ABSTRACT
AIM: This study aimed to test biofilm inhibition activities of each of essential oils (EOs), main compounds of EOs and enzymes against pathogenic Klebsiella pneumoniae. METHODS AND RESULTS: The effect of seven EOs and three enzymes was tested on formation and eradication of K. pneumoniae biofilm. Peppermint oil showed a robust biofilm inhibitory effect, causing inhibition that ranged from 69·2 to 98·2% at 5 µl ml-1 . Thyme oil was found to have the best biofilm eradication ability, causing eradication that ranged from 80·1 to 98·0% at 10 µl ml-1 . The most effective EOs were analysed by GC/MS, to determine the major chemical constitutes of each oil. Pure menthol was found to cause 75·3-97·5% biofilm inhibition at 2·5 µg ml-1 , whereas thymol caused 85·1-97·8% biofilm eradication at 5 µg ml-1 . However, moderate inhibition activity was detected for α-amylase and bromelain, while poor activity was detected for ß-amylase. Ciprofloxacin combination with thyme oil and thymol was found to enhance antibiotic activity, and affect biofilm cell viability. The observed inhibitory/eradication activity on K. pneumoniae biofilms was confirmed by scanning electron microscopy. CONCLUSIONS: Thyme and peppermint EOs, and their active components are promising antibiofilm agents alone and/or in combination with ciprofloxacin to inhibit/eradicate biofilms of K. pneumoniae. SIGNIFICANCE AND IMPACT OF THE STUDY: The presented results suggest the potential application of EOs against infections, caused by biofilm-producing K. pneumoniae, to prevent biofilm formation or decrease their resistance threshold. Moreover, the combination of EOs with ciprofloxacin minimizes the antibiotic concentration used and accordingly the potential accompanying toxic side effects.
