Ulcerogenic Helicobacter pylori Strains Isolated from Children: A Contribution to Get Insight into the Virulence of the Bacteria

Abstract

Infection with Helicobacter pylori is the major cause for the development of peptic ulcer disease (PUD). In children, with no other etiology for the disease, this rare event occurs shortly after infection. In these young patients, habits of smoking, diet, consumption of alcohol and non-steroid anti-inflammatory drugs and stress, in addition to the genetic susceptibility of the patient, represent a minor influence. Accordingly, the virulence of the implicated H. pylori strain should play a crucial role in the development of PUD. Corroborating this, our in vitro infection assays comparing a pool of five H. pylori strains isolated from children with PUD to a pool of five other pediatric clinical isolates associated with non-ulcer dyspepsia (NUD) showed the greater ability of PUD strains to induce a marked decrease in the viability of gastric cells and to cause severe damage in the cells cytoskeleton as well as an impairment in the production/secretion of mucins. To uncover virulence features, we compared the proteome of these two groups of H. pylori strains. Two-dimensional gel electrophoresis followed by mass-spectrometry allowed us to detect 27 differentially expressed proteins between them. In addition to the presence of genes encoding well established virulence factors, namely cagA, vacAs1, oipA “on” status, homB and jhp562 genes, the pediatric ulcerogenic strains shared a proteome profile characterized by changes in the abundance of: motility-associated proteins, accounting for higher motility; antioxidant proteins, which may confer increased resistance to inflammation; and enzymes involved in key steps in the metabolism of glucose, amino acids and urea, which may be advantageous to face fluctuations of nutrients. In conclusion, the enhanced virulence of the pediatric ulcerogenic H. pylori strains may result from a synergy between their natural ability to better adapt to the hostile human stomach and the expression of the established virulence factors.

Helicobacter pylori—Associated Dyspepsia in Paediatrics

“…Its urease enzyme, a Ni 2+ -containing dodecameric protein of approximately 1100 kDa, composed of 12 small subunits, UreA (27 kDa), and 12 large subunits, UreB (62 kDa), catalyzes the hydrolysis of urea into ammonia and carbon dioxide, buffering both the bacteria cytoplasm and periplasm [39]. Accounting for 5-10% of the total protein content, urease is one of the most abundant proteins in the H. pylori proteome [16,30]. Probably due to the toxicity of ammonia, urease activity is known to be dependent on low pH and/or Ni 2+ concentration conditions [39,40], being essential for bacteria survival only under acidic conditions.…”

“…Nevertheless, H. pylori-associated peptic ulcer disease may also occur shortly after infection in childhood [4][5][6][7][8]. This rare event may be due to more virulent strains [9][10][11][12][13][14][15][16], and/or more predisposed subjects [17][18][19]. The two forms of H. pylori-associated peptic ulcers, i.e., gastric ulcer and duodenal ulcers, are divergent in prevalence and physiopathology, but both cause considerable patients' morbidity entailing high annual costs of treatment [93].…”

“…But, what makes it possible for H. pylori to be involved in both ends of disease spectrum? Although the mechanisms are unclear, the infecting strain itself may play a crucial role on the diverging point of this disease spectrum [16,93]. Moreover, the similarity between the phenotype of gastric ulcer and gastric cancer raises questions about the carcinogenic potential of the associated H. pylori strains [93].…”

“…There is no gene or protein that acts alone to establish the virulence of H. pylori [74]. Accordingly, we investigated further virulence-associated genes by comparing the proteome of a group of genetically/epidemiologically-unlinked H. pylori strains, all isolated from Portuguese children, half suffering with peptic ulcer disease, and the other presenting only active gastritis [16]. Despite the typical proteome profile of all the H. pylori strains grown under the same laboratorial conditions [129], the ulcerogenic paediatric H. pylori strains presented differences suggestive of higher motility, better antioxidant defences and a metabolism favouring the biosynthesis of aromatic amino acids.…”

“…If often asymptomatic, the H. pylori-associated non-ulcer dyspepsia is clearly the strongest aetiological factor for severe gastric diseases that will develop late in adult life in a minority of infected patients, i.e., peptic ulcer disease, both gastric and duodenal ulcers, and gastric cancer, namely, adenocarcinoma and mucosa associated lymphoid tissue (MALT) lymphoma (reviewed in [3]). Peptic ulcer disease rarely occurs soon after H. pylori infection [4][5][6][7][8] that generally starts in childhood; this presumably reflects marked differences in the virulence [9][10][11][12][13][14][15][16] and/or in the susceptibility of young patients [17][18][19].…”