Antimicrobial resistance and pharmacodynamics of canine and feline pathogenic E. coli in the United States

Population pharmacokinetic analysis of enrofloxacin and its active metabolite ciprofloxacin after intravenous injection to cats with reduced kidney function

BACKGROUND

It is unknown if enrofloxacin accumulates in plasma of cats with reduced kidney function.

HYPOTHESIS

To determine if enrofloxacin and its active metabolite ciprofloxacin have reduced clearance in azotemic cats.

ANIMALS

Thirty-four cats hospitalized for clinical illness with variable degree of kidney function.

METHODS

Prospective study. After enrofloxacin (dose 5 mg/kg) administration to cats, sparse blood sampling was used to obtain 2 compartment population pharmacokinetic results using nonlinear mixed-effects modeling. Plasma enrofloxacin and ciprofloxacin concentrations were measured and summed to obtain the total fluoroquinolone concentration. A model of ciprofloxacin metabolism from enrofloxacin was created and evaluated for covariate effects on clearance, volume of distribution, and the metabolic rate of ciprofloxacin generation from enrofloxacin.

RESULTS

Body weight was the only covariate found to affect total fluoroquinolone volume of distribution (effect 1.63, SE 0.19, P < .01) and clearance (effect 1.63, SE 0.27, P < .01). Kidney function did not have a significant effect on total fluoroquinolone clearance (median 440.8 mL/kg/h (range 191.4-538.0 mL/kg/h) in cats with normal kidney function, 365.8 mL/kg/h (range 89.49-1092.0 mL/kg/h) in cats with moderate kidney dysfunction, and 308.5 mL/kg/h (range 140.20-480.0 mL/kg/h) in cats with severe kidney dysfunction (P = .64). Blood urea nitrogen concentration influenced the metabolic generation of ciprofloxacin from enrofloxacin (effect 0.51, SE 0.08, P < .01), but other markers of kidney function did not.

CONCLUSIONS AND CLINICAL IMPORTANCE

Adjustment of enrofloxacin dosage is not indicated for azotemic cats.

Bioequivalence of two tablet formulations of cefpodoxime proxetil in beagle dogs

The pharmacokinetic profiles and bioequivalence of two cefpodoxime proxetil tablets were investigated in Beagle dogs. A single-dose, four-way complete replication and crossover design was used in the present study. A total of 28 healthy Beagle dogs (half male and female) with an average body weight of 11.1 kg were randomly allocated to this study. A whole reference or test tablet containing the equivalent of 100 mg of cefpodoxime was administered orally to each dog. Serial plasma samples were collected, and cefpodoxime concentrations were determined by ultra-performance liquid chromatography-mass spectrometry (UPLC-MS/MS). Then a non-compartmental method was used to calculate the pharmacokinetic parameters of both tablet formulations. The average bioequivalence (ABE) or reference-scaled average bioequivalence (RSABE) methods were used to determine the 90% confidence interval (CI) of AUC_{INF_obs} and C_max. No significant differences were observed for both parameters between both tablets. The test formulation was bioequivalent to the reference one because the 90% CI ranges of C_max and AUC_{INF_obs} were all between 80 and 125%.

Antimicrobial susceptibility and risk factors for resistance among Escherichia coli isolated from canine specimens submitted to a diagnostic laboratory in Indiana, 2010–2019

