Purpose: The purpose of this work was to evaluate the potential transfer of extended-spectrum β-lactamase gene (blashv18) on shredded lettuce and characterize its transconjugants.
Methods: Klebsiella pneumoniae strain ATCC 700603 served as the donor and 3 recipient (KP342, KP4, KP8) were used for the mating experiments. Shredded lettuce was dipped in the sterile tap water containing 7 - 8 log CFU ml-1 mixture of a donor and a recipient for 1 min. Inoculated lettuce (25 g) was placed into a sterile sampling bag and stored at 15°C and 24°C. After 1 and 2 days of storage the lettuce samples were plated out on TSA containing appropriate antibiotics. Presumptive transconjugants were verified by detection of transferred gene as well as comparing by random amplified polymorphic DNA (RAPD) patterns. Transfer frequency and antimicrobial susceptibility of transconjugants were compared.
Results: At 15°C, transconjugants were only detected on day 2 post-mating. At 24°C, the transfer of blaSHV18 gene occurred at a frequency of 1.12E-05 to 2.98E-04 at day 1 and 2 post-mating. In particular, the transfer rate on day 2 at 24°C was significantly greater than under other conditions and days (P < 0.05). The blashv18 gene carried by transconjugants was detected by PCR. According to the RAPD profile, transconjugant and recipient exhibited similar band patterns that were different from the donor. Resistances to trimenthoprim/sulfamethoxazole, ceftazidime and cefotaxime were co-transferred with blashv18 gene.
Significance: These results suggest that transfer of antibiotic resistance genes on fresh produce may permit the spread of antibiotic resistance genes into the community having a negative impact on human health.