D-075. Gene Expression in ica (+) Clinical S. epidermidis Strains with Distinct Biofilm Phenotypes

N. Y. Ng, M. Liu, V. Milisavljevic;
Univ. of California, Los Angeles, CA.

Background: Staphylococcus epidermidis, a normal commensal of the skin and mucous membranes, is the most frequent cause of nosocomial infections. The pathogenesis of infections caused by this organism is associated with its ability to form biofilms. The main component of staphylococcal biofilms is polysaccharide intercellular adhesion (PIA), encoded by the ica locus. The objective of this study was to identify gene expression profiles in two clinical ica+ S. epidermidis strains with distinct biofilm phenotypes, and compare them with genes that are differentially expressed in alcohol-induced biofilm production. Methods: We evaluated global gene expression profiles in 3 clinical ica+ S. epidermidis strains with identical PFGE patterns, A5, A10 and A26. Biofilm production in A5 is strongly induced by benzyl alcohol. A10 is biofilm-negative and A26 strongly produces biofilm, independent of alcohol supplementation. We used expression arrays for S. epidermidis RP62A. Bacterial cultures were grown to mid-log phase in TSB media, and TSB media supplemented with 0.4% benzyl alcohol for RNA isolation. Results: The total number of genes represented on the array was 2526. We found 259 genes (145 coding for hypothetical proteins) that were differentially expressed in the A26 versus A10 strain, with 108 genes showing increased and 151 decreased expression in A26 by at least 2-fold. Benzyl alcohol regulated 122 genes in A5; 56 were repressed and 66 induced. In both sets the icaADBC operon was induced, as well as genes for capsule/poly-gamma-glutamate synthesis proteins. Surprisingly, icaR was repressed less than 2-fold. In addition, we found distinct sets of genes (86 total, 43 hypothetical) that were differentially regulated in response to alcohol. Conclusion: The presence of the ica operon and PFGE patterns are not predictive of biofilm phenotype. Biofilm production can be constitutively high, or inducible by alcohol. Changes in biofilm phenotype are associated with differential expression of diverse sets of genes, some distinctly in response to stress (alcohol).