P3-129 Irrigation Water as a Source of Antibiotic Resistant and Virulent Escherichia coli on Lettuce

Wednesday, July 31, 2013
Exhibit Hall (Charlotte Convention Center)
Elna Buys, University of Pretoria, Pretoria, South Africa
Matthew Aijuka, University of Pretoria, Pretoria, South Africa
Introduction : Irrigation water has been noted a source of foodborne bacterial pathogens on fresh produce. Escherichia coli is a major foodborne pathogen associated with fresh produce and increase in antibiotic resistance has been noted. Antibiotic resistance can provide information on relationships between environmental E. coli while virulence factors determine ability to cause illness.

Purpose : The purpose of this study was to determine whether irrigation water was a source of antibiotic resistant and virulent E. coli on irrigated lettuce grown under field conditions.

Methods : Twenty-two E. coli isolates (12 irrigation water and 10 lettuce) were subjected to 11 antibiotics on Muller-Hinton agar, incubated at 35°C for 24 h. The result recorded as resistant or susceptible based upon size of inhibition zones compared using ANOVA. Numerical classification was done using Euclidean metric, average linkage method. Isolates were tested for Shiga toxin-producing genes Shigatoxin 1 (stx 1), Shiga toxin 2 (stx 2) and Intimin (eae) using real time PCR iQ-CheckTMSTEC VirX.

Results : There was a significant difference in resistance (P ≤ 0.05) between isolates from irrigation water and lettuce. High resistance to Cephalothin (50 and 60%) and Ampicillin (50 and 50%) was noted in isolates from irrigation water and lettuce, respectively. Resistance to the same antibiotics (Ampicillin, Cephalothin, Oxytetracycline, Amoxicillin) was noted in both irrigation water and lettuce. Isolates from lettuce were resistant to fewer antibiotics (4/11) than irrigation water (7/11). All isolates in irrigation water clustered in one group while 50% of isolates from lettuce clustered together with those from irrigation water. Three isolates in irrigation water were positive for Stx1/Stx2 and eae and one each for Stx1/Stx2 and eae. Two isolates on lettuce were positive for Stx1/Stx2.

Significance : Results indicate that irrigation water prevalent in antibiotic resistant and virulent bacteria may be a source of contamination on produce grown under field conditions thereby posing a food safety risk to the final consumer.