Table 1.
Distribution [no. (%)] of Klebsiella species isolates, by ceftiofur and cephalothin MIC, recovered from milk samples submitted to the Wisconsin Veterinary Diagnostic Laboratory between 2008 and 2019 (n = 483)
| Year | Total isolates (no.) | MIC distribution1 |
|||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Ceftiofur (μg/mL) |
Cephalothin (μg/mL) |
||||||||||
| ≤0.5 | 1 | 2 | 4 | >4 | ≤2 | 4 | 8 | 16 | >16 | ||
| 2008 | 58 | 53 (91.4) | 4 (6.9) | — | — | 1 (1.7) | 44 (75.9) | — | 5 (8.6) | — | 9 (15.5) |
| 2009 | 50 | 41 (82.0) | 8 (16.0) | — | — | 1 (2.0) | 39 (78.0) | 5 (10.0) | 1 (2.0) | 1 (2.0) | 4 (8.0) |
| 2010 | 51 | 45 (88.2) | 6 (11.8) | — | — | — | 38 (74.5) | 7 (13.7) | 5 (9.8) | — | 1 (2.0) |
| 2011 | 31 | 24 (77.4) | 4 (12.9) | 1 (3.2) | — | 2 (6.5) | 18 (58.1) | 9 (29.0) | 1 (3.2) | — | 3 (9.7) |
| 2012 | 35 | 27 (77.1) | 5 (14.3) | — | 2 (5.7) | 1 (2.9) | 25 (71.4) | 1 (2.9) | 4 (11.4) | — | 5 (14.3) |
| 2013 | 43 | 30 (69.8) | 6 (14.0) | 2 (4.7) | 1 (2.3) | 4 (9.3) | 23 (53.5) | 3 (7.0) | 1 (2.3) | 2 (4.7) | 14 (32.6) |
| 2014 | 42 | 34 (81.0) | 5 (11.9) | — | 2 (4.8) | 1 (2.4) | 29 (69.0) | 4 (9.5) | 4 (9.5) | — | 5 (11.9) |
| 2015 | 38 | 27 (71.1) | 8 (21.1) | — | — | 3 (7.9) | 25 (65.8) | 7 (18.4) | 1 (2.6) | 1 (2.6) | 4 (10.5) |
| 2016 | 29 | 18 (62.1) | 10 (34.5) | — | — | 1 (3.4) | 21 (72.4) | 2 (6.9) | 4 (13.8) | 1 (3.4) | 1 (3.4) |
| 2017 | 76 | 44 (57.9) | 14 (18.4) | 1 (1.3) | — | 17 (22.4) | 44 (57.9) | 11 (14.5) | 3 (3.9) | — | 18 (23.7) |
| 2018 | 17 | 13 (76.5) | 3 (17.6) | 1 (5.9) | — | — | 11 (64.7) | 5 (29.4) | — | — | 1 (5.9) |
| 2019 | 13 | 12 (92.3) | 1 (7.7) | 7 (53.8) | 5 (38.5) | — | — | 1 (7.71) | |||
1
The MIC breakpoints for ceftiofur were based on Clinical and Laboratory Standards Institute guidelines (CLSI, 2018b). Klebsiella isolates were considered resistant to ceftiofur or cephalothin when the MIC exceeded 4.0 μg/mL.