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Extracellular enzyme production and enterotoxigenic gene profiles of Bacillus cereus and Bacillus thuringiensis strains isolated from cheese in Turkey
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The aim of the present study was to investigate the biochemical characteristics, extracellular enzyme production and enterotoxigenic genes contents of 6 Bacillus cereus and 22 Bacillus thuringiensis strains, isolated from 100 cheese samples in Turkey. Crystal morphologies of B. thuringiensis strains were found either spherical (n = 12) or spherical and irregular-shaped (n = 10) by phase contrast microscopy. B. cereus and B. thuringiensis strains were found to produce extracellular enzymes, respectively: gelatinase (83% and 91%), DNase (83% and 77%), lecithinase (83% and 95%), protease on skim milk agar (100% and 100%), protease on milk agar (100% and 91%), protease on casein agar (83% and 77%), xylanase (100% and 45%), and cellulase (0% and 41%), and amylase (83% and 27%). All of the strains, except for Bt-D1, hydrolyzed Tween 20 (96%), but not Tween 80 or tributyrin. Pectinolytic activity was obtained to be the least frequent (4%). PCR analysis showed that all strains contained nheA, nheB, nheC and hblD genes. The hblA and hblC genes were present in 2 and 4 of B. thuringiensis strains, respectively. The bceT gene was detected in 1 B. cereus and 9 B. thuringiensis strains. The entFM gene was detected more frequently in B. thuringiensis (82%) than in B. cereus strains (50%). To our knowledge, this is the first report about the isolation and identification of enterotoxigenic B. cereus and B. thuringiensis strains from cheese samples in Turkey.