Genetic characterization of the mechanism by which certain strains of Escherichia coli survive in high kanamycin concentrations.

By genetic studies, it was tried to find the mechanism by which a bacterial fraction from different isolated clinical cultures resistant to 25 micrograms/ml of kanamycin can grow in media containing 500 micrograms/ml of kanamycin (at a frequency of about 10(-5)). This study was done in six clinical isolates of Escherichia coli resistant to more than three antibiotics. The results from the bacterial fraction (subpopulation) resistant to high concentrations of kanamycin in the level of resistance to aminoglycoside and non-aminoglycoside antibiotics, in the conjugation experiments, and in the percentage of resistant bacteria to 500 micrograms/ml of kanamycin when the subpopulations were subsequently cultivated in the absence of antibiotics suggest that genetic amplification occurred when one of the strains was growing in the presence of 500 micrograms/ml of kanamycin. Moreover, this strain increased its frequency of survival in high kanamycin concentrations when it was transduced by bacteriophage P1, propagated in cultures resistant to 500 micrograms/ml of kanamycin.