Comparison of in vitro and in vivo ampicillin susceptibility of Escherichia coli pretreated with low concentrations of mecillinam and ampicillin.
The ampicillin susceptibility of Escherichia coli showing morphological changes after pretreatment with low concentrations of mecillinam (spherical forms) or ampicillin (filaments) was compared in vitro and in vivo in short term experiments. Normal non-pretreated bacteria and mecillinam- or ampicillin-pretreated bacteria were cultured in vitro in the presence and absence of ampicillin. The growth curves were mathematically described as quadratic functions of time and these functions provided parameters characterizing the growth kinetics. The mecillinam pretreatment did not affect the growth rate relative to that of normal non-pretreated bacteria. The ampicillin susceptibility of these mecillinam-pretreated forms was, however, strongly increased. The ampicillin pretreatment resulted in an increased initial growth rate of the bacteria which normalized after about 1 1/2 h. The ampicillin susceptibility of these bacteria was unchanged. The growth and the ampicillin susceptibility of these ampicillin- or mecillinam-pretreated bacteria in an intramuscular infection in irradiated granulopenic mice were comparable with those seen in vitro. This outcome in vivo was influenced by the granulocytes when growth and ampicillin susceptibility were determined in non-irradiated mice. The mecillinam-pretreated bacteria were slightly more affected by both granulocytes and ampicillin than normal bacteria were. The ampicillin-pretreated bacteria were affected by both these factors to the same extent as normal bacteria.
D000560:Amdinocillin / Q000032:analysis / Q000494:pharmacology*; D000667:Ampicillin / Q000032:analysis / Q000494:pharmacology*; D000818:Animals; D003114:Colony-Forming Units Assay; D004195:Disease Models, Animal; D004357:Drug Synergism; D004926:Escherichia coli / Q000187:drug effects* / Q000254:growth & development; D006098:Granulocytes / Q000528:radiation effects; D007970:Leukopenia / Q000209:etiology*; D008297:Male; D051379:Mice; D008826:Microbial Sensitivity Tests; D010397:Penicillanic Acid / Q000494:pharmacology*
D000667:Ampicillin; D010397:Penicillanic Acid; D000560:Amdinocillin