Characterization of Tn 1546 in Vancomycin-Resistant Enterococcus faecium Isolated from Canine Urinary Tract Infections: Evidence of Gene Exchange between Human and Animal Enterococci

Abstract

Thirty-five enterococcal isolates were recovered from dogs diagnosed with urinary tract infections at the Michigan State University Veterinary Teaching Hospital over a 2-year period (1996 to 1998). Isolated species included Enterococcus faecium ( n = 13), Enterococcus faecalis ( n = 7), Enterococcus gallinarum ( n = 11), and Enterococcus casseliflavus ( n = 4). Antimicrobial susceptibility testing revealed several different resistance phenotypes, with the majority of the enterococcal isolates exhibiting resistance to three or more antibiotics. One E. faecium isolate, CVM1869, displayed high-level resistance to vancomycin (MIC > 32 μg/ml) and gentamicin (MIC > 2,048 μg/ml). Molecular analysis of this isolate revealed the presence of Tn 1546 ( vanA ), responsible for high-level vancomycin resistance, and Tn 5281 carrying aac6′-aph2" , conferring high-level aminoglycoside resistance. Pulsed-field gel electrophoresis analysis revealed that CVM1869 was a canine E. faecium clone that had acquired Tn 1546 , perhaps from a human vancomycin-resistant E. faecium . Transposons Tn 5281 and Tn 1546 were located on two different conjugative plasmids. Sequence analysis revealed that in Tn 1546 , ORF1 had an 889-bp deletion and an IS 1216V insertion at the 5′ end and an IS 1251 insertion between vanS and vanH . To date, this particular form of Tn 1546 has only been described in human clinical vancomycin-resistant enterococcus isolates unique to the United States. Additionally, this is the first report of a vancomycin-resistant E. faecium isolated from a companion animal in the United States.