New genetic context of composed of two multi-resistance gene clusters in clinical ST-19 strains.

Background: Clindamycin is a lincosamide antibiotic used to treat staphylococcal and streptococcal infections. Reports of clinical isolates with the rare lincosamide resistance/macrolide susceptibility (L/M) phenotype are increasing worldwide. In this study, we characterised three clinical strains with the unusual L phenotype from China.

Methods: Three clinical strains, Sag3, Sag27 and Sag4104, with the L phenotype were identified from 186 isolates collected from 2016 to 2018 in Shanghai, China. The MICs of clindamycin, erythromycin, tetracycline, levofloxacin, and penicillin were determined using Etest. PCR for the gene was conducted. Whole genome sequencing and sequence analysis were carried out to investigate the genetic context of . Efforts to transfer lincomycin resistance by conjugation and to identify the circular form by inverse PCR were made.

Results: Sag3, Sag27, and Sag4104 were susceptible to erythromycin (MIC ≤0.25 mg/L) but resistant to clindamycin (MIC ≥1 mg/L). was found to be responsible for the L phenotype. in Sag3 and Sag27 were chromosomally located in an resistance gene cluster adjacent to an upstream 7-kb resistance gene cluster. Two resistance gene clusters were flanked by the IS6-like element, IS1216. Sag4104 only contained partial genes of resistance gene cluster and was also flanked by IS1216.

Conclusion: These results established the presence of the L phenotype associated with in clinical isolates in China. The -containing multi-resistance gene cluster possibly acts as a composite transposon flanked by IS1216 and as a vehicle for the dissemination of multidrug resistance among .