Activities of beta-lactams and macrolides against Helicobacter pylori

A continuous-culture system (chemostat) was used to study the activities of beta-lactam antimicrobial agents, clarithromycin, and 14-OH-clarithromycin against slowly growing Helicobacter pylori NCTC 11637, H. pylori was grown to steady state before exposure to these antimicrobial agents at x8 the MI C. The bactericidal actions of combinations of amoxicillin and clarithromyc in were also studied. Viable counts (numbers of CFU per milliliter) were de termined at 2-h intervals for 12 h and at 20 h after the addition of antibi otics. The effects of pH changes (6.5 to 7.4) on the activities of amoxicil lin, clarithromycin, and the combination of these against H. pylori NCTC 11 637 were also studied. Viable counts following exposure to ampicillin, cefi xime, ceftazidime, cefuroxime, cefotaxime, azlocillin, and piperacillin at 20 h shelved bacteriostatic activity. Imipenem, meropenem, amoxicillin, cla rithromycin, and 14-OH-clarithromycin reduced the viable counts by 3 log(10 ) CFU/ml (greater than or equal to 99.9% killing). Imipenem was the most ra pidly bactericidal against H. pylori NCTC 11637, Results of the pH experime nts showed that amoxicillin was bactericidal at pHs 6.5 to 7.4. Clarithromy cin was bactericidal at pH 7.0 to 7.4 but was bacteriostatic at pH 6.5. The combination of amoxicillin and clarithromycin was bactericidal at pHs 6.5 and 7.0, A batch culture (flask system) was also used to investigate 12 str ains of H. pylori for their susceptibilities to beta-lactams, clarithromyci n, and/or 14-OH-clarithromycin in order to determine whether results from t he chemostat model can be reproduced with batch cultures. Results of the ch emostat time-kill kinetic study were reproducible in our batch culture flas k system. The role of carbapenems in the eradication of H. pylori should be investigated.