Recent Vibrio Cholerae O1 Epidemic Strains Are Unable To Replicate Ctx Phi Prophage Genome

Cholera, an acute diarrheal disease, is caused by pathogenic strains of Vibrio cholerae generated by the lysogenization of the filamentous cholera toxin phage CTX Phi. Although CTX Phi phage in the classical biotype are usually integrated solitarily or with a truncated copy, those in El Tor biotypes are generally found in tandem and/or with related genetic elements. Due to this structural difference in the CTX Phi prophage array, the prophage in the classical biotype strains does not yield extrachromosomal CTX Phi DNA and does not produce virions, whereas the El Tor bio-type strains can replicate the CTX Phi genome and secrete infectious CTX Phi phage par-ticles. However, information on the CTX Phi prophage array structure of pathogenic V. cholerae is limited. Therefore, we investigated the complete genomic sequences of five clinical V. cholerae isolates obtained in Kolkata (India) during 2007 to 2011. The analysis revealed that recent isolates possessed an altered CTX Phi prophage array of the prototype El Tor strain. These strains were defective in replicating the CTX Phi ge-nome. All recent isolates possessed identical rstA and intergenic sequence 1 (Ig-1) sequences and comparable rstA expression in the prototype El Tor strain, suggesting that the altered CTX Phi array was responsible for the defective replication of the pro-phage. Therefore, CTX Phi structures available in the database and literatures can be classified as replicative and nonreplicative. Furthermore, V. cholerae epidemic strains became capable of producing CTX Phi phage particles since the 1970s. However, V. cholerae epidemic strains again lost the capacity for CTX Phi production around the year 2010, suggesting that a significant change in the dissemination pattern of the current cholera pandemic occurred.IMPORTANCE Cholera is an acute diarrheal disease caused by pathogenic strains of V. cholerae generated by lysogenization of the filamentous cholera toxin phage CTX Phi. The analysis revealed that recent isolates possessed altered CTX Phi prophage array of prototype El Tor strain and were defective in replicating the CTX Phi genome. Classification of CTX Phi structures in isolated years suggested that V. cholerae epi-demic strains became capable of producing CTX Phi phage particles since the 1970s. However, V. cholerae epidemic strains again lost the capacity for CTX Phi production around the year 2010, suggesting that a critical change had occurred in the dissemi-nation pattern of the current cholera pandemic.