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

Abstract

In vivo transfer of a typical H2 plasmid (pJT4) was not detected in groups of calves experimentally given large numbers of donor and genetically marked recipient Escherichia coli strains when the calves were muzzled and so denied oral contact with their surroundings. Transfer to the marked recipient and to a number of other Esch. coli strains 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 of Esch. 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 of Salmonella typhimurium that carry H2 plasmids.

Antibiotic Resistance: Consequences of Inaction

“…Resistance genes, carried on transportable elements, such as plasmids and transposons, can spread readily in the environment. Some time ago, workers showed that the transfer of a temperature-sensitive, transferable, multidrug-resistant H2 plasmid among Escherichia coli in cows occurred in the environment, not in the animals, whose body temperature did not permit the transfer [9]. Outside the animal, the lower ambient temperature allowed transfer of the plasmids to new E. coli recipients.…”

Transfer of plasmids between strains of Escherichia coli under rumen conditions

“…No evidence was found for transfer under normal rumen conditions, although the E. coli strains tested were isolated from the faeces rather than the rumen of sheep, and viable cell counts decreased rapidly following inoculation under normal rumen conditions (Smith 1975). In another study, transfer of H2 plasmids was found to occur mainly in voided faeces rather than in the gut of calves, but this was attributable to the temperaturesensitive transfer of H2 plasmids (Timoney and Linton 1982). Another study failed to detect onward transfer of pSL222 from E. coli in viva (Marshall et al 1990).…”

Is ‘dosing-to-cure’ appropriate in the face of antimicrobial resistance?

“…Since such transfer can occur at high frequency in the environment [13,27] and as it can involve a variety of diverse bacterial species [13], contamination of the environment with antimicrobials is likely to foster the dispersal of resistance genes. The problem of environmental contamination is outside the scope of the present review.…”