Genetic diversity in the Helicobacter pylori cag pathogenicity island and effect on expression of anti-CagA serum antibody in UK patients with dyspepsia

T M Peters¹, R J Owen², E Slater², R Varea², E L Teare¹, S Saverymuttu³

¹ Public Health Laboratory, Chelmsford CM2 0YX, UK
² Helicobacter Reference Unit, Laboratory of Enteric Pathogens, Central Public Health Laboratory, 61 Colindale Avenue, London NW9 5HT, UK
³ Department of Gastroenterology, Broomfield Hospital, Chelmsford CM1 7ET, UK

Correspondence to:
Dr Owen rowen{at}phls.nhs.uk

Aims—To investigate variation within the cag pathogenicity island (PAI) of Helicobacter pylori isolated from patients with dyspepsia in mid-Essex, and to evaluate the effect on expression of anti-CagA antibody.

Methods—Sixty two isolates of H pylori cultured from gastric biopsies were screened by specific PCR assays for the presence of cagA and other gene markers (cagD and cagE, and virD4) in the cag PAI. An enzyme linked immunosorbent assay (ELISA) kit (Viva Diagnostica helicobacter p120) was used to test for anti-CagA IgG antibody in matching sera. Isolates were also genotyped by vacuolating cytotoxin polymerase chain reaction (PCR) analysis, and tested for absence of the complete cag PAI (empty site PCR assay).

Results—Forty one of the H pylori isolates had a cag PAI containing cagA. One strain had no cagA but other cag PAI loci were present, whereas the remaining 20 strains had no detectable cag PAI markers. Anti-CagA IgG antibody was detected in 34 sera by the ELISA assay, and when compared with the cag PAI genotype of the infecting strain, accuracy, sensitivity, and specificity were 92%, 87%, and 100%, respectively. The seven discrepant or borderline strains in the ELISA were all vacA s1 but differed in other genotypic markers.

Conclusions—The cag PAI was widely distributed in H pylori from patients with dyspepsia in mid-Essex who had different gastric pathologies. Infection with a strain having an uninterrupted cag PAI was associated with the presence of anti-CagA antibody in most patients. Discrepant ELISA results, mostly for elderly patients with duodenal ulcers, were attributed to cagA associated variation, particularly to the presence of mixed cagA+/cagA- cell variants in the infecting strain population. Tests for anti-CagA serum antibody were unreliable for predicting severity of clinical disease associated with H pylori infection in this series of patients.

Key Words: Helicobacter pylori • cagA • cag pathogenicity island • CagA antibody assay

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