Somanath, Sushela Devi; (1991) Colicinogenic plasmids and inhibitor sensitivity in Escherichia coli. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The effects of Col plasmids on sensitivities of E.coli K-12 derivatives, especially 1829 and P678-54" to hydrophobic, hydrophilic and aminoglycoside antibiotics and to other inhibitors such as copper ions and Tris-EDTA have been examined. It was found that the colicinogenic plasmid ColVIK-94 sensitised the strains to hydrophobic antibiotics as well as to some of the hydrophilic and aminoglycoside antibiotics whilst Col BK-98 sensitised the strains to rifampicin and some of the aminoglycosides and hydrophilic antibiotics but not to most of the hydrophobic agents. The various effects of the above mentioned antibiotics and inhibitors were also tested on strains carrying mutant derivatives of the Col VIK-94. This was to investigate which plasmid components were responsible for sensitivities particularly to rifampicin and novobiocin. It was shown that both mutant plasmids sensitise 1829 to these two agents. It seems that both transfer and colicin components were Important for increased rifampicin sensitivity whereas transfer components were needed for novobiocin sensitivity. The effects of divalent cations, namely magnesium and calcium ions were investigated and it was found that they reversed the Inhibitory effects of the hydrophobic and aminoglycoside antibiotics on strain 1829 bearing the Col VIK-94 but there was no effect on those strains bearing Col BK-98. This probably indicates that the divalent cations in some way stabilise the outer membrane preventing the entry of some antibiotics into the cell. A prior growth temperature of 25° C seemed to reduce the sensitisation effects to hydrophobic antibiotics of the ColV plasmids without affecting the sensitivity of the parent strain 1829 whereas the effects of the hydrophilic and aminoglycoside e antibiotics were unaffected by a 25° C prior growth temperature. A Synthesis of colicin and transfer components are reduced at 25° C, hence the results are In accordance with the conclusion concerning the components involved in sensitivity especially with regards to rifampicin and novobiocin. The Col V and Col B plasmids sensitised the strains 1829 and P678-54 to copper sulphate and to the effects of the Tris-EDTA. The sensitivity to copper ions is due to the uptake of the ions by the Omp F porin. The plasmid may affect porin function or open up another entry pathway. The effects of the plasmids on the Tris-EDTA sensitivity was probably due to the weakening of the LPS-LPS bonds by this combination of agents.

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