Microbial composition affects the performance of an artificial Tephritid larval diet.

The present study investigated the patterns of microorganisms in an artificial larval diet during Dacus ciliatus (Diptera; Tephritidae) larval development. Microbial population contents in the diet of total heterotrophic bacteria, yeast and molds, coliform and lactobacilli, and their dynamics during development, were monitored. Initially, the microbial composition in diet trays failing to produce viable pupae and in trays successfully producing pupae and adult flies was characterized. The failing diet trays contained large populations of lactobacilli that increased during larval development, and low populations of coliforms. In contrast, the successful diet showed an increasing population of coliforms and a low, or undetected, population of lactobacilli. To study the hypothesis that lactobacilli affect D. ciliatus larval development, we conducted controlled inoculation experiments in which Lactobacillus plantarum was added into fresh diet at the time of egg seeding. L. plantarum inoculated trays showed no production of D. ciliatus. Control trays without lactobacilli inoculation showed variable results. One tray successfully produced viable pupae and adults, and showed a slight and slow increase in the indigenous populations of lactobacilli. The second tray, however, failed to produce pupae and showed a fast increase of the indigenous lactobacilli to very high levels. Monitored pH trends in L. plantarum-inoculated diet showed a sharp pH decrease during the first 4 days of larval development from 5 to less than 4 units, while successful diet, producing viable D. ciliatus pupae and adults, showed a moderate pH drop during most of the larval development period. The paper discusses the possible ecological interactions between D. ciliatus larvae, the microbial content of the diet and the physical properties of the diet. The discussion also points out at the usefulness of this approach in understanding and managing mass production parameters of tephritid fruit flies industrial diets used for Sterile Insect Technique.

Identification of Salmonella enterica genes with a role in persistence on lettuce leaves during cold storage by recombinase-based in vivo expression technology.

Recurrent outbreaks of enteric illness linked to lettuce and a lack of efficacious strategies to decontaminate produce underscores the need for a better understanding of the molecular interactions of foodborne pathogens with plants. This study aimed at identifying Salmonella enterica genes involved in the persistence of this organism on post-harvest lettuce during cold storage using recombinase-based in vivo expression technology (RIVET). In total, 37 potentially induced loci were identified in four distinct screenings. Knockout mutations in eight upregulated genes revealed that four of them have a role in persistence of the pathogen in this system. These genes included stfC, bcsA, misL, and yidR, encoding a fimbrial outer membrane usher, a cellulose synthase catalytic subunit, an adhesin of the autotransporter family expressed from the Salmonella pathogenicity island-3, and a putative ATP/GTP-binding protein, respectively. bcsA, misL, and yidR but not stfC mutants were impaired also in attachment and biofilm formation, suggesting that these functions are required for survival of S. enterica on post-harvest lettuce. This is the first report that MisL, which has a role in Salmonella binding to fibronectin in animal hosts, is involved also in adhesion to plant tissue. Hence, our study uncovered a new plant attachment factor in Salmonella and demonstrates that RIVET is an effective approach for investigating human pathogen-plant interactions in a post-harvest leafy vegetable.

Inhibition of Escherichia coli in cultivated cattle manure.

A common practice on Israeli dairy barns comprises daily cultivation of the manure. Cultivation is a mechanical process used to break up and till the manure bedding and it results in a drier and aerated bedding and cleaner cows, which consequently reduces the incidence of mastitis. Cultivation was associated with a shorter survival of Escherichia coli in cultivated manure as compared with noncultivated manure. The objective of the current study was to elucidate the mechanism responsible for the shorter survival duration of E. coli in the cultivated manure. We hypothesized that microorganisms that are antagonistic to E. coli, developing in the cultivated manure, are responsible for this phenomenon. A cow manure derived E. coli strain expressing the green fluorescence protein and antibiotic resistance markers was used to inoculate cow manure in 1.5-L jars. Manure treatments included cultivated and noncultivated manure. Half the jars of each cultivation treatment were autoclave sterilized at 121°C for 1 h on 3 successive days to eliminate from the manure antagonistic microorganisms. Each cultivation-sterilization treatment was performed in triplicate jars. Following sterilization, E. coli numbers in the cultivated and noncultivated manure were comparable, while in the nonsterilized manure the numbers were lower in the cultivated compared with the noncultivated manure. Several fungi isolated from the cultivated manure samples displayed inhibition effect on the tagged E. coli. Antagonistic fungi were also isolated from large-scale cultivated manure samples collected on several dairy farms in Israel. These findings support the notion that manure cultivation might facilitate the development of microorganisms that are antagonistic to E. coli, thus contributing to the general hygiene of the cattle. Identifying the mechanisms by which the antagonistic fungi affect the survival of E. coli in manure could be exploited for improvement of the animal health and for limiting the transmission of zoonotic pathogens to food and water.