No abstract

Staphylococcus xylosus is a commensal of the skin of humans and animals and a ubiquitous bacterium naturally present in food. It is one of the major starter cultures used for meat fermentation, but a few strains could potentially be hazardous and are related to animal opportunistic infections. To better understand the genetic diversity of S. xylosus intraspecies, suppressive and subtractive hybridization (SSH) was carried out with the S. xylosus C2a strain, a commensal of human skin, used as the driver for three tester strains, S04002 used as a starter culture, S04009 isolated from cow mastitis, and 00-1747, responsible for mouse dermatitis. SSH revealed 122 tester-specific fragments corresponding to 149 open reading frames (ORFs). A large proportion of these ORFs resembled genes involved in specific metabolisms. Analysis of the distribution of the tester-specific fragments in 20 S. xylosus strains of various origins showed that the S. xylosus species could be divided into two clusters with one composed only of potentially hazardous strains. The genetic content diversity of this species is colocalized in a region near the origin of replication of the chromosome. This region of speciation previously observed in the Staphylococcus genus corresponded in S. xylosus species to a strain-specific region potentially implicated in ecological fitness.

Rapid and reliable detection and identification of Francisella tularensis (a Tier 1 select agent) are of primary interest for both medical and biological threat surveillance purposes. The Biotoxis qPCR detection® kit is a real-time PCR (qPCR) assay designed for the detection of Bacillus anthracis, Yersinia pestis, and F. tularensis in environmental or biological samples. Here, we evaluated its performance for detecting F. tularensis in comparison to previously validated qPCR assays. The Biotoxis qPCR was positive for 87/87 F. tularensis subsp. holarctica (type B) strains, but also for F. tularensis subsp. novicida. It was negative for F. philomiragia and 24/24 strains belonging to other bacterial species. For 31 tularemia clinical specimens, the Biotoxis qPCR displayed a sensitivity between 90.32% and 96.55%, compared to qPCR tests targeting the ISFtu2 (ISFtu2-qPCR) or a Type B-specific DNA sequence (Type B-qPCR), respectively. All 30 non-tularemia clinical specimens were Biotoxis qPCR negative. For water samples, the Biotoxis qPCR limit of detection was 1,000 CFU/l of F. tularensis. For 57 environmental water samples collected in France, the Biotoxis qPCR was positive for 6/15 samples positive for ISFtu2-qPCR and 4/4 positive for Type B-qPCR. In conclusion, the Biotoxis qPCR detection® kit demonstrated good performances for F. tularensis detection in various biological and environmental samples, although cross-amplification of F. tularensis subsp. novicida must be considered. This plate format assay could be useful to test a large number of clinical or environmental specimens, especially in the context of natural or intentional tularemia outbreaks.