Description of a "phoenix" phenomenon in the growth of Campylobacter jejuni at temperatures close to the minimum for growth.

When Campylobacter jejuni cultures that had been grown in broth at 39 degrees C were subcultured into fresh medium at 30 degrees C, there was a transient period of growth followed by a decline in viable-cell numbers before growth resumed once more. We propose that this complex behavior is the net effect of the growth of inoculum cells followed by a loss of viability due to oxidative stress and the subsequent emergence of a spontaneously arising mutant population that takes over the culture.

Measurements and predictions of growth for Listeria monocytogenes and Salmonella during fluctuating temperature II. Rapidly changing temperatures.

Growth of Listeria monocytogenes and Salmonella was examined during various rates of increase and decrease in temperature from and to the minimum for growth. Growth was little affected by even the most rapid changes and injury or lag was not observed. Subsequent investigations of growth during periods of rapid variation in temperature from and to temperatures below the growth minimum again had little effect and growth was satisfactorily predicted using the dynamic model of Baranyi and Roberts [Int. J. Food Microbiol. 23 (1994) 277] in conjunction with the data of Food Micromodel.

Resuscitation of 'non-culturable' cells from aged cultures of Campylobacter jejuni.

When stationary phase batch cultures of Campylobacter jejuni were stored in sealed flasks under static conditions, viable numbers declined from 2 x 10(9) c.f.u. ml-1 to around 10(3)-10(6) c.f.u. ml-1 within 4-6 weeks. When the aged cultures were sparged with a microaerobic gas mixture, there was a rapid increase in viable numbers accompanied by a change from predominantly coccoid to vibrioid morphology. The most probable number (MPN) technique was used to distinguish resuscitation of injured or dormant cells from multiplication of residual viable cells. MPN estimates using fresh Brucella broth containing 0.2% mucin revealed that plate counts underestimated the true viable count by up to 23-fold. The experiments clearly demonstrated that a proportion of surviving cells in aged cultures were in an injured or latent state that prevented growth on agar plates. It is possible that the size of this fraction is greater than was demonstrated and that much higher recoveries would be obtained under other recovery conditions. Nevertheless, from presently available evidence, it must be concluded that the size of the latent fraction is quite small and that most of the increase in count that occurs on regassing a spent culture comes from multiplication of residual viable cells.

Comparison of the fluorescent redox dye 5-cyano-2,3-ditolyltetrazolium chloride with p-iodonitrotetrazolium violet to detect metabolic activity in heat-stressed Listeria monocytogenes cells.

The fluorogenic redox indicator 5-cyano-2,3-ditolyltetrazolium chloride (CTC) was compared with the chromogenic p-iodonitrotetrazolium violet (INT) and conventional methods to assess cellular viability. Mild heat treatment was used as well-controlled method for producing non-viable and sub-lethally injured cells. CTC gave an underestimation of the viability of Listeria monocytogenes cells when compared with classical plating methods whereas INT gave an overestimation. However, CTC proved to be a sensitive indicator of uninjured cells. The difference between the total count and the CTC count was equivalent to the injured cell population. The fluorescent formazan formed on reduction of CTC was readily detected with a charge coupled device and cells enumerated automatically using image analysis.