Optisch-Molekulare Diagnostik und Systemtechnologie

Background: Panton-Valentine leukocidin (PVL)-positive community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) are increasingly associated with infection outbreaks. Aim: To investigate multiple suspected PVL-positive CA-MRSA outbreaks using whole genome sequencing (WGS). Methods: Forty-six suspected outbreak-associated isolates from 36 individuals at three separate Irish hospitals (H1-H3) and from separate incidents involving separate families associated with H2 were investigated by whole-genome multilocus sequence typing (wgMLST). Findings: Two clusters (CH1 and CH2) consisting of 8/10- and 6/6- PVL-positive t008 ST8-MRSA-IVa isolates from H1 and H2, respectively, were identified. Within each cluster, neighbouring isolates were separated by ≤5 allelic differences; however ≥73 allelic differences were identified between the clusters, indicative of two independent outbreaks. Isolates from the H3 maternity unit formed two clusters (CH3-SCI and CH3-SCII) composed f four PVL-negative t4667 ST5-MRSA-V and 14 PVL-positive t002 ST5-MRSA-IVc isolates, respectively. Within clusters, neighbouring isolates were separated by ≤24 allelic differences, whereas both clusters were separated by 1822 allelic differences, indicative of two distinct H3 outbreaks. Eight PVL-positive t127 ST1-MRSA-V+fus and three PVL negative t267 ST97-MRSA-V+fus isolates from two distinct H2-associated families FC1 (N=4) and FC2 (N=7), formed three separate clusters (FC1 [t127], FC2 [t127] and FC2 [t267]). Neighbouring isolates within clusters were closely related and exhibited ≤7 allelic differences. Intra-familial transmission was apparent, but the detection of ≥48 allelic differences between clusters indicated no interfamilial transmission. Conclusion: The frequent importation of PVL-positive CA-MRSA into healthcare settings, transmission and association with outbreaks is a serious ongoing concern. WGS is a highly discriminatory, informative method for deciphering such outbreaks conclusively.