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Zhou K.,Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Center oe | Michiels C.W.,Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Center oe | Aertsen A.,Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Center oe
PLoS ONE | Year: 2012

In recent work we discovered that the intragenic tandem repeat (TR) region of the tolA gene is highly variable among different Escherichia coli strains. The aim of this study was therefore to investigate the biological function and dynamics of TR variation in E. coli tolA. The biological impact of TR variation was examined by comparing the ability of a set of synthetic tolA variants with in frame repeat copies varying from 2 to 39 to rescue the altered susceptibility of an E. coli ΔtolA mutant to deoxycholic acid, sodium dodecyl sulfate, hyperosmolarity, and infection with filamentous bacteriophage. Interestingly, although each of the TolA variants was able to at least partly rescue the ΔtolA mutant, the extent was clearly dependent on both the repeat number and the type of stress imposed, indicating the existence of opposing selective forces with regard to the optimal TR copy number. Subsequently, TR dynamics in a clonal population were assayed, and we could demonstrate that TR contractions are RecA dependent and enhanced in a DNA repair deficient uvrD background, and can occur at a frequency of 6.9×10-5. © 2012 Zhou et al. Source


Vanlint D.,Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Center oe | Rutten N.,Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Center oe | Michiels C.W.,Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Center oe | Aertsen A.,Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Center oe
Applied and Environmental Microbiology | Year: 2012

High hydrostatic pressure (HHP) processing is becoming a valuable nonthermal food pasteurization technique, although there is reasonable concern that bacterial HHP resistance could compromise the safety and stability of HHP-processed foods. While the degree of natural HHP resistance has already been shown to vary greatly among and within bacterial species, a still unresolved question remains as to what extent different food-borne pathogens can actually develop HHP resistance. In this study, we therefore examined and compared the intrinsic potentials for HHP resistance development among strains of Escherichia coli, Shigella flexneri, Salmonella enterica serovars Typhimurium and Enteritidis, Yersinia enterocolitica, Aeromonas hydrophila, Pseudomonas aeruginosa, and Listeria innocua using a selective enrichment approach. Interestingly, of all strains examined, the acquisition of extreme HHP resistance could be detected in only some of the E. coli strains, indicating that a specific genetic predisposition might be required for resistance development. Furthermore, once acquired, HHP resistance proved to be a very stable trait that was maintained for > 80 generations in the absence of HHP exposure. Finally, at the mechanistic level, HHP resistance was not necessarily linked to derepression of the heat shock genes and was not related to the phenomenon of persistence. © 2012, American Society for Microbiology. Source


Nurlinawati,Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Center oe | Vanoirbeek K.,Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Center oe | Aertsen A.,Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Center oe | Michiels C.W.,Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Center oe
Research in Microbiology | Year: 2015

A mutant with a transposon insertion just upstream of the lysophosphatidic acid acyltansferase gene plsC was isolated in a screen for mutants affected in growth at low temperature of the psychrotroph Serratia plymuthica RVH1. This mutant had lost its ability to grow at 4°C and was severely affected in growth at 10°C, but showed only slightly reduced growth at 30°C. Fatty acid analysis of membrane extracts showed that the ratio of C16:1/C18:1 fatty acids was six-to sevenfold reduced in the mutant, although the ratio of unsaturated to saturated fatty acids was unaffected. The homeoviscous adaptation ability of the mutant was also unaffected. Growth and fatty acid composition were mostly restored by overexpressing plsC on a plasmid. Supplementation of C16:1 (palmitoleic acid) into the growth medium partially rescued low temperature growth, indicating that a balanced ratio of the two main unsaturated fatty acids is required for psychrotrophy. The mutant was significantly more strongly inactivated by high pressure treatment at 250MPa, but not at higher pressures. It also showed reduced growth at low pH, but not at increased NaCl concentrations. This work provides novel information on the role of membrane fatty acid composition in stress tolerance. © 2014 Institut Pasteur. Source


Vanlint D.,Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Center oe | Rutten N.,Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Center oe | Govers S.K.,Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Center oe | Michiels C.W.,Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Center oe | Aertsen A.,Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Center oe
International Journal of Food Microbiology | Year: 2013

Exposure to high hydrostatic pressure (HHP) is increasingly being used in food preservation as a non-thermal pasteurization process, and its further implementation necessitates a more thorough understanding of bacterial resistance development and intraspecies variability with regard to inactivation by HHP. In this report, we discovered that exposure to high hydrostatic pressure stress can rapidly select for strongly increased RpoS activity in a hypersensitive Escherichia coli O157:H7 strain (ATCC 43888), leading to a simultaneous increase in HHP and heat resistance. Moreover, the level of RpoS activity correlated well with the original hypersensitivity and the extent of acquired HHP resistance, and extremely HHP-resistant mutants of ATCC 43888 clearly incurred a number of additional RpoS-dependent phenotypes. These findings suggest that implementation of novel processing techniques in the food production chain can readily affect the physiology of food-borne pathogens. © 2013 Elsevier B.V. Source


Vanlint D.,Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Center oe | Pype B.J.Y.,Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Center oe | Rutten N.,Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Center oe | Vanoirbeek K.G.A.,Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Center oe | And 2 more authors.
International Journal of Food Microbiology | Year: 2013

Application of high hydrostatic pressure (HHP) constitutes a valuable non-thermal pasteurization process in modern food conservation. Triggered by our interest in the rapid adaptive evolution towards HHP resistance in the food-borne pathogen E. coli O157:H7 (strain ATCC 43888) that was demonstrated earlier, we used genetic screening to identify specific loci in which a loss-of-function mutation would be sufficient to markedly increase HHP survival. As such, individual loss of RssB (anti RpoS-factor), CRP (catabolite response protein) and CyaA (adenylate cyclase) were each found to confer significant HHP resistance in the 300. MPa range (i.e. >. 1,000-fold), and this phenotype invariably coincided with increased resistance against heat as well. In contrast to loss of RssB, however, loss of CRP or CyaA also conferred significantly increased resistance to 600. MPa (i.e. >. 10,000-fold), suggesting cAMP/CRP homeostasis to affect extreme HHP resistance independently of increased RpoS activity. Surprisingly, none of the rapidly emerging HHP-resistant mutants of ATCC 43888 that were isolated previously did incur any mutations in rssB, crp or cyaA, indicating that a number of other loci can guide the rapid emergence of HHP resistance in E. coli O157:H7 as well. The inability of spontaneous rssB, crp or cyaA mutants to emerge during selective enrichment under HHP selection likely stems from their decreased competitive fitness during growth. Overall, this study is the first to shed light on the possible genetic strategies supporting the acquisition of HHP resistance in E. coli O157:H7. © 2013 Elsevier B.V. Source

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