Effect of monensin and lysocellin on growth and fermentation by pure cultures of ruminal bacteria

Abstract

In an effort to gain further insight into factors that cause increased ruminal propionate when ionophores are fed to ruminants, ruminal bacteria were tested for their susceptibility and fermentation end-product response to monensin or lysocellin. Growth of two strains each of Ruminococcus flavefaciens and Butyrivibrio fibrisolvens in broth media was inhibited by 2μg monen-sin/ml (2 ppm), whereas this concentration did not inhibit the growth of two strains each of Megasphaera elsdenii or Selenomonoas ruminantium, or three strains of Succinimonas amylolytica. Monensin at 2 ppm in the media did not change the ratio of VFA formed by pure cultures of the above strains or by 40 other ruminal bacteria representing a wide variety of acetate and propionate producers. In additional studies, Fibrobacter succinogenec and Lachnospira multiparus were more resistant to lysocellin than to monensin, while B. fibrisolvens, M. elsdenii, Ruminococcus flavefaciens, Ruminobacter amylophilus, Selenomonas ruminantium, Selenomonas lactolytica and Streptococcus bovis had similar sensitivity whereas Ruminococcus albus and Bacteriodes ruminicola had slight differences in sensitivity to these antibiotics. Except for minor differences, production of VFA and lactate by the bacteria was similar whether the organism was grown in medium with or without the ionophore. Though a wide variety of pure cultures of ruminal bacteria were tested substantive evidence was not obtained to show end-products formed by the organisms changed any when they were grown in presence of ionophores. © Taylor & Francis Group, LLC.