Genomic and Toxigenic Heterogeneity of Bacillus cereus sensu lato Isolated from Ready-to-Eat Foods and Powdered Milk in Day Care Centers in Colombia

Abstract

Bacillus cereus sensu lato (s.l.) is a group of bacteria commonly found in diverse environments, including foods, with potential to cause emesis and diarrhea. In Colombia, it is one of the main foodborne pathogens. The aim of this study was to determine the genomic and toxigenic heterogeneity of B. cereus s.l. isolated from ready-to-eat foods and powdered milk collected in day care centers of Medellin, Colombia. Of 112 B. cereus s.l. isolates obtained, 94% were b-hemolytic. Toxigenic heterogeneity was established by the presence of nheABC, hblCDAB, cytK2, entFM, and cesB toxigenic genes. The nheABC operon and entFM gene were most frequently detected in the isolates, whereas the cesB gene was not found. According to the toxin genes content, nine toxigenic profiles were identified. A 44% of isolates had profiles with all genes for nonhemolytic enterotoxin, hemolysin BL, and enterotoxin FM production (profiles II and IV). Pulsed-field gel electrophoresis analysis indicated a high genomic heterogeneity among the B. cereus s.l., with 68 isolates grouping into 16 clusters and 33 placed separately in the dendrogram. This study provides useful information on the safety of ready-to-eat foods and powdered milk in day care centers where children, a susceptible population, are exposed and it should incentive for more studies to understand the distribution of different toxin-encoding genes among B. cereus s.l. isolates, enabling detailed risk assessment.

Enterotoxin Gene Distribution and Genotypes of Bacillus cereus sensu lato Isolated from Cassava Starch

“…Worldwide, incidences of B. cereus s.l. are variable; the values reported are either higher or lower than the ones obtained in this study; however, as long as the food raw-materials and flours are handcrafted and slightly processed, they are susceptible to contamination by B. cereus spores and vegetative cells, constituting great risk for human health [12,13]. Studies performed in countries such as Korea found B. cereus in 40% of raw rice samples [23]; in Iran, 42% of infant formula analyzed carried B. cereus [24] and in New Zealand, B. cereus incidences in dehydrated potato ranged from 10% to 40% [25].…”

“…Various works around the world have reported a high genomic diversity on B. cereus s.l. from foods such as ready-to-eat [11,12] and powdered products [13], milk [6,14] and others [15], as well as a broad distribution of toxin genes in B. cereus s.l. isolated from foods.…”

“…In Colombia, B. cereus s.l. isolated from powdered foods [13] and ready-to-eat foods [12] contained the genes for enterotoxins production. Also, a previous study reported the detection of B. cereus s.l.…”

Structural Modeling of Cell Wall Peptidase CwpFM (EntFM) Reveals Distinct Intrinsically Disordered Extensions Specific to Pathogenic Bacillus cereus Strains

“…Presence of the gene is now routinely assessed in combination with other diarrheal toxins-encoded genes such as ces, nhe and hbl to determine the potential pathogenicity of a strain. Data show that cwpFM is widely distributed (detection rate of 68-98%) in B. cereus isolated from diverse food matrices [53][54][55][56][57]. cwpFM is also detected in strains associated with food-borne illnesses [33,58] and is even present in emetic strains [59].…”

The Bacillus cereus Food Infection as Multifactorial Process

“…However, it must be pointed out that in several studies the ces gene cluster (encoding cereulide synthetase) is not investigated or not mentioned [119][120][121], and that several studies do not distinguish between emetic and enteropathogenic B. cereus at all [122,123]. If the emetic toxin genes are investigated, their occurrence is rather rare compared to the enterotoxin genes ( Table 2 and [124][125][126][127][128][129]). Other studies challenge the tight association of emetic B. cereus with starchy foodstuffs and suggest a rather heterogeneous distribution.…”