Abstract
In the course of an annual 3-month bloodstream infections (BSI) survey conducted during a four-year period in 31 healthcare institutions located in three noncontiguous French regions, we report 18 ST398 Staphylococcus aureus BSI. ST398 BSI incidence showed a seven-fold increase during the study period (0.002 per 1,000 patient days in 2007 vs. 0.014 in 2010). ST398 BSI isolates differed from the pig-borne multiresistant clone: 17/18 BSI isolates were methicillin susceptible and none was of t011, t034 or t108 pig-borne spa-types. ST398 BSI isolates had homogenous resistance patterns (15/18 with only Eryr) and prophagic content (all harboured the hlb-converting Sau3int phage). The clustering of BSI and pig-borne isolates by spa-typing and MLVA, the occurrence of Sau3int phage in BSI isolates and the lack of this phage in pig-borne isolates suggest that the emergence of BSI isolates could have arisen from horizontal transfer, at least of the Sau3int phage, in genetically diverse MSSA ST398 isolates. The acquisition of the phage likely plays a role in the increasing ability of the lysogenic ST398 isolates to colonize human. The mode of acquisition of the non pig-borne ST398 isolates by our 18 patients remains unclear. ST398 BSI were diagnosed in patients lacking livestock exposure and were significantly associated with digestive portals of entry (3/18 [16.7%] for ST398 vs. 19/767 [2.5%] for non ST398 BSI; p = .012). This raises the question of possible foodborne human infections. We suggest the need for active surveillance to study and control the spread of this human-adapted subclone increasingly isolated in the hospital setting.
Highlights
Described in Europe, ST398 methicillin-resistant S.aureus (MRSA) is a worldwide threat associated with livestock, their human contact and food products [1]
Previous characterization of ST398 pig-borne isolates have indicated that most are methicillin-resistant S.aureus (MRSA) strains of agr type I, do not contain any genes encoding the major staphylococcal virulence factors, harbour genes involved in the colonization and the early respectively, by PCR amplification using a procedure previously described by Jarraud et al [10]. spa-types were determined for all isolates as previously described and were assigned through the spatype database www.ridom.de/spaserver [11]
ST398 isolates by antimicrobial susceptibility testing and luk, tst, eta, and etb gene detection.Using pulsed-field gel electrophoresis (PFGE) typing, multiple-locus variable-number tandem-repeat analysis (MLVA) and prophagic gene content analysis, we studied the genetic diversity of the population of bloodstream infections (BSI) isolates and compared BSI isolates with a set of 12 isolates representative of the major ‘‘classical’’ pig-borne clones
Summary
Described in Europe, ST398 methicillin-resistant S.aureus (MRSA) is a worldwide threat associated with livestock, their human contact and food products [1]. There are few recent reports of infections caused by ST398 S. aureus in persons lacking livestockassociated (LA) risk factors. Most of these involve MSSA of spa-type t571 [2,3,4]. Previous characterization of ST398 pig-borne isolates have indicated that most are MRSA strains of agr type I, do not contain any genes encoding the major staphylococcal virulence factors, harbour genes involved in the colonization and the early respectively, by PCR amplification using a procedure previously described by Jarraud et al [10]. According to François et al [13], multiplex PCR amplifications with eight primer pairs that target gene regions with variable numbers of tandem repeats were resolved by microcapillary electrophoresis and automatically assessed by cluster analysis to compare ST398
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