Fig. 2.

Role of CVEC and diverse environmental and host factors in cholera outbreaks. Diagrammatic representation of the formation and resuscitation of CVEC, and their involvement with environmental and host factors in the occurrence of periodic cholera outbreaks. Stools of cholera patients contain V. cholerae as a heterogenous mixture of active planktonic cells, and biofilm-like clumped cells. Upon introduction of cholera stools into environmental water which vastly dilutes extracellular autoinduecrs (AIs), a temporary loss of quorum sensing occurs. As a result, quorum-mediated regulatory responses that would normally disperse biofilm-associated cells are blocked and the cells exist embedded in thick exopolysaccharides in a dormant form referred to as CVEC. Presumably, the CVEC form of V. cholerae survives phage predation, and persists in water during the inter-epidemic time. The CVEC can provide a large dose of the pathogen when ingested by a potential victim, and may be resuscitated in the intestine in response to AIs produced by the gastrointestinal microbiota. On the other hand, CVEC may be resuscitated in the environment when climatic factors lead to multiplication of diverse environmental bacteria many of which produce AIs. The resulting planktonic cells seed the environment for rapid spread and amplification of the strain, together with selective enrichment of the pathogen in the human gastrointestinal environment. The gradual build up of the pathogenic clone in the environmental water and consumption of contaminated food or drinks may causes an index case of cholera and may eventually initiate an epidemic