Frontiers in Microbiology (Nov 2019)

MexAB-OprM Efflux Pump of Pseudomonas aeruginosa Offers Resistance to Carvacrol: A Herbal Antimicrobial Agent

  • Prasanna Vadhana Pesingi,
  • Bhoj Raj Singh,
  • Pavan Kumar Pesingi,
  • Monika Bhardwaj,
  • Shiv Varan Singh,
  • Manoj Kumawat,
  • Dharmendra Kumar Sinha,
  • Ravi Kumar Gandham

DOI
https://doi.org/10.3389/fmicb.2019.02664
Journal volume & issue
Vol. 10

Abstract

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Carvacrol is a herbal antimicrobial agent with in vitro activity against several bacterial pathogens. However, multidrug resistant strains of Pseudomonas aeruginosa are resistant to herbal antimicrobial compounds including carvacrol. Resistance of P. aeruginosa to carvacrol is not well studied. This study was aimed to identify the gene(s) associated with carvacrol resistance, thus to understand its mechanisms in P. aeruginosa. A herbal drug resistant strain was isolated from a hospital environment. Carvacrol sensitive mutant was generated using transposon mutagenesis. The inactivated gene in the mutant was identified as mexA, which is part of the mexAB-oprM operon. Inactivation of the mexA gene resulted in a >31-fold reduction in MIC of carvacrol, whereas a >80-fold reduction was observed in the presence of drug efflux inhibitor phenylalanine-arginine β-naphthylamide (PAβN). The parental herbal-resistant strain was completely killed within 3 h of incubation in the presence of carvacrol and PAβN. The mexA inactivation did not affect the resistance to other herbal compounds used. The results demonstrate that resistance to carvacrol in P. aeruginosa is mediated by the MexAB-OprM efflux pump.

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