ISOLATION AND MOLECULAR CHARACTERIZATION OF Bacillus cereus ISOLATED FROM MILK AND MILK PRODUCTS
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Date
2023-04
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Abstract
The present study was undertaken to characterize the incidence,
enterotoxigenic gene profile, antibiogram profile and genetic diversity of Bacillus
cereus isolated from milk and different milk products. A total of 320 samples
comprising of 150 raw milk and 170 milk product samples were analyzed for the
presence of B. cereus. Overall prevalence of B. cereus in milk and milk products samples was found to
be 9.68% (31/320) by species specific PCR targeting gyrB gene with 8% (12/150), 15%
(3/20), 12.1% (4/33), 11.8% (2/17), 10.8% (4/37) and 21.4% (6/28) from raw milk,
basundi, burfi, colostrum milk pudding (junnu), kalakhand and khoa samples,
respectively. Out of 31 genotypically positive B. cereus isolates, 23 (74.1%) isolates were
carrying atleast one of the virulence genes with nheA in 10 isolates (32.3%), nheB in 12
isolates (38.7%), nheC in 16 (51.6%) isolates and entFM in 14 isolates (45.2%) and
none of the isolates were positive for hblA, hblC, hblD and cytK genes.
Antibiogram profiling of 31 B. cereus isolates revealed that all the isolates (100%)
were resistant to pencillin and amoxicillin-clavulanic acid followed by cefepime
(87.1%), clindamycin (32.31%), rifampicin (29.0%), vancomycin (25.8%), colistin
(19.4%) ciprofloxacin, chloramphenicol and erythromycin (6.5%) each and none of the
isolates were resistant to gentamicin and tetracycline. None of the B. cereus isolates
were positive for any of the ESBL genes (bla TEM, bla SHV, blaOXA and bla CTX-M).
A greater degree of heterogeneity among the genotypically positive B. cereus
isolates isolated from milk and different milk products was revealed by the presence of
28 genotypes by ERIC-PCR and 29 genotypes by REP-PCR analysis. Genotyping of B.
cereus by ERIC-PCR and REP-PCR were found to be highly suitable since the
discriminatory power above 0.9 are considered as highly significant (0.997 for ERIC PCR and 0.995 for REP-PCR). As the discriminatory power of ERIC-PCR is more than
the REP-PCR, ERIC-PCR was able to differentiate the isolates better than REP-PCR.
Cluster analysis using dendrograms revealed molecular heterogeneity and varying
homogeneity among different isolates recovered from varied sources