Escherichia coli (E. coli) is the most common Gram-negative pathogen isolated in human infections. Antimicrobial resistant (AMR) E. coli originating from dogs may directly or indirectly cause disease in humans. The objective of this study was to calculate the proportion of antimicrobial susceptible E. coli isolated from canine specimens submitted to the Indiana Animal Disease Diagnostic Laboratory and to identify temporal patterns of susceptibility among these isolates. Susceptibility data of 2,738 E. coli isolates from dogs from 2010 through 2019 were used in this study. Proportions of isolates susceptible to the various antimicrobials were calculated using SAS statistical software and the Cochran-Armitage trend test was used to investigate the temporal trends in susceptibility. A multivariable binary logistic regression model was built to investigate the association between host factors and AMR. Overall, 553/2,738 (20.2%) of the isolates were susceptible to 17 of the 27 antimicrobials examined. Of the 2,638 isolates examined for amikacin susceptibility, 2,706 (97.5%) were susceptible, 2,657/2,673 (99.4%) isolates were susceptible to imipenem, and 2,099/2,670 (78.6%) were susceptible to marbofloxacin. A significant decreasing trend in susceptibility was observed for amoxicillin-clavulanic acid (P<0.0001), ampicillin (P<0.0001), Cefazolin (P<0.0001), ceftazidime (P = 0.0067), chloramphenicol (P<0.0001), and orbifloxacin (P = 0.008). The overall percentage of AMR isolates (isolates not susceptible to at least one antimicrobial) was 61.7% (1,690/2,738) and 29.3% (801/2,738) of isolates were multidrug resistant. Multivariable regression analyses showed significant associations between AMR and age (P = 0.0091), breed (P = 0.0008), and sample isolation site/source (P<0.0001). The decreasing trend in the proportion of isolates susceptible to several beta-lactam antimicrobials suggests that resistance of Escherichia coli in dogs to these antimicrobials could be increasing in Indiana. The decreasing trend in susceptibility to these drugs could be due to selection pressure from antimicrobial use.

Nitrofurantoin plasma- and urine exposure in eight healthy beagle dogs following standard nitrofurantoin dosing regimen

Bacterial cystitis is common in dogs and is usually treated with antibiotics. Nitrofurantoin is used for treatment of bacterial cystitis in humans and might provide a feasible treatment option in dogs. The aim of this study was to investigate the nitrofurantoin plasma concentration-time course and potential adverse effects in dogs. Nitrofurantoin (4.4-5.0 mg/kg) was administered orally to eight healthy beagles every 8 h for five days before repeated plasma and urine samples were collected. An additional four beagles served as untreated controls. The nitrofurantoin plasma and urine concentrations were measured using ultra high precision liquid chromatography coupled to tandem mass-spectrometry and further analysed using a non-compartmental pharmacokinetic model. In plasma, the median C_max was 2.1 μg/mL, t_max was 2 h, the terminal rate constant was 0.9 per h and the terminal half-life was 0.8 h. In urine, median C_max was 56 μg/mL, t_max was 1 h and the terminal half-life was 4.3 h. No adverse effects were observed clinically or in haematology or biochemistry. The data presented in this study combined with in vitro sensitivity data from common urine pathogens and the lack of observed adverse effects suggest that nitrofurantoin in a standard dosing regimen could be effective in sporadic bacterial cystitis treatment in dogs. Further clinical studies are highly warranted to verify the effectiveness in clinical cases.

Antimicrobial Resistance of Clinical and Commensal Escherichia coli Canine Isolates: Profile Characterization and Comparison of Antimicrobial Susceptibility Results According to Different Guidelines

Background: Pyometra is a diestrual chronic disease frequently associated with Escherichia coli. Initial pyometra treatment involves empiric antimicrobial therapy whose suitability should be confirmed by antimicrobial susceptibility testing. Antimicrobial resistance is a major health issue for veterinary medicine, rendering surveillance studies essential. Our goal was to determine the susceptibility profile of E. coli isolates obtained from healthy and pyometra-presenting dogs and to compare the application of different antimicrobial susceptibility guidelines. Methods: The antimicrobial susceptibility profile (ASP) of 74 E. coli isolates was determined by disk diffusion, using six antimicrobials commonly used in veterinary medicine. Profiles were assessed by CLSI VET01S, CLSI M100 and EUCAST guidelines. β-lactamases-encoding genes blaTEM, blaSHV and blaOXA were detected by multiplex PCR. Biofilm production ability was evaluated by pellicle formation assays in Luria–Bertani medium. Results: Variations in the resistance frequency were observed for amoxicillin/clavulanic acid, cephalexin and cefotaxime (29.7–54.1%, 10.8–16.2% and 1.4–4.1%, respectively). Results varied slightly between clinical and commensal isolates, as well as their biofilm-forming ability. Genes blaTEM, blaSHV and blaOXA were detected in 25.5%, 11.8% and 9.8% of isolates, respectively. Conclusions: Results show the importance of ASP determination in veterinary isolates and the need for using standardized and validated testing methods and harmonized interpretive criteria.

