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Bacillus cereus is a food pathogen of major concern to the dairy industry. Strains of B. cereus were isolated in 2006 and 2010 from a pasteurized milk processing line in a dairy plant in Algeria. Pasteurized milk is obtained from reconstituted and processed milk powder. This study was designed to discriminate between the isolated B. cereus strains and to predict their food poisoning potential. Strains were fingerprinted by M13-PCR, and identified at the phylogenetic group level by amplified panC gene sequence analysis. They were clustered into three distinct M13-PCR groups: one major group which included 17 strains and two minor groups which contained two and one strains, respectively. Strains originating from both the process equipment and milk powder were from the major group indicating that milk powder was the main source of initial contamination. Strains from the major and second group were affiliated to the mesophilic phylogenetic group III while the unique strain of the third group was classified into the mesophilic phylogenetic group IV. The data presented in this study showed a very low genetic diversity among B. cereus strains identified in milk powder and secondly by milk processing systems, as well as persistence in the dairy environment of specific B. cereus genotypes, across 4 years. M13-PCR typing and phylogenetic affiliation were useful for characterizing B. cereus dairy isolates, permitting their differentiation within the B. cereus group, and showing homogeneous contamination throughout the pasteurized milk processing line. The recurrent genotypes which belong to the potentially toxigenic group III B. cereus could threaten pasteurized milk safety. [ABSTRACT FROM AUTHOR]

Abstract: The effect of acidification of carrot extract on the heat resistance of Bacillus cereus (ATCC 7004 and 4342) spores was studied. Malic, acetic, citric, ascorbic, lactic and hydrochloric acids were used as acidulants. Thermal resistance experiments were performed over the range 82–108°C with continuous monitoring of pH. Non-acidified carrot extract (pH 5.2) had a protective effect on the thermal inactivation of spores when compared with the reference McIlvaine buffer at the same pH value. Acidification of carrot extract reduced the D-values obtained for spores, this effect occurring whatever the type of acidulant used. For both strains and all treatment temperatures, as pH decreased the D-values decreased exponentially over the pH range studied (5.2–4.0), yielding straight lines, basically parallel, with an average slope of 0.203±0.023. Significant decreases in survivor counts and apparent D-values were observed when injured spores were recovered using the usual recovery medium containing carrot extract. [Copyright &y& Elsevier]

Although mathematical modelling has reached a degree of maturity in the last decades, microbial ecology is still developing, albeit at a rapid pace thanks to new insights provided by modern molecular tools. However, whilst microbiologists have long enjoyed the perspectives that particular mathematical frameworks can provide, there remains a reluctance to fully embrace the potential of models, which appear too complex, esoteric or distant from the “real-world”. Nevertheless there is a strong case for pursuing the development of mathematical models to describe microbial behaviour and interactions, dynamically, spatially and across scales. Here we put forward perspectives on the current state of mathematical modelling in microbial ecology, looking back at the developments that have defined the synergies between the disciplines, and outline some of the existing challenges that motivate us to provide practical models in the hope that greater engagement with empiricists and practitioners in the microbiological domain may be achieved. We also indicate recent advances in modelling that have had impact in both the fundamental understanding of microbial ecology and its practical application in engineered biological systems. In this way, it is anticipated that interest can be garnered from across the microbiological spectrum resulting in a broader uptake of mathematical concepts in lecture theatres, laboratories and industrial systems. [ABSTRACT FROM AUTHOR]