LAUSR

The objective of the present study was to investigate the genomic arrangement of CTX/RS1 prophages in 30 Vibrio cholerae strains obtained from 2 consecutive years of cholera outbreak and to compare the role of different CTX/RS1 arrangements in cholera toxin expression among the El Tor strains. Profile A with TLC-RS1-CTX-RTX arrangement was observed in 46.7% of the isolates with RS1 phage locating adjacent to TLC element. About 50% of the isolates showed Profile B with TLC-CTX-RS1-RTX arrangement and one single isolate (3.3%) revealed TLC-CTX-RS1-RS1-RTX arrangement (Profile C). No RS1 element was detected to be adjacent to TLC element in B and C profiles. No truncated CTX phage genome was detected among the isolates of 2 years. Different CTX-RS1 arrangement profiles (A, B, and C) with different RS1 copy numbers and locations uniformly showed low level of cholera toxin production in El Tor strains with no significant difference, revealing that different RS1 copy numbers and locations have no effect on cholera toxin production level (p-value >0.05). However, increased cholera toxin expression was observed for control V. cholerae classical biotype strain. In conclusion, variations in RS1 prophage did not affect CT expression level in related El Tor V. cholerae strains. CTX genotyping establishes a more valuable database for epidemiologic, pathogenesis, and source tracking purposes.