title: A clerodane diterpene from Polyalthia longifolia as a modifying agent of the resistance of methicillin resistant Staphylococcus aureus.
abstract: BACKGROUND
  Staphylococcus aureus infections are raising serious concern across the world. The effectiveness of conventional drugs is continuously decreasing due to global emergence of multidrug resistance (MDR) and therefore, new resistance-modifying agents (RMAs) are highly needed.
  
  
  OBJECTIVE
  Clerodane diterpene 16α-hydroxycleroda-3,13(14)-Z-dien-15,16-olide (CD) from leaves of Polyalthia longifolia (Sonn.) Thwaites (Annonaceae) as RAM will be useful in improving the current treatment strategies for staphylococcal infections.
  
  
  METHODS
  In the present study, we determine the resistance-modifying activity of CD using clinical isolates of MRSA. Further, the influence of CD on innate immune response was also evaluated in vitro and in vivo. The nature of potential interactions was determined by fractional inhibitory concentration indices (FICIs) calculated from microdilution assays and time-kill curves.
  
  
  RESULTS
  The result of in vitro combination study showed that CD significantly reduced MIC of fluoroquinolones up to 16-folds (FICI 0.315-0.500), while in S. aureus infected Swiss albino mice model, combination of CD with norfloxacin, significantly (p<0.01, p<0.001) lowered the systemic microbial burden in blood, liver, kidney, lung and spleen tissues in comparison to CD, norfloxacin alone as well as untreated control. Flow cytometry analysis clearly showed that CD significantly inhibited EtBr efflux and extended post-antibiotic effect. In qRT-PCR analysis, CD alone as well as in combination, significantly modulated the expression of various efflux pump genes including norA up to 2-fold in clinical isolate MRSA-ST2071. Further, the in vitro combination study of the CD (10, 5, 2.5µg/ml) along with the norfloxacin (10µg/ml) depicted a significant decline in the pro-inflammatory cytokines, IL6 and TNF-α. In septic shock mice model, CD did not exhibit any significant changes in the level of pro-inflammatory cytokines.
  
  
  CONCLUSIONS
  This is the first report on drug resistance-modifying potential of CD through inhibition of MDR efflux pump.
authors.affiliation: Molecular Bioprospection Department, CSIR-Central Institute of Medicinal and Aromatic Plants, P.O. CIMAP, Lucknow-226015, India.
authors.forename: Vivek Kumar
authors.initials: VK
authors.lastname: Gupta
authors.affiliation: Molecular Bioprospection Department, CSIR-Central Institute of Medicinal and Aromatic Plants, P.O. CIMAP, Lucknow-226015, India.
authors.forename: Nimisha
authors.initials: N
authors.lastname: Tiwari
authors.affiliation: Molecular Bioprospection Department, CSIR-Central Institute of Medicinal and Aromatic Plants, P.O. CIMAP, Lucknow-226015, India.
authors.forename: Priyanka
authors.initials: P
authors.lastname: Gupta
authors.affiliation: Medicinal Chemistry Division, CSIR-Central Institute of Medicinal and Aromatic Plants, P.O. CIMAP, Lucknow-226015, India.
authors.forename: Surjeet
authors.initials: S
authors.lastname: Verma
authors.affiliation: Molecular Bioprospection Department, CSIR-Central Institute of Medicinal and Aromatic Plants, P.O. CIMAP, Lucknow-226015, India.
authors.forename: Anirban
authors.initials: A
authors.lastname: Pal
authors.affiliation: Medicinal Chemistry Division, CSIR-Central Institute of Medicinal and Aromatic Plants, P.O. CIMAP, Lucknow-226015, India.
authors.forename: Santosh Kumar
authors.initials: SK
authors.lastname: Srivastava
authors.affiliation: Molecular Bioprospection Department, CSIR-Central Institute of Medicinal and Aromatic Plants, P.O. CIMAP, Lucknow-226015, India. Electronic address: mpdarokar@yahoo.com.
authors.forename: Mahendra Pandurang
authors.initials: MP
authors.lastname: Darokar
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology* / Q000627:therapeutic use; D045785:Diterpenes, Clerodane / Q000302:isolation & purification / Q000494:pharmacology* / Q000627:therapeutic use; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects*; D051379:Mice; D008826:Microbial Sensitivity Tests; D010936:Plant Extracts / Q000494:pharmacology* / Q000627:therapeutic use; D018515:Plant Leaves / Q000737:chemistry; D031044:Polyalthia / Q000737:chemistry; D013203:Staphylococcal Infections / Q000188:drug therapy*; D013211:Staphylococcus aureus / Q000187:drug effects*
chemical_list: D000900:Anti-Bacterial Agents; D045785:Diterpenes, Clerodane; D010936:Plant Extracts
keywords: Clerodane diterpene; Efflux pump inhibitor; Fluoroquinolones; MRSA; Resistance- modifying agents