Prevalence, distribution, enterotoxin profiles, antimicrobial resistance, and genetic diversity of Bacillus cereus group isolates from lettuce farms in Korea

Virulence potential of Bacillus cereus sensu lato group bacteria isolated from green leafy vegetables

In this study, the virulence potential-including hemolytic activity, toxin gene content, and antibiotic resistance patterns-of Bacillus cereus sensu lato (B. cereus s.l.) group bacteria isolated from green leafy vegetables (mint, parsley, purslane, dill, cress, arugula, lettuce, and baby spinach) was investigated. A total of 59 presumptive B. cereus s.l. bacteria were isolated from 40 vegetable samples. Fourty-six isolates were confirmed as members of the B. cereus s.l. group by polymerase chain reaction (PCR). Species-specific PCR identified 42 of the 46 isolates as B. cereus sensu stricto (B. cereus) and four as B. mycoides. All isolates showed β-hemolytic activity on Columbia sheep blood agar. Except for B. cereus 472 and B. mycoides 571, all isolates harbored between one and eight toxin genes. The most frequently detected toxin gene was entFM, found in 81.0% (34/42) of B. cereus and 75.0% (3/4) of B. mycoides strains. The hblACD and nheABC gene clusters were identified in only 19.1% (8/42) and 7.1% (3/42) of B. cereus strains, respectively. Similarly, the emetic toxin genes ces (9.5%, 4/42) and CER (4.8%, 2/42) were detected exclusively in B. cereus strains. In total, 31 distinct toxin gene profiles were observed. Linezolid and vancomycin were the most effective antibiotics against both B. cereus and B. mycoides strains. However, B. cereus strains exhibited varying degrees of resistance to all tested antibiotics. All B. mycoides strains were resistant to clindamycin, and 75.0% (3/4) were also resistant to ciprofloxacin, imipenem, levofloxacin, meropenem, and norfloxacin. The multiple antibiotic resistance (MAR) index was greater than 0.20 in 60.9% (28/46) of the B. cereus s.l. isolates, and 52.2% (24/46)-including 21 B. cereus and three B. mycoides isolates-exhibited multidrug resistance (MDR). In conclusion, these findings suggest that B. cereus s.l. group isolates from green leafy vegetables may pose a potential risk to public health.

Prevalence Trends of Foodborne Pathogens Bacillus cereus, Non-STEC Escherichia coli and Staphylococcus aureus in Ready-to-Eat Foods Sourced from Restaurants, Cafés, Catering and Takeaway Food Premises

Foodborne pathogens of Bacillus cereus (B. cereus), non-STEC Escherichia coli (non-STEC E. coli) and Staphylococcus aureus (S. aureus) are currently non-notifiable in Australia unless attributed to a food poisoning outbreak. Due to the lack of data around individual cases and isolations in foods, any changes in prevalence may go undetected. The aim of this study was to determine any changes in the prevalence of B. cereus, non-STEC E. coli and S. aureus in ready-to-eat (RTE) foods sampled from Western Australian restaurants, cafés, catering facilities and takeaway food premises from July 2009 to June 2022. A total of 21,822 microbiological test results from 7329 food samples analysed over this 13-year period were reviewed and analysed. Linear trend graphs derived from the annual prevalence and binary logistic regression models were used to analyse the sample results, which indicated an increase in prevalence for B. cereus. In contrast, a decrease in prevalence for both S. aureus and non-STEC E. coli was determined. Additionally, there were changes in prevalence for the three bacteria in specific months, seasons, specific RTE foods and food premises types. Further research is needed to gain a better understanding of the potential drivers behind these changes in prevalence, including the potential impacts of climate change, COVID-19, legislation and guidelines targeting specific RTE foods, and the difficulty of differentiating B. cereus from B. thuringeniesis using standard testing methods.

Potential risk of biofilm-forming Bacillus cereus group in fresh-cut lettuce production chain

Bacillus cereus and Bacillus thuringiensis, which belong to the B. cereus group, are widely distributed in nature and can cause food poisoning symptoms. In this study, we collected 131 isolates belonging to the B. cereus group, comprising 124B. cereus and seven B. thuringiensis isolates, from fresh-cut lettuce production chain and investigated their potential risk by analyzing genotypic (enterotoxin and emetic toxin gene profiles) and phenotypic (antibiotic susceptibility, sporulation, and biofilm formation) characteristics. Enterotoxin genes were present only in B. cereus, whereas the emetic toxin gene was not detected in any of the B. cereus isolates. All isolates were susceptible to vancomycin, which is a last resort for treating B. cereus group infection symptoms, but generally resistant to β-lactam antimicrobials, and had the ability to form spores (at an average sporulation rate of 24.6 %) and biofilms at 30 °C. Isolates that formed strong biofilms at 30 °C had a superior possibility of forming a dense biofilm by proliferating at 10 °C compared to other isolates. Additionally, confocal laser scanning microscopy (CLSM) images revealed a notable presence of spores within the submerged biofilm formed at 10 °C, and the strengthened attachment of biofilm inner cells to the substrate was further revealed through biofilm structure parameters analysis. Collectively, our study revealed the prevalence and contamination levels of B. cereus and B. thuringiensis at fresh-cut lettuce production chain and investigated their genotypic and phenotypic characteristics, aiming to provide valuable insights for the development of potential risk management strategies to ensure food safety, especially along the cold chain.