Antimicrobial Resistance in Bacteria Isolated From Canine Urine Samples Submitted to a Veterinary Diagnostic Laboratory, Illinois, United States

The emergence of antimicrobial resistance (AMR) in dogs constitutes a threat to animal and human health. There is a lack of studies in Illinois that evaluated the prevalence of AMR among urinary bacterial pathogens. In the study, we included 803 isolates (299 Gram-positive and 504 Gram-negative) that were isolated from 2,583 canine urine samples submitted to the Veterinary Diagnostic Laboratory, the University of Illinois between 2019 and 2020 from dogs suspected of urinary tract infections (UTI). The most common Gram-positive isolates included Staphylococcus pseudintermedius (17.93%), Enterococcus faecalis (9.46%), Streptococcus canis (6.10%), and Enterococcus faecium (3.74%), while Gram-negative isolates included Escherichia coli (45.58%), Proteus mirabilis (11.08%), Klebsiella pneumoniae (3.11%), and Pseudomonas aeruginosa (2.99%). Among the Gram-positive isolates, Staphylococcus pseudintermedius isolates showed a very high prevalence of resistance to penicillin (56.94%), a high prevalence of resistance to trimethoprim-sulfamethoxazole (31.94%), enrofloxacin (29.17%), and oxacillin (27.08%). Among Gram-negative bacteria, Escherichia coli isolates showed a high prevalence of resistance to ampicillin (31.42%). Considering the high prevalence of resistance to antimicrobials commonly used to treat UTI in dogs, urine samples should be collected for bacterial culture and susceptibility testing before treatment initiation to prevent treatment failures and the development of multidrug resistance. Given the possibility of zoonotic transmission of antimicrobial-resistant bacteria, veterinarians when treating UTI cases, should inform dog owners of the potential transmission risk.

Use of Local Antibiogram Data and Antimicrobial Importance Ratings to Select Optimal Empirical Therapies for Urinary Tract Infections in Dogs and Cats

International and Australian veterinary antimicrobial use guidelines recommend amoxicillin or trimethoprim-sulfonamide (TMS) for the empirical treatment of sporadic urinary tract infections (UTIs) in dogs and cats. However, in practice, these antibiotics are rarely used, and no large-scale analyses have examined the antibiograms of bacteria isolated from UTIs to validate these recommendations in Australia. We analyzed five years of urine culture and antimicrobial susceptibility data from an Australian veterinary laboratory. The analysis included 6196 urinary isolates from dogs and cats, 78% of which were from samples submitted by first-opinion veterinary clinics. Escherichia coli, Enterococcus faecalis, Staphylococcus pseudintermedius and Proteus spp. were the most prevalent organisms. More than 80% of all isolated cocci were susceptible to amoxicillin, and more than 80% of bacilli were susceptible to TMS. A total of 94% of isolates were susceptible to at least one antimicrobial drug categorized as low-importance in Australia. The prevalence of multi-drug resistance (MDR) was highest in E. coli, at 9.7%; 84% of these MDR isolates were susceptible to amoxicillin-clavulanate. We performed population-level antimicrobial treatment simulations and proposed a novel method for integrating antimicrobial importance ratings with antibiogram data to optimize the selection of empirical therapy. Our findings support current guideline recommendations to use amoxicillin or TMS. We also found that bacterial morphology assisted with selection; amoxicillin was a better choice for cocci and TMS for bacilli.

