Sporulation is dispensable for the vegetable-associated life cycle of the human pathogenBacillus cereus

Abstract

Bacillus cereus is a common food-borne pathogen that is responsible for important outbreaks of food poisoning in humans. Diseases caused by B. cereus usually exhibit two major symptoms, emetic or diarrheic, depending on the toxins produced. It is assumed that after the ingestion of contaminated vegetables or processed food, spores of enterotoxigenic B. cereus reach the intestine, where they germinate and produce the enterotoxins that are responsible for food poisoning. In our study, we observed that sporulation is required for the survival of B. cereus in leaves but is dispensable in ready-to-eat vegetables, such as endives. We demonstrate that vegetative cells of B. cereus that are originally impaired in sporulation but not biofilm formation are able to reach the intestine and cause severe disorders in a murine model. We propose that loss of part of the sporulation programme and reinforcement of structural factors related to adhesion, biofilm formation and pathogenic interaction with the host are adaptive traits of B. cereus with a life cycle primarily related to human hosts. Furthermore, our findings emphasise that the number of food poisoning cases associated with B. cereus is underestimated and suggest the need to revise the detection protocols, which are based primarily on spores and toxins.

Peer Review #1 of "Genetic diversity of enterotoxigenic Bacillus cereus strains in coriander in southwestern Mexico (v0.1)"

“…Sporulation protects the strains against adverse environmental conditions in the plant. For example, it has been described that carbon and nitrogen sources are scarce in melon leaves, and there is a high level of secondary metabolites such as flavonoids (Antequera-Gómez et al, 2021). The evaluation of genetic diversity by the (GTG) 5 genotyping showed that 12 strains grouped into at least six clusters.…”

Image-based Automatic Counting of Bacillus cereus Colonies using Smartphone

“…The second, diarrheal syndrome, is characterized by abdominal pain and diarrhea [3] and occurs within 3-4 hours of consumption of contaminated food. Besides B. cereus, other members of the Bacillus group of bacteria can cause food poisoning outbreaks through consumption of raw fruits and vegetables, and this is a major concern in food safety [4][5][6].…”

“…B. cereus concentrations reaching approximately 10 6 cells/gram of food will typically provoke abdominal pain and bloody diarrhea. There is an incubation period of 4-16 hours following ingestion, with symptoms lasting for 12-24 hours [4]. In Slovakia, B. cereus colonies in pasteurized milk at 30°C are not allowed to exceed a total dish count of 3 × 10 4 CFU/ml.…”

A sporulation-independent way of life for Bacillus thuringiensis in the late stages of an infection

“…Moreover, spontaneous mutants in spo0A , the gene specifying the master regulator of sporulation [7, 8], were isolated alongside spores after a month-long incubation of the food-borne pathogen Bacillus cereus under abiotic conditions in groundwater [9]. Furthermore, a B. cereus strain impaired in sporulation was shown to persist for several days on ready-to-eat vegetables and retained its ability to cause illness in a mammalian host [10]. In addition, it was shown that spores represented only 30% of the bacterial population that survived in an insect cadaver 4 days pi (dpi) with Bacillus thuringiensis and that a sporulation mutant was able to persist in the cadaver during that time [11].…”