High primary resistance to metronidazole and levofloxacin, and a moderate resistance to clarithromycin in Helicobacter pylori isolated from Karnataka patients

Due to increased prevalence of H. pylori antimicrobial resistance worldwide and more importantly the resistance patterns vary between different geographical regions, it is important to survey local H. pylori antibiotic resistance profile to provide physicians with more informed drug choices to better treat H. pylori infection. To our knowledge, this is the first study to examine the prevalence of antimicrobial resistance of H. pylori in Karnataka state of South India. A total of 113 H. pylori strains were isolated from gastric biopsies and tested: 81.4% were resistant to metronidazole, 54.9% were resistant to levofloxacin, 20.4% were resistant to clarithromycin, 5.3% were resistant to tetracycline and 7.1% were resistant to amoxicillin. Multidrug resistance was detected in 59.3% of total isolated strains, among which 86.6% were resistant to at least both metronidazole and levofloxacin. In this study, 38 out of 113 H. pylori strains had been whole-genome sequenced. Based on the draft genomes, RdxA and/or FrxA inactivation mutations were found to present in 75% of metronidazole-resistant strains. Clarithromycin-resistant strains had mainly A2143G and G2224A mutations in the 23 rRNA gene. While 87.1% levofloxacin-resistant strains had amino acid substitution mutations occurring predominantly at N87 and D91 in GyrA, novel mutations in the same protein including an insertion of five amino acid residues (QDNSV), immediately after the start codon, and a substitution mutation at R295 were identified. High primary resistance to metronidazole and levofloxacin, and a modest occurrence of clarithromycin resistance were revealed in H. pylori strains isolated from Karnataka patients. Therefore metronidazole-, levofloxacin- and clarithromycin-based triple therapies are not suitable as first-line treatment in Karnataka. Both amoxicillin and tetracycline can still be used to eradicate H. pylori infection in this region. We also revealed novel mutations in GyrA protein that possibly contribute to H. pylori resistance in levofloxacin, which merit further investigations.