Antimicrobial resistance in companion animals

Longitudinal antimicrobial susceptibility trends of canine Staphylococcus pseudintermedius

Antimicrobial resistance within Staphylococcus pseudintermedius poses a significant risk for the treatment of canine pyoderma and as a reservoir for resistance and potential zoonoses, but few studies examine long-term temporal trends of resistance. This study assesses the antimicrobial resistance prevalence and minimum inhibitory concentration (MIC) trends in S. pseudintermedius (n=1804) isolated from canine skin samples at the Cornell University Animal Health Diagnostic Center (AHDC) between 2007 and 2020. Not susceptible (NS) prevalence, Cochran-Armitage tests, logrank tests, MIC50 and MIC90 quantiles, and survival analysis models were used to evaluate resistance prevalence and temporal trends to 23 antimicrobials. We use splines as predictors in accelerated failure time (AFT) models to model non-linear temporal trends in MICs. Multidrug resistance was common among isolates (47%), and isolates had moderate to high NS prevalence to the beta-lactams, chloramphenicol, the fluoroquinolones, gentamicin, the macrolides/lincosamides, the tetracyclines, and trimethoprim-sulfamethoxazole. However, low levels of NS to amikacin, rifampin, and vancomycin were observed. Around one third of isolates (38%) were found to be methicillin resistant S. pseudintermedius (MRSP), and these isolates had a higher prevalence of NS to all tested antimicrobials than methicillin susceptible isolates. Amongst the MRSP isolates, one phenotypically vancomycin resistant isolate (MIC >16 µg/mL) was identified, but genomic sequence data was unavailable. AFT models showed increasing MICs across time to the beta-lactams, chloramphenicol, the fluoroquinolones, gentamicin, and the macrolides/lincosamides, and decreasing temporal resistance (decreasing MICs) to doxycycline was observed amongst isolates. Notably, ATF modeling showed changes in MIC distributions that were not identified using Cochran-Armitage tests on prevalence, MIC quantiles, and logrank tests. Increasing resistance amongst these S. pseudintermedius isolates highlights the need for rational, empirical prescribing practices and increased antimicrobial resistance (AMR) surveillance to maintain the efficacy of current therapeutic agents. AFT models with non-linear predictors may be a useful, breakpoint-independent, surveillance tool alongside other modeling methods and antibiograms.

Antimicrobial Resistance in Romania: Updates on Gram-Negative ESCAPE Pathogens in the Clinical, Veterinary, and Aquatic Sectors

Multidrug-resistant Gram-negative bacteria such as Acinetobacter baumannii, Pseudomonas aeruginosa, and members of the Enterobacterales order are a challenging multi-sectorial and global threat, being listed by the WHO in the priority list of pathogens requiring the urgent discovery and development of therapeutic strategies. We present here an overview of the antibiotic resistance profiles and epidemiology of Gram-negative pathogens listed in the ESCAPE group circulating in Romania. The review starts with a discussion of the mechanisms and clinical significance of Gram-negative bacteria, the most frequent genetic determinants of resistance, and then summarizes and discusses the epidemiological studies reported for A. baumannii, P. aeruginosa, and Enterobacterales-resistant strains circulating in Romania, both in hospital and veterinary settings and mirrored in the aquatic environment. The Romanian landscape of Gram-negative pathogens included in the ESCAPE list reveals that all significant, clinically relevant, globally spread antibiotic resistance genes and carrying platforms are well established in different geographical areas of Romania and have already been disseminated beyond clinical settings.

Concomitant Campylobacteriosis in a Puppy and in Its Caregiver: A One Health Perspective Paradigm in Human-Pet Relationship

