Use of an autobioluminescent Campylobacter jejuni to monitor cell survival as a function of temperature, pH, and sodium chloride

The effects of storage temperature (4, 22, and 30 degrees C), pH (4.0 to 8.5), and sodium chloride concentration (0.25 to 7.5%, wt/vol) on the survival of a strain of Campylobacter jejuni ATCC 35921 with an autobioluminescent phenotype (generated from the fusion of luxCDABE genes from Xenorhabdus luminescens to the C. jejuni flaA promoter) in Mueller-Hinton broth under aerobic conditions were determined. At comparable pHs, autobioluminescent C. jejuni cells die most rapidly at 30 degrees C and most slowly at 4 degrees C. For example, at pH 5.5, a 1.2-log decrease in the cell count was observed after 4 days of storage at 4 degrees C, while 3.7- and 4.8-log reductions in cell numbers were observed after 4 days of storage at 22 and 30 degrees C, respectively. At 4 degrees C, C. jejuni was sensitive to NaCl concentrations of > or = 2.5%. However, the degree of inactivation at this storage temperature was also significantly lower than that observed at 22 degrees C, which, in turn, was substantially lower than that observed at 30 degrees C. In the presence of different NaCl concentrations at 22 and 30 degrees C, a strong correlation (r = 0.98) between plate count and bioluminescence output was obtained. However, at low pHs (4.0 and 4.5) and/or a low storage temperature (4 degrees C), bioluminescence did not correlate well with plate count. Despite these limitations, an autobioluminescent phenotype of C. jejuni proved to be a useful tool for studying the behavior of C. jejuni exposed to environmental stresses.