The aim of this study was to evaluate the secondary resistance in Helicobacter pylori (Hp) infected patients who had failed a first-line
therapy, and to compare the genotypic tests performed directly on gastric samples with phenotypic tests performed on
culture media. The eradication rate of patients treated with
bismuth quadruple
therapy (BQT) is also evaluated. A total of 80 positive specimens were retrospectively examined.
Antibiotic susceptibility testing of Hp strains was performed by E-test, whereas a molecular commercially available method was used for detecting the mutations involved in
clarithromycin and
levofloxacin resistance. High resistance levels to
metronidazole and
clarithromycin (61.6% and 35%, respectively) and worrying resistance levels to
levofloxacin (15%) were found phenotypically. Multiple resistance to two or three
antibiotics was observed as well. The polymorphism A2143G on
clarithromycin 23S rRNA gene was found in 34/80 (42.5%) isolates including 10
mixed infections (29%), whereas 28/80 (35%) strains were resistant phenotypically.
Levofloxacin resistance corresponded to 30% by PCR and 15% by E-test (statistically significant, p < 0.05). The knowledge of
clarithromycin and
levofloxacin resistance is crucial to establish an appropriate
therapy in different geographical areas. The genetic methods were superior to phenotypic techniques in the absence of live bacteria or for identifying
mixed infections that may lead to a resistance underestimation. The BQT eradication rate was effective (90%).