title: Helicobacter pylori resistance to six antibiotics by two breakpoint systems and resistance evolution in Bulgaria.
abstract: BACKGROUND
  Helicobacter pylori resistance to antibiotics is the main cause for eradication failures.
  
  
  METHODS
  Antibiotic resistance in 299 H. pylori strains from 233 untreated adults, 26 treated adults, and 40 untreated children was assessed by E tests and, for metronidazole, by breakpoint susceptibility testing and two breakpoint systems.
  
  
  RESULTS
  Using EUCAST breakpoints (EBPs) and previous breakpoints (PBPs), overall resistance rates were: amoxicillin 4.0 and 0.6%, metronidazole 33.8 and 33.8%, clarithromycin 28.1 and 27.4%, levofloxacin 19.4 and 19.4%, tetracycline 3.7 and 1.5%, respectively, and rifampin 8.3% (EBP). Multidrug resistance was detected in treated and untreated adults and an untreated child and included 17 (EBPs) and 15 strains (PBPs). Differences between susceptibility categories were found for amoxicillin (3.5% of strains), clarithromycin (0.7%), and tetracycline (2.2%). Using PBPs, from 2005-2007 to 2010-2015, overall primary clarithromycin resistance continued to increase (17.9-25.6%) as noted in our previous study. However, in 2010-2015, overall primary metronidazole (24.0-31.5%) and fluoroquinolone (7.6-18.3%) resistance rates also increased. Primary resistance rates in children and adults were comparable.
  
  
  CONCLUSIONS
  Briefly, differences in resistance rates by the two breakpoint systems affected the results for three antibiotics. National antibiotic consumption was linked to macrolide resistance in adults. Current primary H. pylori resistance to three antibiotics increased in all untreated patients and in the untreated adults, with the sharpest rise for the fluoroquinolones. The presence of fivefold H. pylori resistance to metronidazole, clarithromycin, tetracycline, levofloxacin, and amoxicillin according to EBPs is alarming.
authors.affiliation: a From the Department of Medical Microbiology , Medical University of Sofia , Sofia , Bulgaria.
authors.forename: Lyudmila
authors.initials: L
authors.lastname: Boyanova
authors.affiliation: a From the Department of Medical Microbiology , Medical University of Sofia , Sofia , Bulgaria.
authors.forename: Galina
authors.initials: G
authors.lastname: Gergova
authors.affiliation: b Department of Gastroenterology , University Hospital St Ekaterina , Sofia , Bulgaria.
authors.forename: Ivailo
authors.initials: I
authors.lastname: Evstatiev
authors.affiliation: c Department of Gastroenterology , University Hospital St Ivan Rilski , Sofia , Bulgaria.
authors.forename: Zoya
authors.initials: Z
authors.lastname: Spassova
authors.affiliation: d Department of General and Hepatobiliary Pancreatic Surgery , Medical University - Sofia , Sofia , Bulgaria.
authors.forename: Naiden
authors.initials: N
authors.lastname: Kandilarov
authors.affiliation: e Gastroenterology Clinic, Department of Pediatrics , University Pediatric Hospital , Sofia , Bulgaria.
authors.forename: Penka
authors.initials: P
authors.lastname: Yaneva
authors.affiliation: a From the Department of Medical Microbiology , Medical University of Sofia , Sofia , Bulgaria.
authors.forename: Rumyana
authors.initials: R
authors.lastname: Markovska
authors.affiliation: a From the Department of Medical Microbiology , Medical University of Sofia , Sofia , Bulgaria.
authors.forename: Ivan
authors.initials: I
authors.lastname: Mitov
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000658:Amoxicillin / Q000494:pharmacology*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002031:Bulgaria; D002648:Child; D017291:Clarithromycin / Q000494:pharmacology*; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics; D019143:Evolution, Molecular; D005260:Female; D016481:Helicobacter Infections / Q000382:microbiology; D016480:Helicobacter pylori / Q000187:drug effects*; D006801:Humans; D064704:Levofloxacin / Q000494:pharmacology*; D008297:Male; D008826:Microbial Sensitivity Tests; D008875:Middle Aged; D055815:Young Adult
chemical_list: D000900:Anti-Bacterial Agents; D064704:Levofloxacin; D000658:Amoxicillin; D017291:Clarithromycin
keywords: Helicobacter pylori; antibiotic resistance; breakpoint system; evolution; multidrug resistance