In vitro susceptibility of beta-lactamase producing Pseudomaonas aeruginosa isolates to antibiotics and essential oils
Background : As antibiotic resistance in microorganisms is increasing and becoming a global problem, essential oils should be considered as new chemical substances with potenial therapeutic effects. Aim of the study : Determine the susceptibility of beta-lactamase clinical isolates of Pseudomonas aeruginosa to antibiotics and essential oils, define the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) for tested oils. Material and Methods : This study included 120 P. aeruginosa isolates from clinical material. A disc diffusion method was used to for determination of antibiotic and essential oil susceptibility profile. For the phenotypic detection of beta-lactamase isolates, a disk diffusion method was used according to the CLSI guidelines with clavulanic acid. MIC was determined by microdilution test in broth. MBC was recorded after determination of MIC, it was corresponded to the lowest concentration of the essential oil yielding negative subcultures after incubation at appropriate temperature for 24 h. Results : Of the three tested oils, Origanum compactum had the strongest antimicrobial effect (MIC 6.4 mg/ml - 9.3 mg / ml) on P. aeruginosa isolates followed by Thymus serpylum (MIC 13 mg / ml to 78 mg / ml) and Origanum majorana ( MIC 21,5 mg/ml do 43 mg/ml ). Conclusion : Beta-lactamase producing P. aeruginosa isolates resistant to third and forth genetration of cephalosporin antibiotics, showed susceptibility against tested essential oils.