Extracellular enzyme production and enterotoxigenic gene profiles of Bacillus cereus and Bacillus thuringiensis strains isolated from cheese in Turkey

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

Investigation of chromosomal and plasmid dna profiles of lactococcus lactics ssp. lactis

Thesis (Master)--İzmir Institute of Technology, Biology, İzmir, 2005Includes bibliographical references (leaves: 58-63)Text in English; Abstract:Turkish and Englishxi, 79 leavesLactic acid bacteria used in the manufacturing of cheese and other fermented milk products are known as starter cultures. Starters play an important role in the sensory properties of fermented milk products by lactic acid production which influences desirable quality characteristics. In dairy industry, diversity of starter strains of Lactococcus lactis is very limited. There is a considerable demand for novel starters with technologically desirable properties. Gene products responsible for lactose fermentation are encoded on plasmid DNA. Therefore, the plasmid stability of lactic acid bacteria is an important industrial property for starter culture. In the previous study, Lc. lactis ssp. lactis strains were isolated from an artisanal "comlek peyniri'" from Cappodocia and these strains were selected as good acid producers. The aim of this study was to investigate intraspecific diversity of 54 Lc. lactis ssp. lactis by choromosomal and plasmid profiling. In addition, the plasmid stability of 35 artisanal starters was determined by the examination -galactosidase activity. First of all, partial DNA sequencing of the 16S rRNA genes was carried out in order to confirm that the previously identified isolates were Lc. lactis ssp. lactis. The partial DNA sequencing and blast search results indicated that representative isolates showed 90 % homology with Lactococcus lactis. Based on chromosome and plasmid profiling results, 35 Lactococcus lactis artisanal starters exhibiting good acidifying activities were classified into ten different genotypes and nine plasmid groups. None of the reference strains of Lactococcus lactis ssp. lactis and Lc. lactis ssp. cremoris and Lc. lactis ssp. lactis biovar. diacetylactis were included into these genotypes and plasmid groups. The rest of the 17 isolates which were defined as low acid producers by technological methods were clustered into thirteen unique genotypes and seven plasmid groups. Only four of the isolates were found to contain the most stable plasmids by instability studies and these kept their lactase activities during prolonged subculturing. As a result, chromosome and plasmid DNA profiling allowed us to classify artisanal starter strains in certain groups. The strains with stable and instable plasmids will serve us to characterize and improve technological features of these artisanal starter strains in future studies

High genetic and phenotypic variability of Streptococcus thermophilus strains isolated from artisanal Yuruk yoghurts

Streptococcus thermophilus is a commonly used starter bacterium in dairy industry. It reduces the pH of milk rapidly and equilibrates the medium for the growth of Lactobacillus delbrueckii subsp. bulgaricus during yoghurt fermentation. Efforts to increase the diversity of artisanal yoghurt starters are not only important to bring new strains with novel and desirable characteristics, but also for the preservation of natural diversity which diminishes with the overuse and spread of industrial starters to natural resources. In the present study, 14 artisanal yoghurt samples were processed for the isolation of promising strains for yoghurt starter culture production and 66 strains were subsequently characterized. They were all identified as S. thermophilus using species-specific PCR and 16S rRNA gene sequencing. Genotypic diversity at the strain level was investigated by pulsed field gel electrophoresis (PFGE), and 22 homology groups were obtained. Further phenotypic characterization unearthed a significant phenotypic heterogeneity within homology groups, mostly with atypical novel character. Only 7 out of 66 strains showed S. thermophilus type-strain like phenotypic traits. Majority of the isolates were determined to be protease positive and fast milk acidifier to be used as yoghurt starter culture