Detection of biofilm-producing and methicillin resistance genes in Staphylococcus epidermidis isolated from healthy humans and in blood culture tests

The detection of biofilm-producing (ica AB) and methicillin resistance genes (mec A) was investigated in 70 blood culture isolates of Staphylococcus epidermidis and in 66 and 51 isolates from human hands and the vestibules of the nose, respectively, of 77 healthy subjects who gave consent. Of the 70 strains isolated from blood culture testing, both ica AB and mec A were detected in 36 (51.4%), and neither was detected in 4 (5.7%). The mec A gene only was detected in 30 (42.9%), but no isolate from blood culture testing possessed the ica AB gene alone. In contrast, of the 66 isolates from healthy hands, only one isolate (1.5%) possessed both genes, whereas neither was detected in 56 (84.8%), but the mec A gene was detected in 9 (13.6%). Of the 51 isolates from the nasal vestibules, both genes were detected in 12 (23.5%), and neither in 15 (29.4%). Moreover, the mec A gene was detected in 17 (33.3%). Thus, S. epidermidis strains that normally inhabit the nasal vestibule were found to carry the ica AB and mec A genes more frequently than those that inhabit the fingers. The ica AB and mec A genes were detected in S. epidermidis isolated in blood culture tests from patients diagnosed with sepsis associated with catheter-related bloodstream infection (CR-BSI). Both genes were detected in 7 (70.0%) of 10 isolates, and the mec A gene alone was detected in 3 (30.0%). In fact, we could not detect any strain carrying only the ica AB gene from S. epidermidis, an infecting organism of CR-BSI. This suggests that surviving strains carrying the mec A gene cause severe infection on empirical administration of an antibacterial drug, although biofilm formation by the ica AB gene is also important for CR-BSI. Based on these findings, most strains of S. epidermidis causing CR-BSI are biofilm-producing β-lactam-resistant (methicillin-resistant) bacteria. When S. epidermidis is isolated from blood culture testing, the identification of both ica AB and mec A genes may be significant with regard to judging whether the detected strain is the etiologic agent of CR-BSI.