5. Antimicrobial use and antimicrobial resistance.
Don
says, How does antimicrobial use affect antimicrobial
resistance?
Sue says, Antimicrobial use is an important
contributor to the occurrence of antimicrobial resistance in both
animals and humans. Several epidemiological studies in dogs have
demonstrated that prior antimicrobial exposure was associated with
antimicrobial resistance in a number of bacterial species including
E. coli isolates from feces (2,9,10), and opportunistic
pathogens (11,12), including methicillin-resistant Staphylococcus
aureus (13). An experimental study demonstrated that dogs treated
with enrofloxacin were more effectively colonized with
multidrug-resistant E. coli (14).
Recently, associations were observed between cephalexin use (a
first-generation cephalosporin) in dogs and antimicrobial resistance to
a B-lactam inhibitor combination (amoxicillin-clavulanic acid), third
generation cephalosporins (ceftriaxone, cefoxitin) and cephamycins
(ceftiofur). Dogs that were treated with cephalexin had a higher risk
of resistance to these antimicrobials, from 3-8 times higher risk, when
compared to dogs not treated with antimicrobials. The development
of antimicrobial resistance was faster in dogs treated with cephalexin
than in dogs not treated with antimicrobials. These are extremely
important findings since cephalexin is the most commonly prescribed
antimicrobial in dogs and these antimicrobials are critically important
in the treatment of human infections. It suggests that the use of
cephalexin may provide significant selection pressure for the
occurrence of antimicrobial resistance.
Figure 1 A comparison of the times to loss of susceptibility
(or the occurrence of antimicrobial resistance) in fecal E.
coli isolates in dogs treated with cephalexin (red line) compared
to dogs untreated with antimicrobials (black line).
Susceptibility to Ceftiofur |
Susceptibility to Amoxicillin-clavulanic Acid |
Susceptibility to Ceftriaxone |
Legend: Cephalexin Treated Dogs Dogs Untreated With AntimicrobialsInterpretation At any given time, the percentage of fecal E. coli isolates that were susceptible to the above antimicrobials was significantly lower in dogs treated with cephalexin (red line) than in dogs that were not treated with antimicrobials (black line). In other words, antimicrobial resistant fecal E.coli isolates from dogs treated with cephalexin were isolated more frequently and at a faster rate than in dogs that were not treated with antimicrobials. |
Note:
- Cephalexin treatment was started 0-12 hours after the Day 0 sample was collected and duration of cephalexin treatment ranged from 5 to 14 days.
- The study population were dogs (n=33 cephalexin treated, n=8 untreated) from primary-care (i.e. non-referral) small animal veterinary hospitals (n=21) in southern Ontario and were treated with cephalexin for a disease condition that was diagnosed and managed by the attending veterinarian
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