Study on the association between drug-resistance and gene mutations of the active efflux pump acrAB-tolC gene and its regulatory genes

The aim of the present study was to investigate the correlation between the multi-drug resistance of Shigella flexneri and the drug-resistant gene cassette carried by integrons; in the meanwhile, to detect the associations between drug-resistance and gene mutations of the active efflux pump acrAB-tolC gene and its regulatory genes, including marOR, acrR and soxS. A total of 158 isolates were isolated from the stool samples of 1,026 children with diarrhoea aged 14 years old between May 2012 and October 2015 in Henan. The K-B method was applied for the determination of drug resistance of Shigella flexneri, and polymerase chain reaction amplification was used for class 1, 2 and 3 integrase genes. Enzyme digestion and sequence analysis were performed for the variable regions of positive strains. Based on the drug sensitivity assessment, multi-drug resistant strains that were resistant to five or more antibiotics, and sensitive strains were selected for amplification. Their active efflux pump genes, acrA and acrB, and regulatory genes, marOR, acrR and soxS, were selected for sequencing. The results revealed that 91.1% of the 158 strains were multi-resistant to ampicillin, chloramphenicol, tetracycline and streptomycin, and 69.6% of the strains were multi-resistant to sulfamethoxazole/trimethoprim. The resistance to ceftazidime, ciprofloxacin and levofloxacin was <32.9%. All strains (100%) were sensitive to cefoxitin, cefoperazone/sulbactam and imipenem. The rate of the class 1 integron positivity was 91.9% (144/158). Among these class 1 integron-positive strains, 18 strains exhibited the resistance gene cassette dfrV in the variable region of the strain, four strains exhibited dfrA17-aadA5 in the variable region and 140 strains exhibited blaOXA-30-aadA1 in the variable region. Four strains showed no resistance gene in the variable regions. The rate of class 2 integron positivity was 86.1% (136/158), and all positive strains harboured the dfrA1-sat1-aadA resistance gene cassette in the variable region. The class 3 integrase gene was not detected in these strains. The gene sequencing showed the deletion of base CATT in the 36, 37, 38, 39 site in the marOR gene, which is a regulatory gene of the active efflux pump, AcrAB-TolC. Taken together, the multi-drug resistance of Shigella flexneri was closely associated with gene mutations of class 1 and 2 integrons and the marOR gene.