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One major factor in the decline is disease caused by infection with <jats:italic>Chlamydia<\/jats:italic>. Current therapeutic strategies to treat chlamydiosis in the koala are limited. This study examines the effectiveness of an inhibitor, JO146, which targets the HtrA serine protease for treatment of <jats:italic>C. pecorum<\/jats:italic> and <jats:italic>C. pneumoniae in vitro<\/jats:italic> and <jats:italic>ex vivo<\/jats:italic> with the aim of developing a novel therapeutic for koala <jats:italic>Chlamydia<\/jats:italic> infections. Clinical isolates from koalas were examined for their susceptibility to JO146. <jats:italic>In vitro<\/jats:italic> studies demonstrated that treatment with JO146 during the mid-replicative phase of <jats:italic>C. pecorum<\/jats:italic> or <jats:italic>C. pneumoniae<\/jats:italic> infections resulted in a significant loss of infectious progeny. <jats:italic>Ex vivo<\/jats:italic> primary koala tissue cultures were used to demonstrate the efficacy of JO146 and the non-toxic nature of this compound on peripheral blood mononuclear cells and primary cell lines established from koala tissues collected at necropsy. Our results suggest that inhibition of the serine protease HtrA could be a novel treatment strategy for chlamydiosis in koalas.<\/jats:p>","DOI":"10.1038\/srep31466","type":"journal-article","created":{"date-parts":[[2016,8,17]],"date-time":"2016-08-17T09:08:33Z","timestamp":1471424913000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":31,"title":["Chlamydia Serine Protease Inhibitor, targeting HtrA, as a New Treatment for Koala Chlamydia infection"],"prefix":"10.1038","volume":"6","author":[{"given":"Amba","family":"Lawrence","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Tamieka","family":"Fraser","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Amber","family":"Gillett","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Joel D. 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