TABLE 2.
PFGE cluster group | No. (%) of isolates within antimicrobial treatment and time intervalb |
|||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
A44 |
AS700 |
Control |
||||||||||
Short | Moderate | Long | Overall | Short | Moderate | Long | Overall | Short | Moderate | Long | Overall | |
C1T | 6 (17.1) | 2 (11.8) | 4 (17.4) | 12 (16.0) | ||||||||
C2T | 2 (5.7) | 2 (8.7) | 4 (5.3) | |||||||||
C3T | 3 (8.6) | 3 (4.0) | ||||||||||
C4T | 1 (3.2) | 3 (17.6) | 2 (5.7) | 6 (7.2) | ||||||||
C5T | 2 (11.8) | 2 (8.7) | 4 (5.3) | |||||||||
C6T | 11 (35.5) | 6 (35.3) | 11 (31.4) | 28 (33.7) | 3 (13.0) | 3 (4.0) | ||||||
C7T | 20 (57.1) | 12 (70.6) | 8 (34.8) | 40 (53.3) | ||||||||
C8T | 6 (20.7) | 5 (27.8) | 8 (25.0) | 19 (24.1) | 4 (12.9) | 6 (35.3) | 18 (51.4) | 28 (33.7) | ||||
C9T | 2 (6.5) | 2 (2.4) | ||||||||||
C10T | 4 (12.9) | 1 (2.9) | 5 (6.0) | |||||||||
C11T | 8 (25.8) | 8 (9.6) | 1 (5.9) | 1 (1.3) | ||||||||
C12T | 1 (3.2) | 1 (1.2) | 3 (13.0) | 3 (4.0) | ||||||||
C13T | 5 (17.2) | 4 (22.2) | 9 (28.1) | 18 (22.8) | 2 (11.8) | 2 (2.4) | ||||||
C14T | 2 (6.9) | 2 (2.5) | ||||||||||
C15T | 2 (6.9) | 1 (5.6) | 1 (3.1) | 4 (5.1) | ||||||||
C16T | 2 (6.9) | 2 (2.5) | ||||||||||
C17T | 3 (8.6) | 3 (3.6) | ||||||||||
C18T | 5 (17.2) | 5 (6.3) | ||||||||||
C19T | 2 (11.1) | 2 (2.5) | ||||||||||
C20T | 5 (17.2) | 1 (5.6) | 12 (37.5) | 18 (22.8) | ||||||||
C21T | 3 (16.7) | 3 (3.8) | ||||||||||
C22T | 3 (8.6) | 3 (4.0) | ||||||||||
Uniquec | 2 (6.9) | 2 (11.1) | 2 (6.3) | 6 (7.6) | 1 (2.9) | 1 (4.3) | 2 (2.7) | |||||
Total | 29 | 18 | 32 | 79 | 31 | 17 | 35 | 83 | 35 | 17 | 23 | 75 |
The degree of relatedness was calculated by using the Dice similarity index of PFGE profiles from isolates across all treatments and time points. E. coli was isolated on MacConkey agar amended with tetracycline (16 μg ml−1).
The treatments were as follows: control, no antimicrobial agents added to the diets of steers from which fecal deposits originated; A44, chlortetracycline (44 ppm); AS700, chlortetracycline and sulfamethazine (each at 44 ppm). Each time interval represents the duration of environmental exposure of fecal deposits prior to sampling: short, days 0 and 7; moderate, days 56 and 70; long, days 126 and 175. “Overall” represents the genotype across all time intervals, within each treatment group.
E. coli PFGE patterns categorized as unique did not show ≥90% homology to any other isolate patterns.