Transfer of R Factors from Escherichia Coli to Salmonellas in the Rumen of Sheep

Abstract

Adult sheep were given intrarumenally .apprx. 108 cells each of donor strains of E. coli containing an R factor and prospective Salmonella-recipient organisms and were maintained on a diet of lucerne chaff; the animals excreted the organisms, remained healthy and no transfer of the R factor was detected. When the animals were starved for 48 h before inoculation, the ruminal environment was altered so that, on resumption of feeding, small numbers (.apprx. 102-104 cells.sbd.less than 1 cell/ml of rumen fluid) of the introduced organisms were able to multiply and reach sufficient numbers for the transfer of R factors to occur within the rumen. One animal, given 7.8 .times. 103 cells of recipient S. lomita after starvation for 48 h, became a carrier of this organism. A 2nd animal, given 4.4 .times. 102 cells of S. typhimurium after starvation for 48 h, developed acute, fatal salmonellosis 5 days later; at the time of death, large numbers of salmonella organisms (.apprx. 109 cells/g) were present in the feces; these included many (.apprx. 106 cells/g) that received the R factor by transfer in vivo. Short periods of starvation may enhance the transfer of R factors and possibly other plasmids between suitable microorganisms in vivo and may increase the susceptibility of animals to pathogenic microorganisms.