Isolation And Characterization Of Bacillus Cereus From Piglet

Bacillus cereus (B. cereus) is strongly resistant to unfavourable conditions and widely distributed environmentally. There is a big difference between different strains upon their pathogenic characteristics. Some strains have been widely used as probiotics in animal husbandry and aquaculture, while other strains are considered to be conditional pathogenic bacteria causing food-borne diseases in human. And some strains of B. cereus are also reported to cause "the rotten skin syndrome" of a trepang, camel impetigo, cow mastitis, etc. But B. cereus infection in piglet has not been reported.A pure culture of bacteria was isolated from liver samples of a piglet survived an attack of newborn piglet diarrhea from a pig farm at Huaihua district in Hunan province. A systematic analysis, such as biochemical identification, DNA testing and animal challenging experiment, proved the isolated bacteria to be a pathogenic strain of B. cereus. In addition, a screen detection of B. cereus was carried out in five pig farms different regions of Hunan province. Two stains of B. cereus have been isolated, one from a pig farm’s sewage, and the other from piglet manure.The experimental results showed that the strain isolated from piglets liver samples to be a new pathogenic strain of B. cereus, named as HN1203. The16S rDNA sequence of HN1203was submitted to GendBank and filed as No. JX294967. Moreover, the drug susceptibility test results showed that the three isolated B. cereus strains are resistant (R) to cefoperazone, amoxicillin, ampicillin, penicillin G, intermediate sensitive (Ⅰ) to chloramphenicol, neomycin ZhongMin, and sensitive (S) to streptomycin, gentamicin, tetracycline, amikaci. The results of toxin-genes-detection experiments showed that B. cereus HN1203carries enterotoxin genes, such as hbl, nhe, entFM and cytK. Multilocus sequence typing (MLST) detected a new allele of housekeeping gene pta assigned as ptal53, and assigned B. cereus HN1203a new genotype as ST611. Assay of HN1203’s16s rDNA sequence showed that it is consistent with that of B. anthracis. The results of animal challenge experiments showed that HN1203can kill mice. Results of current work proved that the pathogenic B. cereus can be existed in pig farms, and highlighted the needs of increased awareness of its potential dangers to the environment and food safety. It also warns us when choosing this organism as probiotic bacteria its pathogenicity must be scrutinized carefully to clear the bio-safe concern.