Pathogen reduction by predatory bacteria and survival of Bdellovibrio bacteriovorus and Escherichia coli on produce and buffer treated with low-dose gamma radiation

Abstract

Bdellovibrio bacteriovorus is a predator of Gram-negative bacteria and there is limited research on its utility for decontamination of post-harvest produce. The objective of this research was to determine reduction of E. coli O157:H7 and Salmonella on lettuce and carrot by B. bacteriovorus 109 (Bb109) and evaluate its survival and E. coli in buffer and on lettuce following gamma radiation exposure. Bb109 was cultured on ML35, filtered, and predator cells were suspended in buffer. Produce and buffer were co-inoculated with E. coli and Salmonella, separately; and Bb109 applied. In a separate experiment, Bb109 were inoculated on lettuce and suspended in buffer, then irradiated at 0.25–1.0 kGy treatments. E. coli and Salmonella in buffer were reduced by Bb109 0.4–3.9 and 0.9–2.6 logs, respectively. The predation of E. coli by Bb109 on carrot and lettuce resulted in 0.3–1.8 log reductions, and for Salmonella on the same produce, they were 0.9 and 1.2 logs, respectively. In radiation sensitivity assays, Bb109 populations in buffer and lettuce were inactivated by 3–5 logs (0.5 kGy). Bdellovibrio could aid the mortality of pathogenic bacteria during post-harvest treatment or in hurdle interventions of post-harvest produce. No previous data on Bdellovibrio exposure to radiation is available.