Yan Wei-hui, Chen Jie, Hu Hua-jian, Yu Jin-dan, Huang Xiao-lei, Li Zhong-yue
Department of Gastroenterology, Children's Hospital, Zhejiang University School of Medicine, Hangzhou, Zhejiang 310003, China.
Zhonghua Er Ke Za Zhi. 2007 Sep;45(9):708-11.
Many clinical studies indicated that Helicobacter pylori (Hp) strains rarely acquired resistance to amoxicillin but easily to clarithromycin and metronidazole. However, it was unclear whether the antibiotic resistance of Hp strains was induced or passively selected during long-term or frequent treatment with metronidazole, clarithromycin and amoxicillin. To compare the propensity of acquired resistance to antibiotics, Hp strains were exposed to amoxicillin, clarithromycin and metronidazole in vitro in this study.
All Hp strains were clinical isolates, derived from biopsy specimens of patients taken during endoscopy in the Affiliated Children's Hospital, Zhejiang University School of Medicine from December 2004 to July 2005. To seek susceptible strains, the minimum inhibitory concentrations (MICs) of the three antibiotics were determined by using Epsilometer test (E-test) method. In vitro induction was carried out on serially doubling concentrations of antibiotics incorporated into agar. Isolates were also transferred at least three times on antimicrobial agent-free medium, followed by a redetermination of the final MICs to assess the stability of the selected resistance.
7 strains were exposed to antibiotics in vitro. After 6 - 17 passages on antibiotic plates, 7 and 3 strains respectively acquired resistance to metronidazole and clarithromycin, while none of the strains were resistant to amoxicillin. The inductive folds were different among three groups: 8 - 128 folds in metronidazole group; 1 - 256 folds in clarithromycin group; 2 - 16 folds in amoxicillin group. After three transfers on antimicrobial agent-free medium, the MICs decreased significantly in amoxicillin group (P < 0.05) but had no change in metronidazole group and clarithromycin group (P > 0.05).
The metronidazole resistance in Hp was easily selected. Strains resistant to clarithromycin could be selected, but the amoxicillin resistance could not be selected after in vitro induction for Hp isolated from children. The correlation between in vitro and in vivo outcomes suggests that acquired resistance was the main cause for the resistance in Hp strains. The laboratory results of in vitro antibiotic induction could help predict the actual rate of resistance and select appropriate antibiotics for treatment.
许多临床研究表明，幽门螺杆菌（Hp）菌株很少对阿莫西林产生耐药性，但很容易对克拉霉素和甲硝唑产生耐药性。然而，尚不清楚Hp菌株的抗生素耐药性是在长期或频繁使用甲硝唑、克拉霉素和阿莫西林治疗期间诱导产生的还是被动选择的。为了比较获得性抗生素耐药性的倾向，本研究在体外使Hp菌株接触阿莫西林、克拉霉素和甲硝唑。
所有Hp菌株均为临床分离株，取自2004年12月至2005年7月浙江大学医学院附属儿童医院内镜检查时患者的活检标本。为了寻找敏感菌株，采用Epsilometer试验（E-test）方法测定三种抗生素的最低抑菌浓度（MICs）。在含系列倍增浓度抗生素的琼脂上进行体外诱导。分离株还在不含抗菌剂的培养基上转接至少三次，然后重新测定最终的MICs以评估所选耐药性的稳定性。
7株菌株在体外接触抗生素。在抗生素平板上传代6 - 17次后，7株和3株菌株分别对甲硝唑和克拉霉素产生耐药性，而没有菌株对阿莫西林耐药。三组的诱导倍数不同：甲硝唑组为8 - 128倍；克拉霉素组为1 - 256倍；阿莫西林组为2 - 16倍。在不含抗菌剂的培养基上转接三次后，阿莫西林组的MICs显著降低（P < 0.05），但甲硝唑组和克拉霉素组没有变化（P > 0.05）。
Hp对甲硝唑的耐药性很容易被选择出来。可以选择出对克拉霉素耐药的菌株，但对从儿童分离出的Hp进行体外诱导后不能选择出对阿莫西林的耐药性。体外和体内结果之间的相关性表明，获得性耐药是Hp菌株耐药的主要原因。体外抗生素诱导的实验室结果有助于预测实际耐药率并选择合适的治疗抗生素。
