[Growth characteristics of mutant strains of Escherichia coli isolated from poultry in the presence of streptomycin].

Three Escherichia coli strains--302(O111), 311(O78), and 331(O2) as well as streptomycin sensitive and streptomycin resistant mutants obtained from them by mutagenesis were studied. The sensitivity of all strains to streptomycin was tested in dilution series on hard and fluid medium. Growth curves were worked out by the biophotometer of Bonet, Maury and Jonan, adding various streptomycin concentrations to the medium at the very beginning of the experiment and 90 min after that. It was established that streptomycin concentrations above 15 microgram/cm3 added to bacteria sensitive to it at the beginning of their log-phase, shortens its duration by about 40%.