Molecular Epidemiology of Staphyloccocus aureus in Children with Bacteremia
Methods: We performed a retrospective analysis of S. aureus isolates causing bacteremia collected from 2010 to 2011. Isolates were characterized using the Identibac S. aureus Array Tube platform. This is a unique method that is capable of analyzing the presence of up to 334 S. aureus target sequences covering 180 distinct genes and their allelic variants. The genes analyzed include resistance determinants, toxin genes, core variable elements, capsule determinants, and other virulence factors, allowing characterization of the overall genetic background of the bacterial isolate. The genetic profile identified by Identibac allows affiliation of the isolates with clonal complexes (CC) based on a data base maintained in the software.
Results: A total of 121 S. aureus isolates were analyzed. Isolates belonged to 17 different CCs. The most common CC was CC8 (35.5%), followed by CC5 (20.6%), CC30 (8.3%) and CC59 (7.4%). Forty-one isolates (33.8%) were methicillin-resistant S. aureus (MRSA). MRSA isolates were only associated with CC8 and CC5. The majority of MRSA isolates harbored Panton-Valentine leukocidin (71.8 %) compared to MSSA isolates (28.2 %). The most abundant enterotoxin genes were those of the enterotoxin gene cluster (egc (seg, sei, sem, sen, seo, seu) which were present in 43 % of all isolates. Other common virulence factors identified included the toxic shock syndrome toxin in 9.9% of isolates, the staphylokinase in 11.5%, the hemolysin alpha in 99% and the collagen binding adhesin in 20.6% of isolates. Mup A gene which encodes for mupirocin resistance was present in 2.5 % of isolates and qac gene encoding resistance to quaternary ammonium compound was present in 4.9% of isolates.
Conclusion: We describe a collection of invasive S. aureus isolates. Our data suggests that certain clonal complexes, CC8 and CC5 are predominant in bacteremia. Bacteremia was mostly caused by MSSA. The Identibac S. aureus Array Tube technology was able to generate comprehensive molecular genotypic information that will allow us to understand the complex epidemiology of S. aureus.
D. Kingsmore, None
R. Selvarangan, Alere: Investigator, Research grant