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.