Study On The Factors Affecting Staphylococcus Aureus Biofilm Formation

In this study, the microtitre plate assay was used to evaluate the effects of environmental factors on Staphylococcus aureus biofilm formation. Based on this,proper conditions for biofilm culture were determined and the biofilm formation ability of 112 S. aureus isolates were assessed. Then the presence of biofilm related genes in these strains was investigated, and their correlations with biofilm formation were analyzed.First, the effects of culture materials, culture time, culture temperature and nutrients on biofilm formation were evaluated. Then, hydrophilic microtitre plate, growth in TSB for 48h at 37℃was chosen to determine biofilm production of 112 S. aureus isolates. The results showed that S. aureus could generally produce biofilm, 30 of 112 strains (26.8%) were classi?ed as strong, 21 of 112 strains (18.8%) as moderate, 51 of 112 strains (45.5%) as weak, and only 10 of 112 strains (8.9%) as negative bio?lm formers. There was no significant deviation in biofilm production between clinic (phlegm, pus, blood and urine) and food isolates, while strains from the same source could produce discrepant quantities of bio?lm,which suggests that biofilm formation of a particular S. aureus strain depends more on its genetic make-up than its origin.All strains were also genotyped with respect to their agr-types by both ScaI-restriction fragment length polymorphism and agr group-speci?c multiple PCR. And the presence of other biofilm related genes ica, rbf, and bap were detected by PCR. The correlations between the prevalence of the agr-types, the investigated genes and bio?lm formation were statistically analyzed. Four different agr-allele groups all existed in 112 strains. Agr-Ⅰstrains were found to be the most prevalent (61.8% of the strains) group. There were significant differences in biofilm formation between different agr-genotypes, and agr-Ⅰstrains produced larger amounts of biofilm than other agr-genotypes. The ica and rbf genes were widespread in 112 strains, taking 98.2% and 96.4% separately, and their presence interrelated with biofilm formation. While bap only accounted for 8.0%, but strains with bap were all strong bio?lm formers. However, strains without the investigated genes could also form biofilm, which suggests the existence of other regulation mechanisms of biofilm formation in S. aureus.