Table 2.

Summary of in vitro susceptibilities of E. faecium isolates to quinupristin-dalfopristin

Group (age [days])No. (%) of resistantaisolates/totalNo. (%) of animals with resistant strains/no. with E. faeciumTotal no. of animals with culture (% of animals with resistant E. faecium)
1 (24)b4/17 (23)4/13 (31)20 (20)
2 (28)c0/0 (0)0/21 (0)25 (0)
3 (59)3/16 (19)3/15 (20)20 (15)
4 (80)9/16 (56)7/13 (54)20 (35)
5 (130)9/9 (100)d5/5 (100)e20 (25)
  • a MIC of ≥4.0 defines resistance.

  • b Groups 1 and 5 are the same flock (P = 0.0002 for isolates; P = 0.01 for group 1 versus group 5 animals).

  • c Groups 2 and 3 are the same flock (P = 0.9 for isolates; P = 0.05 for group 2 versus group 3 animals).

  • d P = 0.07 for comparison of isolates in groups 1 through 5.

  • e P = 0.14 for comparison of animals in groups 1 through 5.