Evidence of non-coccoid viable but non-culturable Campylobacter jejuni cells in microcosm water by direct viable count, CTC-DAPI double staining, and scanning electron microscopy

Production of viable but non-culturable (VNC) Campylobacter jejuni cells was studied using 36 strains resuspended in microcosm wafer. Cells in stationary phase were resuspended at 4 degrees C, with gentle stirring at 100 r min(-1), in filtered surface water adjusted to pH 6.0. The culturability of starved cell suspensions was determined by spread plate counts, and the activity of cells by the direct viable count technique and CTC-DAPI double staining. Although most C. jejuni strains died within a few days of suspension in microcosm water, three strains (Bf, 79 and 85) demonstrated a complete decrease of culturability within 15 days of suspension. A constant activity level was found in these three strains, even after 30 days of starvation in microcosm water; and an almost constant concomitant level of adenosine triphosphate was measured in VNC cell suspensions. Scanning electron microscopy of C. jejuni VNC cells showed that the spiral-shaped cells of strain 85 cultures became coccoid in ageing microcosm-water cell suspensions, whereas most VNC cells of strains Bf and 79 remained spiral-shaped after 30 days of starvation. (C) 1998 Academic Press.