Bacterial communities in aerosols and manure samples from two different dairies in central and Sonoma valleys of California

Authors: Ravva, Subbarao; Sarreal, Chester; Mandrell, Robert

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2011
Publication Date: 2/18/2011
Citation: Ravva, S.V., Sarreal, C.Z., Mandrell, R.E. 2011. Bacterial communities in aerosols and manure samples from two different dairies in central and Sonoma valleys of California. PLoS One. 6(2):e17281.

Interpretive Summary: Major outbreaks associated with produce 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 transport of these pathogens through aerosols to crops grown in close proximity to 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 bacterial communities characterized by using 16S rRNA sequencing of aerosols, fresh and dry manure samples collected from two dairies, one from Sonoma in Coastal valley and the other from Modesto in Central Valley of California are presented.

Technical Abstract: Aerosols have been suspected to transport food pathogens and contaminate fruits and vegetables grown in close proximity to animal raising operations, but studies are lacking that substantiates such transport. Thus, we determined by 16S rRNA sequencing if bacteria in aerosols collected with in 2 to 3 meters away from the dairy cows were originated from fresh or dry manure collected on-site from two dairies. Gram-positive Firmicutes dominated the bacteria in aerosols from a dairy in Sonoma of Coastal California surrounded by wineries whereas sequences of Gram-negative Proteobacteria were dominant in aerosols from the dairy in Modesto of Central Valley surrounded by other dairies. Although Firmicutes represented almost half of the 10 abundant sequences, aerosols from Sonoma also contained sequences from phyla Bacteriodetes and Actinobacteria that were previously characterized from animal feces. While none of the 10 abundant sequences from fresh or dry manure from Modesto were detected in aerosols, two of the abundant sequences from order Bacteriodetes and one from family Ruminoccaceae from fresh manure were characterized in aerosols collected from Sonoma dairy. Interestingly, none of the sequences from dry manure were in the top 10 sequences in aerosols from both dairies. The 10 most abundant sequences in aerosols from Modesto were all from Proteobacteria and half of them were from genus Massilia that were previously isolated from immune-compromised people, polluted soils and air samples. Since, aerosol sequences originated in manure from one of the two dairies and were previously characterized from other animal sources, a possibility exists for using them to source-track them to crops grown in proximity.