Cantaloupe facilitates Salmonella Typhimurium survival within and transmission among adult house flies (Musca domestica L.)

Authors: THOMSON, JESSICA - Kansas State University; CERNICCHIARO, NATALIA - Kansas State University; ZUREK, LUDEK - Mendel University; Nayduch, Dana

Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/2020
Publication Date: 1/11/2021
Citation: Thomson, J.L., Cernicchiaro, N., Zurek, L., Nayduch, D. 2021. Cantaloupe facilitates Salmonella Typhimurium survival within and transmission among adult house flies (Musca domestica L.). Foodborne Pathogens and Disease. 18(1):49-55. https://doi.org/10.1089/fpd.2020.2818.
DOI: https://doi.org/10.1089/fpd.2020.2818

Interpretive Summary: Salmonella enterica ser. Typhimurium (S. Typhimurium) is a pathogen harbored by livestock and shed in their feces, which serves as an acquisition source for adult house flies. This study assessed S. Typhimurium acquisition by and survival within house flies, and transmission from and between flies in the presence or absence of cantaloupe. Female house flies were exposed to manure inoculated with either sterile saline or S. Typhimurium for 12 h, then were used in 4 experiments that each were performed over 24 h. Experiment 1 assessed the survival of GFP S. Typhimurium within flies that acquired bacteria from inoculated manure. Experiment 2 determined the transmission of S. Typhimurium from infected flies to cantaloupe. Experiment 3 assessed whether flies could acquire S. Typhimurium from inoculated cantaloupe. Experiment 4 evaluated the transmission of S. Typhimurium between infected and uninfected flies in the presence and absence of cantaloupe. Bacterial culture was used to enumerate S. Typhimurium from flies and cantaloupe at 0, 6, 12, and 24 h and 6, 12, and 24 h, respectively in the experiments. Flies acquired S. Typhimurium from inoculated manure, but bacterial abundance decreased between 0 and 6 h without cantaloupe present and between 0 and 6 h and 6 and 24 h with cantaloupe present. Flies acquired S. Typhimurium from inoculated cantaloupe and bacterial abundance increased in cantaloupe and flies from 6 to 24 h. S. Typhimurium transmission between flies was facilitated when cantaloupe was present, indicating that the presence of a shared food source helped with transferring bacteria between flies. Understanding the dynamics of bacterial acquisition and transmission of bacteria between flies and food helps in assessing the risk flies pose to food safety and human health.

Technical Abstract: Salmonella enterica ser. Typhimurium (S. Typhimurium) is a pathogen harbored by livestock and shed in their feces, which serves as an acquisition source for adult house flies. This study used a green fluorescent protein (GFP) expressing strain of S. Typhimurium to assess its acquisition by and survival within house flies, and transmission from and between flies in the presence or absence of cantaloupe. Female house flies were exposed to manure inoculated with either sterile PBS or GFP-S. Typhimurium for 12 h, then used in 4 experiments each performed over 24 h. Experiment 1 assessed the survival of GFP-S. Typhimurium within inoculated flies. Experiment 2 determined transmission of GFP-S. Typhimurium from inoculated flies to cantaloupe. Experiment 3 assessed fly acquisition of GFP-S. Typhimurium from inoculated cantaloupe. Experiment 4 evaluated transmission of GFP-S. Typhimurium between inoculated flies and uninoculated flies in the presence and absence of cantaloupe. GFP-S. Typhimurium survived in inoculated flies but bacterial abundance decreased between 0 and 6 h without cantaloupe present and between 0 and 6 h and 6 and 24 h with cantaloupe present. Uninoculated flies acquired GFP-S. Typhimurium from inoculated cantaloupe and bacterial abundance increased in cantaloupe and flies from 6 to 24 h. More uninoculated flies exposed to inoculated flies acquired GFP-S. Typhimurium when cantaloupe was present than when absent. We infer that the presence of a shared food source facilitated the transfer of GFP-S. Typhimurium from inoculated to uninoculated flies. Our study demonstrated that house flies acquired, harbored and excreted viable GFP-S. Typhimurium and transferred bacteria to food and each other. Understanding the dynamics of bacterial acquisition and transmission of bacteria between flies and food helps in assessing the risk flies pose to food safety and human health.