Ngwai YB*, Garasin UM, Ngbede FE, Nkene IH, Akpotu MO
The susceptibility of infecting bacteria to antibiotics is among the many factors that influence the in vivo response of the host and the bacteria to treatment with such antibiotics. Exposure of bacteria to subgrowth inhibitory concentrations of antibiotics does not only cause reduced susceptibility (that is, resistance), but may also modify the physicochemical characteristics and the architecture of the bacterial outermost surface, and may interfere with some bacterial functions. This study compares some phenotypes of Escherichia coli ATCC 25922 (Type Strain) with those of its ceftriaxone- and gentamicin-induced resistance mutants. Resistant mutants generated by growing the type strain for 7 days in sub-growth inhibitory concentrations of ceftriaxone or gentamicin were compared with the type strain in respect of the size and morphology of colonies, growth, motility and biochemical characteristics. It was observed that the type strain grew more with larger colonies than the mutant. In addition, the elevation of the colonies changed from flat (in type organism) to convex (mutant strain). Indole reaction of the ceftriaxone resistant mutant was negative as opposed to the type organism which was positive. Delay in time of colony formation, smaller and fewer colonies resulted following the exposure of E. coli to ceftriaxone and gentamicin sub-MICs. In addition, a change in the indole reaction of ceftriaxone-induced mutants to negative was also observed. The significance of these observations is the subject of further study by our group.
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