Cellular Response of Campylobacter jejuni to Trisodium Phosphate

Abstract

The highly alkaline compound trisodium phosphate (TSP) is used as an intervention to reduce the load of Campylobacter on poultry meat in U.S. poultry slaughter plants. The aim of the present study was to investigate the cellular responses of Campylobacter jejuni NCTC11168 when exposed to sublethal concentrations of TSP. Preexposure of C. jejuni to TSP resulted in a significant increase in heat sensitivity, suggesting that a combined heat and TSP treatment may increase reduction of C. jejuni. A microarray analysis identified a limited number of genes that were differently expressed after sublethal TSP exposure; however, the response was mainly associated with ion transport processes. C. jejuni NCTC11168 nhaA1 (Cj1655c) and nhaA2 (Cj1654c), which encode orthologues to the Escherichia coli NhaA cation/proton antiporter, were able to partially restore TSP, alkaline, and sodium resistance phenotypes to an E. coli cation/proton antiporter mutant. In addition, inhibition of resistance-nodulationcell division (RND) multidrug efflux pumps by the inhibitor Pa␤N (Phe-Arg ␤-naphthylamide dihydrochloride) decreased tolerance to sublethal TSP. Therefore, we propose that NhaA1/NhaA2 cation/proton antiporters and RND multidrug efflux pumps function in tolerance to sublethal TSP exposure in C. jejuni. Chemical decontamination has been used widely for decades in the U.S. poultry slaughter plants to reduce the presence of human pathogens on the meat (22). Currently, the highly alkaline compound trisodium phosphate (TSP) is applied as a dip or spray of prechilled or chilled poultry carcasses (6, 22) and is effective against Campylobacter, Salmonella, and Listeria (6). In the European Union (EU), an ongoing debate questions the safety of chemical decontamination, and more data, such as the development of resistance, cross protection, and virulence, are needed for the risk assessments required by the EU (8).The alkalinity of TSP causes bacterial death through disruption of cell membranes (18, 30), and it acts as a detergent that removes fat from the surface of poultry carcasses that further increases the killing action of TSP (13). Sublethal concentrations of TSP may be encountered by the bacteria when the compound is inadequately distributed on the surface of the carcass or inactivated by excessive amounts of organic material or when leftover TSP residues are present on the carcass during storage (1, 2, 31). A major concern is that exposure to sublethal concentrations of TSP may increase bacterial tolerance to food processing interventions, preservation treatments, and antibacterial conditions within the human hosts.Campylobacter jejuni is one of the most frequently reported causes of bacterial food-borne infections in developed countries (7, 9), leading to self-limiting acute gastroenteritis. The consumption and handling of poultry meat products is the major source of human campylobacteriosis, and the use of TSP during poultry meat processing is known to reduce levels of C. jejuni (4,28,29,37). The aim of the present study was to s...

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