Journal Article

The susceptibility of ionophore-resistant <i>Clostridium aminophilum</i> F to other antibiotics

Adam J. Houlihan and James B. Russell

in Journal of Antimicrobial Chemotherapy

Published on behalf of British Society for Antimicrobial Chemotherapy

Volume 52, issue 4, pages 623-628
Published in print October 2003 | ISSN: 0305-7453
Published online October 2003 | e-ISSN: 1460-2091 | DOI: http://dx.doi.org/10.1093/jac/dkg398
The susceptibility of ionophore-resistant Clostridium aminophilum F to other antibiotics

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  • Medical Oncology
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Objective: To determine if ionophore-resistant ruminal bacteria are cross-resistant to other classes of antibiotics. Clostridiumaminophilum was used as a model organism because this Gram-positive ruminal bacterium can adapt to ionophores (monensin and lasalocid). Non-adapted cultures lagged for at least 12 h with 1 µM monensin or lasalocid, but initiated no growth if the concentration was 10 µM. Adapted cultures did not lag with 1 µM monensin or lasalocid, grew well even if the ionophore concentration was 10 µM and contained cells at least 100 000-fold more resistant than those in non-adapted cultures.

Methods: Ionophore-adapted and non-adapted cultures were assayed for their susceptibility to other classes of antibiotics (penicillin G, ampicillin, cephalosporin C, vancomycin, carbenicillin, tetracycline, chloramphenicol, erythromycin, streptomycin, linocomycin, rifampicin, trimethoprim, novobiocin, polymyxin B and bacitracin) using a broth microdilution method.

Results: Adapted cultures retained their resistance phenotype for at least 28 generations even if ionophore was no longer present. Monensin-adapted cultures were as resistant to lasalocid as those adapted to lasalocid, but lasalocid-adapted cultures lagged with 1 µM monensin. Monensin- and lasalocid-resistant C. aminophilum F cultures were as susceptible to most antibiotics as non-adapted cultures. The only antibiotic that seemed to have a common mechanism of resistance was bacitracin, and the ionophore-adapted cultures had a 32-fold greater MIC.

Conclusion: The use of ionophores in cattle feed and the selection of ionophore-resistant ruminal bacteria does not necessarily lead to other types of antibiotic resistance.

Keywords: Keywords: antibiotics, ionophores, resistance, monensin, lasalocid

Journal Article.  3812 words.  Illustrated.

Subjects: Medical Oncology ; Critical Care

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