Resistance to Third Generation Cephalosporins Due to Small Animal Escherichia Coli Strains Producing Extended Spectrum B-Lactamases
World Small Animal Veterinary Association World Congress Proceedings, 2004
C. Pomba,1 N. Mendonça,2 D. Louro,2 J. Duarte-Correia,1 and M. Caniça2
1CIISA, Faculty of Veterinary Medicine, UTL, Lisbon, Portugal; 2Antibiotic Resistance Unit, NIH Dr. Ricardo Jorge, Lisbon, Portugal

There is only limited data on β-lactams resistance in small animals. The aim of this study was to evaluate in vitro efficacy of β-lactams against E. coli strains from small animals with urinary tract infection (UTI) and to detect Extended-Spectrum β-Lactamases (ESBL).

The in vitro activities (Minimal Inhibitory Concentrations, MIC) of 10 β-lactams (amoxicillin-AML, amoxicillin/clavulanate-AMC, ticarcillin-TIC, mecillinam-MEC, cefuroxime-CXM, aztreonam-ATM, ceftazidime-CAZ, ceftriaxone-CRO, cefotaxime-CTX, cefoxitin-FOX), against 132 and 27 uropathogenic E. coli strains were examined by agar dilution method, according to NCCLS guidelines. Multiplex PCR was used to detect the presence of genes encoding β-lactamases responsible for β-lactam resistance. For ESBL detection E-test assay was performed.

MIC50 and MIC90 (% of resistance) in µg/ml of β-lactams against feline E. coli strains were as follows: 256, 4096 for AML (56%); 64, 4096 for TIC (48%); 4, 256 for AMC (19%); 4, 64 for FOX (11%); 0.125, 4 for ATM (7%) and 0.25, 4 for CAZ (4%). MIC50 and MIC90 (% of resistance) in µg/ml of β-lactams against canine E. coli strains were as follows: 8, >2048 for AML (42%); 8, 4096 for TIC (39%); 4, 128 for AMC (15%); 0.5, 8 for MEC (8%); 4, 8 for FOX (3%); 4, 8 for CXM (2%); 0.25, 0.5 for CAZ (2%); 0.062, 0.125 for CRO (2%) and 0.125, 0.5 for ATM (1%). β-Lactam resistance among 17 feline E. coli strains was related to the production of TEM (8 strains), SHV (3 strains) and SHV plus TEM (2 strains) β-lactamases. β-Lactam resistance among 64 canine E. coli strains was related to the production of TEM (39 strains), SHV (5 strains), OXA (2 strains), OXA plus TEM (2 strains) and AmpC (1 strain) β-lactamases. Three cat E. coli strains had a positive E-test due to the production of SHV β-lactamase with extended-spectrum activity.

We found an important level of resistance towards β-lactams in feline and canine E. coli strains isolated from UTI and an emergence of resistance to third generation cephalosporins. This is the first report of ESBL producing strains in cats with UTI in Portugal. These results suggest that occurring ESBL-SHV enzymes are a result of antimicrobial pressure with third generation cephalosporins used not only in humans but also in veterinary therapy. This work shows the need for antimicrobial resistance surveillance in veterinary medicine.

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C. Pomba
CIISA, Faculty of Veterinary Medicine
UTL, Lisbon, Portugal

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