Comparison of genotypic method of mexX gene expression and phenotypic method of minimum inhibitory concentration in clinical isolates of Pseudomonas aeruginosa

  Background: The MexXY-OprM efflux pump contributes to the intrinsic resistance to various antimicrobial agents in Pseudomonas aeruginosa isolated from patients. Detection of the expression of genes encoding components of the MexXY-OprM efflux pump such as mexX using real time polymerase chain reaction (PCR) can be helpful in selecting suitable antibiotic treatment.   Objective: The aim of this study was to compare the genotypic method of mexX gene expression and the phenotypic method of minimum inhibitory concentration in clinical isolates of Pseudomonas aeruginosa.   Methods: This descriptive-laboratory study was conducted in University of Catholique de Louvain in 2012. After RNA extraction from 16 clinical isolates and cDNA synthesis, expression of mexX was detected by real time PCR using P. aeruginosa mex Q-TesT. According to the mex Q-TesT guideline, which is based on student T-test with 95% confidence interval and P<0.05, values equal or greater than 5 were considered as overexpression.   Findings: Only 7 out of 11 clinical isolates with increased minimum inhibitory concentration for aminoglycosides showed overexpression of mexX. There was not any relationship between the pump expression and the increase in minimum inhibitory concentration values for various antibiotics.   Conclusion: Since the results of the gene expression and the antimicrobial resistance data are not consistent in all cases, simultaneous use of both genotypic and phenotypic methods is recommended.