Journal of Antimicrobial Chemotherapy (1999) 43, 47-54
© 1999 The British Society for Antimicrobial Chemotherapy
Amoxycillin tolerance in Helicobacter pylori
a VA Medical Center and Baylor College of Medicine, Houston, TX 77030, USA; b Institute of Internal Medicine and c Institute of Hygiene and Preventive Medicine, University of Sassari, Italy
Resistance to amoxycillin in Helicobacter pylori has only recently been
reported. To demonstrate the existence of resistance, and to test for the presence of tolerance, 17
amoxycillin-resistant strains of H. pylori, first isolated in Sardinia (Italy) and the USA,
were studied. Four amoxycillin-sensitive strains were used as controls. Primary isolates of all test
strains exhibited amoxycillin resistance; ß-lactamase activity was not detected. Amoxycillin
resistance was lost after storage of strains at -80°C but could be rescued by plating
these strains on to amoxycillin gradient plates. MICs and MBCs from rescued isolates ranged
from 0.5 to 32 mg/L and from 32 to >1024 mg/L, respectively. MBC/MIC ratios
32 are
characteristic of antibiotic tolerance. The ratios of MBC/MIC of amoxycillin ranged from 32 to
>1024 for the test strains, indicating that these strains were tolerant to the antibiotic.
Amoxycillin resistance does occur in H. pylori. Amoxycillin susceptibility testing of H. pylori isolates in patients who fail therapy should include determination of the MBC
to detect tolerance.
* Corresponding author. Room 3A353 (111D), Department of Medicine, VA Medical Center, 2002 Holcombe Boulevard, Houston, TX 77030, USA. Tel: +1-713-794-7280; Fax: +1-713-790-1040; E-mail: asepulv{at}bcm.tmc.edu
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