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目的：探讨作用于不同ＰＢＰｓ靶位点的β－内酰胺抗生素联合用药对ＭＲＳＡ体外抗菌活性的影响及其分子机制和形态结构改变。方法：分别测定头孢拉啶和头孢噻肟单独或联合用药对ＭＲＳＡ、ＭＳＳＡ的ＭＩＣ（ＦＩＣ）值，ＳＤＳ－ＰＡＧＥ分离两药单用或联用诱导前后的细菌膜蛋白，分光光度扫描仪测定耐药蛋白ＰＢＰ２ａ的相对含量，扫描电镜观察抗生素不同方式处理后的细菌形态改变。结果：头孢拉啶和头孢噻肟单用对２０ 株ＭＲＳＡ的ＭＩＣ５０、ＭＩＣ９０ 分别为１２８、５１２ｍ ｇ／Ｌ和１６、２５６ｍ ｇ／Ｌ；两药联用前者ＦＩＣ５０、ＦＩＣ９０为４、６４ｍ ｇ／Ｌ，后者为２、３２ｍ ｇ／Ｌ，ＦＩＣ≤０．５，提示两药联用有良好的协同作用。两药单用时都能在一定范围诱导ＭＲＳＡ大量表达ＰＢＰ２ａ，而联合用药却不会诱导ＰＢＰ２ａ 的表达增多，其协同作用可能与其不诱导ＰＢＰ２ａ的表达有关，由于两药作用的ＰＢＰｓ靶位点不同及ＰＢＰ２ａ的保护作用造成ＭＲＳＡ和ＭＳＳＡ不同的形态改变。结论：作用于不同ＰＢＰｓ靶位点的头孢拉啶和头孢噻肟联合用药不诱导耐药蛋白ＰＢＰ２ａ的表达，从而具有良好的协同作用并造成细菌形态的明显改变。
OBJECTIVE: To investigate the effects of the combination of β-lactam antibiotics and different target sites of PBPs on the antibacterial activity of MRSA in vitro and its molecular mechanisms and morphological changes. Methods: The MIC (FIC) value of cefradine and cefotaxime alone or in combination on MRSA and MSSA was determined respectively. The bacterial membrane proteins were separated by SDS-PAGE before or after induction of both drugs. Spectrophotometric determination The relative content of drug protein PBP2a, scanning electron microscope to observe the different forms of antibiotics after treatment of bacterial morphological changes. Results: The MIC50 and MIC90 of cefradine and cefotaxime alone were 128,512 m g / L and 16,256 m g / L for 20 MRSA strains respectively. The combination of the two drugs with the former FIC50 and FIC90 was 4,64 m g / L , The latter is 2,32m g / L, FIC≤0.5, suggesting that the two drugs combined have a good synergistic effect. The two drugs alone can induce MRSA to express PBP2a in a certain range, but the combined treatment does not induce the increase of PBP2a expression, and its synergistic effect may be related to the fact that it does not induce the expression of PBP2a. Due to the different target sites of PBPs The protective effect of PBP2a causes different morphological changes of MRSA and MSSA. CONCLUSION: The combination of cefradine and cefotaxime, which act on target sites of different PBPs, does not induce the expression of the drug-resistant protein PBP2a and thus has a good synergistic effect and causes a significant change in the bacterial morphology.