Abstract
Urinary tract infections are common in dogs, necessitating antimicrobial therapy. We determined the speed and extent of in vitro killing of canine urinary tract infection pathogens by five antimicrobial agents (ampicillin, cephalexin, marbofloxacin, pradofloxacin, and trimethoprim/sulfamethoxazole) following the first 3 h of drug exposure. Minimum inhibitory and mutant prevention drug concentrations were determined for each strain. In vitro killing was determined by exposing bacteria to clinically relevant drug concentrations and recording the log10 reduction and percent kill in viable cells at timed intervals. Marbofloxacin and pradofloxacin killed more bacterial cells, and faster than other agents, depending on the time of sampling and drug concentration. Significant differences were seen between drugs for killing Escherichia coli, Proteus mirabilis, Enterococcus faecalis, and Staphylococcus pseudintermedius strains. At the maximum urine drug concentrations, significantly more E. coli cells were killed by marbofloxacin than by ampicillin (p < 0.0001), cephalexin (p < 0.0001), and TMP/SMX (p < 0.0001) and by pradofloxacin than by cephalexin (p < 0.0001) and TMP/SMX (p < 0.0001), following 5 min of drug exposure. Rapid killing of bacteria should inform thinking on drug selection for short course therapy for uncomplicated UTIs, without compromising patient care, and is consistent with appropriate antimicrobial use and stewardship principles.
Highlights
Accepted: 29 October 2021Urinary tract infections (UTI) or sporadic bacterial cystitis (SBC) are common in dogs and less frequently seen in cats [1]
Killing of E. coli by cephalexin and TMP/SMX at the mutant prevention concentration (MPC) were not performed due to MPC values that exceeded clinically achievable drug concentrations
At the Cmax drug concentration (Figure 3), more bacteria were killed by pradofloxacin (3.8 log10, 94% kill) than by TMP/SMX (p = 0.0136) following 60 min of drug exposure
Summary
Urinary tract infections (UTI) or sporadic bacterial cystitis (SBC) are common in dogs and less frequently seen in cats [1]. The frequency of UTIs is less than 1% and increases in frequency with advancing age. UTIs may be undiagnosed and discovered as an incidental finding; the consequences of untreated infections include lower urinary tract dysfunction, urolithiasis, prostatitis, infertility, septicaemia, and pyelonephritis [4,5], some of these complications are rare. Escherichia coli (E. coli) remains the single most common pathogen in acute and recurrent UTI; pathogens, such as Staphylococcus pseudintermedius, Proteus species (spp.), and other Gram-negative bacilli, Streptococcus spp., and Enterococcus spp., may cause infection. E. coli, Staphylococcus spp., Proteus spp., and Enterococcus spp. account for more than 70% of bacterial causes of UTI in dogs [7]
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