No abstract

To investigate amoxicillin and metronidazole resistance of Helicobacter pylori, we compared putative resistance genes between resistant strains obtained in vitro and their sensitive parent strain. All metronidazoleresistant strains had rdxA mutations, and an amoxicillin-resistant strain had pbp1 and pbp2 mutations. By transforming PCR products of these mutated genes into antibiotic-sensitive strains, we showed that rdxA null mutations were sufficient for metronidazole resistance, while pbp1 mutations contributed to amoxicillin resistance of H. pylori.Although most infections with Helicobacter pylori are asymptomatic, and some might even be beneficial for the host, the pathogen is usually eradicated with antibiotics such as amoxicillin and metronidazole in order to cure gastritis and peptic ulcer diseases (3, 4). Resistance against metronidazole is common among H. pylori strains, while there are only a few reports of amoxicillin-resistant H. pylori strains Metronidazole resistance of H. pylori was shown to be due to the mutational inactivation of rdxA (7, 11). In turn, a metronidazole-resistant strain (Mtz r ) was rendered sensitive when complemented with the rdxA gene of a metronidazole-sensitive strain (Mtz s ). It was concluded that RdxA functions as a metronidazole-reducing nitroreductase (11). Resistance against ␤-lactam antibiotics like amoxicillin is generally due to hydrolysis by a ␤-lactamase (5) or by mutational modification of the penicillin binding proteins (13).To investigate the molecular basis for antibiotic resistance in H. pylori, we did an in vitro selection for amoxicillin and metronidazole resistance on the strains 503 (ATCC 43503) and 69A (69A and 888-0: clinical isolates obtained from R. Haas, Max-von Pettenkofer-Institut, Munich, Germany). In contrast to other investigators (12, 15), we performed the selection not on agar plates, but in liquid culture (brain heart infusion medium [BHI; Difco-BD Biosciences, Md.] plus 5% fetal calf serum [FCS; Eurobio, Les Ulis, France]) at 37°C with microaerobic incubation (5 to 6% O 2 , 8 to 10% CO 2 ) in the presence of these antibiotics. The MIC was determined by inoculating logarithmically growing H. pylori cells with an optical density at 578 nm (OD 578 ) of 0.04 in 10 ml of BHI-5% FCS in 50-ml cell culture flasks (Greiner) on a shaker incubator at 90 rpm. The MIC of metronidazole was defined as no OD 578 increase in 10 to 14 days, and that of amoxicillin was defined as growth to an OD 578 lower than 0.4, with no increase after the first 24 h of incubation. We obtained stable metronidazole resistance after three serial passages over the course of 8 to 10 days with increasing metronidazole concentration in the growth medium (from 2 g/ml to 25 g/ml). The metronidazole MIC for nine independently selected 69A/Mtz r and 503/ Mtz r strains was Ͼ25 g/ml, while that for strains 503 and 69A was Ͻ5 g/ml (data not shown). These results correspond to the observation of metronidazole resistance developing de novo during the course of a typical antibiotic therapy (1...

After treatment of millions of patients suffering from gastroesophageal reflux disease (GERD) and other acid-related ailments with proton pump inhibitors, there are still unmet medical needs such as rapid and reliable pain relief, especially for nocturnal acid breakthrough. In this work, we introduce and characterize the biochemistry and pharmacology of the potassium-competitive acid blocker (P-CAB) soraprazan, a novel, reversible, and fast-acting inhibitor of gastric H,K-ATPase. Inhibitory and binding properties of soraprazan were analyzed together with its mode of action, its selectivity, and its in vivo potency. This P-CAB has an IC 50 of 0

To define the basic antisecretory profile of a potassium-competitive antagonism of the gastric acid pump relative to other classes of acid-inhibitory drugs, they were compared to each other against all three major stimuli of acid secretion. Pumaprazole is an imidazo-pyridine derivative that was used in this investigation as an example of reversibly binding acid pump antagonists (APAs). It differs from covalently binding proton pump inhibitors (PPIs), such as omeprazole, both with respect to chemical structure and mode of interaction with the gastric H⁺/K⁺-ATPase (i.e., the acid or proton pump). The present data show that a single dose of pumaprazole is able to elevate intragastric pH in the dog with gastric fistula under pentagastrin or carbachol stimulation from pH 1 to about pH 7 while still displaying a dose-dependent, well-controlable duration of action of a few hours. Ranitidine at the same oral dose also shows a short duration of action, but combined with a far lower efficacy. By contrast, a single oral dose of the PPI omeprazole elevates intragastric pH for a longer time period, but this pH elevation is far lower compared to that of the APA. Regarding the less stringent parameter of inhibition of total acid output in the Heidenhain pouch dog, the modified Shay rat or the Ghosh-Schild rat, pumaprazole is, overall, slightly more efficacious than ranitidine. The M₁-muscarinic antagonist pirenzepine is ineffective (against histamine stimulation) or far less effective than pumaprazole (against pentagastrin-stimulation), but as effective as pumaprazole against carbachol stimulation in the Ghosh-Schild rat. Basal acid output in the same model is more effectively inhibited by pumaprazole than by ranitidine. In conclusion, our data demonstrate the exceptional ability of a reversibly binding APA to elevate intragastric pH up to neutrality even upon a first administration while still displaying a limited, dose-dependent duration of action.

No abstract