Original article
Colonization of an acid resistant Kingella denitrificans in the stomach may contribute to gastric dysbiosis by Helicobacter pylori

https://doi.org/10.1016/j.jiac.2013.09.007Get rights and content

Abstract

In the stomach of a gastric ulcer patient who had been administered an anti-acid, a gram-negative and urease-negative bacillus similar in size to Helicobacter pylori was infected together with H. pylori. According to biochemical test and 16S rRNA gene analysis, the urease-negative bacterium was identified as Kingella denitrificans, a human nasopharyngeal commensal. In contrast to the standard strain of K. denitrificans, the isolate showed catalase activity, did not produce acid from glucose, and exhibited acid tolerance. Acid tolerance of H. pylori was increased by cocultivation with the K. denitrificans isolate, but not with other isolates of K. denitrificans. Disruption of physiological and immunological niche by dysbiotic colonization of bacterium may provide pathological attributes to human stomach. Collectively, a careful administration of anti-acids to the elderly, especially those with atrophic gastritis, is necessary to avoid repression of the gastric barrier to bacteria.

Introduction

Helicobacter pylori (H. pylori) colonizes approximately half of the world's population and causes chronic gastritis, peptic ulcers, and gastric adenocarcinoma [1]. Eradication of this bacterium improves the symptoms of patients with peptic ulcer and gastric lymphoma of mucosa-associated lymphoid tissue [2], [3]. Isolation of H. pylori from endoscopic gastric biopsy specimens is the most reliable method for detecting H. pylori infection and essential for drug susceptibility testing [4].

The gastric acid determines bacterial susceptibility to the stomach and inhibits infectious agents from reaching the intestine [5]. Urease activity is crucial for H. pylori to colonize the stomach through neutralizing the acidic environment and providing chemotactic motility [6]. However, colonization of urease-negative H. pylori and Campylobacter jejuni is reported in patients receiving acid-reducing compounds [7], [8]. Moreover, predisposed decrease of acid secretion, due to therapy, disease, or age, increased bacterial population in gastric juice [9], [10]. Disproportional use of proton pump inhibitors is considered to promote small intestinal bacterial overgrowth, which is prevalent in patients with irritable bowel disease (IBD) [11]. The gastrointestinal microbiota clearly contributes to development of IBD both in mouse models and patients [12].

A gram-negative bacillus, Kingella denitrificans (K. denitrificans), is a component of the normal upper respiratory and genitourinary tract flora and sometimes causes severe infection [13], [14], [15]. Kingella species are plump gram-negative bacilli and positive for cytochrome c oxidase [16]. Unlike the related species, such as Neisseriae and Moraxellae, Kingella species are catalase-negative similar to Cardiobacterium hominis and Eikenella corrodens. However, strain UB-75 of Kingella oralis and strain UB-204 of E. corrodens were catalase positive [17]. The type-strain of K. denitrificans characteristically produces acid from glucose and is positive for prolyl-aminopeptidase. Different from other species in the genus, K. denitrificans reduces nitrate to nitrite [16].

Necessity for careful identification of urease-negative bacteria in the gastric mucosa is highlighted in this paper. Of particular interest, disruption of integrated immunological niche by dysbiotic colonization of commensal bacteria is discussed.

Section snippets

Patient

A 78-year-old man suffering from gastric ulcer had been administered 40 mg of histamine receptor 2 (H2) antagonist, ranitidine, per day for two years. Endoscopic observation revealed multiple gastric ulcer scars with severe atrophic gastritis. Gastric mucosal biopsy from the antrum and the body was performed to determine histological findings and detect H. pylori. The biopsy specimen was positive for the CLO-test (Kimbarly-Clark, Roswell, GA).

The study was approved by the Yamaguchi University

Isolation of a gram-negative and urease-negative bacterium

The histology of the gastric biopsy specimens indicated grandular atrophy and intestinal metaplasia accompanied by infiltration of mononuclear cells to the lamina propria, a typical observation in gastric mucosa infected with H. pylori (Fig. 1A). Though it is not specific, a few bacteria-like organisms could be seen in the gastric lumen (Fig. 1B). H. pylori ureA gene was amplified in the paraffin-embedded gastric tissue (not shown).

A bacterium isolated from the culture of biopsy specimen was

Discussion

The gastric juice represents a barrier to microbes in saliva and ingested food, mainly by the bactericidal activity of hydrochloric acid [23]. A study in patients with hypochlorhydria being treated with anti-acid and histamine receptor 2 (H2) antagonists identified bacteria originating from the mouth in the gastric contents [24]. Moreover, acid-inhibiting proton pump inhibitors caused gastric colonization by oral-type bacteria in healthy volunteers [10]. The gastric barrier to infection has

Conflict of interest

The authors declare no financial or commercial conflict of interest.

Acknowledgments

The authors are grateful to M. Kimoto for providing the electronmicrograph. This work was funded partly by a Grant for Joint Research Program of the Institute for Genetic Medicine, Hokkaido University (to H.Y.) and partly by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Science and Technology of Japan (no. 2500163603 to Y.H.).

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