Skip to main content
ARS Home » Northeast Area » Ithaca, New York » Robert W. Holley Center for Agriculture & Health » Research » Publications at this Location » Publication #101896
Title: THE ABILITY OF "LOW G+G GRAM-POSITIVE" RUMINAL BACTERIA TO RESIST MONENSIN AND COUNTERACT POTASSIUM DEPLETION

Author
item CALLAWAY, TODD - CORNELL UNIVERSITY
item ADAMS, KRISTIN - CORNELL UNIVERSITY
item Russell, James

Submitted to: Current Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/24/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Monensin has been used as feed additive for more than 20 years, and it has routinely modified ruminal fermentation and increased nutrient availability. Monensin is primarily effect against gram-positive ruminal bacteria, but some gram-negative bacteria are now classified as gram-positive species. Results indicated that 'low G+C gram-positive' ruminal bacteria with an outer membrane were indeed more resistant to monensin than bacteria that completely lacked an outer membrane. Gram-positive species without an outer membrane increased their resistance after they were transferred repeatedly with sub-lethal doses of monensin, but they were never as resistant as those that had an outer membrane. Research on monensin has the potential to identify other additives for cattle and to increase the efficiency of cattle production.

Technical Abstract: Gram-negative ruminal bacteria with an outer membrane are more generally resistant to the feed additive, monensin, than gram positive species, but some bacteria can adapt and increase their resistance. 16 rRNA sequencing indicates that a variety of ruminal bacteria are found in the "low G+G gram-positive group," but some of these bacteria are monensin-resistant and dwere previously described as gram-negative species (e.g. Selenomonas ruminantium and Megasphaera elsdenii). The activity of monensin can be assayed by its ability to cause potassium loss, and results indicated that amount of monensin needed to catalyze half maximal potassium depletion (Kd) from "low G+G gram-positive" ruminal bacteria varied by as much as 130-fold. The Kd values for Butyrivibrio fibrisolvens 49, Streptococcus bovis JB1, Clostridium aminophilum F, S. ruminantium HD4 and M. elsdenii B159 were 10, 65, 100, 1020 and 1330 nM, respectively. S. bovis and C. clostridium cultures that were transferred repeatedly with sublethal doses of monensin had higher Kd values than unadapted cultures, but the increase in Kd was less than 10-fold. B. fibrisolvens was always very sensitive to monensin, and S. ruminantium and M. elsdenii cells were always highly resistant. The monensin-resistance of S. ruminantium and M. elsdenii can be explained the ability of these low G+G gram-positive bacteria to synthesized outer membranes.