| Legionella pneumophila, an aquatic gram-negative rod-shaped bacterium, is the causative agent for a severe form of pneumonia called Legionnaires' disease, and a much less severe malady called Pontiac Fever. Currently, the definitive and main method to detect L. pneumophila is by culturing the organism, which is both time-consuming and labor intensive. Real-time detection of L. pneumophila in water found in aerosol disseminating devices will minimize the risk for Legionnaires' disease. Our objective in this study was to develop and evaluate a quartz crystal microbalance (QCM) biosensor for rapid detection of L. pneumophila in both liquid and aerosol forms. This acoustic wave device consists of a quartz crystal coated with a polyclonal antibody specific for L. pneumophila serogroup 1 (SG1) by a modified and patented Langmuir-Blodgett (LB) technique. When the surface of the sensor is exposed to L. pneumophila , the bacteria are captured by the LB film, causing a change in the sensor resonance frequency. This frequency shift, measured as a voltage output by a Maxtek plating monitor, is hypothesized to be due to viscoelastic changes of the LB film-bacteria near surface fluid media and the mass change associated with the binding of bacteria. After several antibody sources were evaluated, a commercial antibody was selected. Our sensitivity experiments showed rapid (<100s) and sensitive (409 mV/decade, R = 0.98) detection of L. pneumophila SG1 in liquid form. Selectivity experiments showed a significantly lower response to Escherichia coli, Aeromonas hydrophila and Salmonella typhimurium. The interaction of the target bacterial species, L. pneumophila, with the surface of the biosensor is specific because the response to antibody-blocked L. pneumophila is significantly less sensitive than that to the unblocked form. Preliminary studies assaying the performance of the biosensor for the detection of aerosolized L. pneumophila were promising, however, more research and development of this system is needed. Further testing and development should yield a hand-held device that can be used in the field. |
