Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz
Gewählte Publikation:
Schmid, P.
Comparison of Bacillus cereus sensu lato from patient, industrial and food packaging samples, its antimicrobial susceptibility and sliding motility as interfering phenotype in AST
Doktoratsstudium der Medizinischen Wissenschaft; Humanmedizin; [ Dissertation ] Medizinische Universität Graz; 2025. pp. 140
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- Autor*innen der Med Uni Graz:
- Betreuer*innen:
- Kittinger Clemens
- Zarfel Gernot
- Altmetrics:
- Abstract:
- The ubiquitous Bacillus cereus group or Bacillus cereus sensu lato (s.l.) comprises several closely related species with manifold impacts on humans. In a clinical context, Bacillus cereus s.l. is primarily known as a causing agent of self-limiting food poisoning. However, non-gastrointestinal infections with Bacillus cereus s.l. may require rapid and targeted anti-infective therapy as these infections can be life-threatening. The aim of this dissertation was therefore to dissect the presence and antimicrobial susceptibility of Bacillus cereus s.l. in different patient samples and environmental, human-associated samples. A total of 353 isolates from patient samples, cranial orthoses, food packaging materials and industrial water and biofilm samples were compared. The isolates from routine patient diagnostics showed the most even distribution of phylogenetic groups, indicating a random origin of the bacterial strains. In contrast, isolates from a clinical trial on cranial orthoses and the corresponding hospital environment indicated potential nosocomial origin. In addition, the patient isolates accumulated more antimicrobial resistances to clinically relevant antibiotics than environmental isolates from food packaging materials. Using the disk diffusion method, the most frequent resistant phenotypes among all isolates were reported for erythromycin, carbapenems and vancomycin, while linezolid, clindamycin, and fluoroquinolones yielded high susceptibility rates. Since putative vancomycin resistance has hardly been studied in the Bacillus cereus group, the subsequent focus was on vancomycin-resistant isolates. The resistance observed in agar diffusion tests could be disproved by utilizing both broth microdilution and agar dilution. Moreover, microscopic imaging revealed a motility strategy of Bacillus cereus s.l. to undermine correct susceptibility testing for vancomycin. Using a food packaging isolate as a model, sliding motility was discovered as the mechanism responsible for the translocation into the inhibition zone during agar diffusion testing. RNA-Seq analysis on the Oxford Nanopore platform confirmed the sliding motility at the gene expression level. The expression of the biofilm machinery was increased in sliding cells, while virulence genes were repressed. In addition, swarming motility could be effectively distinguished from sliding motility, both phenotypically and at the gene expression level. Susceptibility testing based on agar diffusion was shown to be unreliable for vancomycin due to sliding motility, which should be included in relevant guidelines. Future research should also endeavor to elucidate whether this distinct motility may similarly impact the susceptibility testing of other antibiotics including erythromycin and carbapenems.