Growth inhibition by glucose oxidase system of enterotoxic Escherichia coli and Salmonella derby: in vitro studies

The antibacterial effect of different glucose oxidase (GOX)/glucose combina tions was studied on two food-poisoning organisms, enterotoxic Escherichia coli PM 015 and Salmonella derby BP 177. Growth of E. coli in nutrient brot h (NB) was clearly inhibited by 4.0 mg/ml glucose after 24 h when combined with 2.0 U/ml GOX and after 48 h when combined with 0.5 or 1.0 U/ml GOX. Sa lmonella derby was more resistant than E. coli, but showed clear growth inh ibition only after 48 h when inoculated in tubes where 2 mg glucose/ml and 2 U GOX/ml (or 4 mg glucose/ml and 1 U GOX/ml) were combined. In order to u nderstand if the enzyme effect on microbial growth can be attributed to hyd rogen peroxide or to pH decrease as a result of the production of gluconic acid, catalase (CAT) was added to GOX/glucose system. Since CAT decomposes H2O2 to H2O and O-2, the antibacterial effect was ascribed to a pH decrease as a result of gluconic acid in the system.