Starvation survival and viable but nonculturable states in Aeromonas hydrophila

The behavior of Aeromonas hydrophila stored at 4degreesC and 25degreesC in nutrient-poor filtered sterilized distilled water was investigated. At 4degreesC, the A. hydrophila population declined below the detection level (0.1 cell mL(-1)) after 7 weeks, whereas the number of cells with intact membrane as determined by the LIVE/DEAD(R) method decreased only by 1 log unit, Although, this response is reminiscent of the so-called VBNC state, the cells could not be resuscitated by an upshift to 25degreesC. A mixture of rods with normal size and elongated cells was observed in this state. At 25degreesC, viable cells and cells with intact membrane declined only by 0.8 log unit over the 10-week storage period, and thus A. hydrophila entered the classical starvation survival state. During this state, a mixture of rods and cocci was observed. Prestarvation at 25'C for 24 h and especially 49 days delayed significantly the rate of entry into the VBNC state. However, stationary phase cells were not significantly more tolerant than exponential phase cells. No significant improvements in recovery yield were obtained on LB agar plates amended with catalase or sodium pyruvate. During cold incubation, high variability in responses was observed. Intermittent cryptic regrowth might be responsible for this variability in responses.