Multidrug resistance operon emrAB contributes for chromate and ampicillin co-resistance in a Staphylococcus strain isolated from refinery polluted river bank

Abstract

<i>EmrAB</i> operon is known for multidrug resistance in bacteria and yet has not been reported related to heavy metal resistance or antibiotics/heavy metal co-resistance. Strain <i>Staphylococcus aureus</i> LZ-01 which was isolated from industrial wastewater discharging site can co-resist to 6 mM Cr(VI) and 0.75 mg/ml ampicillin. Transcriptome data showed that an <i>emrAB</i> operon was upregulated (1.29-folds for <i>emrA,</i> 2.14-folds for <i>emrB</i>) under 0.4 mM Cr(VI) treatment. Quantitative PCR results revealed that this operon was upregulated (1.60-folds for <i>emrA,</i> 2.34-folds for <i>emrB</i>) after 0.20 mg/ml ampicillin treatment. Mutant strain with <i>emrA</i> gene knockout resulted in a 0.83-folds decrease in chromate resistance, and a 0.80-folds decrease in ampicillin resistance; while <i>emrB</i> knockout strain resulted in a 0.33-folds decrease in chromate resistance, and a 0.60-folds decrease in ampicillin resistance. The complemented strains of both deletion mutants basically restored their resistant performance. The presence of 0.50 mM Cr(VI) induced an elevation in ampicillin resistance from 0.50 to 2.50 mg/ml in the strain LZ-01, similarly, its Cr(VI) resistance was also found to be elevated from 6 to 10 mM by 0.15 mg/ml ampicillin induction. The induction effect could be eliminated by deletion of <i>emrA</i> or <i>emrB</i>. Our results demonstrated that the chromosomal <i>emrAB</i> operon in <i>Staphylococcus aureus</i> LZ-01 was a new type of multidrug resistance system, which conferred both ampicillin and chromate resistance to host cells inhabiting polluted environments.