Abstract
The change of the bacteria from colonizers to pathogens is accompanied by a drastic change in expression profiles. These changes may be due to environmental signals or to mutational changes. We therefore compared the whole genome sequences of four sets of S. aureus isolates. Three sets were from the same patients. The isolates of each pair (S1800/S1805, S2396/S2395, S2398/S2397, an isolate from colonization and an isolate from infection, respectively) were obtained within <30 days of each other and the isolate from infection caused skin infections. The isolates were then compared for differences in gene content and SNPs. In addition, a set of isolates from a colonized pig and a farmer from the same farm at the same time (S0462 and S0460) were analyzed. The isolates pair S1800/S1805 showed a difference in a prophage, but these are easily lost or acquired. However, S1805 contained an integrative conjugative element not present in S1800. In addition, 92 SNPs were present in a variety of genes and the isolates S1800 and S1805 were not considered a pair. Between S2395/S2396 two SNPs were present: one was in an intergenic region and one was a synonymous mutation in a putative membrane protein. Between S2397/S2398 only one synonymous mutation in a putative lipoprotein was found. The two farm isolates were very similar and showed 12 SNPs in genes that belong to a number of different functional categories. However, we cannot pinpoint any gene that explains the change from carrier status to infection. The data indicate that differences between the isolate from infection and the colonizing isolate for S2395/S2396 and S2397/S2398 exist as well as between isolates from different hosts, but S1800/S1805 are not clonal.
Highlights
Staphylococcus aureus generally colonizes human skin and mucous membranes
The change of the bacteria from colonizers to pathogens is accompanied by a drastic change in expression profiles [12]
Both S1800 and S1805 belong to sequence type 80 (ST80) and spa-type t-044 indicating that both isolates belong to the European clone of CA-MRSA
Summary
Staphylococcus aureus generally colonizes human skin and mucous membranes. 30% of the general population will be colonized by S. aureus at one time point [3] and three types of carriership can be distinguished: persistent carriers (~20%), intermittent carriers (~30%) and non-carriers (~50%) [3,4,5,6]. Nasal colonization by S. aureus is one of the most important factors in the pathogenesis of nosocomial infections, mainly in surgical site and vascular device related infections [7,8,9,10]. The change of the bacteria from colonizers to pathogens is accompanied by a drastic change in expression profiles [12]. Similar changes can be expected when bacteria change hosts. These changes in expression profile may be due to environmental signals, and due to mutational changes. For Group A Streptococci (the causative agent of scarlet fever, necrotizing fasciatis and other infections) it was shown that an insertion of 7 nucleotides in a regulator gene was sufficient to alter transcription and turn a benign Group A Streptococcus strain into a highly infectious variant [13]
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