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The effects of cinnamic, propionic, benzoic and sorbic acids on the growth and intracellular pH of Escherichia coli were investigated. The data suggest that the potency of weak acids as food preservatives is related to their capacity to reduce specifically the intracellular pH. The data also suggest that although both the undissociated forms of the acid(More)
The polymerase chain reaction (PCR) was used selectively to amplify specific rDNA sequences of Carnobacterium divergens, C. mobile, C. piscicola and C. gallinarum in purified DNA extracts, crude cell lysates and food samples. The PCR products were visualized by agarose gel electrophoresis and identified, at species level, by hybridization reactions with(More)
The primary habitat of the intracellular pathogen Listeria monocytogenes is considered to be soil and decaying vegetation. As an opportunistic pathogen it must be able to recognize its entry into host tissue and, in response, co-ordinately induce the expression of virulence factors. No signature molecule, which facilitates this regulation, has been(More)
The growth patterns of microcolonies of 59 different pure cultures were studied on eight selective solid media. A method of growing microcolonies on the surface of polycarbonate membrane filters, placed on the selective agar media, followed by staining and examination by epifluorescent microscopy was developed. The patterns of growth of the pure cultures as(More)
A potentially Listeria-specific 28 base oligonucleotide probe was designed from 16S rRNA sequence data. Using either 32P or non-radioactive (alkaline phosphatase) labels, the probe was shown to be highly specific as it hybridised to RNA extracted from all of the species of Listeria but not to any of the other bacteria tested. Both probe methods were highly(More)
A fluorescent antibody-microcolony technique was developed for the rapid detection of salmonellas in pure cultures. Examination of microcolonies made the detection of salmonellas by epifluorescence microscopy easier and more reliable than using fluorescent antibody and single cells. After a study of the most effective selective enrichment media for(More)
The keeping quality (KQ) of pasteurized milk samples stored at 5 degrees C and 10 degrees C was satisfactorily predicted after 18 h pre-incubation with 0.05% benzalkonium chloride at 20 degrees C, by estimating the numbers of Gram-negative psychrotrophic bacteria using the simple, cheap and rapid (5 min) assay of cytochrome c oxidase. Correlation(More)
Uptake of [14C]glycine-betaine by Listeria monocytogenes was stimulated by NaCl with optimal stimulation at 0.4–0.5 M. The glycine-betaine transport system had a K m of 22 μM and a V max of 11.7 nmol-1 min-1 mg-1 protein when grown in the absence of NaCl. When grown in the presence of 0.8 M NaCl the V max increased to 27.0 nmol-1 min-1 mg-1 protein in 0.8 M(More)
The polymerase chain reaction was used to amplify specifically a 448 base pair internal fragment of the flaA gene from bacteria belonging to the genus Listeria. This gene encodes for the flagellin protein and allowed specific genus discrimination between other commonly found Gram-positive and Gram-negative bacteria and all Listeria spp. with the exception(More)
The capacity of E. coli cells to regulate intracellular pH (pHi) during net potassium uptake has been investigated. The data show: (a) that cells sense their intracellular pH; (b) that the pH gradient (delta pH) exerts a feedback regulation on pHi; (c) that a mechanism of regulation of pHi exists which may be independent of Na+ [Zilberstein, Agmon,(More)