Comparing methods of determining Legionella spp. in complex water matrices
Álvaro Díaz-Flores1, Juan Carlos Montero2, Francisco Javier Castro3
1Departamento de Microbiología General III, Facultad de Ciencias Biológicas, Universidad Complutense de Madrid, Campus Moncloa, 28040, Madrid, Spain. alvarodiazflores@pas.ucm.es.
BMC Microbiology
|May 1, 2015
Summary
The immunomagnetic separation (IMS) method significantly improves Legionella detection in water samples compared to traditional culture and qPCR methods. This new approach reduces inconclusive results, enabling more effective risk assessment and management of Legionella exposure.
Area of Science:
- Environmental microbiology
- Water quality analysis
- Infectious disease epidemiology
Background:
- Legionella testing is crucial for water system safety but faces challenges with current methods.
- Culture-based methods can yield up to 20% inconclusive results due to microbiota overgrowth, underestimating risk.
- Quantitative polymerase chain reaction (qPCR) also faces challenges, with inhibitors causing up to 10% inconclusive results.
Purpose of the Study:
- To compare a quantitative immunomagnetic separation (IMS) method with traditional culture and qPCR for Legionella monitoring.
- To evaluate the IMS method's effectiveness in detecting Legionella in environmental samples, especially in the presence of interfering factors.
- To assess the potential of the IMS method for routine monitoring and improved risk management of Legionella.
Main Methods:
- Pilot studies assessed Legionella recovery and detectability using the IMS method with simulated environmental conditions (microbiota, biocides).
- A total of 65 environmental water samples were analyzed using culture, qPCR, and the IMS method.
- The IMS method was evaluated for its ability to overcome limitations of culture (microbiota interference) and qPCR (inhibition).
Main Results:
- The IMS method showed no impact from microbiota, unlike culture methods which were significantly reduced (1.4 log) or negative.
- Of 65 samples, 27 tested positive by at least one method. Culture detected Legionella in 7 samples (25.9%), while IMS detected it in 18 samples (66.7%).
- Culture and qPCR yielded high rates of inconclusive results (36.9% and 12.3% respectively), whereas the IMS method produced no inconclusive results.
Conclusions:
- The IMS method enhances Legionella recovery and detectability in environmental samples.
- The IMS method shows promise as a valuable indicator for assessing Legionella risk.
- Implementing the IMS method can improve understanding of exposure risk and inform evidence-based monitoring and disinfection strategies.
