Construction of mutant strains of methicillin resistant Staphylococcus epidermidis with psm-mec gene deletion

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Objective To construct mutant strains of methicillin resistant Staphylococcus epidermidis (MRSE) with psm-mec gene deletion and to investigate the function of psm-mec gene. Methods The drug sensitivity test and DNA sequence analysis were performed to screen out the tetracycline and chloramphenicol sensitive clinical strains of MRSE, whose upstream and downstream sequences of psm-mec gene were identical to those of the Staphylococcus epidermidis reference strain RP62A. The recombinant plasmid pBT2-Δpsm-mec was constructed by using the fusion PCR and a temperature sensitive shuttle plasmid. After being identified, the plasmid was transformed into the Staphylococcus aureus RN4220 strain by electroporation, and then transformed into the selected clinical isolates of MRSE. The mutant strains of MRSE with psm-mec deletion were screened out and identified after homologous recombination. The differences in biofilm formation between the mutant and wild-type strains were analyzed for further elucidation the relationships between the psm-mec gene and biofilm formation in MRSE strains. Results Three clinical MRSE isolates for the construction of mutant strains with psm-mec gene deletion were screened out and identified by using drug sensitivity test and sequence alignment analysis. The mutants constructed via homogenous recombination were screened out and identified. Compared with the corresponding wild-type strains, the three mutants with psm-mec gene deletion showed significantly decreased ability of biofilm formation, demonstrating that the psm-mec genes strains induced the biofilm formation of MRSE. Conclusion The Δpsm-mec mutant strains were successfully constructed. The psm-mec gene played an important role in the biofilm formation of Staphylococcus epidermdis. Key words: Staphylococcus epidermidis; psm-mec; Homologous recombination; Mutant; Biofilm formation