In vitroefficacy of 16 antimicrobial drugs against a large collection of β-lactamase-producing isolates of extraintestinal pathogenicEscherichia colifrom dogs and cats

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The aim of this study was to assess the in vitro efficacy of candidate antimicrobials against extended-spectrum β-lactamase (ESBL)-producing isolates of extraintestinal pathogenic Escherichia coli (ExPEC) from companion animals.


A total of 90 ESBL-producing ExPEC isolates from dogs and cats were tested for susceptibility to 16 antimicrobials with the agar dilution method. We also identified the ESBLs and AmpC β-lactamases of these isolates with PCR and DNA sequencing.

Results/Key findings.

All isolates were susceptible to meropenem, tebipenem and amikacin (AMK), and various proportions were susceptible to latamoxef (LMX, 97.8%), fosfomycin (FOM, 97.8%), faropenem (FPM, 96.7%), nitrofurantoin (NFT, 96.7%), flomoxef (FMX, 93.3%), piperacillin/tazobactam (PTZ, 92.2%), cefmetazole (CMZ, 91.1%), chloramphenicol (80.0%), trimethoprim/sulfamethoxazole (64.4%), amoxicillin/clavulanic acid (63.3%), ceftibuten (60.0%), tetracycline (52.2%) and enrofloxacin (10.0%). A genetic analysis showed that 83 of the 90 (92.2%) isolates were positive for CTX-M-type genes: CTX-M-14 (n=26), CTX-M-27 (n=20), CTX-M-55 (n=17), CTX-M-15 (n=12), CTX-M-2 (n=5), CTX-M-24 (n=2), CTX-M-104 (n=2) and CTX-M-3 (n=1). Eight isolates also expressed AmpC β-lactamase phenotypes.


This study demonstrates that the susceptibility rates to PTZ, CMZ, LMX, AMK, FOM, FPM, NFT and FMX were similar to those to carbapenems (>90%), implying that these drugs are available alternatives to carbapenems for the treatment of companion animals infected with ExPEC-producing CTX-M-type ESBLs. Further in vivo studies of the effective use of these antimicrobials are required.

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