Third line therapy: patients who fail from second line treatment will be rescue with the following treatment Group (A) Patient who fail from levofloxacin sequential therapy will be retreated with bismuth quadruple therapy for 10 days D1-D10: (esomeprazole 40mg bid + Dibismuth trioxide 120mg qid + metronidazole 500mg tid + tetracycline 500mg qid) for 10 days