Experimental ecological studies on H2 plasmids in the intestine and faeces of the calf

摘要

In vivotransfer of a typical H2 plasmid (pJT4) was not detected in groups of calves experimentally given large numbers of donor and genetically marked recipientEscherichia colistrains when the calves were muzzled and so denied oral contact with their surroundings. Transfer to the marked recipient and to a number of otherEsch. colistrains was, however, observed when muzzles were not used or were removed during an experiment. pJT4 was transferred in voided faeces at 30°C but not at 37°C. These results suggest that H2 plasmids do not transfer in the intestine and most probably are acquired by conjugations in the animal's environment. Experiments with calves using sets of isogenic strains ofEsch. coli, with and without pJT4, showed that the presence of the plasmid greatly increased the persistence of the host organism in the intestine. Strains with the plasmid persisted for 20 d or longer; strains cured of the plasmid decreased rapidly in number after 7 days. This phenomenon may be an important factor in the epidemicity in the calf of strains ofSalmonella typhimuriumthat carry H2 plasmid