Campylobacter jejuni is a pathogenic, microaerophailic, gram-negative, meso
philic bacterium. Three strains isolated from humans with enteric campyloba
cteriosis were able to survive at high population levels (10(7) cells ml(-1
)) as viable-but-nonculturable (VBNC) forms in microcosm water. The VBNC fo
rms of the three C,jejuni strains were enumerated and characterized by usin
g 5-cyano-2,3-ditolyl tetrazolium chloride-4',6-diamino-2-phenylindole stai
ning. Cellular volume, adenylate energy charge, internal pH, intracellular
potassium concentration, and membrane potential values were determined in s
tationary-phase cell suspensions after 48 h of culture on Columbia agar and
after 1 to 30 days of incubation in microcosm water and compared. A notabl
e increase in cell volume was observed with the VBNC state; the average cel
l volumes were 1.73 yl mg of protein(-1) for the culturable form and 10.96
mu l mg of protein-l after 30 days of incubation in microcosm water. Both t
he internal potassium content. and the membrane potential were significantl
y lower in the VBNC state than in the culturable state. Culturable cells we
re able to maintain a difference of 0.6 to 0.9 pH unit between the internal
and external pH values; with VBNC cells this difference decreased progress
ively with time of incubation in microcosm water. Measurements of the cellu
lar adenylate nucleotide concentrations revealed that the, cells had a low
adenylate energy charge (0.66 to 0.26) after 1 day of incubation in microco
sm water, and AMP was the only nucleotide detected in the three strains aft
er 30 days of incubation in microcosm,vater.