Biofilm formation and esp gene carriage in enterococci

Aims: To investigate biofilm production and esp carriage in enterococci. Methods: Biofilm production in vancomycin resistant enterococci (VRE) and vancomycin susceptible enterococci (VSE) was tested on a microtitre plate method, using both brain heart infusion (BHI) broth and human serum as media. Isolates were screened for the esp gene, which has been reported to be essential for biofilm formation in enterococci, by means of the polymerase chain reaction. Results: None of seven VRE and nine of 28 VSE tested formed a biofilm. One initially negative VRE Enterococcus faecium isolate produced a strong biofilm after 21 weeks of dry starvation on a cotton swab. By Fisher’s exact test, there was no significant difference in biofilm formation between VRE and VSE, E faecalis and E faecium, or isolates from different sites. Biofilm formation was independent of possession of the esp gene. One isolate produced a strong biofilm in human serum but only a weak biofilm in BHI, whereas another produced a moderate biofilm in human serum but a weak biofilm in BHI. Conclusions: The acquisition of vancomycin resistance may result in a lower ability to form biofilms, but a larger study using clinical isolates is needed to test this hypothesis. That one initially negative VRE isolate produced a strong biofilm after prolonged dry starvation suggests that biofilm formation may be an adaptive response. The esp gene does not appear to be necessary or sufficient for production of biofilms in enterococci.