Effects of thymol and diphenyliodonium chloride against Campylobacter spp. during pure and mixed culture in vitro

Authors: Anderson, Robin; Krueger, Nathan; Byrd Ii, James - Allen; Harvey, Roger; Callaway, Todd; Edrington, Thomas; Nisbet, David

Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2009
Publication Date: 9/11/2009
Citation: Anderson, R.C., Krueger, N.A., Byrd II, J.A., Harvey, R.B., Callaway, T.R., Edrington, T.S., Nisbet, D.J. 2009. Effects of thymol and diphenyliodonium chloride against Campylobacter spp. during pure and mixed culture in vitro. Journal of Applied Microbiology. 107:1258-1268.

Interpretive Summary: Campylobacter is an important foodborne bacterium that causes nearly two million illnesses in the U.S. each year. Campylobacter readily colonize the gut of food-producing animals and strategies are sought to reduce their carriage, and thus, the risk of food contamination that may occur during processing. Unlike most other beneficial gut bacteria, Campylobacter obtain energy for growth by metabolizing amino acids rather than sugars. We therefore conducted a study to see if we could inhibit the ability of Campylobacter to grow and survive by inhibiting its ability to metabolize amino acids. We found that growth rates and cell viability of Campylobacter were dramtaically reduced when these bacteria were treated with either of two known chemical inhibitors of amino acid metabolism, named diphenyliodonium chloride and thymol. Furthermore, we found these inhibitors also dramatically reduced the amounts of degradation endproduct, ammonia, produced by the Campylobacter, thus confirming our hypothesis that the inhibitors had interupted amino acid breakdown. These results demonstrate that diphenyliodonium chloride and thymol reduced the growth, survivability, and ammonia production by Campylobacter, thereby, revealing a physiological characteristic that may potentially be exploited to develop interventions. Ultimately, these results may help scientists develop new methods to reduce the carriage of Campylobacter in food animals thus helping farmers and ranchers produce more safe and wholesome meat products for the American consumer.

Technical Abstract: Campylobacter spp. are a leading cause of bacterial associated human foodborne illness in the United States, causing greater than 1.9 million illnesses at a cost of more than $1.2 billion annually. The aim of this study was to determine if the purported deaminase inhibitors diphenyliodonium chloride (DIC) and thymol reduced the growth and survivability of Campylobacter. We found that mean specific growth rates of C. jejuni and C. coli were reduced from those of unsupplemented controls during culture in Muellar Hinton broth supplemented with 0.25 mM DIC or thymol but not with 0.01 mM monensin or 1% ethanol. Recovery of C. jejuni and C. coli were reduced greater than 3 log10 CFU from those of controls after 24 h pure or mixed culture, with porcine fecal microbes, in Bolton broth supplemented with 0.25 or 1.0 mM DIC or with 1.0 mM thymol. Treatments with 0.25 mM thymol, 0.01 mM monensin, and 1% ethanol were less effective. Ammonia production during culture or during incubation of crude extracts of C. jejuni and C. coli was reduced by 0.25 or 1.0 mM DIC or by 1.0 mM thymol and intermitantly reduced, if at all, by 0.25 mM thymol and 0.01 mM monensin but not 1% ethanol. These results demonstrate that DIC and thymol reduced the growth, survivability, as well as ammonia production by C. jejuni and C. coli, thereby revealing a physiological characteristic that may potentially be exploited to develop interventions.