Investigation of the deposition behaviour and antibacterial effectivity of allicin aerosols and vapour using a lung model

Allicin is a natural antibiotic produced by garlic as a defence against pathogens and pests. Due to the worldwide increase in antibiotic resistance, new antibiotics are desperately required. Allicin is such a candidate and is active against several multidrug-resistant (MDR) strains of human pathogens, including methicillin-resistant Staphylococcus aureus (MRSA). When administered orally, allicin is titrated out by glutathione in the cells and blood, and effective therapeutic concentrations are difficult to achieve at the site of an infection. However, in the case of lung infections, allicin can be delivered directly to pathogens via the pulmonary route. In this study, we designed and constructed an in vitro lung test rig, which allowed us to model accurately the exposure of lung air-passage surfaces to allicin and gentamicin, in order to examine the feasibility of combating lung infections by direct inhalation. A prototype test rig of lung bronchi with three bifurcations was constructed, which could be coated internally with a thin layer of bacteria-seeded agar medium. The deposition of antimicrobial aerosols on the modelled bronchial surfaces was followed in preliminary tests without the need for animal experiments. The differential sensitivity of the test bacteria to different antibiotics and the dose-dependency of inhibition was shown using the model. Furthermore, a synergistic effect of allicin vapour and ethanol in inhibiting bacterial growth was demonstrated. The modelling of the axial velocity air-flow distribution correlated with the regions indicating the inhibition of bacterial growth, demonstrating that the model has predictive value and can reduce the requirement for animal sacrifice in pre-clinical trials of novel antibiotics.