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Measurement instead of culture – rapid detection of Legionella

There has been an unusually high frequency of Legionella infections in the city of Ulm in the period since mid-December 2009. The search for the source of the infection is well underway, although the use of traditional detection methods make it a time-consuming process. New screening methods developed by the Fraunhofer IPM could considerably reduce the time required to detect the source of infection.

A frequent headline in the regional papers relating to the search of the source of infection has been “Initial results will be available in a week’s time”. The reason it takes so long to obtain laboratory results is due to the bacteria culture method that is commonly used to detect Legionella bacteria. In the time it takes to culture the bacteria, many people are likely to be infected. Certain air conditioning systems – such as the so-called wet cooling systems found in many buildings - are often linked with outbreaks of Legionnaires’ disease. In order to speed up the detection of the sources of infection in future, the Fraunhofer Institute for Physical Measurement Techniques IPM in Freiburg is working on the development of analysis methods that enable the detection of biological particles in just a few hours.

A time-consuming process: Bacteria detection by culture

Legionella bacteria, approximately two to five micrometres in size, are found in humid environments. They grow particularly well in standing water at a temperature of between 25 and 45° C. Common sources of Legionella include water installations, air humidifiers, air conditioning systems, shower heads or whirlpools. The inhalation of water droplets containing Legionella can lead to pneumonia in cases where the bacteria concentration is relatively high (around 1000 bacteria per millilitre) and the droplets are very small. Legionella infections require infected individuals to be treated, and also, and most importantly, the source of infection needs to be removed in order to prevent the further spread of the bacteria. Unfortunately, the standard method of detecting Legionella takes four to seven days: Samples are taken and propagated in a culture medium before it is possible to characterise the bacteria. As it is not possible to speed this method up to any great extent, the Fraunhofer IPM chooses not to employ the culture method and has instead specialised in the rapid detection of individual biological particles and pathogens. Every additional day it takes to search for the source of infection, more infections occur, as has been the case in Ulm.

Rapid: Innovative screening methods

New screening methods such as Fraunhofer IPM’s automated Raman spectroscope enable the rapid and precise characterisation of bacteria. © Fraunhofer IPM

Particles of only a few micrometres in size such as fine dust or pollen can lead to a broad range of respiratory diseases. Airborne pathogens or bacteria, such as the Legionella bacteria currently spreading around the city of Ulm, are far more dangerous than dust and pollen, albeit less frequent. If an early warning system to detect low pathogen concentrations in the air were available, the spread of the pathogens could be contained in good time and infections prevented. The Fraunhofer IPM is currently carrying out four projects that are excellent examples of the IPM researchers' know-how in the development of fully automated systems for the optical detection of particles. These systems are able to measure pollen concentrations and the composition of fine dust as well as to identify different pathogens and their concentration. The Fraunhofer IPM is interested in identifying potential partners to participate in the further development of the systems and their adaptation to special requirements.

BioRaman: Raman spectroscopy enables the identification of individual bacteria via a spectral fingerprint. On the basis of this technology, the Fraunhofer IPM and other Fraunhofer Institutes have joined forces in the "BioRaman" project in order to develop a procedure for the sterility testing of cartilage transplants and cell cultures. This system has the potential to be easily adapted to the detection of Legionella.

Secure Air: In order to develop a test system that can quickly and specifically detect airborne microorganisms at the source of pollution, the Fraunhofer IPM and other Fraunhofer Institutes are working together on the "Secure Air" collaborative project. The scientists are working with the same specific antibodies used by organisms to fend off intruders. The coupling of these antibodies with fluorescent markers enables the optical detection of the type and number of harmful microorganisms. A pilot test system is already available.

MONET: On behalf of the company GIP Messinstrumente GmbH and in cooperation with other partners, the Fraunhofer IPM is developing the "MONET" system for the molecule-specific identification of (fine) dust particles. The system contains a device that enables the rapid online preclassification of aerosol particles according to their composition. In just a few minutes, "MONET" provides information about the total number of particles in the air along with the biotic and abiotic proportions in different size classes. This enables the rapid detection of biotic particles such as Legionella.

Biochip reader: The Fraunhofer IPM has developed a platform for the analysis of biochips that are read in a space-resolved manner using a fluorescence-based optical method. This enables the parallel analysis of a large number of samples in low concentrations. This platform is currently being used for diagnostic applications, but is also used for the detection of microorganisms, providing specific information in a very short time.

Fraunhofer IPM:
The Fraunhofer Institute for Physical Measurement Techniques IPM has long-standing experience in optical 2D and 3D measurement technologies. The Institute develops and produces ready-to-use optical sensor and illumination systems. The Institute's major focus is the automated monitoring of biological samples, involving methods such as microscopy, holography, interferometry, Raman spectroscopy and fluorescence measurement techniques. The systems function autonomously and require minimum maintenance - whether they are used in laboratories or elsewhere.

Website address: https://www.gesundheitsindustrie-bw.de/en/article/press-release/measurement-instead-of-culture-rapid-detection-of-legionella