Phenotypic and genomic characteristics of oxacillin-susceptible mecA-positive Staphylococcus aureus, rapid selection of high-level resistance to beta-lactams

AbstractThe aim of this study is to describe the phenotypic and genetic properties of oxacillin-susceptible methicillin-resistantStaphylococcus aureus (OS-MRSA) isolates and their beta-lactam resistant derivatives obtained after selection with oxacillin. A collection of hospital- (HA-) and community-acquired (CA-) MRSA was screened for oxacillin susceptibility. Antibiotic susceptibility testing, population analysis profile (PAP),mecA expression analysis, and whole genome sequencing (WGS) were performed for 60mecA-positive OS-MRSA isolates. Twelve high-level beta-lactam resistant derivatives selected during PAP were also subjected to WGS. OS-MRSA were more prevalent among CA-MRSA (49/205, 24%) than among HA-MRSA (11/575, 2%). OS-MRSA isolates belonged to twelve sequence types (ST), with a predominance of ST22-t223-SCCmec IVc and ST59-t1950-SCCmec V lineages. OS-MRSA were characterized bymecA promoter mutations at − 33 (C→T) or − 7 (G→T/A) along with PBP2a substitutions (S225R or E246G). The basal and oxacillin-induced levels ofmecA expression in OS-MRSA isolates were significantly lower than those in control ST8-HA-MRSA isolates. Most of the OS-MRSA isolates were heteroresistant to oxacillin. High-level beta-lactam resistant OS-MRSA derivatives selected with oxacillin carried mutations inmecA auxiliary factors:relA (metabolism of purines),tyrS,cysS (metabolism of tRNAs),aroK,cysE (metabolism of amino acids and glycolysis). Cefoxitin-based tests demonstrated high spec...
Source: European Journal of Clinical Microbiology and Infectious Diseases - Category: Microbiology Source Type: research