Showing papers by "Ian Chopra published in 1991"
TL;DR: The chapter discusses two aspects of the use of organic acids: in animal husbandry as animal feed additives and in abattoirs and food-processing plants where they may be used in controlling microbial contamination of carcass meat.
Abstract: Publisher Summary This chapter presents the chemistry and antimicrobial activity of the saturated straight-chain monocarboxylic acids, and reference is made, where appropriate, to derivatives of this group— for example, unsaturated (cinnamic, sorbic), hydroxylic (citric. lactic), phenolic (benzoic, cinnamic, salicylic) and multicarboxylic (azelaic, citric, succinic) acids. Organic acids are distinguished from other acids by the functional group COOH to which an organic group or a hydrogen atom may be attached. Common names used to describe this group of organic compounds include fatty, volatile fatty, lipophilic, weak, or carboxylic acids. There is no standard protocol for studying the antimicrobial activity of organic acids and many reports give only the pH value of the solution under test without indicating the concentration of the acid, thus making evaluation of the results difficult or impossible. In addition, it is difficult to compare the activity of different acids because it is influenced by the physical chemistry of the microbial species, the growth conditions, and the phase of growth. The chapter discusses two aspects of the use of organic acids: in animal husbandry as animal feed additives and in abattoirs and food-processing plants where they may be used in controlling microbial contamination of carcass meat.
379 citations
TL;DR: Cell death was not associated with a reduction in culture turbidity or a loss of membrane integrity since morphologically normal membranes were observed by electron microscopy and only a small proportion of the cytoplasmic enzyme beta-galactosidase leaked into the supernatant fluid of acid-treated E. coli K12 cultures.
Abstract: When strains of Escherichia coli K12 and Salmonella spp. were incubated with 0.5-0.7 mol/l formic or propionic acid at pH 5.0, propionic acid was more active than formic acid. It killed 90% of the cell population within 60 min compared with over 3 h for formic acid. Cell death was not associated with a reduction in culture turbidity or a loss of membrane integrity since morphologically normal membranes were observed by electron microscopy and only a small proportion of the cytoplasmic enzyme beta-galactosidase leaked into the supernatant fluid of acid-treated E. coli K12 cultures.
235 citations
TL;DR: It is concluded that sublethal concentrations of formic and propionic acid inhibit DNA synthesis without physically damaging DNA molecule, or starving the cell of essential thymine or otherwise inducing an SOS response.
Abstract: Sublethal concentrations of formic acid (10 mmol/l) and propionic acid (5 mmol/l) at pH 5.0 preferentially inhibit DNA synthesis and stop cell multiplication in the absence of a corresponding cessation in the increase of culture turbidity. The possibility that the acids induce the SOS response by starving cells of thymine or by causing physical damage to the DNA molecule has now been investigated. Accumulation of thymine into the cytoplasm of whole cells was not inhibited by either acid. Mutants defective in excision repair (uvr A6), recombination repair (rec A56) and polymerase activity (pol A1) were not more sensitive to the acids than their isogenic parent. No significant increase in cell length was observed from measurements of transmission electron microscope images of acid-treated cells. It is concluded, therefore, that sublethal concentrations of formic and propionic acid inhibit DNA synthesis without physically damaging DNA molecule, or starving the cell of essential thymine or otherwise inducing an SOS response.
30 citations
TL;DR: The ability of the cyclic peptide polymyxin B nonapeptide (PMBN) to inhibit haemagglutination of erythrocytes by Escherichia coli bearing K88ab, K99 or F41 fimbriae was examined.
Abstract: The ability of the cyclic peptide polymyxin B nonapeptide (PMBN) to inhibit haemagglutination of erythrocytes by Escherichia coli bearing K88ab, K99 or F41 fimbriae was examined. The agent strongly inhibited K88ab-mediated haemagglutination, but had little or no effect on haemagglutination mediated by K99 or F41 fimbriae. Inhibition of K88ab-mediated haemagglutination did not result from release of fimbrial adhesins from the bacterial cell surface, nor from solubilization of K88ab receptors in erythrocytes. Since PMBN also prevented haemagglutination mediated by partially-purified K88ab fimbriae, the agent may directly obstruct access of fimbriae to their mammalian receptor binding sites.
2 citations