Lena Heining successfully defended her PhD-Thesis - Congratulations!

Abstract
Ever since the identification of the bacterium Legionella pneumophila in 1976, there have been recurrent outbreaks, largely due to contaminated aerosols from evaporative cooling systems. Given the potential risk of infection through inhalation, it is imperative to 
conduct regular testing for L. pneumophila in aerosols. The aim of this dissertation was to uncover novel perspectives on the
collection and analysis strategies for L. pneumophila in aerosols, as well as to enhance our comprehension of the efficiency of biocides in evaporative cooling systems.
The first topic focused on culture-independent analytical methods for the quantitative detection of L. pneumophila in aerosols. This is particularly crucial as the commonly used cultivation method has significant drawbacks, including a lengthy analysis time and the exclusion of living but non-culturable (VBNC) cells. The findings demonstrated that immunomagnetic separation coupled with flow cytometry (IMS-FCM) presents a viable alternative method. Not only did this approach yield results within 2 hours with a recovery rate exceeding 60%, but it also enabled differentiation between intact and damaged cells. Consequently, both cultivable and VBNC cells could be analyzed. This represents a pivotal advantage, particularly for the management of risk in evaporative cooling systems. In the investigation of Legionella in aerosols, the choice of a suitable collection method is crucial. The Coriolis® μ cyclone sampler and the AGI-30 impinger are well-established collection systems. However, the introduction of the Next Generation Impactor (NGI) marked a significant innovation in the application of bacteria-containing bioaerosols. Unlike previous applications, which were primarily experiments involving the inhalation of powdered medications, the NGI has successfully been employed for wet droplet bioaerosols for the first time. It boasts an exceptional biological sampling efficiency of over 90% at 100% relative humidity and allows for the use of culture-independent methods. Notably, its ability to determine droplet size distribution has revealed the dependency of distribution on humidity and the presence of multiple bacterial cells in larger droplets. The presence of L. pneumophila in biofilms is critical for disinfection processes due to its shielding effect. Additionally, the role of amoebae is significant as L. pneumophila can infect and multiply within them. To mimic the nebulization process of real systems, a biofilm chamber was developed, allowing biofilm growth in process water and an aerosol atmosphere. By introducing L. pneumophila and the amoeba Hartmanella vermiformis, we were able to study the impact of amoebae on bacterial survival when a biocide is applied. Our findings revealed that cells within the biofilm exhibited a higher survival rate, with amoebae also demonstrating a protective effect, albeit less prominently. Furthermore, notable differences between oxidizing (H2O2) and non-oxidizing (2,2-dibromo-2-cyanoacetamide) biocides were observed, particularly in achieving increased cell damage and inactivation with the non- oxidizing biocide.