Identification of novel mutations in MTR locus of clinical isolates of Neisseria gonorrhoeae

Abstract number: o128

Ali  M., Kumar  V., Sachdeva  P., Chaudhry  U., Saluja  D.

Objectives: 

Active efflux of antimicrobial hydrophobic agents is one of the most important bacterial defence systems against inhibitory host factors. Two well-characterized MDR efflux pumps mtrCDE and FarAB-mtrE exist in Neisseria gonorrhoeae. The mtrCDE encoded efflux pump of Neisseria gonorrhoeae mediates an energy dependent efflux process of structurally diverse hydrophobic agents in gonococci. Strains of Neisseria gonorrhoeae that show resistance to hydrophobic agents often contain mutations in the coding region or promoter region of the operon. The product of adjacent mtrR gene negatively regulates the expression of mtrCDE operon. mtrE encodes a putative lipoprotein of 48.5 kda, which is associated with the mtr phenotype.

Methods: 

In an earlier study, we have reported mutations in the QRDR region of gyrA and ParC gene in clinical isolates of Neisseria gonorrhoeae showing high resistance to ciprofloxacin (MIC ranging from 4 to 32 mg/ml) (1). To account for the variation in MIC values of the samples showing similar mutations in gyrA and parC gene, we checked for mutations in mtrR and mtrE genes. The nucleotide sequence of PCR amplified mtrR gene was analysed and compared with the nucleotide sequence of wild types Neisseria gonorrhoeae.

Results: 

These isolates show a missense mutation Tyr105-His located downstream of Helix- Turn- Helix motif of mtrR and a base pair addition mutation in the promoter region of mtrR. The nucleotide sequence of mtrE showed distinct mutations in different clinical isolates invariably at the same positions viz. Val204-Glu, Ala303-Gly, Leu455-Pro and Ser429-Ile.

Conclusion: 

We envisage that the altered DNA-mtrR protein interaction, resulting in increased expression of proteins involved in efflux of hydrophobic antibiotics, may be one of the important mechanism by which pathogen becomes resistant to ciprofloxacin.(1). Chaudhry U, Ray K, Bala M, Saluja D. Mutation patterns in gyrA and parC genes of ciprofloxacin resistant isolates of Neisseria gonorrhoeae from India. Sex Transm Infect. 2002; 78:440–4.