Abstract

This study started in February 2022 for two years; swab and water samples were collected from air conditioners. Identification was subsequently confirmed through 16S rRNA sequencing. Minimum inhibitory concentration (MIC) was performed on the isolated strains. Then determine the ability of these isolates for biofilm formation then the ability of some natural products to decrease their presence. In the analysis of 600 samples, four (0.7%) tested positive for Legionella spp. Strains of L. pneumophila displayed sensitivity to meropenem, levofloxacin, clarithromycin, doxycycline and erythromycin and the result of MIC were between 0.01: 0.04 μg/ml, 0.06: 0.5 μg/ml, 0.03: 0.25 μg/ ml, 0.03: 0.67 μg/ ml, 0.13:1 μg/ ml, respectively also, they were able to form strong biofilm. The natural products like clove, lemon grass and rosemary oil have a strong antibacterial effect against L. pneumophila with MIC range 0.78%-1.56%vv, 0.2%-0.78% vv and 0.39%-6.25% vv respectively. The addition of EOs at sub-MIC concentrations to media resulted in a reduction of existing biofilms by a rate of more than 99%. The presence of pathogenic and potentially lethal L. pneumophila infections can be linked to air conditioning systems. Continuous monitoring of these appliances and using natural products are essential to prevent the proliferation of this bacterium and associated health risks.

Key words: Legionella pneumophila, MIC, Biofilm, Natural products, Anti biofilm.