Autoinducer2 affects trimethoprim-sulfamethoxazole susceptibility in avian pathogenic Escherichia coli dependent on the folate synthesis-associate pathway

Avian pathogenic Escherichia coli (APEC) causes airsacculitis, polyserositis, septicemia, and other mainly extraintestinal diseases in chickens, ducks, geese, pigeons, and other avian species, and is responsible for great economic losses in the avian industry. The autoinducer 2 (AI‐2) quorum sensing system is widely present in many species of gram‐negative and gram‐positive bacteria and has been proposed to be involved in interspecies communication. In clinical APEC strains, whether or not AI‐2 affects the expression of antibiotic‐related genes has not been reported. In this study, we have reported that exogenous AI‐2 increase the susceptibility of APEC strains to trimethoprim‐sulfamethoxazole (SXT) in a folate synthesis‐dependent pathway but not in the LsrR‐dependent manner. Our results further explained that exogenous AI‐2 can down regulate the transcription of the folate synthetase encoding genes folA and folC, and the folate synthesis‐related genes luxS, metE, and metH. Gel shift assays confirmed that LsrR, the AI‐2 receptor, did not bind to the promoters of folA and folC, suggesting that exogenous AI‐2 might influence folate metabolism by a feedback inhibition effect but not in the LsrR‐dependent pathway. This study might provide further information in the search for potential drug targets for prophylaxis of avian colibacillosis and for auxiliary antibiotics in the treatment of avian colibacillosis.

Clinicopathologic and Microbiologic Findings Associated with Emphysematous Cystitis in 27 Dogs

This is a retrospective case series of 27 dogs with emphysematous cystitis. Medical records from two veterinary teaching hospitals from 1992 to 2014 were reviewed. The aims of the study were to determine imaging findings, common underlying disease processes, and prevalent bacterial species and their antimicrobial susceptibility patterns in dogs with emphysematous cystitis. The most common lower urinary tract sign was hematuria. Gas was detected in the wall and lumen of the urinary bladder in 14 of 27 dogs (51.9%), in only the wall of the bladder in 9 of 27 dogs (33%), and in only the lumen of the bladder in 4 of 27 dogs (14.8%). Comorbid diseases were identified in all but one case. The most common comorbid disease processes were diabetes mellitus in 33% of dogs, neurologic disease in 26% of dogs, and adrenal disease in 19% of dogs. Bacterial isolates included Escherichia coli, Enterococcus spp., Klebsiella pneumoniae, Proteus mirabilis, Streptococcus spp., and Actinomyces spp. Enterococcus spp. were always isolated in mixed infections with gas-producing bacterial species. During the period of study, most isolates were predicted to be susceptible to beta-lactam drugs, but updated veterinary breakpoints suggest that fluoroquinolones or trimethoprim-sulfamethoxazole would be more appropriate choices for empiric therapy.

Prevalence of antimicrobial resistance in faecal enterococci from vet-visiting pets and assessment of risk factors

The objective of this study was to determine the prevalence of antimicrobial resistance (AMR) exhibited by enterococci isolated from faeces of pets and its underlying risk factors. From September 2009 to May 2012, rectal swabs were collected from 74 dogs and 17 cats, selected from the population of animals visiting the Veterinary Hospital of University of Porto, UPVet, through a systematic random procedure. Animal owners answered a questionnaire about the risk factors that could influence the presence of AMR in faecal enterococci. Enterococci isolation, identification and antimicrobial (AM) susceptibility testing were performed. Data analyses of multilevel, univariable and multivariable generalised linear mixed models were conducted. From all enterococci isolated (n=315), 61 per cent were considered multidrug-resistant, whereas only 9.2 per cent were susceptible to all AMs tested. Highest resistance was found to tetracycline (67.0 per cent), rifampicin (60.3 per cent), azithromycin (58.4 per cent), quinupristin/dalfopristin (54.0 per cent) and erythromycin (53.0 per cent). Previous fluoroquinolone treatments and coprophagic habits were the features more consistently associated with the presence of AMR for three (chloramphenicol, ciprofloxacin and azithromycin) and seven (tetracycline, rifampicin, gentamicin, chloramphenicol, ciprofloxacin, erythromycin and azithromycin), respectively, out of nine AMs assessed. Evaluating risk factors that determine the presence of drug-resistant bacteria in pets, a possible source of resistance determinants to human beings, is crucial for the selection of appropriate treatment guidelines by veterinary practitioners.

