Abstract
The aim of this study was to analyze the antibacterial activity of four essential oils (EOs), Melaleuca alternifolia, Eucalyptus globulus, Mentha piperita, and Thymus vulgaris, in preventing the development and spread of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae, metallo-beta-lactamase (MBL)-producing Pseudomonas aeruginosa and carbapenemase (KPC)-producing Klebsiella pneumoniae. A total of 60 strains were obtained from the stock collection from the Microbiology Laboratory of Hesperia Hospital, Modena, Italy. Twenty ESBL-producing E. coli, 5 K. pneumoniae, 13 KPC-producing K. pneumoniae, and 20 MBL-producing P. aeruginosa were cultured and reconfirmed as ESBL and carbapenamase producers. Polymerase chain reaction was used for the detection of genes responsible for antibiotic resistance (ESBL and KPC/MBL). Antibacterial activity of the EOs was determined using the agar disk diffusion assay, and minimal inhibitory concentrations (MICs) were also evaluated. Lastly, adhesion capability and biofilm formation on polystyrene and glass surfaces were studied in 24 randomly selected strains. M. alternifolia and T. vulgaris EOs showed the best antibacterial activity against all tested strains and, as revealed by agar disk diffusion assay, M. alternifolia was the most effective, even at low concentrations. This effect was also confirmed by MICs, with values ranging from 0.5 to 16 µg/mL and from 1 to 16 µg/mL, for M. alternifolia and T. vulgaris EOs, respectively. The EOs’ antibacterial activity compared to antibiotics confirmed M. alternifolia EO as the best antibacterial agent. T. vulgaris EO also showed a good antibacterial activity with MICs lower than both reference antibiotics. Lastly, a significant anti-biofilm activity was observed for the two EOs (*P < 0.05 and **P < 0.01 for M. alternifolia and T. vulgaris EOs, respectively). A good antibacterial and anti-biofilm activity of M. alternifolia and T. vulgaris EOs against all selected strains was observed, thus demonstrating a future possible use of these EOs to treat infections caused by ESBL/carbapenemase-producing strains, even in association with antibiotics.
Highlights
The improper and uncontrolled use of antibiotics in human and veterinary medicine resulted in the occurrence of multi drug resistant (MDR) strains, which have become a major health concern worldwide [1,2,3,4]
Out of the 60 strains analyzed, 27 (45%) strains showed an increase (5 mm) in the inhibition zone diameter for cefotaxime and ceftazidime in the presence of amoxicillin/clavulanic acid (AMC) compared to when these antibiotics were tested alone: These isolates were classified as extended-spectrum beta-lactamase (ESBL) producers
The results revealed that M. alternifolia essential oils (EOs) had a wide antibacterial spectrum and inhibited the growth of almost all tested strains (Figure 1)
Summary
The improper and uncontrolled use of antibiotics in human and veterinary medicine resulted in the occurrence of multi drug resistant (MDR) strains, which have become a major health concern worldwide [1,2,3,4]. The widespread use of antimicrobials, primarily antibiotics, and the transmissibility of resistance determinants mediated by plasmids, transposons, and gene cassettes in integrons contributed to the spread of resistance [7]. This problem of increasing resistance imposed the search for safe and effective factors that might be used to treat persistent bacterial infections. The severity and extent of diseases caused by these pathogens are amplified when the pathogens are organized in biofilms, the most relevant structures responsible for persistent infections, that constitute a major challenge for microbiologists and clinicians
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