Prevalence and genomic characterization of the Bacillus cereus group strains contamination in food products in Southern China

The Bacillus cereus group, as one of the important opportunistic foodborne pathogens, is considered a risk to public health due to foodborne diseases and an important cause of economic losses to food industries. This study aimed to gain essential information on the prevalence, phenotype, and genotype of B. cereus group strains isolated from various food products in China. A total of 890 strains of B. cereus group bacteria from 1181 food samples from 2020 to 2023 were identified using the standardized detection method. These strains were found to be prevalent in various food types, with the highest contamination rates observed in cereal flour (55.8 %) and wheat/rice noodles (45.7 %). The tested strains exhibited high resistance rates against penicillin (98.5 %) and ampicillin (98.9 %). Strains isolated from cereal flour had the highest rate of meropenem resistance (7.8 %), while strains from sausages were most resistant to vancomycin (16.8 %). A total of 234 out of the 891 B. cereus group strains were randomly selected for WGS analysis, 18.4 % of which displayed multidrug resistance. The species identification by WGS analysis revealed the presence of 10 distinct species within the B. cereus group, with B. cereus species being the most prevalent. The highest level of species diversity was observed in sausages. Notably, B. anthracis strains lacking the anthrax toxin genes were detected in flour-based food products and sausages. A total of 20 antibiotic resistance genes have been identified, with β-lactam resistance genes (bla1, bla2, BcI, BcII, and blaTEM-116) being the most common. The B. tropicus strains exhibit the highest average number of virulence genes (23.4). The diarrheal virulence genes nheABC, hblACD, and cytK were found in numerous strains. Only 4 of the 234 (1.7 %) sequenced strains contain the ces gene cluster linked to emetic symptoms. These data offer valuable insights for public health policymakers on addressing foodborne B. cereus group infections and ensuring food safety.

Antibiotic Resistance of Bacillus cereus in Plant Foods and Edible Wild Mushrooms in a Province

Bacillus cereus is a common pathogen causing foodborne diseases, secreting and producing a large number of toxins that can cause a variety of diseases and pose many threats to human health. In this study, 73 strains of Bacillus cereus were isolated and identified from six types of foods from seven different cities in a province, and the antibiotic-resistant phenotype was detected by using the Bauer-Kirby method. Results showed that the 73 isolates were completely sensitive to gentamicin and 100% resistant to chloramphenicol, in addition to which all strains showed varying degrees of resistance to 13 other common antibiotics, and a large number of strains resistant to multiple antibiotics were found. A bioinformatic analysis of the expression of resistance genes in Bacillus cereus showed three classes of antibiotic-resistant genes, which were three of the six classes of antibiotics identified according to the resistance phenotype. The presence of other classes of antibiotic-resistant genes was identified from genome-wide information. Antibiotic-resistant phenotypes were analyzed for correlations with genotype, and remarkable differences were found among the phenotypes. The spread of antibiotic-resistant strains is a serious public health problem that requires the long-term monitoring of antimicrobial resistance in Bacillus cereus, and the present study provides important information for monitoring antibiotic resistance in bacteria from different types of food.

Characterization of the Toxigenic Potential of Bacillus cereus sensu lato Isolated from Raw Berries and Their Products

Bacillus cereus is estimated to be responsible for 1.4-12% of all food poisoning outbreaks worldwide. The objective of this study was to investigate the toxigenic potential of 181 isolates of B. cereus previously recovered from different types of berries and berry products (strawberries, raspberries, blackberries, and blueberries) by assessing the presence of enterotoxin genes (hblA, hblC, hblD, nheA, nheB, nheC, and cytK) and an emetic toxin cereulide synthetase gene (ces). The cytotoxic activity on Caco-2 cells was also evaluated for the two isolates containing the gene cytK. Twenty-three toxigenic profiles were found. The nheABC (91.7%) and hblACD (89.0%) complexes were the most prevalent among the isolates, while the cytK and ces genes were detected in low percentages, 1.1% and 3.3%, respectively. In addition, the nheABC/hblACD complex and ces genes were detected in isolates recovered throughout the production process of blackberries and strawberries. The cytotoxic activity on Caco-2 cells was also observed to be greater than 60% for isolates containing the cytK gene.