MICROBIAL ECOLOGY AND SAFETY OF FRESH ON-FARM ORGANICALLY GROWN PRODUCE
Title: Characterization of microbial content of organic and conventional produce in Maryland relative to production practices and inputs
Submitted to: International Association for Food Protection Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: March 5, 2008
Publication Date: August 4, 2008
Citation: Millner, P.D., Ingram, D.T., Reynolds, S.L., Shelton, D.R., Patel, J.R. 2008. Characterization of microbial content of organic and conventional produce in Maryland relative to production practices and inputs. International Association for Food Protection Abstract Book. Paper No. P1-29. p. 62.
Introduction: Production inputs/practices such as soil amendments, water quality, animal intrusion, and human activity can influence microbial quality of fresh produce. Limited data on production practices relative to microbial/pathogen content of fresh produce are currently available for either organic or conventional farms in the Mid-Atlantic region, some of which market directly to consumers.
Purpose: Microbial content of seasonal produce grown during 2006-2007 relative to various production practices/inputs was evaluated with emphasis on E. coli (generic and pathogenic), Salmonella spp., and Listeria spp.
Methods: Produce (n=335), water (n=66), and soil (n=335) samples from tomatoes, leafy greens, strawberries, green onions, and herbs were collected from matched pairs of organic and conventional farms and analyzed for E. coli, Salmonella, and Listeria spp. E. coli were confirmed by biochemical and FAME profiles and further screened by multiplex PCR for specific detection of stx1, stx2, and eae genes of E. coli O157:H7. Farm practices at each site were obtained by interviews, on-site observations, and written responses from participants.
Results: Confirmed isolates of E. coli included 34 and 46 soil and 5 and 15 commodity samples in 2006 and 2007, respectively. No EHEC strains were determined from PCR screening. No biochemically confirmed salmonellae were detected. Pathogenic Listeria spp. were recovered from strawberry and soil samples on one farm by enrichments in 2007. E. coli counts in excess of USEPA drinking water quality limits were determined from 7 of 17 and 11 of 28 samples in 2006 and 2007, respectively.
Significance: Interview and observation data indicate both organic and conventional producers are aware of the need for clean irrigation water for fresh produce. Most avoid direct contact of all commodities with animal manure. For drip irrigated crops, growers often used surface water, but were aware of the need to avoid contact on fruits.