Antimicrobial Activity of Antibiotics, Oregano and Thyme Essential Oils against Extended Spectrum Beta Lactamase Producing Klebsiella pneumoniae Clinical Isolates

Aims: The aims of this study was to investigate the susceptibility of extended-spectrum beta-lactamase (ESBL) producing Klebsiella pneumoniae clinical isolates to antibiotics and essential oils - Origanum compactum, Origanum majorana and Thymus serpyllum.

Study Design: Study included 30 isolates of Klebsiella pneumoniae obtained from clinical material provided from the University Clinical Center Tuzla.

Place and Duration of Study: Department of Biology, Faculty of Science, University of Tuzla, BiH, between September 2019 to September 2020.

Methodology: Antibiotic susceptibility testing was performed by the Kirby-Bauer disk diffusion method. The following commercially available antibiotic discs were used: amoxicillin (30µg), cefalexin (30 µg), gentamicin (10 µg), amikacin (30 µg), imipenem (10 µg), piperacillin (75µg), ampicilin (10 µg), meropenem (10 µg), ciprofloksacin (10 µg), ceftazidim (30 µg), cefotaksim (30 µg), ceftriaxone (30 µg), cefepime (30 µg) and aztreonam (30 µg). The antibacterial effect of the essential oils was tested for ESBL K. pneumoniae isolates using the diffusion method according to Clinical laboratory standards institute (CLSI) guidelines.

Results: O. compactum and O. majorana essential oils showed the same antimicrobial activity with 80.0% effect on ESBL K. pneumoniae isolates, Thymus serpyllum EO showed antimicrobial activity of 60.0%. The lowest MIC value had the O. compactum essential oil (MIC 6 mg/ml-10.5 mg/ml), followed by the T. serpyllum (MIC 17.2 mg/ml-43 mg/ml), while the O. majorana essential oil showed MIC values in range from 11 mg/ml to 39 mg/ml.

Conclusion: The results of the study showed the exceptional sensitivity of ESBL K. pneumoniae clinical isolates to the essential oils from Origanum and Thymus genera, which highly suggests their potential application in the struggle against these pathogens in the future.