Medium-chain fatty acids and plant-derived antimicrobials to prevent Campylobacter colonization in broiler chickens

Campylobacter jejuni is the most common cause of bacterial-mediated diarrhoeal disease worldwide. Because poultry products are a major source of C. jejuni infections in humans, efforts should be taken to develop strategies to decrease Campylobacter colonization of poultry during primary production. Organic acids and plant-derived antimicrobial compounds possess marked bactericidal activity toward C. jejuni in vitro and might therefore have potential as feed additives to control C. jejuni colonization in broiler chickens. In vitro screening of several plant-derived compounds revealed strong anti-Campylobacter activity for trans-cinnamaldehyde in particular, while medium-chain fatty acids (caproic, caprylic and especially capric acid) were shown to be the most potent organic acids. However, supplementing these promising additives to the feed of broiler chickens before (prophylaxis) or after (therapeutic) oral inoculation with C. jejuni, did not result in a reduction of the cecal Campylobacter load in these animals. In a cecal loop experiment, neither sodium caprate nor trans-cinnamaldehyde were capable of killing or inhibiting growth of C. jejuni, despite direct injection into the ceca at concentrations of several times their respective minimal inhibitory concentration. When incubated in chicken intestinal mucus, C. jejuni was less susceptible to the antimicrobial effect of capric acid, indicating a protective role for the intestinal mucus layer. Thus, despite the marked bactericidal effect of organic acids and trans-cinnamaldehyde in vitro, neither supplementing these compounds to the feed, nor direct injection in the ceca was able to reduce cecal Campylobacter colonization in broiler chickens. Probably, the mucus layer forms a protective niche rendering the bacterium unresponsive to the bactericidal effects of these compounds observed in vitro, making their potential use as feed additives for controlling Campylobacter in poultry doubtful