Drug resistance and virulence characteristics of of Staphylococcus aureus isolated from skin sites of suppurative infections in Inner Mongolia / 中华皮肤科杂志

ABSTRACT

Objective:To analyze drug resistance, virulence and molecular epidemiological characteristics of Staphylococcus aureus ( S. aureus) isolated from skin sites of suppurative infections, and to provide an experimental basis for clinical anti-infective therapies. Methods:Swab samples from suppurative skin lesions and nasal secretions were collected from inpatients in Department of Dermatology, the Affiliated Hospital of Inner Mongolia Medical University from May 2020 to December 2020, and subjected to bacterial isolation and culture. Suspected S. aureus colonies were identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Drug sensitivity test was conducted by using the broth microdilution method. Virulence genes of S. aureus were amplified by PCR, and real-time fluorescence-based quantitative PCR was performed to determine the relative expression of 4 virulence genes including tsst-1, pvl, hla and clfA in S. aureus strains from different sources. S. aureus strains were genotyped by multilocus sequence typing. Drug resistance rates and detection rates of virulence genes were compared by using chi-square test or Fisher′s exact test, and measurement data among groups were compared by using t test or Mann-Whitney U test. Results:A total of 85 strains of S. aureus were isolated from 210 inpatients, including 54 isolates from skin sites of suppurative infections (case group) and 31 isolates from the nasal cavity (control group) . Drug sensitivity test showed that 14 strains of methicillin-resistant S. aureus (MRSA) were identified among 85 strains of S. aureus. The resistance rate to penicillin was the highest (90.59%, 77/85) in the 85 S. aureus strains; the resistance rates to clindamycin and erythromycin were 60.00% (51/85) and 61.18% (52/85) respectively; no strains showed resistance to rifampicin, vancomycin or linezolid. PCR showed that the detection rate of the pvl gene was 33.33% (18/54) in the case group, which was significantly higher than that in the control group (12.90%, 4/31; χ2= 4.28, P= 0.038) . Real-time fluorescence-based quantitative PCR showed that the relative expression level of the clfA gene was significantly higher in the control group (3.87[2.30, 5.94]) than in the case group (1.63[0.95, 2.62], P= 0.007) . A total of 17 ST types were identified among the 85 strains of S. aureus, and the dominant types were ST398-methicillin-susceptible S. aureus (20/71) and ST22-MRSA (9/14) . The detection rate of the virulence gene pvl was significantly higher in the ST22-MRSA strain (14/14) than in the non-ST22 MRSA strains (0, P < 0.001) . Conclusions:S. aureus strains isolated from the skin sites of suppurative infections were highly resistant to penicillin, clindamycin and erythromycin, so these antibiotics should not be used as the first-choice empiric treatment. The occurrence of cutaneous S. aureus infections may be associated with the virulence gene pvl, and the nasal colonization of S. aureus may be associated with the clfA gene.