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Systematics and Evolution |
Istituto Cantonale Batteriosierologico, Via Ospedale 6, 6904 Lugano, Switzerland1
Delft Diagnostic Laboratory, R. de Graafweg 7, 2625 AD Delft, The Netherlands2
Author for correspondence: Jean-Claude Piffaretti. Tel: +41 91 923 25 22. Fax: +41 91 922 09 93. e-mail: jean-claude.piffaretti{at}ti.ch
The population biology of 78 Helicobacter pylori strains (71 from Swiss Italian, 4 from East Asian and 3 from South African patients) was investigated by sequence analysis of four housekeeping genes: atpD, scoB, glnA and recA. The vacA genotype, the presence of cagA and IS605, the iceA allelic type, and the resistance to metronidazole, clarithromycin and amoxycillin were determined. A high percentage of DNA polymorphic sites (19·8% for atpD, 21·3% for scoB, 23·7% for glnA and 20·3% for recA) was found. The phylogenetic trees based on the nucleotide sequences of the four gene fragments showed different topologies and were incongruent. The virulence-associated markers were distributed over the dendrograms and no association was found with phylogenetic clusters or clinical manifestations (chronic gastritis, gastric or duodenal ulcer, MALT lymphoma). Moreover, the H ratios (calculated with the homoplasy test) ranged from 0·742 to 0·799, depending on the gene fragment examined. All these observations suggest that H. pylori exists as a recombinant population. The clustering of the strains according to their geographical origin (USA/Europe, East Asia, South Africa) that has recently been demonstrated elsewhere could only be confirmed for the East Asian vacA s1c strains. In contrast, the South African strains clustered together only in the atpD tree. Presumably, recombination at the different loci has masked the evolutionary relationship among the strains.
Keywords: H. pylori, housekeeping genes, antibiotic resistance
Abbreviations: MALT lymphoma, gastric mucosa-associated lymphoid tissue lymphoma
The GenBank accession numbers for the sequences reported in this paper are AY004351AY004662
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