Antimicrobial Resistance of Salmonella spp. Isolates and Heavy Metal Traces from Rodent Meat Purchased from Roadside Markets, Central Thailand.

Although game meat consumption is widespread across the globe, involving a great diversity of species in very different ecological and sociocultural environments, the safety of wild meat products is rarely assessed routinely. We conducted a survey to evaluate the safety of two rodents products (Rattus tanezumi and Bandicota indica) purchased from roadside markets in central Thailand. Total aerobic bacteria and Escherichia coli counts measured were above Thai poultry product standards for 83.3% and 100% of the samples, respectively (n = 108), although there was no difference between rat species (analysis of variance [ANOVA], p > 0.05). Salmonella spp. were isolated from 32% of the swabs collected (67/208), including 19 different serovars. All strains were resistant or partially resistant to at least 2 of the 16 antibiotics tested, with levels of resistance varying greatly among antibiotics (e.g., 97% of strains sensitive to ciprofloxacin and 98.5% of strains resistant to cloxacillin). Detectable traces of Cd and Pb were found in 98% and 46% of the samples analyzed, respectively (n = 61). Pb and Cd concentrations measured in the kidneys of R. tanezumi were significantly higher than in the liver and muscles and significantly higher than B. indica muscles and kidneys but not liver (ANOVA, p < 0.05). These results highlight potential health hazards that may be associated with rodent-meat consumption, including contamination by coliform bacteria, multiresistant Salmonella spp. strains, and heavy metals. The significance of these results for public health cannot be determined precisely in the absence of appropriate standards, and information gaps remain regarding the frequency of rodent-meat consumption and the origin of bacterial and heavy metal contaminations (i.e., capture environment or during carcass handling and processing). We suggest that appropriate information and training on best hygienic practices for preparing, cooking, and preserving rodent meat should be provided to the producers and to the consumers.

Development of a lateral flow dipstick test for the detection of 4 strains of Salmonella spp. in animal products and animal production environmental samples based on loop-mediated isothermal amplification.

OBJECTIVE: This study aimed to develop loop-mediated isothermal amplification (LAMP) combined with lateral flow dipstick (LFD) and compare it with LAMP-AGE, polymerase chain reaction (PCR), and standard Salmonella culture as reference methods for detecting Salmonella contamination in animal products and animal production environmental samples. METHODS: The SalInvA01 primer, derived from the InvA gene and designed as a new probe for LFD detection, was used in developing this study. Adjusting for optimal conditions by temperature, time, and reagent concentration includes evaluating the specificity and limit of detection. The sampling of 120 animal product samples and 350 animal production environmental samples was determined by LAMP-LFD, comparing LAMP-AGE, PCR, and the culture method. RESULTS: Salmonella was amplified using optimal conditions for the LAMP reaction and a DNA probe for LFD at 63°C for 60 minutes. The specificity test revealed no cross-reactivity with other microorganisms. The limit of detection of LAMP-LFD in pure culture was 3×102 CFU/mL (6 CFU/reaction) and 9.01 pg/µL in genomic DNA. The limit of detection of the LAMP-LFD using artificially inoculated in minced chicken samples with 5 hours of pre-enrichment was 3.4×104 CFU/mL (680 CFU/reaction). For 120 animal product samples, Salmonella was detected by the culture method, LAMP-LFD, LAMP-AGE, and PCR in 10/120 (8.3%). In three hundred fifty animal production environmental samples, Salmonella was detected in 91/350 (26%) by the culture method, equivalent to the detection rates of LAMP-LFD and LAMP-AGE, while PCR achieved 86/350 (24.6%). When comparing sensitivity, specificity, positive predictive value, and accuracy, LAMP-LFD showed the best results at 100%, 95.7%, 86.3%, and 96.6%, respectively. For Kappa index of LAMP-LFD, indicated nearly perfect agreement with culture method. CONCLUSION: The LAMP-LFD Salmonella detection, which used InvA gene, was highly specific, sensitive, and convenient for identifying Salmonella. Furthermore, this method could be used for Salmonella monitoring and primary screening in animal products and animal production environmental samples.

Development of loop-mediated isothermal amplification-lateral flow dipstick as a rapid screening test for detecting Listeria monocytogenes in frozen food products using a specific region on the ferrous iron transport protein B gene.

Background and Aim: Listeria monocytogenes is a critical foodborne pathogen that infects pregnant females and their newborns and older adults and individuals with comorbidities. It contaminates fresh vegetables, fruits, ready-to-eat foods, and frozen food products consumed by individuals. The culture conventional detection methods for L. monocytogenes are time-consuming, taking 4 days. This study aimed to describe the development and comparison of loop-mediated isothermal amplification (LAMP)- lateral flow dipstick (LFD), LAMP assay to PCR, and conventional culture for detecting L. monocytogenes in frozen food products. Materials and Methods: Five LAMP primer sets, including F3, B3, forward inner primer, and backward inner primer, were designed from a specific region on ferrous iron transport protein B gene (feoB gene) to amplify LAMP products. The DNA probe was created, and the detection limit was determined in pure culture and purified DNA, as well as the detection in 20 frozen food product samples. Results: The LMfeoB4 LAMP primer sets and DNA probe were LAMP products amplified at 60°C for 50 min. The specificity of the assay revealed no cross-reactivity with other pathogenic bacteria. The limit of detection (LOD) of the LAMP-LFD and LAMP assays using purified genomic DNA was 219 fg/µL both in LAMP and LAMP-LFD assays. The LOD of LAMP and LAMP-LFD assays in pure culture was 4.3×102 colony-forming unit (CFU)/mL and 43 CFU/mL, respectively. The LOD of the LAMP-LFD assay using artificially inoculated chicken in frozen food samples with pre-enrichment was 3.2×102 CFU/mL. The LAMP-LFD was also more sensitive than the LAMP assay and polymerase chain reaction. Finally, LAMP-LFD revealed no false positives in any of the 20 frozen food product samples. Conclusion: LAMP-LFD assay using a specific region on the feoB gene to detect L. monocytogenes was highly specific, sensitive, faster, and convenient, making it a valuable tool for the monitoring and rapid screening of L. monocytogenes in frozen food products. This technique is applicable to the development of detection technologies for other pathogens in food products.