Isolation and characterization of <i>Helicobacter suis</i> from human stomach.

Abstract

<i>Helicobacter suis</i>, a bacterial species naturally hosted by pigs, can colonize the human stomach in the context of gastric diseases such as gastric mucosa-associated lymphoid tissue (MALT) lymphoma. Because <i>H. suis</i> has been successfully isolated from pigs, but not from humans, evidence linking human <i>H. suis</i> infection to gastric diseases has remained incomplete. In this study, we successfully in vitro cultured <i>H. suis</i> directly from human stomachs. Unlike <i>Helicobacter pylori</i>, the viability of <i>H. suis</i> decreases significantly on neutral pH; therefore, we achieved this using a low-pH medium for transport of gastric biopsies. Ultimately, we isolated <i>H. suis</i> from three patients with gastric diseases, including gastric MALT lymphoma. Successful eradication of <i>H. suis</i> yielded significant improvements in endoscopic and histopathological findings. Oral infection of mice with <i>H. suis</i> clinical isolates elicited gastric and systemic inflammatory responses; in addition, progression of gastric mucosal metaplasia was observed 4 mo postinfection. Because <i>H. suis</i> could be isolated from the stomachs of infected mice, our findings satisfied Koch's postulates. Although further prospective clinical studies are needed, <i>H. suis</i>, like <i>H. pylori</i>, is likely a gastric pathogen in humans. Furthermore, comparative genomic analysis of <i>H. suis</i> using complete genomes of clinical isolates revealed that the genome of each <i>H. suis</i> isolate contained highly plastic genomic regions encoding putative strain-specific virulence factors, including type IV secretion system-associated genes, and that <i>H. suis</i> isolates from humans and pigs were genetically very similar, suggesting possible pig-to-human transmission.