In Situ Evidence of the VBNC Response

This review has so far described laboratory findings regarding the VBNC state. One can validly question whether this response actually occurs in natural environments. We have conducted studies employing membrane diffusion chambers which clearly demonstrated the entry of V vulnificus into the VBNC state when the estuarine waters into which they were submerged were cold.16 Similarly, when cells in the VBNC state were placed into chambers which were suspended into warm (summer) estuarine waters, resuscitation from the VBNC state occurred rapidly and to levels approximating those of the original population (Fig. 1.6). Thus, it is likely that our inability to isolate V. vulnificus during the winter months may be accounted for by entrance into the VBNC state, and that recovery from this state in natural environments may result from a temperature upshift. Taking these observations to their logical conclusions, it seems quite likely that the VBNC response may be a significant source of the variations seen in natural populations as they undergo various environmentally-induced stresses, and for inability to culture many of the microorganisms observed in natural environments. Indeed, Wilson and Lindow17 examined the culturability of P. syringae inoculated onto leaf surfaces, and found that up to 75% of the cells became nonculturable after 80 hours.

Fig. 1.6. Entry into (Fig. 1.6A) and resuscitation from (Fig. 1.6B) the VBNC state by V vulnificus placed into membrane diffusion chambers in estuarine waters of the coast of North Carolina. A. Cells were placed into water at a temperature of 10-15°C. Shown are plate counts (O), total direct counts (•), and direct viability assays (□). B. Plate counts of both the encapsulated (•) and non-encapsulated (O) forms of V. vulnificus induced into the VBNC state in the laboratory at 5°C. Four days after entry into the VBNC state (day 11), resuscitation of the cells is seen when placed into estuarine waters at a temperature of 16-19°C. Reprinted with permission from: Oliver JD, Hite MF, McDougald D et al. Appl Environ Microbiol 1995; 61:2624-2630.

Fig. 1.6. Entry into (Fig. 1.6A) and resuscitation from (Fig. 1.6B) the VBNC state by V vulnificus placed into membrane diffusion chambers in estuarine waters of the coast of North Carolina. A. Cells were placed into water at a temperature of 10-15°C. Shown are plate counts (O), total direct counts (•), and direct viability assays (□). B. Plate counts of both the encapsulated (•) and non-encapsulated (O) forms of V. vulnificus induced into the VBNC state in the laboratory at 5°C. Four days after entry into the VBNC state (day 11), resuscitation of the cells is seen when placed into estuarine waters at a temperature of 16-19°C. Reprinted with permission from: Oliver JD, Hite MF, McDougald D et al. Appl Environ Microbiol 1995; 61:2624-2630.

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