TABLE 2.
Resistant C. coli, C. fetus, and C. jejuni isolates by isolation medium and sample timea
| Species and drug | MIC breakpoint (μg ml−1) | % (no.) of resistant isolates on mCCDA in indicated sample
|
MIC50 (μg ml−1) on mCCDA | % (no.) of resistant isolates on cCCDA in indicated sample
|
MIC50 (μg ml−1) on cCCDA | Total % (no.) of resistant isolatesb | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Entry | Interim | Exit | Dead | Entry | Interim | Exit | Dead | |||||
| C. coli | ||||||||||||
| Azithromycin | 2 | 0 (0) | 1.9 (1) | 0 (0) | 7.7 (1) | 0.56 | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0.47 | 3.9 (6) |
| Ciprofloxacin | 4 | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0.18 | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0.18 | 0 (0) |
| Doxycycline | 16 | 11.1 (1) | 90.7 (49) | 88.9 (16) | 100 (13) | 20.5 | 0 (0) | 75.0 (9) | 100 (7) | 100 (5) | 12.0 | 83.8 (129) |
| Enrofloxacin | 2 | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0.12 | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0.12 | 0 (0) |
| Erythromycin | 8 | 44.4 (4) | 83.3 (45) | 94.4 (17) | 100 (13) | 5.8 | 40.0 (2) | 83.3 (10) | 57.1 (4) | 100 (5) | 5.2 | 82.5 (127) |
| Gentamicin | 16 | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0.50 | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0.40 | 0 (0) |
| Meropenem | 0.25 | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0.023 | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0.02 | 0 (0) |
| Nalidixic acid | 32 | 0 (0) | 0 (0) | 0 (0) | 15.4 (2) | 11.0 | 0 (0) | 8.3 (1) | 0 (0) | 0 (0) | 7.7 | 1.9 (3) |
| Tetracycline | 16 | 11.1 (1) | 100 (54) | 88.9 (16) | 100 (13) | 178.0 | 0 (0) | 100 (12) | 100 (7) | 100 (5) | 82.0 | 89.0 (137) |
| C. fetus | ||||||||||||
| Azithromycin | 2 | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0.18 | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0.18 | 0 (0) |
| Ciprofloxacin | 4 | 0 (0) | 0 (0) | 3.4 (1) | 0 (0) | 0.46 | 0.4 (1) | 0 (0) | 0.7 (4) | 0 (0) | 0.51 | 0.6 (6) |
| Doxycycline | 16 | 0 (0) | 62.5 (5) | 69.0 (20) | 50.0 (1) | 3.0 | 0.8 (2) | 32.4 (36) | 57.5 (316) | 60.0 (3) | 0.46 | 39.0 (388) |
| Enrofloxacin | 2 | 0 (0) | 0 (0) | 3.4 (1) | 0 (0) | 0.38 | 0.4 (1) | 0 (0) | 0.9 (5) | 0 (0) | 0.43 | 0.7 (7) |
| Erythromycin | 8 | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0.95 | 0 (0) | 0.9 (1) | 0 (0) | 0 (0) | 0.90 | 0.1 (1) |
| Gentamicin | 16 | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0.58 | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0.60 | 0 (0) |
| Meropenem | 0.25 | 6.7 (1) | 0 (0) | 0 (0) | 0 (0) | 0.02 | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0.02 | 0.1 (1) |
| Nalidixic acid | 32 | 100 (15) | 100 (8) | 100 (29) | 100 (2) | 159.0 | 100 (258) | 99.1 (110) | 94.6 (520) | 100 (5) | 184.0 | 96.9 (963) |
| Tetracycline | 16 | 0 (0) | 75.0 (6) | 69.0 (20) | 50.0 (1) | 2.20 | 0.8 (2) | 33.3 (37) | 57.1 (314) | 60.0 (3) | 0.41 | 39.0 (388) |
| C. jejuni | ||||||||||||
| Azithromycin | 2 | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0.12 | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0.13 | 0.2 (1) |
| Ciprofloxacin | 4 | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0.15 | 2.0 (2) | 0 (0) | 0 (0) | 0 (0) | 0.11 | 0.5 (2) |
| Doxycycline | 16 | 8.5 (4) | 60.0 (66) | 82.3 (107) | 66.7 (4) | 10.0 | 6.1 (6) | 83.3 (15) | 77.8 (7) | 100 (2) | 0.11 | 50.1 (216) |
| Enrofloxacin | 2 | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0.06 | 2.1 (2) | 0 (0) | 0 (0) | 0 (0) | 0.07 | 0.5 (2) |
| Erythromycin | 8 | 0 (0) | 2.7 (3) | 0.8 (1) | 0 (0) | 1.28 | 1.0 (1) | 0 (0) | 22.2 (2) | 0 (0) | 1.39 | 2.8 (12) |
| Gentamicin | 16 | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0.39 | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0.36 | 0 (0) |
| Meropenem | 0.25 | 0 (0) | 0.9 (1) | 0 (0) | 0 (0) | 0.004 | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0.01 | 0.2 (1) |
| Nalidixic acid | 32 | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0.49 | 5.1 (5) | 0 (0) | 11.1 (1) | 0 (0) | 0.48 | 1.4 (6) |
| Tetracycline | 16 | 8.5 (4) | 94.6 (104) | 93.1 (121) | 83.3 (5) | 38.0 | 8.2 (8) | 100 (18) | 77.8 (7) | 100 (2) | 0.12 | 63.6 (274) |
a
Percent values were based on the total number of isolates recovered for each species on each medium and for each sample time (see Table 1). Samples were collected upon the arrival of the cattle at the feedlot (i.e., entry sample), ca. 70 days thereafter (i.e., interim sample), and just before cattle were shipped for slaughter (i.e., exit sample). Only one isolate was recovered per sample. See Materials and Methods for details on isolation media.
b
Combined data for mCCDA, cCCDA, and eCCDA.