Influence of different extracellular DNA levels in Staphylococccus epidermidis isolates on the ability of biofilm formation / 中华微生物学和免疫学杂志

ABSTRACT

ObjectiveTo determine the ability of biofilm formation of Staphylococcus epidermidis isolates and study the influence of different extracellular DNA(eDNA) levels in S.epidermidis isolates on the ability of biofilm formation.MethodsDetect the biofilm-formation ability of 227 S.epidermidis isolates with adhesion assays,amplify the icaA gene fragment with PCR.The S.epidermidis isolates were divided into biofilm formation(BF) group and non-biofilm formation (NBF) group according to adhesion assays and icaA amplification.Detect eDNA levels of S.epidermidis in planktonic culture and microtitre plate static culture.The eDNA in S.epidermidis biofilms stained by AO-PI was observed by CLSM.Results26 isolates were positive in adhesion assays and 32 isolates existed icaA gene among 227 S.epidermidis isolates.Select 20 isolates with positive adhesion assays and positive icaA amplification for BF group.Select 19 isolates with negative adhesion assays and negative icaA amplification for NBF group.The eDNA levels were (32.2±10.1)μg/ml,(33.6±11.9) μg/ml,(34.3±10.0) μg/ml in BF group when cultured in planktonic condition for 2,4,6 h,while the eDNA levels in NBF group were (28.7±8.9) μg/ml,(31.5±11.7) μg/ml,(31.8±12.7) μg/ml respectively.There were no significant differences between the two groups for these three phases(P＞0.05),though the eDNA levels of BF group were higher than that of NBF group.The eDNA levels were (740.0±264.4) ng/A600 in BF group when cultured in static microtitre plate,higher than that of NBF group,(80.1 ±31.1) ng/A600,and the difference between these two groups was significant.The eDNA in BF isolate Y36 biofilms could be visualized by staining with AO and PI when observed by CLSM,while neither biofilm structure nor eDNA appeard when NBF isolate Y26 was cultured for 24 h.ConclusionS.epidermidis isolates have the ability of biofilm formation.eDNA is one of the important matrix components in the S.epidermidis biofilm-forming process.The eDNA of static culture in microtitre plate was more efficient than planktonic culture in the case of estimating the ability of biofilm formation of S.epidermidis.