We report a case of laboratory-confirmed Campylobacter (C). jejuni and C. upsaliensis symptomatic infection in a puppy, a French Bouledogue, female, 6 months of age, fed a raw, unbalanced, poultry-based diet (RPD), (48.1 CP, 33% EE, 0.3% Ca, 0.5% Phos, 0.5 Ca/P, on a dry-matter basis), and in its owner. Soon after adoption, the pet and the caregiver showed severe gastrointestinal signs and needed hospitalization. Fecal PCR assays, selective cultures, and antibiotic susceptibility testing were performed, and multi-drug resistant C. jejuni and C. upsaliensis were isolated from the feces of both. The same bacteria were also identified by FISH in the dog colonic biopsies collected during endoscopy. The puppy was prescribed a complete commercial diet for growing dogs, (30.00% CP, 21.00% EE, 1.2% Ca; 1% Phos; as fed) and treated with ciprofloxacin. The dog and the man healed uneventfully and tested negative for further fecal PCR analyses. This report focuses on dog nutritional management and explores the potential routes of exposure, with emphasis on emerging outbreaks related to current pet food fads. Our data support the One Health approach, where veterinarians, physicians, and owners are challenged to build effective stewardship to prevent the spread of zoonoses.

Emergence and Transmission of Plasmid-Mediated Mobile Colistin Resistance Gene mcr-10 in Humans and Companion Animals

Mobile colistin resistance (mcr) genes mediated by plasmids have widely disseminated throughout the world. Recently, 10 mcr genes (mcr-1 to mcr-10) and a large number of variants have been identified in more than 60 countries. However, only a few instances of Enterobacter cloacae complex (ECC) bearing mcr-10 from animal origin have been reported globally. The aim of this study was to fill a knowledge gap in mcr-10-positive ECC of animal origin and analyze the potential transmission trend and different characteristics between human and companion animal isolates. The mcr-10 gene was identified on a self-transmissible plasmid in the human isolate and non-transmissible plasmids in other three animal strains. mcr-10 was adjacent to a XerC-type tyrosine recombinase-gene, and various insertion sequences were located on the downstream of core conservative structure xerC-mcr-10, thus indicating this region might be a candidate for insertions of mobile genetic elements and mcr-10 might be mobilized by IS-mediated mechanisms. Moreover, phylogenetic analysis found that mcr-10-positive isolates were mainly distributed in the clade of Enterobacter roggenkampii, exhibiting significant species specificity. These findings indicated that mcr-10 has emerged among Enterobacter spp. within humans and companion animals, highlighting that the importance of taking effective control measures to monitor the dissemination and evolution of mcr genes. IMPORTANCE Colistin was considered as the last-resort drug against severe clinical infections caused by multidrug-resistant Gram-negative pathogens. Mobile colistin resistance (mcr) genes and its variants carried by plasmids have been reported in diverse niches in recent years, and yet few studies reported carriage of mcr-10 in ECC strains of companion animal origin. How plasmid-borne mcr-10 transmitted in opportunistic pathogens and different characteristics of mcr-10-bearing strains isolated from humans and companion animals are not well understood. In this study, we discovered mcr-10-harboring strains in multidrug-resistant ECC isolates of companion animal origin for the first time and conducted a comprehensive analysis of the genetic environment of mcr-10 from multiple countries around the world, providing the potential basis for formulating control measures to slow down the spread of colistin resistance.

Prevalence of antibiotic-resistant bacteria amongst dogs in Africa: A meta-analysis review

Antimicrobial resistance (AMR) is a global public health threat for both human and veterinary medicine. Increasing evidence suggests that animals are important sources of AMR to humans; however, most of these studies focus on production animals. In order to determine the pattern of AMR in pets, mainly in dogs in Africa, a meta-analysis was performed with AMR studies conducted in African countries and published between January 2000 and January 2021 in four databases: Medline (PubMed), Scopus, Cab abstract and Google Scholar. Seven bacterial strains, namely Staphylococcus aureus, Escherichia coli, Salmonella spp., Pseudomonas aeruginosa, Streptococcus pyogenes, coagulase-negative Staphylococcus (SNC) and Staphylococcus pseudintermedius were included in this study. A total of 18 out of 234 indexed articles met the study criteria. The results revealed that multiple bacteria were resistant to various commonly used antibiotics including enrofloxacin, ciprofloxacin, gentamicin, amoxicillin, clavulanic acid, cotrimoxazole, streptomycin, tetracycline and chloramphenicol. Concerning multidrug resistance, E. coli strains came first with the highest prevalence of 98%, followed by P. aeroginosa (92%) and Salmonella spp. (53%). In contrast, the overall prevalence of multidrug resistance was low for S. aureus (18%) and S. pseudintermedius (25%). It is therefore urgent to find, as soon as possible, alternatives to replace these antibiotics, which have become ineffective in controlling these bacteria in dogs in Africa. Moreover, further metagenomic studies are needed to describe the full resistome and mobilome in dogs regardless of the bacteria.

