A synergistic anti-bacterial and anti-adhesion activity of tea tree (Melaleuca alternifolia) and lemon eucalyptus tree (Eucalyptus citriodora Hook) essential oils on Legionella pneumophila

Legionella pneumophila is a Gram-negative bacterial pathogen that colonizes natural and artificial water systems and has the ability to form a biofilm. The biofilm protects L. pneumophila from various environmental factors and makes it more resistant to chlorine-based disinfectants. This study investigated the anti-bacterial properties of tea tree (Melaleuca alternifolia (Maiden and Betche) Cheel) oil and lemon eucalyptus tree (Eucalyptus citriodora Hook) essential oils (EOs) and their synergistic, additive inhibitory and anti-adhesive effects against L. pneumophila biofilm formation on polystyrene. The minimum effective concentration (MEC) for tea tree is 12.8 mg ml-1 and for lemon eucalyptus tree EO 6.4 mg ml-1. In the checkerboard assay, different combinations of these two EO show synergistic and additive anti-microbial activity. The minimum anti-adhesive concentration (MAC) for tea tree is 12.8 mg ml-1 and for lemon eucalyptus tree EO 6.4 mg ml-1. A combination of 3.2 mg ml-1 tea tree EO and 0.8 mg ml-1 lemon eucalyptus tree EO showed the strongest anti-adhesive effect against L. pneumophila on polystyrene. The tested oils and their combination showed intriguing potential to inhibit L. pneumophila biofilm formation.

Ozone disinfection efficiency against airborne microorganisms in hospital environment: a case study

Even though ozone has shown its potential for air disinfection in hospital environment, its more frequent use has earned attention only with the COVID-19 pandemic due to its proven antimicrobial effect and low cost of production. The aim of this study was to determine its antimicrobial efficiency against the most common bacterial species in a real-life setting, that is, in the air of one postoperative room of the General Hospital Dr Ivo Pedišić (Sisak, Croatia). Air was sampled for aiborne bacteria before and after treatment with the ozone concentration of 15.71 mg/m3 for one hour. The most dominant Gram-positive bacteria of the genera Micrococcus, Staphylococcus, and Bacillus were reduced by 33 %, 58 %, and 61 %, respectively. The genus Micrococcus proved to be the most resistant. Considering our findings, we recommend longer air treatment with higher ozone concentrations in combination with mechanical cleaning and frequent ventilation.

Disinfecting Action of Gaseous Ozone on OXA-48-Producing Klebsiella pneumoniae Biofilm In Vitro

Klebsiella pneumoniae is an emerging multidrug-resistant pathogen that can contaminate hospital surfaces in the form of a biofilm which is hard to remove with standard disinfectants. Because of biofilm resistance to conservative disinfectants, the application of new disinfection technologies is becoming more frequent. Ozone gas has antimicrobial activity but there is lack of data on its action against K. pneumoniae biofilm. The aim of this study was to investigate the effects and mechanisms of action of gaseous ozone on the OXA-48-procuding K. pneumoniae biofilm. A 24 h biofilm of K. pneumoniae formed on ceramic tiles was subsequently exposed to different concentrations of ozone during one and two hours to determine the optimal ozone concentration. Afterwards, the total bacteria count, total biomass and oxidative stress levels were monitored. A total of 25 ppm of gaseous ozone was determined to be optimal ozone concentration and caused reduction in total bacteria number in all strains of K. pneumoniae for 2.0 log₁₀ CFU/cm², followed by reduction in total biomass up to 88.15%. Reactive oxygen species levels significantly increased after the ozone treatment at 182% for the representative K. pneumoniae NCTC 13442 strain. Ozone gas in the concentration of 25 ppm caused significant biofilm reduction but did not completely eradicate the K. pneumoniae biofilm formed on ceramics. In conclusion, ozone gas has great potential to be used as an additional hygiene measure in joint combat against biofilm in hospital environments.