Evaluation of a Bead-Based Salmonella Molecular Serotyping Method for Salmonella Isolated from Food and Environmental Samples

M M Moore; M J Nucci; S M Madson; G S Wagley; C E Keys; E W Brown; J R McQUISTON; P I Fields

doi:10.4315/0362-028X.JFP-18-600

Evaluation of a Bead-Based Salmonella Molecular Serotyping Method for Salmonella Isolated from Food and Environmental Samples

J Food Prot. 2019 Nov;82(11):1973-1987. doi: 10.4315/0362-028X.JFP-18-600.

Authors

M M Moore¹, M J Nucci², S M Madson³, G S Wagley⁴, C E Keys⁵, E W Brown⁵, J R McQUISTON⁶, P I Fields⁶

Affiliations

¹ U.S. Food and Drug Administration, Office of Regulatory Affairs, Pacific Northwest Laboratory, Applied Technology Center, Bothell, Washington 98021.
² U.S. Food and Drug Administration, Office of Regulatory Affairs, Denver Laboratory, Lakewood, Colorado 80225.
³ U.S. Food and Drug Administration, Office of Regulatory Affairs, Arkansas Laboratory, Jefferson, Arkansas 72079.
⁴ U.S. Food and Drug Administration, Office of Regulatory Affairs, Southeast Food and Feed Laboratory, Atlanta, Georgia 30309.
⁵ U.S. Food and Drug Administration, Center for Food Safety and Applied Nutrition, Office of Regulatory Science, College Park, Maryland 20740.
⁶ Centers for Disease Control and Prevention, Division of Foodborne, Waterborne and Environmental Diseases, Enteric Diseases Laboratory Branch, Atlanta, Georgia 30333, USA.

PMID: 31644335
DOI: 10.4315/0362-028X.JFP-18-600

Abstract

Salmonella is a leading cause of foodborne illness worldwide, and foods containing Salmonella (except raw meat and poultry products) are considered adulterated. Serotyping of Salmonella is an essential part of surveillance and investigation of outbreaks. This study evaluated a bead-based Salmonella molecular serotyping (SMS) method, which included the O-group 1, H-antigen, alternate target, and O-group 2 assays, compared with traditional serotyping. Salmonella was isolated from food, pet food, and environmental samples or were reference strains. A total of 572 isolates were analyzed by using two formats of the SMS method in comparison with traditional methods: 485 were analyzed by using Radix SMS (a custom user-mixed format), 218 were analyzed by using Luminex SMS (a commercial kit format), and 131 of the total isolates were analyzed by both formats for comparison. The SMS method was evaluated on the basis of the successful identification of antigens by the probes included in the method. The method identified 550 (96.2%) isolates as expected, 6 (1.0%) isolates were not identified as initially expected but were shown to be correctly identified by SMS after reanalysis by traditional serotyping, and 16 (2.8%) isolates not identified as expected possessed an antigen that should have been detected by the method but was not. Among the isolates considered correctly identified, 255 (44.6%) were identified to a single serovar, 44 (7.7%) required additional biochemical testing to differentiate variants or subspecies, and 251 (43.9%) were partially serotyped because probes for some antigens were not in the assay or had allelic variation for known serovars. Whole genome sequencing, SeqSero, and the Salmonella In Silico Typing Resource gave added confirmation for three isolates. Addition of the O-group 2 assay enabled the identification of 55 (9.6%) of 572 isolates. The SMS method could fully or partially serotype most isolates within a day. The SMS method should be a valuable tool when faster screening methods are needed, such as outbreaks and screening large numbers of environmental isolates.

Keywords: Molecular serotyping; Salmonella; Salmonella In Silico Typing Resource; SeqSero; Whole genome sequencing.

MeSH terms

Environmental Microbiology
Environmental Monitoring* / methods
Food Microbiology / methods*
Salmonella* / genetics
Salmonella* / isolation & purification
Serogroup
Serotyping