Maria Teresa Mascellino
Sapienza University, Italy
Title: Secondary antibiotic resistance, correlation between genotypic and phenotypic methods and treatment in helicobacter pylori infected patients: A retrospective study
Biography
Biography: Maria Teresa Mascellino
Abstract
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) was 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 method was used for detecting the mutations involved in clarithromycin (CLA) and levofloxacin (LEV) resistance. High resistance levels to metronidazole (MZ) and CLA (61.6% and 35%, respectively) and worrying resistance levels to LEV (15%) were found phenotypically. Multiple resistance to two or three antibiotics was observed as well. The combination MZ+TE (tetracycline) recommended in BQT was detected just in one strain (1.25%) and resulted as being much inferior to all other combinations including MZ, CLA and LEV. The polymorphism A2143G on clarithromycin 23S rRNA gene was found in 34/80 (42.5%) isolates including 10 mixed infections (29%) which indicated the simultaneous presence of resistant and susceptible strains in the stomach antrum, whereas 28/80 (35%) strains were resistant phenotypically (difference not statistically significant, p>0.05). In contrast levofloxacin resistance was 30% by PCR and 15% by E-test (difference statistically significant, p < 0.05). The genetic methods turned out to be better than the phenotypic techniques especially in the absence of live bacteria or for identifying mixed infections that may lead to a resistance underestimation or in contaminated cultures. The BQT (PPI+Bismuth+MZ+TE) eradication rate was effective (90%). This therapy has proven high efficacy despite MZ resistance also bypassing the quinolone resistance and overcoming the CLA-resistance. The knowledge of clarithromycin and levofloxacin resistance is crucial to establish an appropriate therapy in different geographical areas.