ABSTRACT
Objective To detect the mutations of the marOR gene and study the relations with the expressing level of the acrAB-tolC efflux pump in Shigella. Methods marOR genes were amplified by PCR for 100 clinical isolates and 5 reference strains of Shigella. The PCR products were digested by restriction endonuclease Taq Ⅰ , then analyzed by single strand conformation polymorphism(SSCP). The marOR genes of the mutated strains and sensitive strain were sequenced and the expressing leveLs of acrA, acrB and talC were determined by RT-PCR. Susceptibility tests of tetracycline (TE), chloramphenicol (C), ampicillin (Am) , gentamycin (GM), norfloxacin (NOR) and selectrin (SMZ-TMP) were performed in sequenced strains. Results marOR genes were found in all strains detected. SSCP analysis found the rate of mutations in marOR genes was 23%. Among 11 marOR gene-mutated strains which were sequenced, there were 9 strains having a four-base absence and three single-base mutations in different loci. The expressing levels of the acrAB-tolC efflux pump in the 11 strains were higher than those in sensitive strains and reference strain. Furthermore the 11 strains were multi-drug resistance. Conclusion The mutation rate of marOR gene in Shigella was high and the acrAB-tolC efflux pump genes were over-expressive in marOR gene-mutated strains which were multi-antibiotic resistance in the study.