A research team based at the University of Georgia (UGA) College of Veterinary Medicine has discovered a novel gene – erm(46) – that confers antibiotic resistance in Rhodococcus equi, a soil-dwelling bacterium that commonly infects foals and causes opportunistic infections in immunocompromised people.
The finding was made in collaboration with researchers at the University of Edinburgh, Texas A&M University and the University of Washington.
Rhodococcus equi (R. equi), a gram-positive intracellular pathogen, is one of the most important causes of disease in foals between 3 weeks and 5 months of age, said team lead Dr. Steeve Giguère, the Marguerite Thomas Hodgson Chair of Equine Studies at UGA and a board-certified large animal internal medicine specialist.
The researchers sequenced the genomes of antibiotic-resistant and antibiotic-susceptible R. equi isolates collected from foals in four states. They searched each isolate’s genome for genes with similar sequences to known genes that cause bacterial resistance to the macrolide class of antibiotics in other bacterial species. Through their search, they discovered the new gene, named erm(46) by the Nomenclature Center for MLS Genes at the University of Washington.
When the team cloned erm(46) into susceptible R. equi isolates normally inhibited by antibiotics, they found that erm(46) induced a high level of resistance to macrolide, lincosamide and streptogramin B antibiotics. They also found that the gene can be transferred from resistant to susceptible isolates of R. equi during bacterial mating.
“This process likely contributes to the spread of resistance,” Giguère said.
Their finding, recently published in the Journal of Antimicrobial Chemotherapy, is the first molecular characterization of resistance to these three classes of antibiotics in R. equi.
“Before, we knew we had resistant isolates, but we did not know how resistance occurred, and we had no molecular markers to identify and track the resistant bacteria,” Giguère said.