Genotyping of Nigerian Helicobacter pylori isolates by pulsed-field gel

Helicobacter pylori is the causative agent ofchronic gastritis and peptic ulcer and is arisk factor in the development of gastriccancer(Blaser,1987;Parsonnetetal.,1991).H. pylori infects up to 50% of the humanpopulationworldwide.TremendousgeneticdiversityhasbeenreportedforH.pyloriandTaylor et al. (1992) reported that thisbacteriumpossessesagreatdealofdiversityin genomic DNA restriction profiles whenanalysed by pulsed-field gel electrophoresis(PFGE);themolecularandepidemiologicalbases for this phenomenon are notunderstood.The aim of the study was to compare DNAprofiles of H. pylori strains isolated fromLagosandIfe,Nigeriaandalsotodetermineiftheisolatesobtainedfromtheantrumandcorpus of the same patient weregenotypically similar.Genomic DNA of 41 H. pylori strainsisolated from 38 patients was prepared forPFGE,asdescribedpreviously(Tayloretal.,1992).Sixofthe41isolateswerefromthreepatients, from whom biopsies were takenfrom both the antrum and the corpus. Theremaining isolates were obtained from theantrum. DNA plugs were digested with therestriction enzymes NotI/NruI and DNAfragments were separated using thecontour-clamped homogeneous electric-field electrophoresis system of PFGE. DNApatterns were visualized by staining withethidium bromide and photographingunder a UV light source.DNA from 15 of the 41 H. pylori strainscould not be digested with the restrictionendonuclease NotI, while DNA from 25 ofthe41H.pyloristrainscouldnotbedigestedwith the restriction endonuclease NruI.Nineofthe15H.pyloristrainsthatwerenotdigestedwithNotIwereisolatesfromLagos;15 of the 25 H. pylori isolates not digestedwith NruI were isolates also from Lagos. Insome cases, the isolates (seven isolates)overlapped in that they were not digestedwitheitherrestrictionenzyme.Amongsttheisolates from Ife, only three isolatesoverlapped in their inability to be digestedwithbothrestrictionenzymes.Therewasnochange in the restriction profile of theisolates,evenafterseveral(four)passagesofthese isolates on culture medium.Therefore, the possibility exists that thisrestriction profile could be region-specific,asanearlierreportbyTakahamietal.(1993)from Japan showed that 12 of 24 isolateswere not digested by the restriction enzymeNotI.TheDNAdigestedfromdifferentpatientsindifferent geographical regions showeddifferent patterns, while the six strainsisolated from the three patients at differentsites (antrum and corpus) showed identicalgenomicDNArestrictionprofilesfromeachsite when the DNA was analysed by PFGE.An exception is that the H. pylori DNAisolated from the corpus and antrum fromone patient had different band patterns. Asimilar report was given by Smith et al.(2002) on these same isolates using PCR.Other workers have also corroborated thisview,inthatsomepatientsareinfected byasingle and individual strain of uniformgenotype (Salama et al., 1995; Han et al.,2000).In conclusion, PFGE was found useful intyping some of our isolates from Nigeria,although its main disadvantage is the non-digestion of some H. pylori DNA by therestriction endonucleases NotI/NruI.Acknowledgements