Table 2.
Distribution [no. (%)] of Klebsiella species isolates, by tetracycline and sulfadimethoxine MIC, recovered from milk samples submitted to the Wisconsin Veterinary Diagnostic Laboratory between 2008 and 2019 (n = 483)
| Year | Total isolates (no.) | MIC distribution1 |
|||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Tetracycline (μg/mL)2 |
Sulfadimethoxine (μg/mL)3 |
||||||||||
| ≤1 | 2 | 4 | 8 | >8 | ≤32 | 64 | 128 | 256 | >256 | ||
| 2008 | 58 | 25 (43.1) | 21 (36.2) | 1 (1.7) | — | 11 (19.0) | 1 (1.7) | 5 (8.6) | 16 (27.6) | 10 (17.2) | 26 (44.8) |
| 2009 | 50 | 22 (44.0) | 18 (36.0) | 1 (2.0) | — | 9 (18.0) | — | 2 (4.0) | 11 (22.0) | 10 (20.0) | 27 (54.0) |
| 2010 | 51 | 9 (17.6) | 26 (51.0) | 2 (3.9) | — | 14 (27.5) | — | — | 2 (3.9) | 19 (37.3) | 30 (58.8) |
| 2011 | 31 | 15 (48.4) | 9 (29.0) | 2 (6.5) | — | 5 (16.1) | — | — | 3 (9.7) | 5 (16.1) | 23 (74.2) |
| 2012 | 35 | 13 (37.1) | 6 (17.1) | — | — | 16 (45.7) | — | 1 (2.9) | 2 (5.7) | 12 (34.3) | 20 (57.1) |
| 2013 | 43 | 15 (34.9) | 10 (23.3) | 1 (2.3) | 1 (2.3) | 16 (37.2) | — | 2 (4.7) | 8 (18.6) | 15 (34.9) | 18 (41.9) |
| 2014 | 42 | 20 (47.6) | 12 (28.6) | — | — | 10 (23.8) | — | 2 (4.8) | 8 (19.0) | 20 (47.6) | 12 (28.6) |
| 20154 | 38 | 16 (42.1) | 9 (23.7) | 2 (5.3) | — | 11 (28.9) | — | — | 3 (8.1) | 16 (43.2) | 18 (48.7) |
| 2016 | 29 | 15 (51.7) | 6 (20.7) | 1 (3.4) | — | 7 (24.1) | — | 2 (7.0) | 5 (17.2) | 11 (37.9) | 11 (37.9) |
| 2017 | 76 | 44 (57.9) | 12 (15.8) | — | — | 20 (26.3) | — | 1 (1.3) | 6 (7.9) | 42 (55.3) | 27 (35.5) |
| 2018 | 17 | 4 (23.5) | 8 (47.1) | 2 (11.8) | — | 3 (17.6) | 1 (5.9) | 3 (17.6) | 4 (23.6) | 3 (17.6) | 6 (35.3) |
| 20195 | 13 | 2 (15.4) | 10 (76.9) | — | — | 1 (7.7) | 2 (18.2) | 2 (18.2) | 1 (9.1) | 2 (18.2) | 4 (36.4) |
1
The MIC breakpoints for tetracycline were based on Clinical and Laboratory Standards Institute (CLSI) guidelines (CLSI, 2020).
2
Klebsiella isolates were considered resistant to tetracycline when the MIC exceeded 8.0 μg/mL.
3
CLSI does not provide breakpoints for sulfadimethoxine. Klebsiella isolates were considered resistant to sulfadimethoxine when MIC exceeded 256 μg/mL.
4
Sulfadimethoxine susceptibility testing was not conducted in 1 isolate.
5
Sulfadimethoxine susceptibility testing was not conducted in 2 isolates.