Reduction of Legionella spp. in water and in soil by a citrus plant extract vapor

Legionnaires disease is a severe form of pneumonia caused by Legionella spp. often isolated from environmental sources including soil and water. Legionella spp. are capable of replicating intracellularly within free living protozoa, once this has occurred Legionella spp. is particularly resistant to disinfectants. Citrus Essential Oils (EOs) vapours are effective antimicrobials against a range of microorganisms, with reductions of 5 log cells ml(-1) on a variety of surfaces. The aim of this investigation was to assess the efficacy of a citrus EO vapour against Legionella spp. in water and in soil systems. Reductions of viable cells of Legionella pneumophila, Legionella longbeachae, Legionella bozemanii and intra-amoebal culture of Legionella pneumophila (water system only), were assessed in soil and in water after exposure to a citrus EO vapour at concentrations ranging from 3.75 mg/l air to 15g/l air. Antimicrobial efficacy via different delivery systems (passive and active sintering of the vapour) was conducted in water and GC-MS analysis of the antimicrobial components (linalool, citral and β-pinene) determined. There was up to a 5 log cells ml(-1) reduction in Legionella spp. in soil after exposure to the citrus EOs vapour (15 mg/l air). The most susceptible strain in water was L. pneumophila with a 4 log cells ml(-1) reduction after 24 hrs via sintering (15 g/l air). Sintering the vapour through water increased the presence of the antimicrobial components, with a 61% increase of linalool. Therefore, the appropriate method of delivery of an antimicrobial citrus EO vapour may go some way in controlling Legionella spp. from environmental sources.