The Influence of Bacteriocins on Resistance to Infection by Gram-negative Bacteria. I. The Effect of Colicin on Bactericidal Power of Blood

duced in rats with colicinogenic Escherichia coli CF1, elaborating colicin V in the urine, and coli-cin-sensitive E. coli 9224 by injecting each organ-ism into the medulla of opposite kidneys. The coli-cin-sensitive organism was eradicated from the urine of 24.3 % of rats and the degree of infection by E. coli 9224 reduced to less than half of the control group. Colicin-resistant mutants of E. coli 9224 were not inhibited in mixed infections with colicin producing E. coli CF1. No evidence of inhibitory activity by colicin V was found in the kidneys. The bladder urine, but not the kidney, was also the site for transfer of colicinogeny be-tween homologous (E. coli) and heterologous (E. coli and Aerobacter aerogenes) species. Episomes controlling colicin V and J + I were transferred within 24 hr after establishing the mixed infection. Since E. coli 9224 was resistant to streptomycin and tetracycline, observations were also made on transmission of multiple drug resistance. Strep-tomycin and tetracycline resistance was readily transferred to E. coli CF1 within 48 hr in the bladder. These results demonstrate that in urinary infections colicins can kill susceptible bacteria and that bacterial genetic elements are transferred