Objective—To measure minimum inhibitory concentrations
(MIC) of 17 antimicrobials for Escherichia coli
isolates from a turkey operation and assess whether
small samples provide precise estimates of geometric
Sample Population—105 clinical isolates from birds
and 1,104 fecal isolates from 20 flocks (poults and finisher
Procedure—A Mueller-Hinton broth dilution panel
was used to measure MIC, and MIC of fecal and
clinical isolates were compared. We drew random
samples of 5, 10, 15, 20, 25, 30, 35, 40, and 45 isolates
from each finisher flock and between 100 and
105 isolates from 5, 7, 10, and 20 flocks.
Antimicrobial usage was determined for enrolled
Results—Six of 12 poult and 18 of 20 finisher
flocks had been treated with antimicrobials, often
for respiratory illnesses consistent with colibacillosis.
All birds received gentamicin at the hatchery.
More fecal than clinical isolates were resistant to
ampicillin; however, more clinical isolates were
resistant to ciprofloxacin, gentamicin, and sulfamethoxazole.
Precise estimates of geometric
mean MIC for flocks were obtained when ≥ 15
fecal isolates were obtained per flock and, for the
operation, when 105 isolates were obtained from ≥
Conclusions and Clinical Relevance—Antimicrobial
usage was common and may have contributed to the
resistance patterns of isolates. With a modest allocation
of laboratory resources, producers can monitor
antimicrobial susceptibilities of clinical and fecal E coli
to manage risks of antimicrobial usage and resistance.
(J Am Vet Med Assoc 2002;221:411–416)