Abu-Ghazaleh, Bayan M F; (1990) Effect of ColV plasmids on the heat sensitivity of Escherichia coli. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The heat sensitivity of E. coli K12 strains harbouring the ColV,I-K94 plasmid was examined after exposure to 52°C or 60°C. The presence of this plasmid rendered the cells more sensitive to heat, and the production of both colicin and transfer components by the ColV+ cells was involved in this increased heat sensitivity. Exposure to high temperature damaged the outer and cytoplasmic membranes of both ColV+ and ColV- cells with a greater effect on the ColV+ strains. Heating at 60°C resulted in release of lipopolysaccharide into the heating medium. It reduced the interactions between some of the proteins of the cell envelope and other constituents of the envelope causing weakening of the outer membrane structure as observed by analysis of the proteins of the cell envelopes of heated and unheated strains. Also, the permeability of the outer membrane of ColV- and Colv+ cells to hydrophobic compounds was increased in heated strains compared with the unheated ones. Heating also caused leakage of internal constituents of p- and ColV plasmid-bearing cells, and the amount released from ColV+ cells was twice that released from the p- cells. In addition to these effects, damage to other cytoplasmic compounds and DNA damage occur in heated cells. The thermal sensitivity of a polA strain was much higher than that of the parental strain, but the presence of the ColV,I-K94 plasmid in this polA strain did not enhance its heat sensitivity. Some of the conditions influencing the thermal resistance of ColV+ cells were examined. Growth of these cells in magnesium enriched medium increased their heat resistance and greatly reduced the difference between the heat sensitivity of the p- and the ColV+ cells. Exposure to a gradual rise in temperature from 34 to 50°C before heating at 60°C resulted in marked increase in the percentage of survival of the heated ED1829 and its ColV+ derivative, and this increase was much greater in the ColV plasmid- bearing cells. The incidence and properties of wild type Colv+ strains isolated from samples obtained from chicken processing plants were studied. A high proportion of these strains was resistant to cotrimoxazole and tetracycline. About 30% and 40% of the strains were resistant to chloramphenicol and ampicillin, respectively; and multiple antibiotic resistance was frequently observed in the isolates. Forty six percent of the coli strains produced colicin(s), and 31% of these produced colicin V and la and harboured plasmids resembling the ColV,I-K94 plasmid in mobility on agarose gels. Three of the five ColV+ strains produced VmpA protein.

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