大肠杆菌多重耐药株的体外诱导初步研究

摘要

为了解不同抗菌药物对大肠杆菌体外耐药诱导株的 MIC 变化特点，以盐酸四环素、盐酸环丙沙星、水杨酸钠、氯霉素作为诱导剂，采用1/2×MIC 诱导法，对大肠杆菌质控菌株 ATCC 25922进行体外诱导试验。于诱导前对试验菌株进行形态学观察和生化鉴定，并于诱导过程中对试验菌株进行形态学观察。于诱导前测定16种抗菌药物对质控菌株的MIC，并于诱导剂浓度达到128×MIC时，测定16种抗菌药物对4株诱导菌株的MIC。结果表明，试验菌株的形态特征和生化反应特性与大肠杆菌一致。诱导前，16种抗菌药物对质控菌株的MIC 为0.25～64.00μg/mL；头孢噻肟、盐酸四环素、土霉素、甲砜霉素、诺氟沙星、头孢西丁等抗菌药物对盐酸四环素诱导株的 MIC 与质控菌株相比，提高幅度均达到或超过4倍，均具有显著性意义；头孢噻肟对盐酸环丙沙星诱导株和氯霉素诱导株的MIC与质控菌株相比，提高倍数都超过了4倍，而其余抗菌药物的MIC 变化均无显著性意义。水杨酸钠诱导剂浓度大于16×MIC 时，菌株不能生长。结果提示，抗菌药物对盐酸四环素诱导株的MIC变化最明显，表明大肠杆菌在四环素的选择性压力下较易产生耐药性。%In order to understand the characteristic of change of MICs of different antimicrobial agents against the resistant E. coli strains induced by certain antibiotics in vitro, induction experiment of E. coli ATCC 25922 was conducted using tetracycline hydrochloride, ciprofloxacin hydrochloride, sodium salicylate and chloramphenicol as inducers by 1/2 ×MIC method. Prior to the induction experiment, the tested strain was morphologically and biochemically identified. During the induction experiment, the tested strains were morphologically identified. The MICs of 16 antimicrobial agents against the quality control strain were determined ahead of induction, and the MICs of 16 antimicrobial agents against the 4 induced strains were also determined when the concentrations of inducers reached to 128×MIC. The results showed that the morphological and biochemical characteristics of the tested strains were identical to E. coli. Before induction, the MICs of 16 antimicrobial agents against the quality control strain ranged from 0.25 to 64.00 μg/mL. MICs of cefotaxime, tetracycline hydrochloride, oxytetracycline, thiamphenicol, norfloxacin, cefoxitin and some of other antibiotics against the tetracycline hydrochloride induced strains were increased by 4 fold or more than 4 fold compared with those against the quality control strain, which showed a statistical significance. While MICs of cefotaxime against the ciprofloxacin hydrochloride induced strain and chloramphenicol induced strain were increased by more than 4 fold compared with that against the quality control strain, no statistical significances were found in the change of MICs of other antibiotics against the ciprofloxacin hydrochloride induced strain and chloramphenicol induced strain. When the concentration of sodium salicylate exceeded 16 ×MIC, the induced strain were not able to grow. It was indicated that the change of MICs of the tested antibiotics against the tetracycline hydrochloride induced strain was most obvious, and the E. coli was prone to become resistant under the selective pressure of tetracycline.