Can bacterial virulence factors predict antibiotic resistant Helicobacter pylori infection?

AIM: To evaluate the association between virulence factor status and antibiotic resistance in Helicobacter pylori ( H. pylori )-infected patients in Ireland.

METHODS: DNA was extracted from antral and corpus biopsies obtained from 165 H. pylori -infected patients. Genotyping for clarithromycin and fluoroquinolone-mediating mutations was performed using the Genotype HelicoDR assay. cagA and vacA genotypes were investigated using PCR.

RESULTS: Primary, secondary and overall resistance rates for clarithromycin were 50.5% ( n = 53/105), 78.3% ( n = 47/60) and 60.6% ( n = 100/165), respectively. Primary, secondary and overall resistance rates for fluoroquinolones were 15.2% ( n = 16/105) and 28.3% ( n = 17/60) and 20% ( n = 33/165), respectively. Resistance to both antibiotics was 12.4% ( n = 13/105) in treatment-naïve patients, 25% ( n = 15/60) in those previously treated and 17% ( n = 28/165) overall. A cagA -positive genotype was detected in 22.4% ( n = 37/165) of patient samples. The dominant vacA genotype was S1/M2 at 44.8% ( n = 74/165), followed by S2/M2 at 26.7% ( n = 44/165), S1/M1 at 23.6% ( n = 39/165) and S2/M1 at 4.8% ( n = 8/165). Primary clarithromycin resistance was significantly lower in cagA -positive strains than in cagA -negative strains [32% ( n = 8/25) vs 56.3% ( n = 45/80) P = 0.03]. Similarly, in patients infected with more virulent H. pylori strains bearing the vacA s1 genotype, primary clarithromycin resistance was significantly lower than in those infected with less virulent strains bearing the vacA s2 genotype, [41% ( n = 32/78) vs 77.8% ( n = 21/27) P = 0.0001]. No statistically significant association was found between primary fluoroquinolone resistance and virulence factor status.

CONCLUSION: Genotypic H. pylori clarithromycin resistance is high and cagA -negative strains are dominant in our population. Less virulent ( cagA -negative and vacA S2-containing) strains of H. pylori are associated with primary clarithromycin resistance.