金黄色葡萄球菌耐药表型与femA表达水平关系研究

Study on the Correlation between Resistance Phenotype and Expression Level of femA of Staphylococcus Aureus

目的探讨不同表型金黄色葡萄球菌femA基因的表达。方法用琼脂对倍稀释法和产β-内酰胺酶纸片法筛选出来不同表型（苯唑西林敏感、低水平耐药、高水平耐药）、非产酶金黄色葡萄球菌临床株共15株以及瑞士捐赠的实验株4株，提取RNA，进行电泳分析及实时荧光定量PCR检测femA表达，实验株BB270的femA表达量设为100％，其他菌株值与之相比。结果所有的菌株均检测到femA的表达，femA缺失株BB308表达量为37．82％，重组株BB586表达量为240．50％，同质性耐药株COL表达量为862．61％。4株敏感株表达量介于0．00353％～29．92％，4株低耐株表达量介于0．00554％～310％，7株高耐株表达量介于13．88％～55000％，3组间femA表达水平不全相同，苯唑西林敏感组与低水平耐药组之间femA表达量的差异无统计学意义（P1=0．83），高水平耐药组与敏感组及低水平耐药组之间femA表达量的差异均有统计学意义（P2=0．006、P3=0．01））。结论非产酶金黄色葡萄球菌femA的表达水平在甲氧西林高水平耐药组中高于低水平耐药组和敏感组，femA是耐甲氧西林金黄色葡萄球菌高水平耐药表达的必需因子。

Objective To detect the expression level of femA of Staphylococcus aureus strains with different phenotype. Methods 15 strains of the non-β-lactamase-producing clinical isolates with different phenotype by agar dilution and by nitrocephin paper strip method were chosen as the object of test, in addition to 4 donative strains （BB270、BB308、BB586、COL）. Total RNA were extracted and analysed by agarose gel electrophoresis. Real time fluorescent quantitative PCR was performed to quantify the expression of femA gene. The expression level of femA of BB270 was set to be standard（100%）. Results The expressions of feraA were observed in all the tested strains. The amount of feraA-specific mRNA in the mutant strain BB308 was approximately 37. 82%and that of stain BB588 was 240. 50%, homogeneous resistant strain COL was 862. 81%. The amounts in MSSA strains were from 0. 00353% to 29. 92%, that in low-level MRSA strains were from 0. 00554% to 310%, otherwise that in high-level MRSA strains were from 13.88% to 55000%, which were different among these groups. There was no significant difference in amount of feraA-mRNA between MSSA and low-level MRSA strains （P1 = 0. 83）but marked between high-level MRSA and low-level MRSA/MSSA strains （P2 = 0. 008, P3 = 0. 01））. Conclusion Expression level of feraA in high-level MRSA was significant higher than that in low-level MRSA and MSSA. feraA was essential for the expression of high-level methicillin resistance in MRSA.