Abstract
The high prevalence of methicillin-resistant Staphylococcus aureus (MRSA) ST398 among pigs in certain European countries and North America and its occurrence in other animal species raises a question concerning the molecular mechanisms mediating the success of this lineage. In this study a panel of S. aureus strains belonging to sequence type (ST) 5 (n = 4), ST8 (n = 5), ST15 (n = 5), ST22 (n = 8), clonal complex (CC) 30 (n = 8), CC97 (n = 8), CC130 (n = 4), CC151 (n = 4) and ST398 (n = 18) were screened by DNA microarray and PCR for the carriage of virulence and antimicrobial resistance genes. Isolates belonging to the same sequence type/clonal complex (ST/CC) were found to share similar virulence gene profiles. The ST398 lineage displayed the lowest content of virulence genes, which consisted mainly of genes detected among the majority or all of the analysed lineages. All MRSA ST398 isolates lacked accessory virulence genes that were detected in other ST/CC. In contrast to virulence genotype, the antimicrobial resistance genes profiles varied between isolates belonging to the same ST/CC and profile similarities could be observed for isolates from different lineages. MRSA ST398 isolates in particular displayed significant diversity and high content of antimicrobial resistance genes. This was comparable with certain MRSA belonging to other sequence types particularly the equine MRSA ST8. The apparent lack of significant virulence genes among MRSA ST398 strains, demonstrates that the lineage features a unique genetic background but no ST398-specific virulence markers could be identified.
Highlights
Molecular epidemiological studies on S. aureus in humans has shown that the population consists of several prevalent lineages [1], which are best illustrated by the hospital- and communityacquired methicillin-resistant S. aureus strains where specific clonal complexes are dominant
Spa type t011 was the most prevalent among methicillin-resistant Staphylococcus aureus (MRSA) ST398 isolates (n = 10). t034 and t567 were identified in 3 isolates each, with t1451 and t4872 detected in single isolate only
The DNA microarray-based analysis revealed a limited content of virulence determinants among MRSA ST398 isolates in comparison to the representatives of other sequence type (ST)/clonal complex (CC) included in this study
Summary
Molecular epidemiological studies on S. aureus in humans has shown that the population consists of several prevalent lineages [1], which are best illustrated by the hospital- and communityacquired methicillin-resistant S. aureus strains where specific clonal complexes are dominant. The existence of such lineages among animal-associated isolates has been identified and can be exemplified by strains causing mastitis in cattle. Transfer of MRSA ST398 between animals and humans has been reported but the strain has been isolated from persons with no history of livestock contact [13,14,15] This exemplifies a probable lack of host specificity of this S. aureus strain. Identification of genetic markers that distinguish the ST398 lineage might help in determining and understanding the mechanisms behind MRSA ST398 capacity for livestock colonisation
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