الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
”Clostridioides difficile Infection (CDI) is classified in the USA as an urgent threat by the Centers for Disease Control and Prevention (CDC). CDI is the leading cause of nosocomial diarrhea and accounts for 4% of all hospital acquired infections (HAIs) with ” ” ” " ~ " ” ” ” 15% case fatality rates. The CDI prevalence is increasing and associated with the rise of the hypervirulent ribotypes (HVR RTs) like RT023, RT027, and RT078. HVR RTs are nowadays responsible for numerous outbreaks in the hospital setting. Usually driven by antibiotic treatment of a hospitalized patient for other reasons, CDI is often difficult to treat by antimicrobials commonly used in the hospital setting, as HVR RT isolates are frequently multidrug-resistant (MDR) (i.e. resistant to three and more antibiotic classes), leaving only a few antibiotics such as vancomycin or fidaxomicin currently as treatments of choice against CDI.
Thus, the evaluation of new drug candidates against C. difficile is essential, particularly, in times of emerging antimicrobial resistance (AMR). Ideally, these drug candidates display a high activity against C. difficile but are less effective against other members of the gut microbiota thought to suppress the growth of this pathogen in the colon. My studies show that the natural compound argyrin B and some other argyrin derivatives display a promising in vitro antimicrobial activity against a wide variety of epidemiologically important RTs. Notably, these argyrin derivatives were clearly less effective against some members of the healthy gut flora such as Clostridium scindens, Bacteroides fragilis, and Bifidobacterium bifidum, suggesting that the latter bacterial species might be spared by these drug candidates when used for treatment of CDI and thus may help also to prevent the recurrence, which is a common feature of this disease. First preliminary drug susceptibility tests were also carried out for new nucleoside analogues and C. difficile, which suggest that some of these compounds might be also effective against this bacterial species in the low μg/mL range. Further in vitro drug testing studies revealed a promising activity for the Energy coupling factor transporters inhibitors K4104497 and HHPS77 against Clostridium perfringens in the low μg/mL range, while growth of other Clostridium spp. and C. difficile was less affected. Knowledge about the C. difficile strain composition circulating in Germany and their AMR profiles is important for epidemiological and therapeutic reasons. The implementation of a standardized German-wide surveillance for C. difficile in the German hospital setting was thus an important aim of this work and was successfully attained to detect the circulating RTs and their AMR profiles. This study allows for the first time to get an idea about the real situation in the clinical setting by avoiding the bias by the disease severity or the random acquisition of isolates. This study revealed that isolates of the HVR RT027 are less frequently seen nowadays in the German healthcare system than before, and basically the same holds truth for the in Europe epidemiologically relevant RT001, for which the incidence also declined in recent years. MDR was encountered on a low level, but was particularly evident for RT027, supporting earlier findings suggesting that this HVR RT is a major driver for MDR.The identification of C. difficile HVR RTs by ribotyping or whole genome sequencing is costly and time consuming. In order to find a cost-effective and swift way to reliably discriminate between HVR RTs and non-HVR RTs, MALDI-TOF MS was tested here in combination with bioinformatics as third part of my thesis for its suitability to distinguish between both aforementioned groups. Here, my studies revealed that epidemiologically relevant HVR RTs circulating in Europe, such as RTs 023, 027, 045, 078, 126 and 176, could be indeed distinguished by this method from non-HVR-RTs with an accuracy >95% when MALDI-TOF mass spectra were compared to a TICp-based peak matrix in combination with the RF (random forest) or PLS-DA (partial least squares-discriminant analysis) prediction algorithms. A closer look at the HVR RTs revealed that some of the C. difficile HVR RTs such as RTs 023 and 027/176 could be even further subcategorized with an accuracy >94% from other HVR RTs circulating in Germany such as RTs 045, 078, 126 and 127. These findings suggest that MALDI-TOF MS is a fast and powerful tool to inform the clinician if a CDI is caused by a HVR C. difficile isolate that may require special attention.”