Analysis of antimicrobial resistance and staphylococcal cassette chromosome mec (SCCmec) in 99 Staphylococcus epidermidis strains isolated from early pregnancy cervical swabs and external environment

Abstract

Objective To analyze the antimicrobial resistance, distribution of resistance genes and staphylococcal cassette chromosome mec (SCCmec) in 99 strains of mecA gene-positive Staphylococcus epidermidis strains isolated from early pregnancy cervical swabs and external environment in Beijing Chaoyang District from 2015 to 2016. Methods Kirby-Bauer disk diffusion method was performed to detect the susceptibility of the 99 Staphylococcus epidermidis strains to cefoxitin. Microbroth dilution method was used to test their susceptibility to vancomycin, daptomycin, penicillin, erythromycin, compound sulfamethoxazole, tetracycline, ciprofloxacin, clindamycin, gentamicin and chloramphenicol. PCR was used to detect drug resistance genes of ermA, ermB, ermC, msrA, norA1, norA2, sul1, sul2, sul3, aac(6′)/aph(2″), ant(4′, 4″), ant(6) and tetM and to analyze the SCCmec types ofⅠ, Ⅱ, Ⅲ, Ⅳa, Ⅳb, Ⅳc, Ⅳd and Ⅴ. The results were compared with those of capillary electrophoresis. SPSS was used for data analysis. Results All of the 99 mecA-positive Staphylococcus epidermidis strains were sensitive to vancomycin and 93.94% of them were sensitive to datomycin. The resistance rates to penicillin, erythromycin, cefoxitin, compound sulfamethoxazole, tetracycline, ciprofloxacin, clindamycin, gentamicin and chloramphenicol were 97.98%, 85.86%, 79.80%, 52.54%, 27.27%, 43.43%, 36.36%, 23.23% and 11.11%. The strains that carried the genes of norA1, norA2, ermA, ermB, ermC, msrA, sul1, sul2, sul3, aac(6′)/aph(2″), ant(4′, 4″), ant(6) and tetM accounted for 100%, 93.94%, 0.00%, 3.03%, 17.17%, 57.58%, 50.51%, 12.12%, 4.04%, 30.30%, 8.08%, 4.04% and 25.26%, respectively. Among the 99 strains, 5.05%, 0%, 43.43%, 10.10%, 0.00%, 3.03%, 3.03% and 19.19% belonged to SCCmecⅠ, Ⅱ, Ⅲ, Ⅳa, Ⅳb, Ⅳc, Ⅳd and Ⅴ, respectively, and 4.04% (4/99) were positive to two SCCmec types. The types of 12.12% (12/99) of the strains were unidentified. Conclusions All of the 99 strains of mecA-positive Staphylococcus epidermidis were sensitive to vancomycin. Among them, the strains carrying multidrug resistance genes accounted for 89.90%. The main mechanisms of resistance to macrolides, sulfonamides and aminoglycosides in local strains were related to the resistance genes of msrA, sul1 and aac(6′)/aph(2″). SCCmec Ⅲ was the prevalent type. There were 88.37% of SCCmec Ⅲ type strains and 75% of unknown type strains carrying multiple resistance genes. Apart from that, the isolated strains of other SCCmec Ⅲ types all carried multiple resistance genes. Key words: Staphylococcus epidermidis; mecA; MSSE; MRSE; Drug-resistance gene; SCCmec