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Re-growth of fecal indicator bacteria and Escherichia coli 0157:H7 B6914 in cow fecal extract
Citation:
Oladeinde, A., E. Lipp, C. Chen, R. Zepp, AND M. Molina. Re-growth of fecal indicator bacteria and Escherichia coli 0157:H7 B6914 in cow fecal extract. International Symposium on Waterborne Pathogens, Savannah, GA, April 13 - 14, 2015.
Impact/Purpose:
Presented at the International Symposium on Waterborne Pathogens in Savannah, GA, April 13 - 14, 2015.
Description:
The health risks that pathogens pose to water and food resources are highly dependent on their fate and transport in agricultural settings. In order to assess these risks, an understanding of the factors that influence pathogen fate in agricultural settings is needed and is critical in developing control and adaptation strategies to minimize their transfer. The re-growth potential of fecal indicator bacteria (Escherichia coli and Enterococcusfaecalis) and Escherichia coli 0157:H7 86914 was studied in cow fecal extract. Cow fecal extracts were filter sterilized and diluted to concentrationsthat represent nutrient inputs from direct fecal deposition into streams ( 1: 1 0) and inputs from overland run-off during runoff producing rain events (1: 140). In addition, the effect of solar irradiation was investigated given its ability to breakdown dissolved organic matter (DOM) and dissolved organic nitrogen (DON) into a variety of photo-products that can support or inhibit bacterial growth. Filter sterilized fecal extracts were exposed to UV irradiation (300-600nm) using a solar simulator for 12 hours. Post irradiation, a mid-log phase culture of each bacterium (102-1 03cells/mL) was separately inoculated into the irradiated fecal extract and incubated at 25°C for72 hrs. Triplicate samples were analyzed at 0, 6, 12, 24, 48, 72 hours for microbial and nutrient analysis. In addition, the photoproduction of reactive oxygen species (ROS) including singlet oxygen, hydrogen peroxide and hydroxyl radicals were monitored. Lastly, genes that wereexpressed in response to oxidative stress from ROS exposure were investigated using reverse transcriptase-PCR. E. coli K-12 and E. coli 0157:H7 B6914 populations increased by 3 and 5 logs in 1:140 and 1:10 cow fecal extracts, respectively relative to the control. However, E. faecalis was a log lower than their corresponding control in UV treated 1: 10 fecal extracts and experienced a steady decline in both UV treated and control 1:140 fecal extracts. Irradiation also caused E. coli 0157 :H7 B6914 to experience a 6-hour lag phase in 1:140 fecal extracts, before the onset of growth. Our results suggest that the lag phase and low growth efficiency experienced by E. coli0157:H7 B6914 and E. faecalis, respectively, resulted from their sensitivity to ROS, which was produced at a steady state of 1.64352E-14M in irradiated fecal extracts. This study indicates that under suitable conditions, re-grcnvth of E. coli and E. coli 0 !57: H 7 can occur as result of direct manure impact in a receiving body of water. In addition, UV may have an inhibitory role on bacterial grovvth due to the photoproduction of ROS. Overall, our results pose several implications for modeling the survival of bacteria in environments impacted by agriculture.
URLs/Downloads:
http://www.awwa.org/conferences-education/conferences/waterborne-pathogens/sym15-program.aspx