Antibacterial activity of supercritical Usnea barbata extract against staphylococci, streptococci and enterococci originated from animals

Abstract number: P1246

Misic D., Ivanovic J., Zizovic I.

Objectives: Studies of antimicrobial activity of extracts obtained by the process of supercritical fluid extraction (SFE) are mainly performed on foodborne pathogens because of potential use of supercritical extracts as food additives. Due to the lack of new antibiotics on the market, studies of antibacterial activities of supercritical extracts on pathogenic bacteria are more present nowadays, with the objective to treat humans and animals in cases of infections. It is well known that plant extracts obtained by different technologycal processes have good antimicrobial activity, but mostly, they contain traces of organic solvents so they are unsuitable for pharmaceutical and nutritional use. Plant extracts obtained by SFE do not contain any solvents.

Methods: In this investigation, lichen Usnea barbata was used for the SFE. Supercritical extraction with CO2 as a slovent was performed in the Autoclave Engineers Screening System at pressure of 30 MPa and temperature of 60°C. For the determination of MIC values of supercritical usnea extract, broth microdillution method (CLSI, 2008) was used, and the extract was previously dissolved in 1–2 propanediol. For comparison of the results, erythromycin was included too. The investigation has been performed on 14 Staphylococcus, Streptococcus, and Enterococcus strains of animal origin including VRE, MRSA and ATCC strains.

Results: Determined MIC values of the supercritical usnea extract for all strains ranged from 1.25 to 80 mcg/mL and MIC values of erythromycin ranged from 0.06 to >32 mcg/mL. The strongest antibacterial activity with MIC value of 1.25 mcg/mL usnea extract showed on two S. intermedius strains isolated from dogs' skin swabs. The weakest antibacterial activity with MIC value of 80 mcg/mL supercritical extract showed on S. aureus ATCC 11632 and on 1 MRSA strain isolated from dog's wound swab. Investigated supercritical extract showed good antibacterial activity against streptococci and enterococci including VRE with obtained MIC values of 10 to 40 mcg/mL. One methicillin-resistant S. haemolyticus strain isolated from ear swab of cat and 1 S. uberis strain originated in guinea pig were resistant to erythromycin with MIC value >32 mcg/mL but MIC values of supercritical extract for these two strains were significantly lower, 10 to 20 mcg/mL.

Conclusion: According to obtained low MIC values, investigated supercritical usnea extract showed very strong antibacterial activity against investigated bacteria.