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1 Groupe de Recherche sur les Antimicrobiens et les Micro-organismes (GRAM EA 2656, IFR 23), Université de Rouen, Faculté de Médecine-Pharmacie, 22 Boulevard Gambetta, F-76183 Rouen Cedex, France
2 Département de Microbiologie-Immunologie, Faculté de Pharmacie Paris XI, Châtenay-Malabry, France
Correspondence
Ludovic Lemée
ludovic.lemee{at}chu-rouen.fr
A multilocus sequence analysis of ten virulence-associated genes was performed to study the genetic relationships between 29 Clostridium difficile isolates of various origins, hosts and clinical presentations, and selected from the main lineages previously defined by multilocus sequence typing (MLST) of housekeeping genes. Colonization-factor-encoding genes (cwp66, cwp84, fbp68, fliC, fliD, groEL and slpA), toxin A and B genes (tcdA and tcdB), and the toxin A and B positive regulator gene (tcdD) were investigated. Binary toxin genes (cdtA and cdtB) were also detected, and internal fragments were sequenced for positive isolates. Virulence-associated genes exhibited a moderate polymorphism, comparable to the polymorphism of housekeeping genes, whereas cwp66 and slpA genes appeared highly polymorphic. Isolates recovered from human pseudomembranous colitis cases did not define a specific lineage. The presence of binary toxin genes, detected in five of the 29 isolates (17 %), was also not linked to clinical presentation. Conversely, toxigenic A–B+ isolates defined a very homogeneous lineage, which is distantly related to other isolates. By clustering analysis, animal isolates were intermixed with human isolates. Multilocus sequence analysis of virulence-associated genes is consistent with a clonal population structure for C. difficile and with the lack of host specificity. The data suggest a co-evolution of several of the virulence-associated genes studied (including toxins A and B and the binary toxin genes) with housekeeping genes, reflecting the genetic background of C. difficile, whereas flagellin, cwp66 and slpA genes may undergo recombination events and/or environmental selective pressure.
Nucleotide sequences of the internal fragment genes analysed in this work will be deposited in GenBank under accession numbers DQ102375–DQ102379 (for cdtA), DQ117049–DQ117053 (for cdtB), DQ117054–DQ117074 (for cwp66), DQ117075–DQ117103 (for cwp84), DQ117104–DQ117132 (for fbp68), DQ117133–DQ117161 (for fliC), DQ117162–DQ117189 (for fliD), DQ117190–DQ117218 (for groEL), DQ117219–DQ117240 (for slpA), DQ117241–DQ117265 (for tcdA), DQ117266–DQ117288 (for tcdB) and DQ117289–DQ117311 (for tcdD).
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