The increased bacterial multidrug resistance caused by inappropriate use and overuse of antimicrobials is a global concern. To circumvent this issue, a quest for the development of new active agents has been widely recognized. Some phytochemical products, produced by plants as part of their chemical defense strategies, are regarded as new stimulus to develop novel antimicrobials that are not as vulnerable as current drugs to bacterial resistance mechanisms. In this study, the antimicrobial activity and mode of action of caffeic acid (CAF) and a series of CAF alkyl esters was assessed against Escherichia coli and Staphylococcus aureus, with the aim of analyzing the influence of the alkyl ester side chain length on the activity. Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), changes in physicochemical surface properties and intracellular potassium leakage were used as physiological indices for the antimicrobial mode of action. CAF alkyl esters were found to be effective antimicrobial agents against both bacteria. Their activity was directly dependent on their lipophilicity, which affected bacterial susceptibility, the physicochemical properties of the bacteria and the integrity of the membranes. E. coli was less susceptible than S. aureus to the action of the compounds. Longer alkyl side chains were more effective against the Gram-positive bacterium, while medium length alkyl side chain compounds were more effective against the Gram-negative bacterium. Caffeic acid derivatives are proposed to act as cell permeabilizers, inducing membrane alterations, causing rupture with potassium leakage, particularly on the Gram positive bacterium, and consequent cell death.

Fifty-five (55) samples from five municipalities in the Recôncavo from Bahia region were analyzed between May and July 2015 to evaluate the sanitary quality and the presence of pathogens of crude and processed bovine milk samples. Psichrotrophic, mesophilic and thermophile rates and the count of Escherichia coli, E. coli O157: H7 Staphylococcus aureus and Listeria monocytogenes were done by microbiological methods rapid detection. There was a greater contamination and presence of pathogens in the raw milk when compared to processed milk. However, total coliforms were detected in 14.28%, E. coli in 7.14% and E. coli O157: H7 in 2.04% of processed milk. The enforcement by authorities against the illegal sale of raw milk and the monitoring of steps in milk production up to marketing should be mandatory.

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