Just as it has been used as a biological control agent to selectively eliminate bacterial blooms, Bdellovibrio are now coming into the light as a useful preventative agent against pathogenic microbes and bacteria that cause food spoilage. The issue of food safety is of importance to the food industry, governement regulatory agencies and to all consumers, so this aspect of Bdellovibrio could be quite important. Already, it has been shown to be an effective eliminator of Pseudomonas on crops, such as soybean, and in safe maintenance of food storages (Sherff, 1973). By application of a buffered spray or dip, Bdellovibrio may be applied to manufactered food as an alternative to other, less favorable additives (Jackson and Whiting, 1992).
Fratamico and Whiting (1994) showed that though it varies in its ability to lyse various bacteria, Bdellovibrio can effectively reduce the numbers of Aeromonas spp., E. coli, Pseudomonas spp., Salmonella poona and Shigella spp. Within a time span of 7 hours, and at a temperature of 30�C, reductions of these populations ranged from 0.1 to 7.7 log values. E. coli was most effectively reduced of these, and was optimally eliminated at temperatures of 30-37�C, whereas lowering the temperature to 12-19�C took over 24 hours to achieve the same effect. As Bdellovibrio cannot function well outside neutral pH environments, a pH of 5.6-8.6 was found to be a limiting factor in these tests.
In another study by Jackson and Whiting (1992), activity was found to be extremely diminished below a pH of 6.8. E. coli was found be reduced optimally under the same conditions as above, and with ratios of 2:1, 5:1 and 10:1 of predator to prey. It was found that predation was most effective down to levels of 10ex5 E coli per mL. Generally, though, a high level of predators to hosts is required for efficient control measures. This may be due to the locating of prey by the predator, as they are found merely by chance collision. Bdellovibrio use a lot of energy up while looking for a host, and if a suitable one is not found, when energy stores are diminished they expire. Fratamico and Whiting (1994) also found that the contact rate could be increased by mixing, allowing the predators to come in contact with the prey much more quickly (in a time span of less than 5 minutes).
Though more testing needs to be done before this can become a reality, it appears that Bdellovibrio could make suitable method of preventing food spoilage. As it is operates at near neutral pHs, it is ideally suited for most foods. Also, it is mesophillic which means it will best be applicable towards food stored at room temperature, or as a safety measure for foods exposed to higher temperatures than normal storage. In order to account for the limited range of each strain, multiple strains of Bdellovibrio could be applied with overlapping ranges to account for all susceptable bacteria. Each food product, however, would require a unique combination of strains and need to be determined on an individual basis. |
