Objective—To evaluate the antimicrobial susceptibility
patterns of Salmonella isolates from feedlot cattle.
Sample Population—263 Salmonella isolates.
Procedures—Fecal samples were collected from the
floor of 2 pens in each of 100 feedlots. Two hundred
eighty Salmonella isolates were recovered after bacteriologic
culture from 38 pens. Of these, 263 isolates
were available for antimicrobial susceptibility testing
to 16 antimicrobials, using microbroth dilution breakpoint
Results—Less than 5% of isolates were resistant to
any of the antimicrobials tested, with the exception of
sulfamethoxazole (15; 5.7%) and tetracycline (61;
23.2%). Most isolates (197; 74.9%) were susceptible
to all antimicrobials tested, whereas 18 (6.8%) were
resistant to 2 or more antimicrobials. The percentage
of isolates with resistance to any antimicrobial varied
by serotype. The percentage of isolates resistant to
various antimicrobials was not related to concurrent
use of antimicrobials in the feed.
Conclusions and Clinical Relevance—With the
exception of tetracycline and sulfamethoxazole, resistance
of Salmonella isolates to any of the antimicrobials
was uncommon. Most isolates were susceptible
to all antimicrobials tested. Antimicrobial resistance
was not related to the presence of antimicrobials in
the ration being fed at the time of sample collection.
(J Am Vet Med Assoc 2002;221:268–272)