Table 5.
Statistical evaluation of MICs and standard deviations (± SDs) of the antibiotics showing significant differences among treatments, days, and interactions between treatments and days.
| Antibiotic | Effect of day | Effect of treatment* | Effect of interaction |
|---|---|---|---|
| Amoxicillin—clavulanic acid | 38>17 (P < 0.0001) | AB>NC, CC, FA, SA (P < 0.0001)** | P < 0.0001 |
| Ampicillin | 38>17 (P < 0.0001) | AB>NC, CC, FA, SA (P < 0.0001) | P < 0.0001 |
| Azithromycin | 38>17 (P < 0.0001) | NC>AB (P = 0.02) | P = 0.11 |
| Cefoxitin | 38>17 (P < 0.0001) | AB>SA (P = 0.02) | P = 0.24 |
| Ceftriaxone | P = 0.38 | AB>FA, SA (P = 0.03) | P = 0.44 |
| Chloramphenicol | 38>17 (P < 0.0001) | P = 0.14 | P = 0.93 |
| Ciprofloxacin | 38>17 (P = 0.04) | P = 0.25 | P = 0.44 |
| Gentamicin | 38>17 (P < 0.0001) | P = 0.81 | P = 0.03 |
| Nalidixic acid | 38>17 (P < 0.0001) | P = 0.05 | P = 0.86 |
| Streptomycin | 38>17 (P < 0.0001) | P = 0.72 | P = 0.09 |
| Sulfisoxazole | 38>17 (P < 0.0001) | P = 0.14 | P = 0.85 |
| Tetracycline | 38>17 (P < 0.0001) | AB<NC, SA (P = 0.02)*** | P < 0.0001 |
| Trimethoprim-sulfamethoxazole | 38>17 (P < 0.0001) | P = 0.17 | P < 0.002 |
NC, negative control without E. coli challenge; CC, E. coli challenge control; AB, ampicillin; FA, feed additive based on organic acids; SA, multistrain synbiotic.
*MIXED procedure and multiple comparisons of the MICs adjusted according to the Tukey–Kramer test at a significance level of 5%.
**In-depth analysis did not show significant differences between CC-AB on day 38.
***In-depth analysis did not show significant differences between NC-AB, AB-FA, and AB-SA on day 17 only.