These phenotypic traits could explain the high isolation frequency of S. epidermidis from ocular infections and oblige to review the saprophytic status of these bacteria.