Melons are healthy fruits liked by consumers but have been involved in outbreaks. Listeria monocytogenes contaminated cantaloupes caused 33 deaths in a 2001 outbreak. Understanding contamination vehicles and prevalence of foodborne pathogens will assist in risk-analysis. The objective was to investigate soil and dust as pathogen contamination vehicles and prevalence of foodborne pathogens in AZ grown melons and environmental samples. Ten melon cultivars from 5 growing locations were evaluated. Melon rinds were placed on Salmonella Newport or L. monocytogenes inoculated soil for 1 h. Inoculated dust was sprayed on melon rinds. Melon rinds in Phosphate Buffered Saline (PBS) were sonicated, soil and dust in PBS were vortexed, samples plated on selective media with antibiotics, and enumerated to determine % transfer. 339 cantaloupes, 20 rhizosphere, 20 soil, 20 air and 6 water samples were collected from 4 fields in AZ. Selective enrichment and plating was done to analyze presence/absence of S. enterica and L. monocytogenes and enumerate indicator bacteria. S. Newport % transfer from soil ranged 0.0183±0.0015-0.1227±0.0027, 0.0015±0.00003-0.0542±0.0075, and 0.0029±0.0004-0.704±0.0597 for cantaloupe, honeydew, and hybrid, respectively. L. monocytogenes soil % transfer ranged 0.0014±0.00006-0.0448±0.00402, 0.0005±0.0001-0.0092±0.0009, and 0.0207±0.001-0.1112±0.0049, for cantaloupe, honeydew, and hybrid, respectively. S. Newport % transfer from dust ranged 0.000007±0.000006, 0.000011±0.000006, and 0.000128±0.000054 for cantaloupe, honeydew, and hybrid, respectively. L. monocytogenes dust % transfer ranged 0.00002±0.000004-0.00679±0.001303, 0.00004±0.000036-0.002±0.000159, and 0.00004±0.000013-0.00015±0.000076 for cantaloupe, honeydew, and hybrid, respectively. There was a significant difference for soil having a higher % transfer than dust (P<0.05) for all L. monocytogenes and most S. Newport samples. No pathogens were detected in melons and environmental samples. On cantaloupes, enterococci and coliforms ranged 2.3-2.8 and 3.8-4.1 Logs, respectively. Air samples had the lowest enterococci and coliform counts, <1-3.0 and <1-2.1 Logs, with water samples ranging 1.6-2.2 and 2.1-3.8 Logs, respectively. Two melons were positive for Escherichia coli. All fields had signs of wildlife intrusion. Results will help understand pathogen contamination risk in field conditions and provide data for a science-based risk analysis.

Richard Park

University of Arizona

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