Genetic Characterization of Methicillin-Resistant Isolates from Human Bloodstream Infections: Detection of MLS Resistance.

In this study we aimed to characterize antimicrobial resistance in methicillin-resistant (MRSA) isolated from bloodstream infections as well as the associated genetic lineages of the isolates. Sixteen MRSA isolates were recovered from bacteremia samples from inpatients between 2016 and 2019. The antimicrobial susceptibility of these isolates was tested by the Kirby-Bauer disk diffusion method against 14 antimicrobial agents. To determine the macrolide-lincosamide-streptogramin B (MLS) resistance phenotype of the isolates, erythromycin-resistant isolates were assessed by double-disk diffusion (D-test). The resistance and virulence genes were screened by polymerase chain reaction (PCR). All isolates were characterized by multilocus sequence typing (MLST), typing, staphylococcal chromosomal cassette (SCC) typing, and accessory gene regulator () typing. Isolates showed resistance to cefoxitin, penicillin, ciprofloxacin, erythromycin, fusidic acid, clindamycin, and aminoglycosides, confirmed by the presence of the Z, A, C, C, A/B, (6')-Ie-(2'')-Ia, and (4')-Ia genes. Three isolates were Panton-Valentine-leukocidin-positive. Most strains ( = 12) presented an inducible MLS phenotype. The isolates were ascribed to eight -types (t747, t002, t020, t1084, t008, t10682, t18526, and t1370) and four MLSTs (ST22, ST5, ST105, and ST8). Overall, most ( = 12) MRSA isolates had a multidrug-resistance profile with inducible MLS phenotypes and belonged to epidemic MRSA clones.