Purpose: To understand the natural prevalence of key foodborne pathogens and indicator microorganisms on cantaloupes and associated environmental samples from Arizona production fields.
Methods: Samples including cantaloupe, adjacent soil, water, rhizosphere biomass and air were collected from seasonal commercial fields during 2013. Site assessments of fields were also conducted. For microbiological analysis, cantaloupe rind composites (1 composite = 3 fruit) and environmental samples were enriched in Universal Pre-enrichment Broth (UPB) with 0.05% tween for 18 h at 35°C. For Salmonella, aliquots were then selectively enriched in tetrathionate broth at 42°C for 6 h followed by M Broth for 18 h at 37°C. For Listeria, the samples were selectively enriched in Listeria Enrichment Broth at 35°C for 48 h. Enterococci and coliform populations were determined by plating on ECC CHROMagar® and m-Enterococcus agar. Aliquots of all enriched samples were frozen in glycerol and stored for culture confirmation if judged as positive by Roka Atlas system testing. Presumptive positive samples were confirmed for Salmonella or Listeria by streaking on XLD or MOX, by PCR and biochemical testing.
Results: A total of 315 cantaloupe composites, 53 root, 54 soil, 22 air and 12 water samples were tested. Analysis of enrichments by the combined methods indicated that 7/315 and 6/315 fruit rind composites were positive for Salmonella serovars and Listeria spp., respectively. L. monocytogenes was not detected. Two soil and 3 water samples were positive for Salmonella. One root sample was positive for Listeria spp. The average coliform and enterococci counts on fruit rinds were 4.45 ± 0.53 and 2.49 ± 0.58 log CFU/g, respectively. Surveys of farms indicated no unusual features.
Significance: The results indicate that while vehicles of pathogen contamination on the field during cantaloupe cultivation might exist, detection of pathogens remains rare and challenging.