KENBIKYO Vol.48▶No.1 2013
â– Lectures

Biofilm Formation and VNC (viable but nonculturable) State of Vibrio cholerae

Yoshimitsu Mizunoe

Abstract: In natural environments, bacteria are exposed to various stress conditions, such as starvation or low temperature. To survive under harmful conditions, non-spore-forming gram-negative bacteria are known to undergo an active adaptation program. Vibrio cholerae is the causative agent of cholera and can shift to a rugose colony morphology from its normal translucent smooth colony morphology in response to environmental stress. The rugose strains produce an amorphous exopolysaccharide (EPS) and promote biofilm formation. The rugose strains also exhibit resistance to oxidative and osmotic stress.
V. cholerae can enter the VNC (viable but nonculturable) state after exposure to adverse environmental conditions. A cell considered to be in a VNC state if it is metabolically active while being incapable of undergoing the sustained cellular division required to form a colony on media that are regularly used in standard or recommended procedures for bacterial enumeration. VNC state of V. cholerae cells can be resuscitated when inoculated onto an agar medium amended with catalase or nonenzyme peroxide-degrading compound such as sodium pyruvate.
Phase variation of colony morphology, subsequent biofilm formation and the entering into VNC state might be the starvation-survival response of V. cholerae.

Key words: Vibrio cholerae, Biofilm, phase variation, rugose colony, VNC