BackgroundThe presence of coliform bacteria is routinely assessed to establish the microbiological safety of water supplies and raw or processed foods. Coliforms are a group of lactose-fermenting Enterobacteriaceae, which most likely acquired the lacZ gene by horizontal transfer and therefore constitute a polyphyletic group. Among this group of bacteria is Escherichia coli, the pathogen that is most frequently associated with foodborne disease outbreaks and is often identified by β-glucuronidase enzymatic activity or by the redundant detection of uidA by PCR. Because a significant fraction of essential E. coli genes are preserved throughout the bacterial kingdom, alternative oligonucleotide primers for specific E. coli detection are not easily identified.ResultsIn this manuscript, two strategies were used to design oligonucleotide primers with differing levels of specificity for the simultaneous detection of total coliforms and E. coli by multiplex PCR. A consensus sequence of lacZ and the orphan gene yaiO were chosen as targets for amplification, yielding 234 bp and 115 bp PCR products, respectively.ConclusionsThe assay designed in this work demonstrated superior detection ability when tested with lab collection and dairy isolated lactose-fermenting strains. While lacZ amplicons were found in a wide range of coliforms, yaiO amplification was highly specific for E. coli. Additionally, yaiO detection is non-redundant with enzymatic methods.

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We describe a genetic instability found in natural wine yeasts but not in the common laboratory strains of Saccharomyces cerevisiae. Spontaneous cyh2 R /cyh2 R mutants resistant to high levels of cycloheximide can be directly isolated from cyh2 S /cyh2 S wine yeasts. Heterozygous cyh2 R /cyh2 S hybrid clones vary in genetic instability as measured by loss of heterozygosity at cyh2. There were two main classes of hybrids. The lawn hybrids have high genetic instability and generally become cyh2 R /cyh2 R homozygotes and lose the killer phenotype under nonselective conditions. The papilla hybrids have a much lower rate of loss of heterozygosity and maintain the killer phenotype. The genetic instability in lawn hybrids is 3 to 5 orders of magnitude greater than the highest loss-of-heterozygosity rates previously reported. Molecular mechanisms such as DNA repair by break-induced replication might account for the asymmetrical loss of heterozygosity. This loss-of-heterozygosity phenomenon could be economically important if it causes sudden phenotype changes in industrial or pathogenic yeasts and of more basic importance to the degree that it influences the evolution of naturally occurring yeast populations.

-The microflora of Ibores cheese made with raw goat's milk without any starter addition was studied throughout the ripening period. The microbial counts for total lactic acid bacteria, presumptive lactococci and presumptive lactobacilli attained maxima of 9-10 log units with little or no variation throughout ripening. Leuconostocs and enterococci levels were 2-3 log units lower, also with little variation. Coliforms and staphylococci declined steadily from relatively high initial counts, the coliforms to low levels and the staphylococci disappearing completely. Moulds and yeasts were at low levels throughout ripening. Among the identified isolates, lactococci formed the prevalent group throughout ripening, followed by leuconostocs and enterococci at similar levels to each other, and then lactobacilli at low levels. The prevailing species and subspecies were Lactococcus lactis ssp. lactis, Leuconostoc mesenteroides ssp. dextranicum, Ln. mesenteroides ssp. mesenteroides, Weissella paramesenteroides, Enterococcus faecium, E. faecalis, Lactobacillus casei and Lb. plantarum. Small numbers of other species from each of the genera were also identified. The changes in certain physicochemical parameters during ripening were determined. By 60 days, the values of the pH, total solid content, and NaCl content were 5.18, 58.9% and 2.5%, respectively. The correlation of some of the physicochemical parameters with the log counts of the microbial groups was also established.Goat's milk cheese / ripening / lactic acid bacteria / identification Résumé -Fromage des Ibores : changements microbiologiques et physico-chimiques pendant l'affinage. La microflore de fromages de type Ibores, faits avec du lait cru de chèvre, sans addition de levain, a été suivie pendant l'affinage. Les concentrations de bactéries lactiques totales, de

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