Evaluation of the Impact of Antimicrobial Use Protocols in Porcine Reproductive and Respiratory Syndrome Virus-Infected Swine on Phenotypic Antimicrobial Resistance Patterns

A longitudinal study was conducted to assess the impact of different antimicrobial exposures of nursery-phase pigs on patterns of phenotypic antimicrobial resistance (AMR) in fecal indicator organisms throughout the growing phase. Based on practical approaches used to treat moderate to severe porcine reproductive and respiratory syndrome virus (PRRSV)-associated secondary bacterial infections, two antimicrobial protocols of differing intensities of exposure [44.1 and 181.5 animal-treatment days per 1000 animal days at risk (ATD)] were compared with a control group with minimal antimicrobial exposure (2.1 ATD). Litter-matched pigs (n = 108) with no prior antimicrobial exposure were assigned randomly to the treatment groups. Pen fecal samples were collected nine times during the wean-to-finish period and cultured for Escherichia coli and Enterococcus spp. Antimicrobial-susceptibility testing was conducted using NARMS Gram-negative and Gram-positive antibiotic panels. Despite up to 65-fold difference in ATD, few and modest differences were observed between groups and over time. Resistance patterns at marketing overall remained similar to those observed at weaning, prior to any antimicrobial exposures. Those differences observed could not readily be reconciled with the patterns of antimicrobial exposure. Resistance of E. coli to streptomycin was higher in the group exposed to 44.1 ATD, but no aminoglycosides were used. In all instances where resistances differed between time points, the higher resistance occurred early in the trial prior to any antimicrobial exposures. These minimal impacts on AMR despite substantially different antimicrobial exposures point to the lack of understanding of the drivers of AMR at the population level and the likely importance of factors other than antimicrobial exposure. IMPORTANCE Despite a recognized need for more longitudinal studies to assess the effects of antimicrobial use on resistance in food animals, they remain sparse in the literature, and most longitudinal studies of pigs have been observational. The current experimental study had the advantages of greater control of potential confounding, precise measurement of antimicrobial exposures which differed markedly between groups and tracking of pigs until market age. Overall, resistance patterns were remarkably stable between the treatment groups over time, and the differences observed could not be readily reconciled with the antimicrobial exposures, indicating the likely importance of other determinants of AMR at the population level.

Antimicrobial Resistance of Coagulase-positive Staphylococcus Isolated From Healthy Crioulo Horses and Associated Risk Factors

Antimicrobial resistance (AMR) is a global concern that must be addressed from a one health perspective. Horses are companion animals and their contact with humans facilitates exchange of resistant bacteria. This study aimed to evaluate AMR of coagulase-positive Staphylococcus (CoPS), including Staphylococcus aureus, isolated from healthy Crioulo horses. Swab samples from nostrils (n = 214) and skin (n = 107) of 107 horses from Porto Alegre, South Brazil, were used for CoPS isolation. The isolates were evaluated for AMR and a multivariate logistic regression was applied to identify the risk factors associated to this outcome, using information on horses' management and installations where they were maintained. A total of 143 CoPS were isolated from 79 horses (73.8%), of which 8 (5.6%) were S. aureus. The isolates showed resistance to seven of 10 tested antimicrobials and 38.5% (55/143) of them were resistant to at least one antimicrobial. One isolate (0.7%; 1/143) was classified as multidrug-resistant. Regarding S. aureus, 62.5 % (5/8) showed AMR, but none were methicillin-resistant. The risk factors associated with CoPS' antimicrobial resistance were lower frequency of bed changing (OR = 6.40; P = .001) and nonaccumulation of bed materials (OR = 3.47; P = .002). The results point that healthy horses have antimicrobial-resistant CoPS and S. aureus in their microbiota, which may be of concern for animal and human health. Moreover, bed management was associated with AMR, which can serve as a guide for best practices to be adopted to avoid the occurrence of resistant bacteria in these animals.

