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

Adult sheep were given into the rumen c. 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 ruminai environment was altered so that, on resumption of feeding, small numbers (c. 102−104 cells-less than one cell per 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 × 103 cells of recipient S. lomita after starvation for 48 h, became a carrier of this organism. A second animal, given 4.4 × 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 (c. 109 cells per g) were present in the faeces; these included many (c. 106 cells per g) that had received the R factor by transfer in vivo. These results indicate that short periods of starvation may enhance the transfer of R factors and possibly other plasmids between suitable micro-organisms in vivo, and may increase the susceptibility of animals to pathogenic micro-organisms.