Abstract:
Background: Whole genome sequencing analysis (WGSA) provides the best resolution for
typing of bacterial isolates and has the potential for identification of transmission pathways.
The aim of the study was to apply WGSA to elucidate the possible transmission events involved
in two suspected Staphylococcus aureus hospital outbreaks in Ghana and describe genomic
features of the S. aureus isolates sampled in the outbreaks.
Methods: The study was carried out at Korle-Bu Teaching Hospital and Lekma Hospital where the
suspected outbreaks occurred in 2012 and 2015, respectively. The S. aureus isolates collected from
the two hospitals were from three sources including carriage, invasive disease, and the environment.
Whole genome sequencing of the S. aureus isolates was performed and the sequence reads were
mapped to the S. aureus reference genome of strain USA300_FPR3757. A maximum-likelihood
phylogenetic tree was reconstructed. Multilocus sequence typing together with the analysis of antimicrobial
resistance and virulence genes were performed by short read mapping using the SRST2.
Results: The S. aureus isolates belonged to diverse sequence types (STs) with ST15 and ST152
most common. All isolates carried the blaZ gene, with low prevalence of tetK and dfrG genes
also observed. All isolates were mecA negative. The pvl genes were common and observed in
distinct lineages that revealed diverse Sa2int phages. At Korle-Bu Teaching Hospital, the genomics
data indicated several transmission events of S. aureus ST15 involving contamination of
various surfaces in the pediatric emergency ward where the outbreak occurred.
Conclusion: The pattern of dissemination of the ST15 clone in the emergency ward of Korle-
Bu Teaching Hospital highlights a basic problem with disinfection of environmental surfaces
at the hospital. Diverse phage population rather than a single highly transmissible phage type
likely mediates the high prevalence of pvl genes among the S. aureus isolates.
