Rhodococcus equi infection in cats with skin nodules in Brazil

Abstract

This study aimed to describe and provide a laboratory characterization of three cases of Rhodococcus equi isolates from pyogranulomatous lesions in domestic cats in Brazil, collected between 2015 and 2021. Swabs and aspirates from nodular skin lesions located in the abdominal region (Case 1) and thoracic limbs (Cases 1-3) were subjected to microbiological culture, biochemical and molecular analyses, evaluation of biofilm formation capacity, and antimicrobial sensitivity testing. Cats 1 and 2 were positive for FeLV p27 antigen on SNAP testing. Cat 1 died at home from complications of Rhodococcus infection, and Cat 2 was euthanized following failure of medical and surgical treatment of infection. The cat in Case 3, which was FeLV-negative, received treatment with oral erythromycin and topical rifampicin for 30 days. However, due to failure of antimicrobial therapy to resolve the lesions, the cat underwent amputation of the affected right hindlimb. R. equi, positive for the plasmid-encoded virulence-associated protein A, was identified on the microbiological cultures and PCR from all cases. Biofilm formation analysis categorized all three isolates as weak biofilm formers. Additionally, antimicrobial susceptibility testing revealed that all isolates were sensitive to azithromycin, clarithromycin, erythromycin, imipenem, and rifampicin in vitro. These findings underscore the clinical, epidemiological, and laboratory characteristics of R. equi infection in Brazilian cats, indicating that these microorganisms are phenotypically and molecularly similar to those isolated from horses.