title: Novel ctxB variants of Vibrio cholerae O1 isolates, China.
abstract: We screened 650 isolates from historical collection of Vibrio cholerae O1 during the 7th cholera pandemic in China, by amplifying and sequencing the cholera toxin subunit gene ctxB. Ten isolates were identified as harboring three novel ctxB genotypes based on amino acid residue substitutions. Within them one isolate from a patient in 1964 was similar to the El Tor genotype, except for an 11 amino acid repeat sequence (LAGKREMAIIT) that was inserted after position 62. Six environmental isolates from different regions and years were identified as the Australia El Tor genotype, except at positions 36(T→A), 39(H→Y), and 55(K→N), while three environmental isolates were similar to genotype 5, except at position 24(Q→H). Sequencing of rstR, the marker gene for the CTXΦ allele typing, revealed that two isolates carried the rstR gene of the El Tor type, five carried the classical type rstR, while other isolates carried the rstR232 type. All 10 isolates contained the repeat in the toxin gene rtxC, an El Tor biotype-specific marker, and the El Tor toxin-coregulated pili subunit A gene tcpA, showing the El Tor traits of these isolates. Additionally, by phenotypic biotyping (susceptibility to polymyxin B, positive for chicken erythrocyte agglutination, and Voges-Proskauer test), all isolates except two were typical of the prototype El Tor isolate, while these two isolates had mixed classical phenotypes (hybrid biotype). Furthermore, pulsed-field gel electrophoresis analysis suggested that the new ctxB altered isolates possessed potential transmissibility and thatthey propagated in the local region(s). Taken together, these novel ctxB variants of V. cholerae O1 experienced complex hybrid and genetic exchange but belong to the El Tor lineage, and the pathogenic and epidemic potential of these lineages should be monitored.
authors: National Institute for Communicable Disease Control and Prevention, Chinese Center for Disease Control and Prevention/State Key Laboratory for Infectious Disease Prevention and Control/Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, China.
authors: Ping
authors: P
authors: Zhang
authors: Haijian
authors: H
authors: Zhou
authors: Biao
authors: B
authors: Kan
authors: Duochun
authors: D
authors: Wang
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics; D015373:Bacterial Typing Techniques; D001483:Base Sequence; D002681:China; D002771:Cholera / Q000382:microbiology*; D002772:Cholera Toxin / Q000235:genetics*; D004269:DNA, Bacterial / Q000235:genetics; D004196:Disease Outbreaks; D014644:Genetic Variation; D005838:Genotype; D006801:Humans; D008969:Molecular Sequence Data; D012097:Repressor Proteins / Q000235:genetics; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D041241:Vibrio cholerae O1 / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D012097:Repressor Proteins; C107871:RstR protein, Vibrio cholerae; D002772:Cholera Toxin
keywords: PFGE; Variant; Vibrio cholerae O1; ctxB