Antibacterial activity of oregano essential oil against hospital isolates of Providencia stuartii: possible alternative treatment

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Providencia stuartii, belonging to the order Enterobacteriales and family Morganellaceae, is a Gram-negative, facultative anaerobic, flagellated bacillus commonly found in soil, water, and sewage, besides being part of the normal intestinal microbiota of several animals. However, this microorganism is also associated with various infections and is considered an opportunistic pathogen. This bacterium may be responsible for up to 9% of the cases of urinary tract infections in hospitalized patients, and may also cause skin infections and infections associated with medical devices. P. stuartii is resistant to several antibiotics, such as aminopenicillins, first-generation cephalosporins, and polymyxins, and increased resistance to aminoglycosides and quinolones has been reported. Due to bacterial resistance to conventional antimicrobials, plant-derived compounds, such as essential oils, have presented themselves as an antimicrobial alternative due to their broad spectrum of action at low doses. Among the essential oils, the oregano essential oil (OEO) stands out, whose main bioactives are the terpenes carvacrol and thymol, it interferes in the proton gradient and in the selective permeability of the bacterial cell membrane. OEO stands out because it shows antimicrobial activity even against bacteria resistant to antimicrobials, therefore, there is scientific interest in investigating its antimicrobial effect against resistant pathogens. Thus, the present study shows the antibacterial activity of OEO against four hospital isolates of multidrug-resistant P. stuartii (resistant to up to 8 of the 12 antimicrobials tested), including carbapenems, from urine and blood samples collected in a hospital in the northern part of Paraná, Brazil. OEO used in this study was obtained commercially. Minimum inhibitory concentration (MIC) was determined by broth microdilution according to Clinical & Laboratory Standards Institute (CLSI), adapted for analysis of antimicrobial activity in oils. The MIC of OEO obtained was 0.039% (v/v) for three isolates and 0.078% (v/v) for one isolate. Thus, this is the first report demonstrating the antibacterial activity of OEO against hospital isolates of P. stuartii, which are responsible for causing infections that have few or no treatment options. Therefore, OEO may present itself as a therapeutic alternative for multidrug-resistant P. stuartii. However, it is needed an investigation activity of OEO with a larger amount of multidrug-resistant P. stuartii isolates in order to obtain a more representative result.

  • 1 Centro de Ciências Biológicas / Universidade Estadual de Londrina
  • 2 Universidade Estadual de Londrina
  • 3 Departamento de Microbiologia / Centro de Ciências Biológicas / Universidade Estadual de Londrina
  • Clinical Microbiology
Antibacterial activity
resistance to antimicrobial
antimicrobial alternative
bacterial infection
opportunistic pathogen