resistance. We aimed to investigate the prevalence and mechanism of antibiotic resistance to metronidazole and
clarithromycin in H. pylori isolates collected from patients with gastrointestinal symptoms in Qazvin, Iran. In this
cross-sectional study, antibiotic susceptibility testing to clarithromycin and metronidazole was performed among
80 clinical strains isolated from H. pylori-positive dyspeptic patients referred to Qazvin hospital from July 2018
to November 2018. Polymerase chain reaction (PCR) and sequencing tests were performed to determine the type
of mutations in the rdxA gene in metronidazole-resistant isolates, and the 23SrRNA gene in clarithromycinresistant
isolates. Thirteen (40.6%) and Twenty-one (65.6%) isolates were resistant to clarithromycin and
metronidazole, respectively. 37.5% and 59.4% of clarithromycin and metronidazole resistant isolates had
MIC>256. In clarithromycin-resistant isolates, mutations in the 23SrRNA gene was seen at A2143G (15.6%),
A2142G (9.4%), C2195T (6.3%), C2244T (3.1%), and G2212A (3.1%) locations. In one isolate, three simultaneous
mutations were recorded in locations A2143G, G2110A, and C2121T. Mutations in the rdxA gene in
metronidazole-resistant isolates, were missense. High resistance to metronidazole and clarithromycin antibiotics
were seen in H. pylori isolates in Qazvin province. This is the first report of new mutation sites G2212A, G2110A,
and C2121T on the 23SrRNA gene in clarithromycin-resistant isolates. It is necessary to evaluate the current
situation in terms of resistance and identify the mechanisms involved in its occurrence for the successful
treatment of infections caused by this organism
