Capsaicin, a novel inhibitor of the NorA efflux pump, reduces the intracellular invasion of Staphylococcus aureus.
OBJECTIVE
To delineate the role of capsaicin (8-methyl-N-vanillyl-6-nonenamide) as an inhibitor of the NorA efflux pump and its impact on invasion of macrophages by Staphylococcus aureus.


METHODS
Capsaicin in combination with ciprofloxacin was tested for activity against S. aureus SA-1199B (NorA overproducing), SA-1199 (wild-type) and SA-K1758 (norA knockout). The role of NorA in the intracellular invasion of S. aureus and the ability of capsaicin to inhibit this invasion was established in J774 macrophage cell lines. The three-dimensional structure of NorA was predicted using an in silico approach and docking studies of capsaicin were performed.


RESULTS
Capsaicin significantly reduced the MIC of ciprofloxacin for S. aureus SA-1199 and SA-1199B. Furthermore, capsaicin also extended the post-antibiotic effect of ciprofloxacin by 1.1 h at MIC concentration. There was a decrease in mutation prevention concentration of ciprofloxacin when combined with capsaicin. Inhibition of ethidium bromide efflux by NorA-overproducing S. aureus SA-1199B confirmed the role of capsaicin as a NorA efflux pump inhibitor (EPI). The most significant finding of this study was the ability of capsaicin to reduce the intracellular invasion of S. aureus SA-1199B (NorA overproducing) in J774 macrophage cell lines by 2 log(10).


CONCLUSIONS
This study, for the first time, has shown that capsaicin, a novel EPI, not only inhibits the NorA efflux pump of S. aureus but also reduces the invasiveness of S. aureus, thereby reducing its virulence.
Clinical Microbiology Division,  Indian Institute of Integrative Medicine (CSIR), Canal Road, Jammu 180001,  India.
Nitin Pal
NP
Kalia
Priya
P
Mahajan
Rukmankesh
R
Mehra
Amit
A
Nargotra
Jai Parkash
JP
Sharma
Surrinder
S
Koul
Inshad Ali
IA
Khan
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics; D002211:Capsaicin / Q000494:pharmacology*; D002460:Cell Line; D002939:Ciprofloxacin / Q000494:pharmacology; D004705:Endocytosis / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D055786:Gene Knockout Techniques; D008264:Macrophages / Q000382:microbiology*; D051379:Mice; D008826:Microbial Sensitivity Tests; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics; D011485:Protein Binding; D011487:Protein Conformation; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics / Q000472:pathogenicity*; D014774:Virulence / Q000187:drug effects
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D002211:Capsaicin; D002939:Ciprofloxacin; D004791:Enzyme Inhibitors; D027425:ATP-Binding Cassette, Sub-Family C Proteins; C075040:NorA protein, Staphylococcus