title: SXT constin among Vibrio cholerae isolates from a tertiary care hospital.
abstract: OBJECTIVE
  The SXT element, also known as 'constin' (conjugable, self transmissible, integrating element) is an integrating conjugative element (ICE) in Vibrio cholerae discovered in the chromosome of epidemic V. cholerae O139 strain MO10 (SXT MO10 ) which arose in late 1992 in Chennai, India. SXT related ICEs have become widespread and currently, most if not all Asian V. cholerae clinical isolates contain SXT related ICEs. The present study attempts to determine the presence of SXT Int gene in V. cholerae recovered between 2005 to 2007 in a tertiary care hospital, demonstrate its conjugal nature and also detect co-presence and co-transfer of plasmids in representative isolates.
  
  
  METHODS
  This prospective study was done on 116 V. cholerae isolates [114- O1 (107 ogawa and 7 inaba) and 2 - Non O1 Non O139 V. cholerae] from watery stools between 2005 to 2007 recovered from equal number of patients. PCR was carried out using SXT Int specific primers that produced a 592 bp internal fragment of SXT element, and rifampicin resistant strain of E.coli K-12 was used as recipient in conjugation experiments to study transfer of SXT, as also co-transfer of resistance to tetracycline, erythromycin, and nalidixic acid. Antibiotic susceptibility was performed against various antibiotics.
  
  
  RESULTS
  Of the 116 isolates, 110 (94.8%) were positive for SXT element by PCR. It was demonstrated in 94.7 per cent of the O1, and 100 per cent of non O1 non O139 V. cholerae. All 2005 isolates, 25 per cent of 2006 isolates and 96.6 per cent of 2007 isolates were positive for SXT. Thirty two drug resistance patterns were observed and the 2007 isolates showed resistance to as many as eight antibiotics. The resistance of SXT positive isolates was higher than those of SXT negative and the typical drug resistance pattern corresponding to SXT ET and SXT MO10 was shown by only one V. cholerae O1 isolate. Successful conjugal transfer of SXT was seen in 31 (88.6%) of the 35 isolates studied without any co-transfer while, presence of plasmids was observed in two of the 31 donor V. cholerae studied.
  
  
  CONCLUSIONS
  The demonstration of SXT element and its successful horizontal transfer in V. cholerae isolates studied emphasizes the need for its detection to monitor antibiotic resistance and dissemination in V. cholerae.
authors.affiliation: Department of Microbiology, Mahatma Gandhi Institute of Medical Sciences, Sevagram, Wardha, India.
authors.forename: Kavita
authors.initials: K
authors.lastname: Pande
authors.forename: Deepak Kumar
authors.initials: DK
authors.lastname: Mendiratta
authors.forename: Deotale
authors.initials: D
authors.lastname: Vijayashri
authors.forename: Dipak C
authors.initials: DC
authors.lastname: Thamke
authors.forename: Pratibha
authors.initials: P
authors.lastname: Narang
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002771:Cholera / Q000382:microbiology*; D004251:DNA Transposable Elements; D024881:Drug Resistance, Bacterial; D006801:Humans; D020071:Interspersed Repetitive Sequences; D011446:Prospective Studies; D014734:Vibrio cholerae / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D004251:DNA Transposable Elements; C444447:o1 SXT constin protein, Vibrio cholerae