Topographical localisation of cagA positive and cagA negativeHelicobacter pyloristrains in the gastric mucosa; an in situ hybridisation study

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Abstract
Background: The cagA gene is a marker for the presence of the cag pathogenicity island, and the presence of cagA positive strains of Helicobacter pylori can identify individuals with a higher risk of developing gastrointestinal diseases. Aims: To study the interaction between H pylori cagA(+) and cagA(−) strains and the gastric mucosa. Methods: Patients with H pylori associated gastritis and peptic ulcers were studied. Biopsies were obtained from the antrum, corpus, fundus, and incisura for H pylori culture, and for in situ hybridisation studies. From each biopsy, multiple single H pylori colonies were isolated and propagated for DNA isolation, and cagA was detected by the polymerase chain reaction (PCR). For in situ detection of H pylori an oligonucleotide specific for an H pylori common antigen and an oligonucleotide specific for cagA were used as probes. Biotinylated probes were incubated with biopsy sections, developed with streptavidin–horseradish peroxidase, and amplified with the tyramide system. Results: PCR results for cagA in isolated colonies confirmed the in situ hydridisation studies. In situ hybridisation identified cagA(+) bacteria in patients with cagA(+) isolates; cagA(−) bacteria in patients with cagA(−) isolates, and cagA(+) and cagA (−) bacteria in patients with both cagA(+) and cagA(−) isolates. CagA(−) bacteria usually colonised the mucous gel or the apical epithelial surface, whereas cagA(+) bacteria colonised the immediate vicinity of epithelial cells or the intercellular spaces. Conclusions: These results document a different in vivo interaction between H pyloricagA(+) or cagA(−) strains and the gastric mucosa.