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United States Department of Agriculture

Agricultural Research Service

Title: Klebsiella to Salmonella Gene Transfer Within Rumen Protozoa: Implications for Antibiotic Resistance and Rumen Defaunation

Authors
item McCuddin, Zoe
item Carlson, Steven
item Rasmussen, Mark
item Franklin, Sharon

Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 2, 2005
Publication Date: May 31, 2006
Citation: Mccuddin, Z.P., Carlson, S.A., Rasmussen, M.A., Franklin, S.L. 2006. Klebsiella to Salmonella gene transfer within rumen protozoa: implications for antibiotic resistance and rumen defaunation. Veterinary Microbiology. 114(3-4):275-284

Interpretive Summary: The rumen, i.e., the "first" stomach of cattle, sheep, and goats, has long been known to be a site of gene exchange for microorganisms. Rumen protozoa (RPz) ingest bacteria that can harbor antibiotic resistance genes. In this study, RPz were assessed as sites of gene transfer between two bacterial species, Salmonella and Klebsiella. One Klebsiella isolate carried a gene conferring ceftriaxone resistance, while the Salmonella was susceptible to ceftriaxone yet capable of thriving within protozoa. In vitro studies revealed that ceftriaxone-resistant Salmonella could be isolated following co-incubation of Salmonella and Klebsiella with RPz obtained from adult cattle and goats. This exchange was dependent upon protozoal ingestion of the Klebsiella and the Salmonella. However, the transfer event was not observed in calves and sheep that lacked RPz. These results provide an important basis for evaluating and preventing the spread of antibiotic resistance and other selective advantages for pathogens present in ruminants.

Technical Abstract: The rumen has long been known to be a site of gene transfer for microorganisms. Rumen protozoa (RPz) are active predators of bacteria that can harbor antibiotic resistance genes. In this study, RPz were assessed as sites of gene transfer between two bacterial species, Salmonella and Klebsiella. One Klebsiella isolate carried a plasmid bearing blaCMY-2, encoding an extended-spectrum -lactamase conferring ceftriaxone resistance, while the Salmonella was susceptible to ceftriaxone yet capable of thriving within protozoa. In vitro studies revealed that ceftriaxone-resistant Salmonella could be isolated following co-incubation of Salmonella and Klebsiella with RPz obtained from adult cattle and goats. Ceftriaxone-resistant Salmonella were not recovered in the presence of an inhibitor of protozoa engulfment or when a protozoa-sensitive Salmonella was part of the co-incubation. This transfer event was additionally observed in vitro for protozoa-independent stressors although at a significantly lower frequency. The gene transfer event was related to bacterial conjugation since a conjugation inhibitor, nalidixic acid, perturbed the phenomenon. Ceftriaxone-resistant Salmonella were recovered from calves, sheep, and goats co-challenged with ceftriaxone-resistant Klebsiella and ceftriaxone-sensitive Salmonella. However, the transfer event was not observed in calves and sheep that were defaunated prior to the co-challenge (goat defaunation studies were not performed). Moreover, Salmonella transconjugants were isolated from separate bovine in vivo studies involving a Klebsiella ornithinolytica donor carrying a plasmid conferring colicin activity while no such transconjugants were obtained from defaunated calves. These results provide an important basis for evaluating and preventing the spread of antibiotic resistance and other selective advantages for pathogens present in ruminants.

Last Modified: 4/23/2014
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