|Mcgarvey, Jeffery - Jeff|
Submitted to: Applied Microbiology and Biotechnology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/26/2009
Publication Date: 2/1/2010
Citation: Mcgarvey, J.A., Hamilton, S., Depeters, E., Mitloehner, F. 2010. Effect of dietary monensin on the bacterial population structure of dairy cattle colonic contents. Applied Microbiology and Biotechnology. 85:1947-1952. Interpretive Summary: Monensin is a growth promoting antibiotic that is used in the dairy industry to increase the amount of milk produced per cow, while reducing the amount of food eaten by the animal. Monensin accomplishes this by altering the number and types of bacteria within the animal’s stomach. However several studies have shown that some common foodborne pathogens that are associated with dairy cows (Salmonealla, E. coli, and Campylobacter) are resistant to monensin, and thus the concentration of these pathogens may increase in the waste of animals fed monensin. To explore how monensin effects the bacterial populations within dairy cattle waste we examined the waste of animals fed a diet with or without monensin. We observed no significant difference in the amount or type of bacteria in the waste of animals fed monensin vs. the control animals. Thus it seems unlikely that feeding monensin to animals increases the levels of these pathogens in their waste.
Technical Abstract: Monensin is a carboxylic polyether ionophore antibiotic that is routinely used to improve the performance of beef cattle and was recently approved by the U.S. Food and Drug Administration for the use in dairy cattle to improve milk yields. Previous studies have suggested that monensin improves animal performance by reducing the energetically wasteful processes of methanogenesis and amino acid fermentation within the rumen. Feeding monensin to cattle is believed to accomplish this by reducing the levels of Gram positive bacteria in the rumen. However, selecting for greater levels of Gram negative bacteria in the gastrointestinal tract, and ultimately the manure, is of concern because dairy cattle are known to excrete several pathogenic Gram negative bacteria such as Escherichia coli O157:H7, Salmonella spp. and Campylobacter spp. In the present study we used both cultural and molecular methods to examine the effect of feeding monensin on the bacterial populations within diary cattle waste. Using cultural methods we observed no significant difference in the number aerobic, anaerobic or MacConkey plate counts. We also sequenced 16S rRNA gene libraries derived from the manure of Monensin fed and control animals, containing > 3,000 clones each (estimates of coverage were approximately 88% for both libraries). Using the Library Compare software, we were unable to identify any significant difference in the composition of the libraries, down to the genus level. In addition, rarefaction analysis revealed that both libraries contained similar levels of diversity. In conclusion, we were unable to identify any effect of monensin on the bacterial population structure of dairy cattle waste. Thus, it is unlikely that feeding monensin to dairy cattle will result in an increase in the spread of Gram negative bacterial pathogens.