Staphylococcus epidermidis with the icaA− /icaD− /IS256 − genotype and protein or protein/extracellular-DNA biofilm is frequent in ocular infections

Abstract

In ocular infections (OIs) caused by Staphylococcus epidermidis, biofilms composed mainly of poly-N-acetylglucosamine (PNAG) have been widely studied, but PNAG-independent biofilms have not. Therefore, we searched for a relationship between the ica operon (involved in PNAG-biofilm) and the biochemical composition of biofilms in isolates from OI. Isolates from OI (n = 62), from healthy conjunctiva (HC; n = 45) and from healthy skin (HS; n = 53), were used to detect icaA and icaD genes, and the insertion sequence 256 (IS256) using PCR. The compositions of the biofilms were determined by treatment with NaIO₄, proteinase K and DNase I. Multilocus sequence typing (MLST) was performed to characterize the isolates, and the expression of aap and embp genes was determined by real-time qPCR. A strong relationship between the icaA(-)/icaD(-)/IS256(-) genotype and protein- or protein/extracellular DNA (eDNA)-biofilm composition was found in the isolates from OI (53.6%), whereas the icaA(+)/icaD(+)/IS256(-) genotype and carbohydrate-biofilm was most prevalent in isolates from HC (25%) and HS (25%). Isolates with an icaA(-)/icaD(-)/IS256(-) genotype and protein-biofilm phenotype were predominantly of the ST2 lineage, while carbohydrate-biofilm-producing strains were mainly of the ST9 lineage. The protein-biofilm-producing strains had higher expression levels of aap gene than carbohydrate-biofilm-producing strains; while embp gene did not have the same pattern of expression. These results suggest that S. epidermidis strains with icaA(-)/icaD(-)/IS256(-) genotype and protein- or protein/eDNA-biofilms have a stronger ability to establish in the eye than S. epidermidis strains with icaA(+)/icaD(+)/IS256(-) genotype and PNAG-biofilms.