P3-122 Identification of Epiphytic Bacterial Microbes Antagonistic to Enteric Bacterial Pathogens Recovered from Cantaloupe Rind Surfaces

Wednesday, July 31, 2013
Exhibit Hall (Charlotte Convention Center)
Keila Perez, Texas A&M University, College Station, TX
Mustafa Akbulut, Texas A&M University, College Station, TX
Luis Cisneros-Zevallos, Texas A&M University, College Station, TX
Matthew Taylor, Texas A&M University, College Station, TX
Alejandro Castillo, Texas A&M University, College Station, TX
Introduction:  Interventions that prevent transmission of pathogens on produce surfaces by exploiting epiphytic pathogen-antagonizing native microbes could potentially assist in the protection of produce safety.

Purpose: The research objectives were to identify the native microbiota on surfaces of cantaloupe melon and to identify microorganisms antagonistic towards Salmonella enterica Typhimurium LT2 and Escherichia coli O157:H7 ATCC 700728. 

Methods: Cantaloupes (n = 30) were sampled from two south Texas farms in June 2012. From each melon, three 10 cm2 rind samples were excised, composited and pummeled in 99 ml of 0.1% peptone water for 1 min (n = 30). Aerobic mesophiles, lactic acid bacteria (LAB), yeasts/molds, enterococci, and coliforms were enumerated using appropriate media. For each sample, 4-12 isolated colonies from each medium were subjected to a battery of tests for biochemical identification (Vitek 2; bioMérieux N.A.). Antagonism of recovered isolates against pathogens was determined using the Agar Spot method. Isolates were spotted onto de Man, Rogosa and Sharpe agar for LAB or tryptic soy agar (TSA) surfaces and incubated at 35°C for 24 h. After 24 h, molten TSA was seeded with S. Typhimurium or E. coli O157:H7 to 6.0 log CFU/ml and then overlaid onto spotted plates. These were incubated at 35°C for 24 h. Inhibition halos produced by pathogen-antagonizing isolates were measured by caliper, baseline corrected and averaged; isolates producing a mean inhibition halo >1.0 mm were designated antagonistic to pathogens.

Results: Populations of aerobic mesophiles, fungi, enterococci, LAB and coliforms were 6.1 ± 0.4, 4.9 ± 0.5, 2.6 ± 1.0, 5.0 ± 0.8 and 4.3 ± 0.6 log CFU/cm2, respectively. Isolates of Staphylococcus and Streptococcus exhibited the greatest antagonistic activity against pathogens with inhibition halos ranging from 5.2 to 11.6 mm. 

Significance: These data suggest that native microorganisms present on cantaloupe surfaces can inhibit the growth of pathogens and may be useful in protecting the safety of fresh produce.