AUTHOR=Qu Yang , Wei Chao , Dai Xiaohang , Bai Yalong , Zhao Xin , Lan Qingkuo , Wang Wenbo , Wu Yuanjuan , Gao Min , Tang Weihao , Zhou Changyan , Suo Yujuan 

TITLE=The Possible Transmission and Potential Enterotoxicity of Bacillus cereus on Lettuce Farms in Five Chinese Provinces

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.746632

DOI=10.3389/fmicb.2021.746632

ISSN=1664-302X

ABSTRACT=<p><italic>Bacillus cereus</italic> is a well-characterized human pathogen that produces toxins associated with diarrheal and emetic foodborne diseases. To investigate the possible transmission of <italic>B. cereus</italic> on lettuce farms in China and determine its enterotoxicity, (I) a total of 524 samples (lettuce: 332, soil: 69, water: 57, manure: 57, pesticide: 9) were collected from 46 lettuce farms in five Chinese provinces, (II) multilocus sequence typing (MLST) was used to classify <italic>B. cereus</italic> isolates and for trace analysis, and (III) the presence of toxin genes and enterotoxins (Hbl and Nhe) was detected in 68 strains. The results showed that one hundred and sixty-one lettuce samples (48.5%) tested positive for <italic>B. cereus</italic> at levels ranging from 10 to 5.3 × 10<sup>4</sup> CFU/g. Among the environmental sample categories surveyed, the highest positive rate was that of the pesticide samples at 55.6%, followed by soil samples at 52.2% and manure samples at 12.3%. Moreover, one hundred isolates of <italic>B. cereus</italic> yielded 68 different sequence types (STs) and were classified into five phylogenetic clades. Furthermore, Nhe toxin genes (<italic>nheA</italic>, <italic>nheB</italic>, <italic>nheC</italic>) were broadly distributed and identified in all 68 strains (100%), while Hbl toxin genes (<italic>hblA</italic>, <italic>hblC</italic>, <italic>hblD</italic>) were present in 61 strains (89.7%), <italic>entFM</italic> was detected in 62 strains (91.2%), and <italic>cytK</italic> was found in 29 strains (42.6%). All strains were negative for <italic>ces</italic>. As for the enterotoxin, Nhe was observed in all 68 isolates carrying <italic>nheB</italic>, while Hbl was present in 76.5% (52/68) of the strains harboring <italic>hblC.</italic> This study is the first report of possible <italic>B. cereus</italic> transmission and of its potential enterotoxicity on lettuce farms in China. The results showed that soil and pesticides are the main sources of <italic>B. cereus</italic> on lettuce farms in China, and the possible transmission routes are as follows: soil-lettuce, manure-lettuce, pesticide-lettuce, manure-soil-lettuce, and water-manure-soil-lettuce. Furthermore, the <italic>B. cereus</italic> isolates, whether from lettuce or the environment, pose a potential risk to health.</p>