Trueperella pyogenes-Associated Acute Pneumonia in Korean Native Calves.

Bovine respiratory disease (BRD) is a leading cause of morbidity and mortality in the cattle industry worldwide, resulting in substantial economic losses. Trueperella pyogenes has been recognized as an opportunistic pathogen; however, its role as a primary aetiologic agent of BRD remains poorly defined. Four Korean native calves developed respiratory signs, including coughing, nasal discharge and pneumonia, and died within 1-2 days after onset. Postmortem examination revealed characteristic gross pulmonary lesions. PCR was performed to detect common BRD pathogens and antimicrobial resistance (AMR) genes. T. pyogenes was identified in the lungs of all calves examined. Three calves were infected solely with T. pyogenes, whereas one calf was co-infected with three pathogens (Histophilus somni, Mycoplasma dispar and Pasteurella multocida) as well as T. pyogenes. AMR genes, predominantly the macrolide resistance genes ermX and ermB, were detected in three calves. To the best of our knowledge, this is the first report of T. pyogenes-associated pneumonia and the characterization of AMR genes in Korean native calves. This case indicates that T. pyogenes can act as a major pathogen responsible for BRD in calves. These findings highlight the pathogenic potential of T. pyogenes and the need for targeted therapeutic approaches to support prudent antimicrobial use in cattle.