Submitted to: PLoS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2012
Publication Date: 1/22/2013
Citation: Ravva, S.V., Sarreal, C.Z., Mandrell, R.E. 2013. Protozoan and bacterial community shifts during enhanced survival of Escherichia coli O157:H7 in monensin-treated dairy wastewater. PLoS One. 8(1):e54782.doi:10.1371/journal.pone.0054782.
Interpretive Summary: Major outbreaks associated with produce occurring in the US and in other parts of the world indicate that pre-harvest contamination has occurred in the field, so it is critical to identify sources of pathogens in the environment and interventions for minimizing them Animal manure is a potential pathogen reservoir, and the close proximity of dairy operations to croplands in California cannot be ignored. Since contamination of ‘ready to eat’ produce cannot be washed off, on-site prevention of contamination is vital. Any such attempts require an understanding of the biological and environmental factors that regulate the proliferation of pathogens during their transport from animal reservoirs to produce grown in proximity to livestock operations. We have worked on developing improved detection methods for pathogens, and on understanding how pathogens survive and re-grow in dairy environments. Our long-term goals are to develop on-site prevention and control of pathogens at the source prior to contaminating produce we consume. Data on reduction of a foodborne pathogen, Escherichia coli O157:H7, by altering protozoan communities native to wastewater from dairy lagoons are presented.
Technical Abstract: We determined the role of native protozoa in controlling the populations of Escherichia coli O157:H7 (EcO157) in wastewater from dairy lagoons as both protozoa and EcO157 are released into lagoons through manure washings. We monitored the fate of an outbreak strain of EcO157 in wastewater treated with monensin, known to inhibit rumen ciliates and control bovine coccidiosis. Although monensin failed to decrease the total protozoa or native aerobic bacteria, it increased the survival of EcO157 by increasing the time for 90% decrease in EcO157 from 0.8 day to 5.1 days. We characterized the changes in protozoan and bacterial communities by 18S and 16S rRNA gene sequencing and determined that monensin eliminated almost all colpodean and oligohymenophorean ciliates, probably facilitating extended survival of EcO157. We enriched 3 out of 4 colpodean ciliates by supplementing cereal grass extract to wastewater, but detected also that monensin enriched 94% of protozoan sequences that were not detected from untreated wastewater. Monensin stimulated 30-fold increases in Cyrtohymena citrina, a spirotrichean ciliate, and also biflagellate bicosoecids and cercozoans. Monensin increased the gram-negative Proteobacteria from 1% to 46%, but decreased gram-positive Firmicutes from 93% to 46%. Monensin also significantly enriched Advenella, an herbicide degrader, representing one third of total sequences identified. Since dietary monensin inhibits ciliate protozoa that feed on EcO157, developing methods to enrich these protozoa in dairy cattle manure through feed or organic supplementation of soils could be a novel strategy to control the environmental dissemination of EcO157 in dairy and produce production environments.