Antibacterial Effect of Phenylboronic Acid on Escherichia coli and Its Potential Role as a Decontaminant of Fresh Tomato Fruits.

Research background: Food safety is threatened by the contamination of fresh fruits and vegetables by pathogenic bacteria, among which the particularly widespread ones are coliform bacteria. Due to the continuous increase in the incidence of severe diseases caused by the consumption of fresh (tomato) fruits contaminated with Escherichia coli, antimicrobial postharvest measures are needed. The problem is that many active antimicrobial compounds have a weak and short-lasting effect and/or are not environmentally friendly. Recently, the antibacterial and antifungal activity of environmentally friendly agent phenylboronic acid (PBA), including on two tomato pathogens, has been reported.

Experimental approach: The aim of this study is to determine the antibacterial effect of PBA on E. coli and three enteropathogenic Enterobacterales, and to check its ability to serve as a bacterial decontaminant of fresh tomato fruits.

Results and conclusions: The minimum inhibitory concentration (MIC) of PBA against E. coli, as well as Shigella sonnei, Salmonella enteritidis and Yersinia enterocolitica was 1.0, 1.2, 1.0 and 0.8 mg/mL, respectively. In addition, we have shown that PBA has a bacteriostatic effect on E. coli at lower concentrations and a bactericidal effect at higher (>3.0 mg/mL) concentrations. Importantly, the study found that an E. coli strain resistant to seven commonly used antibiotics, as well as strains producing extended-spectrum beta-lactamases (ESBL), is as sensitive to PBA as the wild-type strain without any resistance, suggesting that the mechanism of action of PBA differs from that of all these antibiotics. Finally, we have shown that washing and incubating contaminated tomato fruits in PBA solution reduces the growth of E. coli washed from fresh tomato fruits in a concentration- (0.5-3.0 mg/mL) and time-dependent manner, while having no adverse effect on the tomato fruits.

Novelty and scientific contribution: This is the first report on the antibacterial effect of PBA on medically important bacteria E. coli, S. enteritidis, S. sonnei and Y. enterocolitica. Moreover, we show that PBA kills multidrug-resistant E. coli, including those producing ESBL, making it a promising agent against such bacteria. Finally, PBA is shown to be an effective decontaminant of E. coli on fresh tomato fruits.