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Table 1 Distribution of isolates characterized in this study

From: Distribution and characterization of ampicillin- and tetracycline-resistant Escherichia colifrom feedlot cattle fed subtherapeutic antimicrobials

Treatmenta

Medium used for selectionb

Number of animals

Sampling dayc

Total

   

B

C

D

E

 

CON

MC

5

5

5

5

5

20

 

MT

50

15

19

47

30

111

 

MA

50

0

8

1

17

26

T

MC

3

3

3

2

3

11

 

MT

30

12

10

27

25

74

 

MA

30

2

0

1

10

13

TS

MC

3

3

3

3

3

12

 

MT

30

23

26

29

29

107

 

MA

30

15

14

7

15

51

V

MC

3

3

3

3

3

12

 

MT

30

11

6

25

27

69

 

MA

30

2

2

5

16

25

Total

  

94

99

155

183

531

  1. a Steers were fed no antibiotics (control, CON), or chlortetracycline and sulfamethazine (44 ppm; TS); chlortetracycline (11 ppm; T) or virginiamycin (31 ppm; V) administered in two discrete periods (see Figure 1).
  2. b Isolates were collected by plating fecal slurries onto (i) MacConkey agar (MAC) containing no antibiotics (control, MC), or amended with tetracycline hydrochloride (4 μg/mL; MT) or with ampicillin (50 μg/mL; MA).
  3. c Sampling days occurred during each of the four phases of the feeding trial (see Figure 1).