Reduction of an Escherichia coli K12 population by Bdellovibrio bacteriovorus under various in vitro conditions of parasitei host ratio, temperature, or pH

Abstract

Intrinsic and extrinsic parameters of food products, as well as bacterial population, were evaluated for their effects on the ability of Bdellovibrio bacteriovorus, a bacterium parasitic upon gramnegative bacteria, to reduce an Escherichia coli population. High concentrations of both parasite and host were the most effective for reducing a specified E. coli population. B. bacteriovorus was able to reduce the E. coli count by 90% (1 log) in < 1 h at ratios of 5:1, 10:1, and 30:1 (parasite:host). Temperatures between 20 and 30°C were more conducive to bdellovibrio attack than temperatures less than 20°C. E. coli populations were reduced by more than 7-log values after 7 h of incubation at 30°C with parasite:host ratios of 2:1, 5:1, and 10:1. Greater than a 5-log reduction in the E. coli population was observed at the ratio of 30:1. B. bacteriovorus reduced the E. coli population by 1 log in approximately 24 min and 20 min at pH 7.2 and 6.8, respectively. At pH values < 6.8, the activity of B. bacteriovorus was diminished. These results define some of the conditions where the application of B. bacteriovorus may aid in the reduction/elimination of some gram-negative pathogens and spoilage flora that may be present in foods.