Intracellular pH in Campylobacter jejuni when treated with aqueous chlorine dioxide

The aim of this study was to investigate the response of Campylobacter jejuni at single-cell level when exposed to different concentrations of chlorine dioxide (ClO(2)). The parameter of choice, intracellular pH (pH(i)), was determined by using fluorescence ratio imaging microscopy with a pH-sensitive, ratiometric 5(6)-carboxyfluorescein diacetate succinimidyl ester probe. In addition, the culturability expressed in colony counts was determined. Our results revealed that several subpopulations with different physiological states, as judged by their pH(i), were created by ClO(2) treatment. The greater the concentration of ClO(2), the smaller the subpopulation of healthy cells with pH(i) > 6.8 and the smaller the colony count as determined on nonselective agar plates. ClO(2) at concentrations (60 ppm) induced injuries that resulted in complete loss of culturability and adversely affected the ability to resuscitate under subsequent more favorable conditions. The presence of injured cells in food could present a risk for public health. Additional hurdles have to be included in food preservation to suppress the survival and recovery of injured cells.