Skip to main content
ARS Home » Northeast Area » Wyndmoor, Pennsylvania » Eastern Regional Research Center » Food Safety and Intervention Technologies Research » Research » Publications at this Location » Publication #349736

Research Project: Development of Alternative Intervention Technologies for Fresh or Minimally Processed Foods

Location: Food Safety and Intervention Technologies Research

Title: Gamma irradiation reduces the survival and regrowth of inoculated antibiotic-resistant bacteria and antibiotic resistant genes on romaine lettuce

item Dharmarha, Vaishali - Virginia Tech
item Trimble, Kelsey - Virginia Tech
item Pruden, Amy - Virginia Tech
item Boyer, Renee - Virginia Tech
item Strawn, Laura - Virginia Tech
item Niemira, Brendan
item Parker, Monica - Virginia Tech

Submitted to: International Association for Food Protection
Publication Type: Abstract Only
Publication Acceptance Date: 2/10/2018
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Introduction: Gamma irradiation effectively reduces foodborne pathogens and spoilage microorganisms on fresh produce. However, limited research is available regarding the effect of gamma irradiation on the survival and regrowth of antibiotic-resistant bacteria (ARB) or the persistence of antibiotic resistant genes (ARG) on fresh produce. Purpose: Determine the effect of gamma irradiation on the survival and regrowth of inoculated ARB and ARGs on romaine lettuce at two different time points over two weeks of 4oC storage. Methods: To provide a background inoculum representing potential carryover of ARB from the field, lettuce leaves (n=3, 100g) were dip-inoculated in compost slurry derived from manure with prior antibiotic dosing to the dairy cows and inoculated with multi-drug resistant E. coli O157:H7 and Pseudomonas aeruginosa. Lettuce was washed with XY-12 (50ppm free chlorine), modified atmosphere packaged, treated with 0 or 1.0 kGy gamma irradiation, and stored for 14 days at 4oC. ARB were enumerated on day 1 and 14 by serial dilution and plating onto antibiotic- supplemented Eosine Methylene Blue or Pseudomonas Isolation Agar. Relative abundance of the ARG, tetA was quantified via real time PCR for each treatment. Results: Irradiation resulted in ~3 log reduction of E. coli O157:H7 (p=0.04) and P. aeruginosa (p<0.0001). No significant regrowth or declines in ARB populations were observed in irradiated or control samples between 1 and 14 days of storage (p>0.05). Washing lettuce samples led to significant reductions in tetA/16S rDNA compared to unwashed samples. However, no statistical difference in tetA/16S rDNA copies was noted between irradiated and control lettuce over time. Significance: Results suggest that gamma irradiation is an effective treatment to reduce ARB populations on romaine lettuce but additional strategies are needed to reduce ARGs. Analysis of 16S rRNA sequencing data is underway to determine the effect of irradiation on the overall bacterial community composition of lettuce.