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. 2009 Oct 2;75(22):7125–7134. doi: 10.1128/AEM.00944-09

TABLE 2.

Temporal PFGE clusters (≥90% relatedness) of tetracycline-resistant E. coli isolated from fecal deposits of steers fed antimicrobial agentsa

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
a

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).

b

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.

c

E. coli PFGE patterns categorized as unique did not show ≥90% homology to any other isolate patterns.