Importance of lipooligosaccharide structure in determining gonococcal resistance to hydrophobic antimicrobial agents resulting from the mtr efflux system

Mol Microbiol. 1995 Jun;16(5):1001-9. doi: 10.1111/j.1365-2958.1995.tb02325.x.


Levels of gonococcal resistance to antimicrobial hydrophobic agents (HAs) are controlled by the mtr (multiple transferrable resistance) system, composed of the mtrRCDE genes. The mtrR gene encodes a transcriptional repressor that appears to regulate expression of the upstream and divergent mtrCDE operon. The mtrCDE genes encode membrane proteins analogous to the MexABOprK proteins of Pseudomonas aeruginosa that mediate export of structurally diverse antimicrobial agents. In this study we found that a single base pair deletion in a 13 bp inverted repeat sequence within the mtrR promoter resulted in increased resistance of gonococci to both crystal violet (CV) and erythromycin (ERY) as well as to the more lipophilic non-ionic detergent Triton X-100 (TX-100). However, this cross-resistance was contingent on the production of a full-length lipooligosaccharide (LOS) by the recipient strain used in transformation experiments. Introduction of this mutation (mtrR-171) into three chemically distinct deep-rough LOS mutants by transformation resulted in a fourfold increase in resistance to TX-100 compared with a 160-fold increase in an isogenic strain producing a full-length LOS. However, both wild-type and deep-rough LOS strains exhibited an eightfold increase in resistance to CV and ERY as a result of the mtrR-171 mutation. This suggests that gonococci have different LOS structural requirements for mtr-mediated resistance to HAs that differ in their lipophilic properties. Evidence is presented that gonococci exclude HAs by an energy-dependent efflux process mediated by the mtr system.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Bacterial Proteins / biosynthesis
  • Bacterial Proteins / genetics
  • Carbohydrate Conformation
  • Carbohydrate Sequence
  • Disease Susceptibility
  • Drug Resistance, Microbial / genetics*
  • Erythromycin / pharmacology
  • Ferredoxin-NADP Reductase*
  • Genes, Bacterial*
  • Gentian Violet / pharmacology
  • Gram-Negative Bacteria / genetics
  • Molecular Sequence Data
  • Neisseria gonorrhoeae / drug effects
  • Neisseria gonorrhoeae / genetics*
  • Octoxynol / pharmacology
  • Operon
  • Promoter Regions, Genetic
  • Pseudomonas aeruginosa / drug effects
  • Pseudomonas aeruginosa / genetics*
  • Repressor Proteins / biosynthesis
  • Repressor Proteins / genetics*


  • Bacterial Proteins
  • Repressor Proteins
  • mtrR protein, Neisseria gonorrhoeae
  • Erythromycin
  • Octoxynol
  • methionine synthase reductase
  • Ferredoxin-NADP Reductase
  • Gentian Violet