Abstract
Members of the Bacillus cereus group are spore-forming organisms commonly associated with food poisoning and intestinal infections. Moreover, some strains of the group (i.e., B. cereus sensu stricto and Bacillus thuringiensis) can cause bacteremia in humans, mainly in immunocompromised individuals. Here we performed the genetic characterization of 17 human clinical strains belonging to B. cereus group isolated from blood culture. The whole-genome sequencing (WGS) revealed that the isolates were closely related to B. cereus sensu stricto and B. thuringiensis–type strain. Multilocus sequence typing analysis performed on the draft genome revealed the genetic diversity of our isolates, which were assigned to different sequence types. Based on panC nucleotide sequence, the isolates were grouped in the phylogenetic groups III and IV. The NHE, cer, and inhA gene cluster, entA, entFM, plcA, and plcB, were the most commonly detected virulence genes. Although we did not assess the ability to generate biofilm by phenotypic tests, we verified the prevalence of biofilm associated genes using an in silico approach. A high prevalence of pur gene cluster, xerC, clpY, codY, tasA, sipW, sinI, and sigB genes, was found. Genes related to the resistance to penicillin, trimethoprim, and ceftriaxone were identified in most of the isolates. Intriguingly, the majority of these virulence and AMR genes appeared to be evenly distributed among B. cereus s.s. isolates, as well as closely related to B. thuringiensis isolates. We showed the WGS represents a good approach to rapidly characterize B. cereus group strains, being able to give useful information about genetic epidemiology, the presence of virulence and antimicrobial genes, and finally about the potential hazard related to this underestimated risk.
Highlights
Bacillus cereus sensu lato (B. cereus s.l.), known as B. cereus group, consists of at least 12 sporeforming Gram-positive bacteria that are optionally motile and facultative anaerobic saprophyte (Liu et al, 2017)
Bacillus species are widely distributed in nature and can colonize hospital environments; there is evidence that strains of B. cereus were found on the hands of nursing staff, in balloons used for manual ventilation and near ventilation system outlets (Kuroki et al, 2009)
Recent reports suggest that B. cereus s.l. can cause nosocomial bacteremia via catheter-related infections caused by the formation of biofilm on biomedical devices (Jensen et al, 2003; Dohmae et al, 2008)
Summary
Bacillus cereus sensu lato (B. cereus s.l.), known as B. cereus group, consists of at least 12 sporeforming Gram-positive bacteria that are optionally motile and facultative anaerobic saprophyte (Liu et al, 2017). Hospital environment sources of B. cereus group include air filtration and ventilation equipment (Bryce et al, 1993), fiber-optic bronchoscopy equipment (Goldstein and Abrutyn, 1985), intravenous catheters (Hernaiz et al, 2003), and alcohol-based hand wash solutions (Hsueh et al, 1999). Some B. thuringiensis strains are able to produce enterotoxins (Damgaard et al, 1997; Ghelardi et al, 2007) and possess genes known to be involved in the pathogenesis of B. cereus infections (Kreig and Lysenko, 1979; Hsieh et al, 1999)
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