Abstract
The aim of this work was to assess a novel pseudo-staphylococcal cassette chromosome mec (ΨSCCmec) element in methicillin-resistant Staphylococcus aureus (MRSA) blood isolates. Community-associated MRSA E16SA093 and healthcare-associated MRSA F17SA003 isolates were recovered from the blood specimens of patients with S. aureus bacteremia in 2016 and in 2017, respectively. Antimicrobial susceptibility was determined via the disk diffusion method, and SCCmec typing was conducted by multiplex polymerase chain reaction. Whole genome sequencing was carried out by single molecule real-time long-read sequencing. Both isolates belonged to sequence type 72 and agr-type I, and they were negative for Panton-Valentine leukocidin and toxic shock syndrome toxin. The spa-types of E16SA093 and F17SA003 were t324 and t2460, respectively. They had a SCCmec IV-like element devoid of the cassette chromosome recombinase (ccr) gene complex, designated as ΨSCCmecE16SA093. The element was manufactured from SCCmec type IV and the deletion of the ccr gene complex and a 7.0- and 31.9-kb portion of each chromosome. The deficiency of the ccr gene complex in the SCCmec unit is likely resulting in mobility loss, which would be an adaptive evolutionary mechanism. The dissemination of this clone should be monitored closely.
Highlights
Methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates were first identified in the early 1960s, immediately after the introduction of penicillinase-stable penicillins in the clinical setting (Jevons et al, 1963)
A unique combination of the mec gene complex class and the ccr gene complex allotype determines the type of the staphylococcal cassette chromosome mec (SCCmec) element, and its variation within the joining- (J-) regions determine the subtypes of each SCCmec type
Following the one-year collection of the 586 S. aureus blood isolates, a total of 319 isolates (54.4%) were MRSA conferred by the mecA gene
Summary
Methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates were first identified in the early 1960s, immediately after the introduction of penicillinase-stable penicillins in the clinical setting (Jevons et al, 1963). The mecA and mecC genes encoding penicillin-binding protein (PBP) 2a of low beta-lactam binding affinity confer beta-lactam resistance to the bacterial host by composing a mobile genetic element, namely, the staphylococcal cassette chromosome mec (SCCmec) (Ito et al, 1999). The SCCmec-like elements devoid of the mecA gene are denominated as an SCC as long as they share the following characteristics with SCCmec: carriage of the ccr gene(s), integration at integrated site sequences in the chromosome, and the presence of flanking direct repeat sequences. Those without the ccr genes are termed as the pseudo-(Ψ) SCCmec element
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