Helicobacter pylori: clonal population structure and restricted transmission within families revealed by molecular typing

Abstract

Helicobacter pylori infects up to 50% of the human population worldwide. The infection occurs predominantly in childhood and persists for decades or a lifetime. H. pylori is believed to be transmitted from person to person. However, tremendous genetic diversity has been reported for these bacteria. In order to gain insight into the epidemiological basis of this phenomenon, we performed molecular typing of H. pylori isolates from different families. Fifty-nine H. pylori isolates from 27 members of nine families were characterized by using restriction fragment length polymorphism analysis of five PCR-amplified genes, by pulsed-field gel electrophoresis (PFGE) of chromosomal DNA, and by vacA and cagA genotyping. The 16S rRNA gene exhibited little allelic variation, as expected for a unique bacterial species. In contrast, the vacA, flaA, ureAB, and lspA-glmM genes were highly polymorphic, with a mean genetic diversity of 0.83, which exceeds the levels recorded for all other bacterial species. In conjunction with PFGE, 59 H. pylori isolates could be differentiated into 21 clonal types. Each individual harbored only one clone, occasionally with a clonal variant. Identical strains were always found either between siblings or between a mother and her children. Statistical analysis revealed clonality of population structure in all isolates. The results of this study suggest the possible coexistence of a large array of clonal lineages that are evolving in each individual in isolation from one another. Transmission appears to occur primarily from mother to child and perhaps between siblings.

FIG. 1

Representative molecular typing results for H. pylori isolates from family A. PCR-RFLP analyses of 16S rDNA fragments digested with HaeIII (A), 16S rDNA fragments digested with HinfI (B), flaA fragments digested with HhaI (C), flaA fragments digested with Sau3AI (D), ureAB fragments digested with HaeIII (E), lspA-glmA fragments digested with HhaI (F), and vacA fragments digested with HphI (G) and PFGE of genomic DNA digested with NotI (H) are shown. Lanes: M, size markers; A1a to A4c, H. pylori isolates, designated according to the origins of the isolates (A, family A; 1 to 4, family members; a, c, and d, antrum, corpus, and duodenum, respectively).

FIG. 2

Genetic relationships among 59 H. pylori isolates from nine different families. The dendrogram was constructed from PCR-RFLP typing data by the unweighted pair group cluster method with arithmetic means. Each distinct combination of 10 individual gene and enzyme patterns was designated a PCR-RFLP type, corresponding to a clonal type. Ten major lineages, termed I through X, separating at a genetic distance of 0.3 are indicated to the left. The columns to the right indicate the designation of H. pylori isolates, the origin of the isolates, and the molecular typing results. n.d., not determined; n.t., not typeable.