Table 3.
Distribution of MIC for Streptococcus uberis (n = 228) isolates from dairy cattle with subclinical or clinical bovine mastitis in northern Thailand during 2010–2017a.
| Antimicrobial agents | Number of isolates with a MIC (μg/mL) of | Resistance rate (%) | MIC50 (μg/mL) | MIC90 (μg/mL) | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| >32 | 32 | 16 | 8 | 4 | 2 | 1 | 0.5 | 0.25 | 0.125 | 0.0625 | 0.03125 | 0.0156 | 0.0078 | 0.0039 | <0.0039 | ||||
| Ceftiofur | 3 | 7 | 7 | 27// | 92 | 58 | 9 | 2 | 15 | 8 | 0 | 19.30 | 4 | 8 | |||||
| Tetracycline | 178 | 7 | 0 | 2// | 3 | 1 | 7 | 19 | 9 | 2 | 0 | 82.02 | >32 | >32 | |||||
| Erythromycin | 16b | 0 | 3// | 0 | 1 | 1 | 1 | 0 | 0 | 1 | 0 | 205 | 8.33 | <0.0039 | <0.0039 | ||||
| Gentamycin | 0// | 0 | 0 | 92 | 75 | 44 | 13 | 2 | 0 | 1 | 1 | 0 | 0 | 0 | 0 | 1 | 2 | ||
| Penicillin G | 0// | 0 | 3 | 2 | 2 | 9 | 13 | 27 | 33 | 97 | 0 | 42 | 0 | 0.0156 | 0.0625 | ||||
a
The shaded areas indicate the concentrations of the different antimicrobial agents for which the bacterial isolates were not tested. Double slashes indicate the breakpoints for resistance according to the Clinical and Laboratory Standards Institute (2008; 2018).
b
Sixteen isolates were observed to grow in all tested dilutions of erythromycin. These isolates were considered to have MIC of >2 μg/mL of erythromycin.
MIC, minimum inhibitory concentration.