Table 2.
Antimicrobial susceptibilities of isolates producing CTX-M-type ESBL from mastitic cows
| Antimicrobial agenta | Group 1 |
Group 2 |
Group 3 |
||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| MIC range (μg/ml) | MIC50 (μg/ml) | MIC90 (μg/ml) | Breakpoint (μg/ml; mm)b | No. of isolates (%) |
MIC range (μg/ml) | No. of resistant isolates (%) (B)h | MIC range (μg/ml) | No. of resistant isolates (%) (C)h | |||
| Susceptible | Intermediate | Resistant (A)h | |||||||||
| Ampicilline | >512 | >512 | >512 | ≥32 | 0 | 0 | 49 (100) | >512 | 10 (100) | >512 | 6 (100) |
| Cefazoline | >256 | >256 | >256 | ≥32 | 0 | 0 | 49 (100) | >256 | 10 (100) | >256 | 6 (100) |
| Cefuroximee | >256 | >256 | >256 | ≥32c | 0 | 0 | 49 (100) | >256 | 10 (100) | >256 | 6 (100) |
| Ceftazidime | ≤2 to 64 | ≤2 | ≤2 | ≥16c | 45 (91.8) | 3 (6.1) | 1 (2.0)**B | 16–64 | 10 (100)**A,C | ≤2 | 0**B |
| CAZ/CLA | ≤0.25 to >8 | ≤0.25 | 0.5 | 0.5 to >8 | ≤0.25 to 0.5 | ||||||
| Cefotaxime | ≤16 to 256 | 64 | 128 | ≥4c | -g | 4 (8.2)g | 45 (91.8) | 512 to >512 | 10 (100) | 128 to >512 | 6 (100) |
| CTX/CLA | ≤1 to >8 | ≤1 | ≤1 | ≤1 to 8 | ≤1 | ||||||
| Cefpodoxime | ≤8 to >64 | >64 | >64 | ≥16 | 1 (2.0) | 0 | 48 (98.0) | >64 | 10 (100) | >64 | 6 (100) |
| Ceftriaxone | 64 to >512 | 512 | >512 | ≥4c | 0 | 0 | 49 (100) | >512 | 10 (100) | 512 to >512 | 6 (100) |
| Ceftiofure | 64 to >512 | >512 | >512 | ≥8 | 0 | 0 | 49 (100) | >512 | 10 (100) | >512 | 6 (100) |
| Cefquinomee | 16 to >128 | 128 | >128 | —d | >128 | >128 | |||||
| Cefepime | ≤8 to 64 | ≤8 | ≤8 | ≥32c | 43 (87.8) | 3 (6.1) | 3 (6.1)**B,C | >64 | 10 (100)**A | ≤8 to >64 | 4 (66.6)**A |
| Cefmetazole | ≤4 to >32 | ≤4 | ≤4 | ≥64c | 47 (95.9) | 0 | 2 (4.1) | ≤4 to 32 | 0 | ≤4 to >32 | 1 (16.6) |
| Moxalactam | ≤8 to >32 | ≤8 | ≤8 | ≥64c | 48 (98.0) | 0 | 1 (2.0) | ≤8 | 0 | ≤8 | 0 |
| Imipenem | ≤1 | ≤1 | ≤1 | ≥16 | 49 (100) | 0 | 0 | ≤1 | 0 | ≤1 | 0 |
| Meropenem | ≤2 to 4 | ≤2 | ≤2 | ≥4c | 48 (98.0) | 0 | 1 (2) | ≤2 | 0 | ≤2 | 0 |
| Aztreonam | ≤8 to >64 | ≤8 | 16 | ≥16c | —g | 43 (87.8)g | 6 (12.2)**B, *C | 64 to >64 | 10 (100)**A,*C | ≤8 to 32 | 3 (50)*A,B |
| Gentamicine | ≤2 to >16 | ≤2 | ≤2 | ≥16 | 46 (93.9) | —d | 3 (6.1) | ≤2 to >16 | 1 (10.0) | ≤2 | 0 |
| Amikacin | ≤4 to >16 | ≤4 | ≤4 | ≥64 | 48 (98.0) | 1 (2.0)g | ≤4 to 8 | 0 | ≤4 | 0 | |
| OTETe | ≤4 to >16 | ≤4 | >16 | ≥16 | 24 (49.0) | 11 (22.4) | 14 (28.6)*B | ≤4 to >16 | 7 (70.0)*A | ≥16 | 6 (100) |
| SXTe | ≤0.5/9.5 to >4/76 | ≤0.5/9.5 | 4/76 | ≥4/76 | 42 (85.7) | —d | 7 (14.3)**B,*C | 4/76 to >4/76 | 7 (70.0)**A | ≤0.5/9.5 to >4/76 | 3 (50)*A |
| Enrofloxacine | ≤0.25 to 2 | ≤0.25 | 2 | ≥2 | 45 (91.8) | 2 (4.1) | 2 (4.1) | ≤0.25 to >2 | 1 (10.0) | ≤0.25 to 0.5 | 0 |
| Ciprofloxacin | ≤0.5 to 2 | ≤0.5 | ≤0.5 | ≥4c | 46 (93.9) | 3 (6.1) | 0*B | ≤0.5 to >2 | 1 (10.0)*A | ≤0.5 to 1 | 0 |
| Cefoxitinf | ≤14 mmc | 48 (98.0) | 1 (2.0) | 0*B,**C | S to R | 1 (10.0)*A | S to R | 1 (16.6)**A | |||
| Kanamycine,f | ≤13 mm | 38 (77.6) | 1 (2.0) | 10 (20.4)*B, C | S to R | 5(50.0)*A | S to R | 4 (66.6)*A | |||
| CHLf | ≤13 mm | 41 (83.7) | 0 | 8 (16.3) | S to R | 4 (40.0) | S to R | 3 (50) | |||
| Levofloxacinf | ≤13 mmc | 49 (100) | 0 | 0*B | S to R | 1(10.0)*A | S | 0 | |||
Assessed by the broth microdilution or disk diffusion method for 41 K. pneumoniae and 6 K. oxytoca isolates producing CTX-M-2 and 2 K. pneumoniae isolates producing CTX-M-14 (group 1), 10 E. coli isolates producing CTX-M-15 (group 2), and other Enterobacteriaceae isolates producing CTX-M-2 or CTX-M-14 (group 3; CTX-M-2: E. coli, n = 1; C. koseri, n = 2; E. aerogenes, n = 1; E. coli, CTX-M-14, n = 2). Abbreviations: CAZ/CLA, ceftazidime/clavlanic acid; CTX, cefotaxime; OTET, oxytetracycline; SXT, trimethoprim/sulfamethoxazol; CHL, chloramphenicol.
Breakpoint for resistance in accordance with CLSI document M31-A3 (2008) (15) for veterinary pathogens.
Breakpoint for resistance in accordance with CLSI document M100-S21 (2011) (20) for isolates from human infections with Enterobacteriaceae.
Breakpoint for resistance or intermediate is not defined in CLSI documents M31-A3 (2008) (15) and M100-S21 (2011) (20).
Antimicrobial agent approved for cattle in Japan; the other 17 antimicrobials in this table are unapproved for cattle.
Susceptibilities were tested by disc diffusion method according to CLSI documents M31-A3 (2008) (15) and M100-S21 (2011) (20).
Isolates in the susceptible, intermediate, and resistant categories could not be differentiated.
Significant differences were determined by the χ2 test for comparison with the group indicated by the capital letter (A, B, or C): *, P < 0.05; **, P < 0.01.