Discussion:

The walls of the bio-clean room were composed of non-interrupted acrylic plates, which are required for the successful aerosolization of bacterial cells. A Hypalon® glove attached to the front down panel of the bio-clean room protected the user's hands against the airborne bacterial cells. In this study, the effects of essential oils on airborne bacteria were examined in a bio-clean room. Essential oils, which are aromatic and volatile products of plant secondary metabolism, are widely used in folk medicine, food flavoring and preservation, and fragrances. The anti-bacterial activities of essential oils from various plants have been described by numerous studies (15–17).

Essential oils have been used medicinally (18,19). The use of essential oils has been revived in the past few decades with the increasing popularity of aromatherapy, a branch of alternative medicine that claims that essential oils and other aromatic compounds have curative effects. The oils are distilled or volatilized in solutions and used for massages. Essential oils can also be dispersed into the air by a spray or heated over a candle flame for aromatherapy (20). In this study, we evaluated the anti-airborne bacterial activities of three concentrations of essential oils (0.0005, 0.005 and 0.05 ppm) dispersed by artificial essential oil humidification on Gram-negative and -positive bacteria.

During the dry seasons, warm and humid environments affect the response of plasma pro- and anti-inflammatory cytokines (21). Dry eye is one of the most common pathological manifestations of chronic graft-versus-host disease, occurring in up to 80% of patients (22). Low or high humidity may cause specific physical discomfort since relative humidity directly affects temperature perception (23). Diseases may be transmitted by airborne pathogens, direct contact with pathogens living on hard surfaces or by touching an infected person. Low humidity has been found to improve the survival of rhinoviruses, influenza virus (24) and human rotavirus (25,26). The incidence of airborne-transmitted infectious disease in an indoor environment is dependent on a number of factors, including the concentration of aerosolized pathogens, ventilation rate and survival of pathogens attached to the aerosol (20). The indoor relative humidity may affect some of these factors, including settling rate of the aerosols and survival of the airborne pathogens (27).

Patients and healthy individuals require optimal humidification to maintain a moisturized respiratory tract necessary for protection against bacterial infection during the drier winter months. However, humidifiers are associated with certain health risks. For example, the water tank and tract of humidifiers are easily polluted by airborne pathogens and allergens. Humidifier disinfectants have been regularly used to clean humidifiers. However, warnings about the health risks associated with humidifier disinfectants have been issued by the Korean Center for Disease Control and Prevention advising against the use of humidifier sterilizers. The notification was issued after a civic group claimed that 18 pregnant females succumbed to lung disease which was considered to have been caused by disinfectants in the machines.

The results from our study demonstrated that the growth of airborne bacterial cells decreased following exposure to three different concentrations of essential oils (0.0005, 0.005 and 0.05 ppm) in a customized bio-clean room. It is possible that these essential oils may be used as anti-airborne bacterial agents, and humidifier disinfectants in commercial humidifiers and air cleaners. However, the mechanisms underlying the anti-airborne bacterial effects of essential oils require further examination.

Note: yellow highlights are mine