Optimized methods for detecting Salmonella Typhi in the environment using validated field sampling, culture and confirmatory molecular approaches.

AIMS: This study evaluated detection methods for Salmonella Typhi (S. Typhi) in the environment, to establish a novel pathway from field sampling to isolation of viable organisms and molecular confirmation from complex environmental samples, thus enabling environmental surveillance of typhoid. METHODS AND RESULTS: Multiple media were assessed using clinical isolates from the Public Health England's (PHE) Culture collection. The culture pathway selected consisted of a primary 2% bile broth and secondary Selenite F broth, followed by modified Chromogenic Agar for Salmonella Esterase (mCASE). A qPCR assay was adapted from a validated S. Typhi PCR panel for confirmation of isolates, with comparison to biochemical and serological tests showing good specificity. Sampling locations in Blantyre, Malawi were used to compare sampling methods. Viable S. Typhi were isolated from a mixture of trap and grab river water samples on six occasions. CONCLUSIONS: Culture of viable S. Typhi from environmental samples was possible using effective capture and culture techniques. SIGNIFICANCE AND IMPACT OF STUDY: Whilst several studies have attempted to detect S. Typhi from the environment, this is the first successful attempt to isolate the organism from river water since the 1980s. Supplementing clinical data with environmental screening offers the potential for enhanced surveillance, which might inform interventions and assess vaccination programmes.

Validation of the One Broth One Plate for Salmonella Method for Detection of Salmonella Spp. in Select Food and Environmental Samples: AOAC Performance Tested MethodSM 102002.

BACKGROUND: One Broth One Plate for Salmonella (OBOP Salmonella) is a rapid and simple method for detection of Salmonella spp. in food and environmental samples using traditional culture methodology. The method utilizes single-step enrichment followed by plating to a selective/differential, chromogenic agar. OBJECTIVE: The purpose of the validation study was to measure the effectiveness of the OBOP Salmonella method in comparison to reference culture procedures. METHOD: Performance of the OBOP Salmonella method was compared to that of the U.S. Food and Drug Administration Bacteriological Analytical Manual Chapter 5 reference method for queso fresco, smoked salmon, cantaloupe, chocolate, black pepper, chili powder, dry pet food, and sponge samples from a stainless steel surface, or to that of the U.S. Department of Agriculture Microbiology Laboratory Guidebook Chapter 4.10 method for raw ground turkey, chicken carcass rinse, and pasteurized liquid egg. Inclusivity/exclusivity, robustness, and stability/lot-to-lot consistency testing was also performed. RESULTS: In the matrix study, there were no statistically significant differences in performance between the OBOP Salmonella and reference methods, as determined by probability of detection analysis (P < 0.05), for any of the matrixes examined. All 104 Salmonella spp. strains produced positive results in inclusivity testing, and all 33 non-salmonellae exclusivity strains tested negative with the OBOP Salmonella method. CONCLUSIONS: Results of the validation study show that the OBOP Salmonella method is a reliable procedure for detection of Salmonella spp. in select matrixes. The method is simple to perform, requires no specialized equipment, and produces results in as little as 37 h. HIGHLIGHTS: The OBOP Salmonella method was awarded AOAC PTMSM (#102002) for detection of Salmonella in queso fresco, smoked salmon, cantaloupe, chocolate, black pepper, chili powder, dry pet food, sponge samples on a stainless steel surface, raw ground turkey, chicken carcass rinse, and pasteurized liquid egg. The method is also approved by MicroVal® for a broad range of foods under certification number 2019LR88.