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 β-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.

The accumulation of xenobiotic compounds in different environments interrupts the natural ecosystem and induces high toxicity in non-target organisms. Diclofenac is one of the commonly used pharmaceutical drugs that persist in the environment due to its low natural degradation rate and high toxicity. Therefore, this study aimed to isolate potential diclofenac-degrading bacteria, detect the intermediate metabolites formed, and determine the enzyme involved in the degradation process. Four bacterial isolates were selected based on their ability to utilize a high concentration of diclofenac (40 mg/L) as the sole carbon source. The growth conditions for diclofenac degradation were optimized, and bacteria were identified as Pseudomonas aeruginosa (S1), Alcaligenes aquatilis (S2), Achromobacter spanius (S11), and Achromobacter piechaudii (S18). The highest percentage of degradation was recorded (97.79 ± 0.84) after six days of incubation for A. spanius S11, as analyzed by HPLC. To detect and identify biodegradation metabolites, the GC-MS technique was conducted for the most efficient bacterial strains. In all tested isolates, the initial hydroxylation of diclofenac was detected. The cleavage step of the NH bridge between the aromatic rings and the subsequent cleavage of the ring adjacent to or in between the two hydroxyl groups of polyhydroxylated derivatives might be a key step that enables the complete biodegradation of diclofenac by A. piechaudii S18, as well as P. aeruginosa S1. Additionally, the laccase, peroxidase, and dioxygenase enzyme activities of the two Achromobacter strains, as well as P. aeruginosa S1, were tested in the presence and absence of diclofenac. The obtained results from this work are expected to be a useful reference for the development of effective detoxification bioprocesses utilizing bacterial cells as biocatalysts. The complete removal of pharmaceuticals from polluted water will stimulate water reuse, meeting the growing worldwide demand for clean and safe freshwater.

Mona Warrad , Yasser M. Hassan , Mahmoud S.M. Mohamed , Nashwa Hagagy , Omar A. Al-Maghrabi , Samy Selim , Ahmed M. Saleh and Hamada AbdElgawad . J. Microbiol. Biotechnol. 2020;30:. https://doi.org/10.4014/jmb.2003.03034