Management of transitional cell carcinoma of the urinary bladder in dogs: a review

Transitional cell carcinoma (TCC), also referred to as urothelial carcinoma, is the most common form of urinary bladder cancer in dogs, affecting tens of thousands of dogs worldwide each year. Canine TCC is usually a high grade invasive cancer. Problems associated with TCC include urinary tract obstruction, distant metastases in >50% of affected dogs, and clinical signs that are troubling both to the dogs and to their owners. Risk factors for TCC include exposure to older types of flea control products and lawn chemicals, obesity, female sex, and a very strong breed-associated risk. This knowledge is allowing pet owners to take steps to reduce the risk of TCC in their dog. The diagnosis of TCC is made by histopathology of tissue biopsies obtained by cystoscopy, surgery, or catheter. Percutaneous aspirates and biopsies should be avoided due to the risk of tumor seeding. TCC is most commonly located in the trigone region of the bladder precluding complete surgical resection. Medical treatment is the mainstay for TCC therapy in dogs. Although TCC is not usually curable in dogs, multiple drugs have activity against it. Approximately 75% of dogs respond favorably to TCC treatment and can enjoy several months to a year or more of good quality life. Many promising new therapies for TCC are emerging and with the close similarity between TCC in dogs and high grade invasive bladder cancer in humans, new treatment strategies found to be successful in canine studies are expected to help dogs and to be subsequently translated to humans.

Diagnostic accuracy of a point-of-care urine bacteriologic culture test in dogs

OBJECTIVE

To determine diagnostic accuracy of a compartmented bacteriologic culture and antimicrobial susceptibility testing plate (CCSP) for detection of bacterial urinary tract infection (UTI) in dogs and antimicrobial susceptibility testing of bacterial isolates.

DESIGN

Evaluation study.

SAMPLE

62 frozen, previously characterized bacterial isolates from canine urine cultures and 147 canine urine samples.

PROCEDURES

The study was conducted in 2 phases: preliminary assay validation (phase 1) and diagnostic validation (phase 2). For phase 1, the frozen bacterial isolates were revitalized and tested with the CCSP and with standard aerobic microbiological culture (SAMC). For phase 2, the urine samples were tested with the CCSP and SAMC in parallel.

RESULTS

For phase 1, after 24 hours of culture, 46 of 62 (74%) bacterial isolates had growth on the CCSP and all (100%) had growth in SAMC. For bacterial isolates with growth, the CCSP allowed correct identification of 45 of 46 (98%) isolates. Isolates yielding no growth on the CCSP were gram-positive cocci (Staphylococcus spp [n = 7] and Enterococcus spp [9]). In phase 2, the overall diagnostic accuracy of the CCSP, compared with SAMC, was 94% (sensitivity, 81%; specificity, 99%). The positive predictive value was 98% and negative predictive value was 92%. Susceptibility results for enrofloxacin and trimethoprim-sulfamethoxazole as determined with the CCSP had greatest concordance with those determined by SAMC (71% and 96%, respectively), compared with other antimicrobial susceptibilities.

CONCLUSIONS AND CLINICAL RELEVANCE

Use of the CCSP led to accurate exclusion of UTI in dogs without a UTI but was less reliable for diagnosis of UTI, particularly infections caused by gram-positive cocci. Standard aerobic microbiological culture remains the gold standard for detection of UTI in dogs.