An amoxicillin-resistant (Amoxr) strain of Helicobacter pylori was selected for by culturing an amoxicillin-sensitive (Amoxs) strain in increasingly higher concentrations of amoxicillin, resulting in a 133-fold increase in MIC, from 0.03 to 0.06 μg/ml to 4 to 8 μg/ml. This resistance was stable upon freezing for at least 6 months and conferred cross-resistance to seven other β-lactam antibiotics. β-Lactamase activity was not detected in this Amoxr strain; however, analysis of the penicillin-binding protein (PBP) profiles generated from isolated bacterial membranes of the Amoxs parental strain and the Amoxr strain revealed a significant decrease in labeling of PBP 1 by biotinylated amoxicillin (bio-Amox) in the Amoxr strain. Comparative binding studies of PBP 1 for several β-lactams demonstrated that PBP 1 in the Amoxr strain had decreased affinity for mezlocillin but not significantly decreased affinity for penicillin G. In addition, PBP profiles prepared from whole bacterial cells showed decreased labeling of PBP 1 and PBP 2 in the Amoxr strain at all bio-Amox concentrations tested, suggesting a diffusional barrier to bio-Amox or a possible antibiotic efflux mechanism. Uptake analysis of 14C-labeled penicillin G showed a significant decrease in uptake of the labeled antibiotic by the Amoxr strain compared to the Amoxs strain, which was not affected by pretreatment with carbonyl cyanide m-chlorophenylhydrazone, eliminating the possibility of an efflux mechanism in the resistant strain. These results demonstrate that alterations in PBP 1 and in the uptake of β-lactam antibiotics in H. pylori can be selected for by prolonged exposure to amoxicillin, resulting in increased resistance to this antibiotic.
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机译:通过在浓度越来越高的阿莫西林中培养对阿莫西林敏感的(Amox s sup>)菌株,筛选出耐阿莫西林(Amox r sup>)的幽门螺杆菌菌株。 MIC增加133倍,从0.03至0.06μg/ ml到4至8μg/ ml。这种抗性在冷冻至少6个月后保持稳定,并与其他7种β-内酰胺类抗生素产生交叉抗性。该Amox r sup>菌株未检测到β-内酰胺酶活性。但是,对由Amox s sup>亲本菌株和Amox r sup>菌株的分离细菌膜产生的青霉素结合蛋白(PBP)谱的分析表明,该菌株的标记显着减少。 Amox r sup>菌株中生物素化的阿莫西林(bio-Amox)产生的PBP 1。 PBP 1与几种β-内酰胺的比较结合研究表明,Amox r sup>菌株中的PBP 1对美洛西林的亲和力降低,但对青霉素G的亲和力却没有显着降低。此外,从整个细菌制备的PBP谱在所有测试的生物Amox浓度下,Amox r sup>菌株中PBP 1和PBP 2的标记细胞均减少,表明对生物Amox的扩散屏障或可能的抗生素外排机制。对 14 sup> C标记的青霉素G的吸收分析表明,与Amox s sup>相比,Amox r sup>菌株对标记的抗生素的吸收显着降低。该菌株不受羰基氰间氯苯hydr预处理的影响,消除了在抗性菌株中外排机理的可能性。这些结果表明,可以通过长时间暴露于阿莫西林来选择幽门螺杆菌中PBP 1的改变和β-内酰胺抗生素的吸收,从而导致对该抗生素的耐药性增加。
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