Prevalence of the resistance to metronidazole, furazolidone and nitrofurantoin in Helicobacter pylori clinical strains PS189 de la Obra Sanz P a , Roman JL a , Lomas E a , Villar H b , Lopez-Brea M a . a Hospital de la Princesa, Microbiology, Madrid, Spain , b Hospital de San Agustin, Microbiology, Aviles, Spain