Table 3.
Distribution of enterococci isolates from feedlot cattle feces grouped according to macrolide (n = 153) and tetracycline (n= 54) resistance genes and by cattle fed tylosin for the FIRST-78%, LAST-75%, or continuously (CON) during the feeding period.
| Treatmenta | No. Positive (%)b | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Macrolide | Tetracycline | ||||||||
| n | erm(B) | msrC | Negative | n | tet(L) | tet(M) | tet(O) | Negative | |
| FIRST-78 | 51 | 49 (96.1) | 1 (2.0) | 2 (3.9) | 17 | 13 (61.9) | 13 (61.9) | 4 (19.0) | 0 (0) |
| LAST-75 | 51 | 48 (94.1) | 3 (5.9) | 3 (5.9) | 21 | 18 (85.7) | 19 (90.5) | 2 (9.5) | 0 (0) |
| CON | 51 | 47 (92.2) | 2 (3.9) | 4 (7.8) | 16 | 10 (62.5) | 10 (62.5) | 5 (31.3) | 1 (6.3) |
| Total | 153 | 144 (94.1) | 6 (3.9) | 9 (5.9) | 54 | 41 (75.9) | 42 (77.8) | 11 (20.4) | 1 (6.3) |
a
Tylosin inclusion at 11 ppm; FIRST-78% = tylosin in-feed from d 0 to d 125; LAST-75% = tylosin in-feed from d 41 to d 161; CON = control, continuous feeding of tylosin (d 0 to d 161).
b
Isolates pooled across all media types and sampling days.