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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).