Abstract
BackgroundHorizontal gene transfer (HGT) is recognized as one of the major forces for bacterial genome evolution. Many clinically important bacteria may acquire virulence factors and antibiotic resistance through HGT. The comparative genomic analysis has become an important tool for identifying HGT in emerging pathogens. In this study, the Serine-Aspartate Repeat (Sdr) family has been compared among different sources of Staphylococcus aureus (S. aureus) to discover sequence diversities within their genomes.Methodology/Principal FindingsFour sdr genes were analyzed for 21 different S. aureus strains and 218 mastitis-associated S. aureus isolates from Canada. Comparative genomic analyses revealed that S. aureus strains from bovine mastitis (RF122 and mastitis isolates in this study), ovine mastitis (ED133), pig (ST398), chicken (ED98), and human methicillin-resistant S. aureus (MRSA) (TCH130, MRSA252, Mu3, Mu50, N315, 04-02981, JH1 and JH9) were highly associated with one another, presumably due to HGT. In addition, several types of insertion and deletion were found in sdr genes of many isolates. A new insertion sequence was found in mastitis isolates, which was presumably responsible for the HGT of sdrC gene among different strains. Moreover, the sdr genes could be used to type S. aureus. Regional difference of sdr genes distribution was also indicated among the tested S. aureus isolates. Finally, certain associations were found between sdr genes and subclinical or clinical mastitis isolates.ConclusionsCertain sdr gene sequences were shared in S. aureus strains and isolates from different species presumably due to HGT. Our results also suggest that the distributional assay of virulence factors should detect the full sequences or full functional regions of these factors. The traditional assay using short conserved regions may not be accurate or credible. These findings have important implications with regard to animal husbandry practices that may inadvertently enhance the contact of human and animal bacterial pathogens.
Highlights
Staphylococcus aureus (S. aureus) is a highly adaptive and versatile gram-positive bacterium that presents growing and formidable global challenges for human and animal health concerns [1]
Certain sdr gene sequences were shared in S. aureus strains and isolates from different species presumably due to Horizontal gene transfer (HGT)
Our results suggest that the distributional assay of virulence factors should detect the full sequences or full functional regions of these factors
Summary
Staphylococcus aureus (S. aureus) is a highly adaptive and versatile gram-positive bacterium that presents growing and formidable global challenges for human and animal health concerns [1]. S. aureus colonizes a range of other mammals including companion animals such as dogs, cats and horses [3], and livestock such as cows, pigs and goats [4,5]. Comparative analyses of different S. aureus genomes have revealed that many strains have independently acquired genes from members of their surrounding microflora that confer antibiotic resistance and/or encode virulence factors [9,10,11]. The horizontal gene transfer (HGT) of mobile genetic elements (MGEs) among bacteria is the primary mode for the spread of antibiotic resistance and virulence factors in clinically important pathogens [11,12]. The Serine-Aspartate Repeat (Sdr) family has been compared among different sources of Staphylococcus aureus (S. aureus) to discover sequence diversities within their genomes
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