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

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.