Modification in the ppk Gene of Helicobacter pylori during Single and Multiple Experimental Murine Infections

Abstract

The bacterial pathogen Helicobacter pylori is highly adapted to the human stomach, and a high level of polymorphism is observed among clinical isolates. This polymorphism may be the consequence of adaptive changes during colonization, making a strain better able to survive, to evade the immune system, and to provoke a chronic infection. To investigate the mechanisms involved in the acquisition of diversity in H. pylori, mouse models of single infections, coinfections, and superinfections were developed. These experimental infections were conducted with strain SS1, well known to be mouse adapted, and with two strains freshly isolated from infected patients: Hp141 and Hp145. Genetic modifications occurring in these strains were studied over time by comparing randomly selected colonies of the emerging strains to those of the infecting strains by using randomly amplified polymorphic DNA fingerprinting with six different primers and by using PCR to amplify the vacA and cagA genes. We showed that, regardless of the number of infecting strains, only one emerged from the animals and that the establishment of a first strain thwarted the implantation of a second strain. During both a single infection and a coinfection with SS1, Hp141 was replaced by a genetic variant (Hp141v) that overcame SS1 in coinfection experiments. Hp141v exhibited a deletion of a 102-bp repeated sequence within the ppk gene, which encodes polyphosphate kinase (PPK), an enzyme involved in the physiological adaptation of the microbial cell to nutritional and environmental stresses. The deletion led to higher enzymatic activity of PPK, and the variant exhibited a better capacity to colonize mice. Considering that the modified gene is known to be involved in adaptation to a new environment, our results are consistent with an adaptive change in strain Hp141 and suggest that PPK is an important virulence factor in H. pylori.Helicobacter pylori is a gastrointestinal pathogen that colonizes the human stomach and is involved in chronic gastritis, peptic ulceration, and gastric carcinoma (25,32,40). Certain strains are able to infect animals, such as mice, which can be used as experimental infection models (13,24). H. pylori is one of the bacteria that show the highest level of genetic polymorphism (1). The mechanisms leading to the diversity of H. pylori include mutation; intrachromosomal shift; variations in the locations of insertion sequences; mosaicism of genes, such as vacA; deletion of others, such as those included in the cag pathogenicity island; and recombination between strains coinfecting the same host (17, 23). The polymorphism of H. pylori could be the consequence of adaptive events during colonization of the human stomach, making a strain more efficient at evading the immune system and thus at surviving and provoking a long-term infection (29,39).In order to study the genetic changes in H. pylori that may occur during an infection, we developed a mouse model with strain SS1, previously adapted to this animal, and two strains freshly isolated f...

Diverse Phenotypes Resulting from Polyphosphate Kinase Gene ( ppk1 ) Inactivation in Different Strains of Helicobacter pylori

“…Many bacterial species contain another enzyme, PPK2, that also synthesizes poly P (18,51), but no ppk2 gene homolog was found in H. pylori genomes (51). In studies complementary to ours, others had reported that the ppk1 gene of Hp141v, a mutant H. pylori strain selected for an ability to maintain chronic infection in mice for 1 year, contained a 102-bp deletion, and that ppk1 inactivation reduced this strain's vigor in mice (7,8). They also suggested that inactivation of ppk1 in the unrelated strain X47-2AL made the strain unable to colonize mice.…”

Polyphosphate Kinase 1 Is a Pathogenesis Determinant in Campylobacter jejuni

“…and P. aeruginosa, and for colonization of certain strains of H. pylori (7,49,63,70). Chickens are a natural zoonotic reservoir for C. jejuni, and contamination of commercial broiler flocks is thought to account for the majority of human C. jejuni infections (47).…”

The new world of inorganic polyphosphates

“…In mammals, polyP seems to play a role in blood coagulation [6][7][8]. In bacteria, polyP has chaperone-like activity [9], and regulates stress response, ion channels [10,11] and infectivity as demonstrated for Pseudomonas aeruginosa [10,11,12] and Helicobacter pylori [13]. In trypanosomes, polyP metabolism has been recently characterized and as in pathogenic bacteria, trypanosomes with reduced polyP levels are significantly less virulent [14].…”