Shown are levels of expression of mtrR and mtrE genes in gonococcal strains FA19 and CDC2 (A), FA19 and CR.100 (B), FA19 and CR.101 (C), and FA19 and CR.102 (D). Gene transcript levels were quantified by qRT-PCR performed in triplicate with three biological replicates. Results are presented as average NER (normalized expression ratio) values (±SD) with P values. **, P ≤ 0.01; ***, P ≤ 0.001; ****, P ≤ 0.0001.