A moderate variability in Tn1546 structure has been detected among unrelated vanA-containing enterococci of different origins, showing three new structures including two new ISs. A high diversity of STs was detected among E. faecium strains, especially among non-clinical strains, and new STs have been identified.
Fifteen newborn chickens were isolated in separate cages after 1 month of living together, divided into three groups, and challenged for 5 weeks with seed food which either was supplemented with avoparcin (10 mg/kg of animal food) or tylosin (40 mg/kg) or was nonsupplemented. At 9 weeks of age and after the 5-week challenge, all chickens received nonsupplemented feed for 4 additional weeks. At 4, 9, and 13 weeks of life, feces were collected and inoculated on M-Enterococcusagar plates with and without vancomycin (4 μg/ml).vanA-containing Enterococcus hirae was isolated from 11 of 15 chickens before antibiotic challenge, without detection of vancomycin-resistant Enterococcus faecium. At 9 weeks of age and after the 5-week avoparcin challenge, vanA E. hiraestrains were no longer detected, but five of five chickens now hadvanA E. faecium. At a lower frequency, vanA E. faecium had also displaced vanA E. hirae in both the tylosin group (one of four chickens) and the control group (two of five chickens). One month after avoparcin discontinuation, the number of chickens colonized with vanA E. faecium decreased from five to one. All vanA-containing E. hirae strains detected in the first month of life and most of thevanA-containing E. faecium strains detected in the second month of life showed identical ApaI andSmaI restriction patterns, respectively, when analyzed by pulsed-field gel electrophoresis. All vanA E. hiraeisolates transferred glycopeptide and macrolide resistance toEnterococcus faecalis JH2-2 in vitro; the level of glycopeptide resistance was higher in the transconjugants than in the donor E. hirae strains. These data suggest that E. hirae may be a significant source of vanAdeterminants with the potential of transfer to other enterococcal species from humans or animals.
During an evaluation of PCR for identification of isolates of Enterococcus hirae, a homologue with 82% identity to E. hirae mur-2 was identified in Enterococcus durans and was named mur-2 ed . PCR using primers for two genes (copY and murG) of E. hirae strains showed amplification with E. hirae strains only. PCR (under high-stringency conditions) with primers for the mur-2 ed gene gave the expected amplification product only with E. durans strains. A combination of murG and mur-2 ed primers in a multiplex PCR assay differentiated E. hirae from E. durans in all cases. PCR using these primers appears to be a rapid alternative for identification of E. hirae and E. durans isolates.
The present study was performed to determine if any of the 45 vanA-containing Enterococcus faecium or 18 vanA-containing E. hirae strains were shared by chickens (32 E. faecium/l7 E. hirae) and humans (13 E. faecium/1 E. hirae) using pulsed field gel electrophoresis (PFGE) and to study quinupristin-dalfopristin (Q-D) resistance. Seven of the 45 E. faecium isolates (from 2 outpatients and from 5 poultry products) were resistant to Q-D (MIC > or = 16 microg/ml); one strain was shown to have satA by PCR and sequencing and, in the other six isolates, the recently described satG gene was demonstrated. Six different PFGE patterns were detected among the 7 Q-D E. faecium-resistant isolates. None of the E. hirae isolates showed Q-D resistance. Among the 45 vanA -containing E. faecium strains, 25 unrelated clones were found by PFGE with highly diverse patterns and an indistinguishable PFGE pattern was observed in vanA-containing E. faecium strains from two humans and two poultry products. A single PFGE pattern was detected in 17 of 18 vanA-containing E. hirae isolates, obtained from one human and 16 chicken samples. Based on the presence of indistinguishable PFGE patterns among VR E. faecium and E. hirae from humans and chickens, we conclude that horizontal transfer of these strains could occur between both groups.
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