TABLE 4.
Distribution of antibiotic resistance phenotypes among tetracycline-resistant E. coli isolates from chickens fed antimicrobialsa
| Class | No. (%) of tetracycline-resistant isolates relative to the total no. of isolates (n) tested per treatment
|
||||||
|---|---|---|---|---|---|---|---|
| Control (n = 19) | BBM (n = 14) | PEN (n = 16) | SAL (n = 20) | BAC (n = 19) | SAL + BAC (n = 16) | Total (n = 104)b | |
| β-Lactams | |||||||
| Amoxicillin | 17 (89.5) | 14 (100) | 16 (100) | 20 (100) | 16 (84.2) | 12 (75) | 95 (91.3) |
| Ampicillin | 17 (89.5) | 14 (100) | 15 (93.7) | 19 (95) | 15 (78.5) | 12 (75) | 92 (88.5) |
| Amoxicillin-clavulanic acid | 17 (89.5) | 12 (85.7) | 15 (93.7) | 19 (95) | 15 (78.5) | 12 (75) | 90 (86.5) |
| Cefoxitin | 17 (89.5) | 12 (85.7) | 15 (93.7) | 19 (95) | 14 (73.7) | 12 (75) | 89 (85.6) |
| Ceftiofur | 14 (73.7) | 12 (85.7) | 14 (87.5) | 19 (95) | 13 (68.4) | 12 (75) | 84 (80.8)* |
| Aminoglycosides | |||||||
| Streptomycin | 13 (68.4) | 11 (78.6) | 12 (75) | 15 (75.0) | 15 (78.9) | 7 (43.7) | 73 (70.2) |
| Spectinomycin | 11 (57.9) | 6 (42.8) | 6 (37.5) | 15 (75.0) | 12 (63.1) | 6 (37.5) | 56 (53.8)* |
| Gentamicin | 7 (36.8) | 6 (42.8) | 4 (25.0) | 11 (55.0) | 11 (57.9) | 5 (31.2) | 44 (42.3)* |
| Sulfonamides | |||||||
| Sulfadimethoxime | 12 (63.1) | 10 (71.4) | 10 (62.5) | 17 (85.0) | 13 (68.4) | 7 (43.7) | 69 (66.3) |
| Sulfathiazole | 12 (63.1) | 10 (71.4) | 10 (62.5) | 17 (85.0) | 13 (68.4) | 5 (31.2) | 67 (64.4) |
| Sulfizoxazole | 12 (63.1) | 9 (64.3) | 10 (62.5) | 16 (80.0) | 13 (68.4) | 5 (31.2) | 65 (62.5) |
| Trimethoprim-sulfamethoxazole | 2 (10.5) | 1 (7.1) | 0 (0.0) | 2 (10.0) | 1 (5.3) | 0 (0.0) | 6 (5.8) |
| Phenicols | |||||||
| Chloramphenicol | 10 (52.6) | 9 (64.3) | 9 (56.2) | 13 (65.0) | 12 (63.2) | 5 (31.2) | 58 (55.8) |
| Quinolones | |||||||
| Nalidixic acid | 2 (10.5) | 2 (14.3) | 4 (25.0) | 3 (15) | 2 (10.5) | 2 (12.5) | 15 (14.4) |
| Sarafloxacin | 2 (10.5) | 1 (7.1) | 3 (18.7) | 3 (15) | 2 (10.5) | 2 (12.5) | 13 (12.5) |
| Ciprofloxacin | 0 (0.0) | 1 (7.1) | 3 (18.5) | 0 (0.0) | 0 (0.0) | 0 (0.0) | 4 (3.8) |
| Enrofloxacin | 0 (0.0) | 0 (0.0) | 2 (12.5) | 0 (0.0) | 0 (0.0) | 0 (0.0) | 2 (1.9) |
a
Distribution of antibiotic resistance phenotypes among tetracycline-resistant E. coli isolates from chickens fed a control diet and diets containing bambermycin (BBM), penicillin (PEN), salinomycin (SAL), bacitracin (BAC), and a salinomycin-bacitracin combination (SAL + BAC) at the concentrations specified in Materials and Methods. All the isolates were resistant to penicillin, erythromycin, tylosin, clindamycin, oxytetracycline, and novobiocin, and all were susceptible to ceftriaxone, kanamycin, and amikacin.
b
*, values are statistically different (P < 0.05).