Abstract
Aerosols have been suspected to transport food pathogens and contaminate fruits and vegetables grown in close proximity to concentrated animal feeding operations, but studies are lacking that substantiate such transport. To monitor the potential transport of bacteria originated from fresh or dry manure through aerosols on a dairy, we identified by 16S rRNA sequencing, bacteria in aerosols collected within 2 to 3 meters from dairy cows at two dairies. Gram-positive Firmicutes were predominant in aerosols from a dairy in Sonoma, California, and surrounded by vineyards, in contrast to sequences of Gram-negative Proteobacteria predominant in aerosols from a dairy in Modesto, California, also surrounded by other dairies. Although Firmicutes represented approximately 50% of the 10 most abundant sequences, aerosols from the Sonoma dairy also contained sequences of Bacteriodetes and Actinobacteria, identified previously with animal feces. While none of the top 10 sequences from fresh or dry manure from Modesto dairy were detected in aerosols, two of the sequences from the phylum Bacteriodetes and one from class Clostridia from fresh manure were detected in aerosols from Sonoma. 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 the Modesto dairy were all from Proteobacteria and nearly half of them were from genus Massilia, which have been isolated previously from immune-compromised people and aerosols. We conclude that the predominant bacteria in aerosols are diverse among locations and that they do not reflect the predominant species of bacteria present in cow feces and/or in close proximity to cows. These results suggest that the aerosol sequences did not originate from manure. Large volumes of aerosols would be required to determine if bacterial sequences from aerosols could be used to track bacteria in manure to crops grown in proximity.
Highlights
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 identify the mechanisms of transport
Enteric bacterial pathogens causing much of the foodborne illnesses, including Salmonellae, Campylobacter sp., Listeria monocytogenes, and Escherichia coli O157:H7, have been reported to survive for long periods in manure and manure slurries [3,4] and a potential exists for their transmission through aerosols
A total of 495 clones representing 6 different bacterial phyla were characterized from aerosol, fresh and dry manure samples collected from the Sonoma dairy (Table 1)
Summary
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 identify the mechanisms of transport. Concentrated animal feeding operations (CAFO) produce large amounts of waste [1], raising concerns of pathogen transport through aerosols generated by waste processing on-site. A mid-size dairy of 1000 cows will produce more than 12,000,000 kg of manure per year [2] and the manure is usually stored/processed on-site. This increases the risk of transporting bacterial pathogens by a number of mechanisms (water, wildlife, dust) and is of special concern where fruit and vegetable crops are grown nearby. Enteric bacterial pathogens causing much of the foodborne illnesses, including Salmonellae, Campylobacter sp., Listeria monocytogenes, and Escherichia coli O157:H7, have been reported to survive for long periods in manure and manure slurries [3,4] and a potential exists for their transmission through aerosols
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