Table 2.
Changes in MIC50 of various antimicrobials for contemporary strains (2012–2016), (n = 63) compared to historical (1980's), (n = 31) strains of Histophilus somni isolated from feedlot cattle in Alberta.
| Antimicrobials | Median MIC value (MIC50) | |||
|---|---|---|---|---|
| Historical | Contemporary | Fold Increasea | P valueb | |
| Ceftiofur | 0.25 | 0.25 | 1 | 1 |
| Danofloxacin | 0.125 | 0.125 | 1 | 0.1 |
| Enrofloxacin | 0.125 | 0.125 | 1 | 1 |
| Ampicillin | 0.25 | 0.25 | 1 | 0.08 |
| Penicillin | 0.125 | 0.25 | 2 | <0.001 |
| Clindamycin | 0.5 | 0.5 | 1 | 0.1 |
| Gentamicin | 8 | 16 | 2 | <0.001 |
| Spectinomycin | 16 | 16 | 1 | 0.06 |
| Neomycin | 16 | 32 | 2 | <0.001 |
| Tulathromycin | 8 | 4 | 0.5 | 0.2 |
| Tilmicosin | 1 | 8 | 8 | 0.001 |
| Tylosin | 4 | 8 | 2 | <0.001 |
| Florfenicol | 0.25 | 0.5 | 2 | 1 |
| Oxytetracycline | 0.125 | 16 | 128 | <0.001 |
| Chlortetracycline | 0.5 | 1 | 2 | <0.001 |
| Tiamulin | 2 | 2 | 1 | 0.6 |
a
Calculated by dividing median MIC value of contemporary isolates by historical isolates. One-fold increase indicates no change in MIC.
b
Mann-Whitney U test was used for statistical comparison.