Survival of Coliform Bacteria in Virgin Olive Oil

Coliform bacteria consist of both nonpathogen commensal and human opportunistic pathogen species isolated from different habitats like animals, man, vegetables, and water. Olives normally carry natural nonpathogenic epiphytic bacteria, but during growth, harvest, and processing, one of the final products, represented by virgin olive oil, can be contaminated with coliform. Present study showed that coliform bacteria can survive and reproduce in virgin olive oil containing low level of phenolic compounds. The laboratory inoculation trials demonstrated that when the bacterium Escherichia coli, isolated from the olives carposphere, was transferred in olive oil containing high polar phenols content, equal to 372 mg caffeic acid equivalent per kg, the survival was completely inhibited after 15 days of storage. On the contrary, the bacterium reproduced quickly when it was inoculated in virgin olive oil samples containing lower concentration of polar phenols. The SDS-PAGE analysis of the E. coli proteins showed different electrophoretic patterns when the bacterium was inoculated in the virgin olive oil with high phenolic compounds content, confirming the strong interaction between the olive oil phenols content and the bacterial wall proteins. The SEM ultrastructural observations confirmed the presence of a more higher number of damaged microbial cells in virgin olive oil rich of polar phenols. This finding needs further studies since, in an era of antibiotic resistance, the development of new strategies to fight unwanted food bacteria is promising way for the future.