Low abundance of respiratory nitrate reductase is essential for Escherichia coli in resistance to aminoglycoside and cephalosporin.

UNLABELLED: In the present study, we have characterized low abundance of NarG and NarH, two components of respiratory nitrate reductase (Nar), in streptomycin (SM)-, gentamicine (GEN)-, ceftazidime (CAZ)-, tetracycline (TET)- and nalidixic acid (NA)-resistant Escherichia coli strains using native/SDS-PAGE based proteomics. We validate the finding using Western blotting and native/SDS-PAGE upon narG and narH deletion mutants. However, further functional evidence indicates that loss of narG and narH results in two types of growth behaviors, higher and lower than control, in these antibiotic-resistant E. coli strains. Specifically, SM-, GEN- and CAZ-resistant bacteria grow faster, whereas NA- and TET-resistant E. coli strains grow slower. Our data indicate that low abundance of respiratory Nar is essential for E. coli in resistance to aminoglycoside and cephalosporin antibiotics. Meanwhile, the results show that differential mechanisms exist in different antibiotic-resistant bacteria. The reason why the reversal growths are detected in NA- and TET-resistant E. coli strains waits investigation. Our findings serve to propose novel strategies for controlling of aminoglycoside- and cephalosporin-resistant E. coli strains through elevation of respiratory Nar activity.

BIOLOGICAL SIGNIFICANCE: Our data indicate that low abundance of respiratory Nar is essential for E. coli in resistance to aminoglycoside and cephalosporin antibiotics. Meanwhile, the results show that differential mechanisms exist in different antibiotic-resistant bacteria. Our findings serve to propose novel strategies for controlling of aminoglycoside- and cephalosporin-resistant E. coli strains through elevation of respiratory Nar activity.