{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,15]],"date-time":"2026-07-15T12:04:38Z","timestamp":1784117078977,"version":"3.55.0"},"reference-count":51,"publisher":"MDPI AG","issue":"12","license":[{"start":{"date-parts":[[2021,12,12]],"date-time":"2021-12-12T00:00:00Z","timestamp":1639267200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"European Union\u2019s Horizon 2020 Fast Track to Innovation Pilot-2015-1 Program","award":["720480\u2014ID-LYME"],"award-info":[{"award-number":["720480\u2014ID-LYME"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Pathogens"],"abstract":"<jats:p>Chlamydia trachomatis is an obligate intracellular pathogenic bacterium with a biphasic developmental cycle manifesting two distinct morphological forms: infectious elementary bodies (EBs) and replicative intracellular reticulate bodies (RBs). Current standard protocols for quantification of the isolates assess infectious particles by titering inclusion-forming units, using permissive cell lines, and analyzing via immunofluorescence. Enumeration of total particle counts is achieved by counting labeled EBs\/RBs using a fluorescence microscope. Both methods are time-consuming with a high risk of observer bias. For a better assessment of C. trachomatis preparations, we developed a simple and time-saving flow cytometry-based workflow for quantifying small particles, such as EBs with a size of 300 nm. This included optimization of gain and threshold settings with the addition of a neutral density filter for small-particle discrimination. The nucleic acid dye SYBR\u00ae Green I (SGI) was used together with propidium iodide and 5(6)-carboxyfluorescein diacetate to enumerate and discriminate between live and dead bacteria. We found no significant differences between the direct particle count of SGI-stained C. trachomatis preparations measured by microscopy or flow cytometry (p &gt; 0.05). Furthermore, we completed our results by introducing a cell culture-independent viability assay. Our measurements showed very good reproducibility and comparability to the existing state-of-the-art methods, indicating that the evaluation of C. trachomatis preparations by flow cytometry is a fast and reliable method. Thus, our method facilitates an improved assessment of the quality of C. trachomatis preparations for downstream applications.<\/jats:p>","DOI":"10.3390\/pathogens10121617","type":"journal-article","created":{"date-parts":[[2021,12,13]],"date-time":"2021-12-13T01:29:33Z","timestamp":1639358973000},"page":"1617","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":7,"title":["A Novel Flow Cytometric Approach for the Quantification and Quality Control of Chlamydia trachomatis Preparations"],"prefix":"10.3390","volume":"10","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-2689-5159","authenticated-orcid":false,"given":"Romana","family":"Klasinc","sequence":"first","affiliation":[{"name":"Institute for Hygiene and Applied Immunology, Center for Pathophysiology, Infectiology and Immunology, Medical University of Vienna, 1090 Vienna, Austria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7435-7999","authenticated-orcid":false,"given":"Michael","family":"Reiter","sequence":"additional","affiliation":[{"name":"Institute for Hygiene and Applied Immunology, Center for Pathophysiology, Infectiology and Immunology, Medical University of Vienna, 1090 Vienna, Austria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8809-2530","authenticated-orcid":false,"given":"Astrid","family":"Digruber","sequence":"additional","affiliation":[{"name":"Institute of Microbiology, Department of Pathobiology, University of Veterinary Medicine Vienna, 1210 Vienna, Austria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Waltraud","family":"Tschulenk","sequence":"additional","affiliation":[{"name":"Institute of Morphology, Department of Pathobiology, University of Veterinary Medicine Vienna, 1210 Vienna, Austria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5038-188X","authenticated-orcid":false,"given":"Ingrid","family":"Walter","sequence":"additional","affiliation":[{"name":"Institute of Morphology, Department of Pathobiology, University of Veterinary Medicine Vienna, 1210 Vienna, Austria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Alexander","family":"Kirschner","sequence":"additional","affiliation":[{"name":"Institute for Hygiene and Applied Immunology, Center for Pathophysiology, Infectiology and Immunology, Medical University of Vienna, 1090 Vienna, Austria"},{"name":"Division Water Quality & Health, Department Pharmacology, Physiology and Microbiology, Karl Landsteiner University of Health Sciences, 3500 Krems, Austria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2657-6836","authenticated-orcid":false,"given":"Andreas","family":"Spittler","sequence":"additional","affiliation":[{"name":"Core Facility Flow Cytometry and Department of Surgery, Research Laboratories, Medical University of Vienna, 1090 Vienna, Austria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6404-4430","authenticated-orcid":false,"given":"Hannes","family":"Stockinger","sequence":"additional","affiliation":[{"name":"Institute for Hygiene and Applied Immunology, Center for Pathophysiology, Infectiology and Immunology, Medical University of Vienna, 1090 Vienna, Austria"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2021,12,12]]},"reference":[{"key":"ref_1","first-page":"e235","article-title":"Sexually transmitted infections: Challenges ahead. 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