Effects of potassium ion concentrations on the antimicrobial activities of ionophores against ruminal anaerobes

Abstract

The antimicrobial activities of monensin and lasalocid against representative strains of ruminal bacteria were evaluated in medium containing three different concentrations of potassium (1.3, 7.9, or 23.3 mM). The growth of Eubacterium ruminantium was inhibited by low concentrations of ionophores (<0.16 mg/liter), while the strain of Streptococcus bovis tested was resistant to high concentrations of ionophores (40 mg/liter) at all potassium concentrations tested. The MICs of the ionophores for strains of Bacteroides succinogenes, Butyrivibriofibrisolvens, Ruminococcus albus, and Ruminococcusfiavefaciens and for one strain of Bacteroides ruminicola increased with increasing potassium concentrations in the medium. High concentrations of ionophores (40 mg/liter) decreased the maximum cell yields or increased the lag times or both in cultures of one strain of Bacteroides ruminicola and two strains of Selenomonas ruminantium but did not completely inhibit the growth of these organisms. Increased potassium concentrations in the medium (from 7.9 to 23.3 mM) decreased the lag times or increased the cell yields or both when these three strains were grown in ionophore-containing medium, while the activities of lasalocid and monensin against these organisms were enhanced in the medium containing low potassium concentrations (1.3 mM). The data from this study suggest that extraceilular potassium concentrations may influence the antimicrobial activities of ionophores in the rumen.

Effect of ionophores on ruminal fermentation

“…This previous proposal was not based on experimental determinations and did not consider the effect of monensin on K. The present scheme (Fig. 2) for monensin is in agreement with the effects of extracellular K. High external K, which would decrease K efflux and proton influx, improved the growth of monensin-sensitive ruminal bacteria (14). Diet can have a marked impact on ruminal K concentrations.…”

“…While the hypothesis that the bacterial outer membrane provides a general pattern of ionophore resistance is attractive, there are several observations which need to be reconciled: (i) some gram-negative species are not resistant to high concentrations of ionophores (14,32); (ii) ionophores increased ion flux in some gram-negative bacteria (Bates et al, Report on 19th Conference on Rumen Function); (iii) gramnegative species that were originally sensitive to ionophores can adapt (33); (iv) there have been reports that grampositive bacteria can develop resistance to ionophores (14,15,27); (v) certain ciliate protozoa (33) and fungi (51) were relatively insensitive to ionophores. Hence, the presence of an outer membrane is not an absolute criterion for resistance.…”

Effect of ionophores and pH on growth of Streptococcus bovis in batch and continuous culture

“…Organism and growth conditions. S. bovis JB1 (22) and Si (4) were grown anaerobically at 39°C in media containing (per liter) 292 mg of K2HPO4, 292 mg of KH2PO4, 480 mg of (NH4)2SO4, 480 mg of NaCl, 100 mg of MgSO4 * 7H20, 64 mg of CaCl2 -2H20, 4 g of Na2CO3, 1.0 g of Trypticase (BBL Microbiology Systems, Cockeysville, Md. ), 0.5 g of yeast extract, and 0.6 g of cysteine hydrochloride.…”

Potentiation by metal ions of the efficacy of the ionophores, monensin and tetronasin, towards four species of ruminal bacteria

“…There has been much speculation about the molecular mode of action of feedlot ionophores, mainly by analogy with the action of ionophores on nonruminal species of bacteria (Bergen & Bates, 1984;Russell, 1987;Russell & Strobel, 1989). How ionophores affect ruminal bacteria has important implications for the possible enhancement of their potency in vivo by altering the dietary content of the cations that they translocate (Rumpler et al, 1986;Chirase et al, 1987;Dawson & Boling, 1987;Schwingel et al, 1989). This strategy may be particularly relevant to tetronasin, because it has a much greater affinity for divalent, particularly Ca 2+ , than monovalent ions, in contrast to other feedlot ionophores, including monensin and lasalocid (Grandjean & Laszlo, 1983).…”