Purpose: This investigation evaluated the performance of a loop mediated isothermal amplification method (LAMP) alternative method for detecting Salmonella spp., E. coli O157:H7 and L. monocytogenes on grape tomatoes according to the Mexican Department of Health Standard.
Methods: Grape tomatoes were collected and held at 4°C up to 24h. Samples were spiked with 6±2CFU of each target microorganism (n=20/organism). Another set (n=20/organism) was inoculated with the target microorganism and 172±18CFU of a non-target organism; Citrobacter freundi, Enterobacter aerogenes, and Listeria innocua for Salmonella spp. analysis, E. coli O157, and L. monocytogenes tests, respectively. Three uninoculated samples/organism were used as a negative control. Each 25g portion was enriched with 225 mL of Buffered Peptone Water for Salmonella and E. coli O157:H7 and with Demi Fraser for Listeria. Enrichments were incubated at 37+1°C for 24h. Detection of Salmonella spp., E. coli O157, Listeria spp., and L. monocytogenes was performed using the LAMP method. Samples were analyzed by two technicians. Repeatability, reproducibility, uncertainty, and limit of detection were determined according to the standard criteria.
Results: Salmonella spp., Listeria spp., and E. coli were detected in inoculated samples with and without a non-target microorganism. Listeria monocytogenes was detected in all inoculated samples; but for those also containing a non-target organism, four true negatives were determined. All uninoculated samples were negative. The alternative method met all the criteria to be considered as suitable for the pathogen recovery and detection in grape tomatoes.
Significance: Use of a LAMP based method for the detection human pathogens on fresh grape tomato provided a rapid and specific approach to monitor the presence of this pathogens and met Mexican standard requirements