Assessment and molecular characterization ofBacillus cereusisolated from edible fungi in China

Background Bacillus cereusis a foodborne pathogen commonly found in nature and food and can cause food spoilage and health issues. Although the prevalence ofB. cereusin foods has been reported worldwide, the extent of contamination in edible fungi, which has become increasingly popular as traditional or functional food, is largely unknown. Here we investigated the prevalence, toxin genes' distribution, antibiotic resistance, and genetic diversity ofB. cereusisolated from edible fungi in China. Results Six hundred and ninety-nine edible fungi samples were collected across China, with 198 (28.3%) samples found to be contaminated byB. cereus, with an average contamination level of 55.4 most probable number (MPN)/g. Two hundred and forty-sevenB. cereusstrains were isolated from the contaminated samples. Seven enterotoxin genes and one cereulide synthetase gene were detected. The detection frequencies of all enterotoxin genes were >= 80%, whereas the positive rate of thecesBgene inB. cereuswas 3%. Most isolates were resistant to penicillins, beta-lactam/beta-lactamase inhibitor combinations, cephems, and ansamycins, but were susceptible to penems, aminoglycosides, macrolides, ketolide, glycopeptides, quinolones, phenylpropanol, tetracyclines, lincosamides, streptogramins, and nitrofurans. Meanwhile, 99.6% of all isolates displayed multiple antimicrobial resistance to three or more classes of antimicrobials. Using genetic diversity analysis, all isolates were defined in 171 sequence types (STs), of which 83 isolates were assigned to 78 new STs. Conclusions This study provides large-scale insight into the prevalence and potential risk ofB. cereusin edible fungi in China. Approximately one-third of the samples were contaminated withB. cereus, and almost all isolates showed multiple antimicrobial resistance. Detection frequencies of all seven enterotoxin genes were equal to or more than 80%. These new findings may indicate a need for proper pre-/post-processing of edible fungi to eliminateB. cereus, thereby preventing the potential risk to public health.