Doctor of Philosophy (PhD)
School of Nutrition and Food Sciences
A comprehensive understanding of the effect biological soil amendments of animal origin and physical soil amendments have on produce contamination is important for developing strategies to mitigate this risk. Our studies investigated the persistence of generic E. coli, E. coli O157:H7 and Salmonella spp. in soil and produce surfaces with different BSAAO and mulch applications, as well as the effectiveness of chlorine treatments in reducing enteric bacteria in the field. Cucumbers harvested from plots with paper mulch had the highest levels of E. coli (3.76 Log CFU/cm2) while samples from maize mulch had the lowest levels (1.68 Log CFU/cm2). E. coli present in plots with raw manure applied was significantly higher than those without it (PE. coli O157:H7 was detected in soil and cucumbers from plots using raw manure. E. coli can significantly die-off cucumbers in a five-day period after final irrigation, with total reductions ranging from 1.37-2.30 Log CFU/cm2. E. coli present in soil from carrot plots with raw manure had significantly higher populations than plots with compost. Generic E. coli present on the surface of carrots can be naturally reduced by 1.07 Log CFU/cm2 but exhibited low daily average reductions of 0.27 Log CFU/day. Non-Shiga toxin producing E. coli O157:H7 was detected in soil and carrots from plots with raw manure application during weeks 1 and 3, however the pathogen was not detected in soil irrigated by water with 3 or 50PPM chlorine after 5 weeks. Salmonella spp. was detected in the surface of carrots from plots with raw manure or compost applied. The results of this study may be useful for developing on-farm risk mitigation strategies related to using soil amendments.
Moreira Calix, Juan Fernando, "Effect of Type of Mulch and Biological Soil Amendments of Animal Origin (BSAAO) on Microbial Food Safety Risk on Cucumbers and Carrots Irrigated with Contaminated or Chlorinated Water" (2023). LSU Doctoral Dissertations. 6065.
Available for download on Saturday, March 21, 2026