{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,23]],"date-time":"2026-10-23T17:40:54Z","timestamp":1792777254349,"version":"4.5.0"},"reference-count":26,"publisher":"American Veterinary Medical Association (AVMA)","license":[{"start":{"date-parts":[[2026,10,23]],"date-time":"2026-10-23T00:00:00Z","timestamp":1792713600000},"content-version":"unspecified","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by-nc\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["javma"],"published-print":{"date-parts":[[2026,10,23]]},"abstract":"Abstract<\/jats:title>\n \n Objective<\/jats:title>\n \n To develop a multiplex real-time PCR assay for simultaneous detection of\n Rhodococcus equi<\/jats:italic>\n (\n choE<\/jats:italic>\n ), virulence (\n vapA<\/jats:italic>\n ), and macrolide-resistance determinants (\n erm<\/jats:italic>\n [46],\n erm<\/jats:italic>\n [51]), and evaluate their clinical and temporal trends.\n <\/jats:p>\n <\/jats:sec>\n \n Methods<\/jats:title>\n \n Clinical\n R equi<\/jats:italic>\n isolates (n = 229) obtained from the Hagyard Equine Medical Institute laboratory were collected sequentially over a 3-year surveillance period (2021 to 2023) from 14 states and underwent broth microdilution susceptibility testing. A cohort of 214 isolates with high-quality DNA was characterized using quantitative PCR. Geographic distribution, seasonal trends, and genotypic-phenotypic concordance were evaluated.\n <\/jats:p>\n <\/jats:sec>\n \n Results<\/jats:title>\n \n The multiplex PCR assay demonstrated 100% analytical specificity. The virulence gene\n vapA<\/jats:italic>\n was present in 94.4% (202 of 214) of isolates. The macrolide resistance determinant\n erm<\/jats:italic>\n (46) was highly prevalent at 62.6% (134 of 214), showing a significant seasonal increase during July to December periods at 76.6% (vs 58.2% in January to June). Crucially,\n erm<\/jats:italic>\n (51) was detected in a single isolate (0.5%), representing its first recorded clinical identification in\n R equi<\/jats:italic>\n . Unstratified genotypic-phenotypic agreement for macrolides was fair (\u03ba = 0.22 to 0.25). However, stratification by genomic copy number revealed near-perfect concordance (\u03ba \u2265 0.97) exclusively among isolates harboring > 50,000 target copies. Alternative agents (gentamicin, ceftiofur, minocycline, doxycycline) maintained 97% to 100% susceptibility, regardless of\n erm<\/jats:italic>\n (46) status.\n <\/jats:p>\n <\/jats:sec>\n \n Conclusions<\/jats:title>\n \n While\n erm<\/jats:italic>\n (46) is widely distributed across\n R equi<\/jats:italic>\n \u2013endemic farms, actual phenotypic resistance expression is strongly copy-number dependent. The clinical emergence of\n erm<\/jats:italic>\n (51) expands the known resistome of this pathogen.\n <\/jats:p>\n <\/jats:sec>\n \n Clinical Relevance<\/jats:title>\n \n Incorporating quantitative molecular screening into routine\n R equi<\/jats:italic>\n diagnostics provides crucial real-time therapeutic guidance, supporting precision medicine and targeted antimicrobial stewardship on endemic equine farms.\n <\/jats:p>\n <\/jats:sec>","DOI":"10.2460\/javma.26.07.0576","type":"journal-article","created":{"date-parts":[[2026,10,23]],"date-time":"2026-10-23T17:24:54Z","timestamp":1792776294000},"page":"1-8","source":"Crossref","is-referenced-by-count":0,"title":["erm(46) copy number determines macrolide resistance in Rhodococcus equi"],"prefix":"10.2460","author":[{"given":"Alex","family":"Awtrey","sequence":"first","affiliation":[{"name":"Department of Pathobiology, College of Veterinary Medicine, Auburn University, Auburn, AL"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Alinne L. R.","family":"Santana-Pereira","sequence":"additional","affiliation":[{"name":"Department of Pathobiology, College of Veterinary Medicine, Auburn University, Auburn, AL"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kiranmayee","family":"Bhimavarapu","sequence":"additional","affiliation":[{"name":"Department of Pathobiology, College of Veterinary Medicine, Auburn University, Auburn, AL"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Nneka","family":"Iduu","sequence":"additional","affiliation":[{"name":"Department of Pathobiology, College of Veterinary Medicine, Auburn University, Auburn, AL"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0384-2903","authenticated-orcid":true,"given":"Noah D.","family":"Cohen","sequence":"additional","affiliation":[{"name":"Department of Large Animal Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, TX"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Nathan","family":"Slovis","sequence":"additional","affiliation":[{"name":"Hagyard Equine Medical Institute, Lexington, KY"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Justine","family":"Elam","sequence":"additional","affiliation":[{"name":"Hagyard Equine Medical Institute, Lexington, KY"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Constantinos","family":"Kyriakis","sequence":"additional","affiliation":[{"name":"Department of Pathobiology, College of Veterinary Medicine, Auburn University, Auburn, AL"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Laura","family":"Huber","sequence":"additional","affiliation":[{"name":"Department of Pathobiology, College of Veterinary Medicine, Auburn University, Auburn, AL"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Chengming","family":"Wang","sequence":"additional","affiliation":[{"name":"Department of Pathobiology, College of Veterinary Medicine, Auburn University, Auburn, AL"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1272","reference":[{"issue":"1","key":"ref1","series-title":"Clin Microbiol Rev","first-page":"20","article-title":"Rhodococcus equi: an animal and human pathogen","volume":"4","author":"Prescott JF","year":"1991","unstructured":"Prescott JF. 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