Abstract
Objectives Bacillus cereus is responsible for food poisoning and rare but severe clinical infections. The pathogenicity of B. cereus strains varies from harmless to lethal strains. The objective of this study was to characterize three B. cereus isolates isolated from the same patient and identify their virulence potentials.MethodsThree isolates of B. cereus were isolated from various blood samples from a patient who developed sepsis following a central venous catheter infection. The three isolates were compared by WGS, genotyping and SNP analysis. Furthermore, the isolates were compared by phenotypical analysis including bacterial growth, morphology, germination efficacy, toxin production, antibiotic susceptibility and virulence in an insect model of infection.ResultsAccording to WGS and genotyping, the 3 isolates were shown to be identical strains. However, the last recovered strain had lost the mega pAH187_270 plasmid. This last strain showed different phenotypes compared to the first isolated strain, such as germination delay, different antibiotic susceptibility and a decreased virulence capacity towards insects. A 50- kbp region of pAH187_270 plasmid was involved in the virulence potential and could thus be defined as a new pathogenicity island of B. cereus.ConclusionsThese new findings help in the understanding of B. cereus pathogenic potential and complexity and provide further hints into the role of large plasmids in the virulence of B. cereus strains. This may provide tools for a better assessment of the risks associated with B. cereus hospital contamination to improve hygiene procedure and patient health.
Highlights
Bacillus cereus is a Gram positive, spore-forming bacterium found in most environments
The isolated strains were confirmed as being B. cereus by MALDI-TOF and no other bacteria were isolated in the blood cultures
We report the identification of a large plasmid, lost over time within the same patient
Summary
Bacillus cereus is a Gram positive, spore-forming bacterium found in most environments. New Pathogenicity Island of Bacillus cereus non-gastrointestinal diseases and can potentially result in pneumonia, septicaemia, endocarditis, and meningitis, with immunocompromised individuals and neonates being susceptible (Bottone, 2010; Cormontagne et al, 2021). B. cereus is able to persist in the environment over long periods and can cause recurrent nosocomial infections (Glasset et al, 2018). The causative agent of emesis, the dodecadepsipeptide cereulide, is restricted to strains carrying pXO-1-like megaplasmids (Carlin et al, 2006). These factors are involved in B. cereus pathogenicity, the differentiation of pathogenic from non-pathogenic strains has proven difficult, even with molecular methods (Ramarao et al, 2020)
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