Multi locus sequence typing (MLST) used as a tool to confirm the ability of susceptible Helicobacter pylori strains to gain resistance to clarithromycin during eradication therapy.

Background/Aims: Primary resistance of H. pylori to clarithromycin is the most common reason for eradication failure, followed by mixed susceptible/resistant H. pylori strain infection. To distinguish between mixed infections and H. pylori switch to resistance phenotype during eradication therapy, we proceeded with multi locus sequence typing (MLST) of H. pylori strains isolated from gastric biopsy samples of patients before and after eradication therapy. Methodology: We collected H. pylori isolates from gastric biopsies from 133 patients who were never treated for H. pylon. Five patients had eradication failure with the first isolate susceptible and second isolate resistant to clarithromycin. To analyse genotypes of first and second H. pylori isolates, we compared H. pylon strain sequences of 7 housekeeping genes with MLST. Results: Five patients had clarithromycin-sensitive H. pylon before eradication therapy and gained H. pylori-resistant to clarithromycin after eradication therapy. The sensitive and resistant colonies of each of the H. pylon populations, taken from patients before/after antibiotic therapy, had identical sequence types (ST) obtained with MLST. Conclusions: The factors favouring H. pylon survival and switch to antibiotic-resistance during eradication therapy probably enable milder environmental conditions for H. pylon persistence during therapy. One of such factor is the ineffective destruction of mucosa-adhered H. pylori by immune cells during therapy which may be due to locally induced immune deficit by H. pylon molecules like strain specific H. pylon lipopolysaccharides.