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 g/ml) and gentamicin (MIC > 2,048 g/ml). Molecular analysis of this isolate revealed the presence of Tn1546 (vanA), responsible for high-level vancomycin resistance, and Tn5281 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 Tn1546, perhaps from a human vancomycin-resistant E. faecium. Transposons Tn5281 and Tn1546 were located on two different conjugative plasmids. Sequence analysis revealed that in Tn1546, ORF1 had an 889-bp deletion and an IS1216V insertion at the 5 end and an IS1251 insertion between vanS and vanH. To date, this particular form of Tn1546 has only been described in human clinical vancomycinresistant 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.

Molecular Structure and Transferability of Tn 1546 -Like Elements in Enterococcus faecium Isolates from Clinical, Sewage, and Surface Water Samples in Iran

“…The enterococcal isolates carrying IS1542 have been reported in Europe (22). To our knowledge, no reports have been published from North America in regard to circulation of IS1542 in enterococcal populations (17). We were also able to detect IS1542 in the majority of our isolates (96%) originating from patients as well as surface water and hospital and municipal sewage, suggesting widespread dissemination of IS1542 among E. fae- (6), we also found that IS1542 and IS1216V elements were positioned at the left and right ends of transposons, respectively.…”

“…In this study, we found that 72% of our isolates obtained from all sources carried IS1216V. The presence of IS1216V has also been reported in majority of isolates obtained from Europe and North America (9,17), suggesting a global distribution of this IS. Furthermore, this IS has been reported in other species, such as Staphylococcus aureus (14).…”

“…Over the last 2 decades vancomycin-resistant enterococci have spread with unanticipated rapidity and have emerged as the major cause of nosocomial infections in clinical settings (3). The rapid rise in the antimicrobial resistance of enterococci has been attributed to clonal dissemination of the isolates and horizontal transfer of transposons containing vancomycin-resistant genes (12,13,17). It has been known that the vanA gene cluster is carried as a part of Tn1546-like elements, which in addition carry a cluster of nine genes mediating high-level of resistance to both vancomycin and teicoplanin (6).…”

Molecular Identification of Pathogenic Enterococci and Evaluation of Multi-drug Resistance in Enterococcus Species Isolated From Clinical samples of Some Hospitals in Tehran, Iran

“…Uncontrolled consumption of broadspectrum beta-lactams as well as long-term hospitalization influenced the spread of multidrugresistant bacteria; the treatment of such infections is difficult and may leads to mortality (3,5,6).…”

“…Enterococcus species show poor pathogenicity due to lack of powerful toxins and remarkable virulence factors, but since they are intrinsically insensitive to penicillins, aminoglycosides, and glycopeptides, and show high competence in receiving resistance genes; can transfer antibiotic resistance genes to other bacterial genera and species through mutations and/or receiving genetic elements via plasmids or transposons, Enterococcus spp. can cause severe problems in diagnosis, treatment, and control of the associated infections (3).…”