Bacterial zoonoses transmitted by household pets and as reservoirs of antimicrobial resistant bacteria

Numerous individuals are committed to growing pet creatures like cats, dogs, and rats etc., pay care for them and as a result of this, there's a boost of their populace in advanced culture. The close interaction between family pets and individuals offers ideal conditions for bacterial transmission. Distinctive sorts of antimicrobial agents are exploited for animal husbandry and studies have revealed that many bacteria have attained confrontation against them viz., Staphylococcus intermedius, Escherichia coli, methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococci and multidrug-resistant Salmonella typhi etc. and a few of these are a prospective for zoonotic transmission. In the current review, the attention has been paid on how household pets, especially dogs disperse the antimicrobial resistance in contrast to that of food animals. A lot of evidences are accessible on food animals and nation-wide scrutiny programmes solely hub on food animals; therefore, for steerage antimicrobial use policy in small animal veterinary exercise as well as for gauging the chance of transmission of antimicrobial resistance to humans' statistics on pet animals are sincerely needed. Transmission of such organisms, especially pathogenic staphylococci, occurs between pets, owners, and veterinary staff, and pets can act as reservoirs of such bacteria; this may additionally have an impact on the use of antimicrobials in human medicine. There is a need to generate statistics concerning each the levels of carriage of such microorganism in pets and the risk factors associated with the switch of the microorganism to human beings who have contact with infected pets, as nicely as to improve hygiene measures in veterinary practice.

Antimicrobial resistance in companion animals - Veterinarians' attitudes and prescription drivers in Portugal

Antimicrobial resistance transmitted from companion animals is a threat to public health increased by the pet's relationship with humans. This study aims to understand the attitude and drivers of antimicrobial (AM) prescription among companion animal veterinarians in Portugal and identify actions to combat antimicrobial resistance (AMR). This cross-sectional study is based on a questionnaire with 417 respondents representing the Portuguese veterinary population. The results allowed grouping the respondents according to the attitude of prescription. Two types of veterinarians were identified: those who prefer to prescribe treatments based on the animals' signs and their own experience - empirical-oriented type - and those who refer to a guidance protocol to assist the prescription decision - protocol-oriented type. Respondents working in hospitals displayed a positive association with the use of guidance protocols. Efficacy was the main driver of prescription for both groups, suggesting that no matter the attitude in prescribing, the veterinarian's aim is achieving positive clinical results. Most respondents prefer empirical-oriented prescriptions, declare the absence of protocols for the prudent use of AM at the workplace and do not refer to AMR issues nor the need for hygiene reinforcement measures with owners. Owners are less likely to request AMs from veterinarians aged over 43 years old. It was discovered that communication between owners and veterinarians about risks associated with AMR was poor and must be improved and the adoption of a national guideline for the adequate use of AM directed for companion animals would be beneficial.

Antimicrobial resistance in clinical bacterial isolates from horses in the UK

BACKGROUND

Surveillance of antimicrobial resistance (AMR) in horses is important to aid empirical treatment decisions and highlight emerging AMR threats.

OBJECTIVE

To describe the AMR patterns of common groups of bacteria from clinical submissions from horses in the UK during 2018, and to determine how this varies by sample site and type of submitting veterinary practice.

STUDY DESIGN

Prospective observational study.

METHODS

All data on bacterial culture and subsequent antimicrobial susceptibility testing (AST) collected in 2018 from six large equine diagnostic laboratories were included. Resistance patterns were analysed including resistance to 1 or 2 antimicrobial classes, multidrug resistance (MDR), extensively drug resistant (XDR), resistance to highest priority critically important antimicrobials and isolates where there was no readily available treatment for adult horses in the UK. Submitting practices were classified according to whether they treated referral cases or not (first opinion). Comparisons between proportions and resistance for each bacterial group and sample site was performed using Chi-squared (or Fisher's exact test).

RESULTS

A total of 6,018 bacterial isolates from 4,038 diagnostic submissions were included from respiratory (n = 1555), urogenital (n = 1,010), skin/hair/wound/abscess (n = 753), surgical site infection (SSI) /catheter-related-infection (CRI) /orthopaedic infections (n = 347) and unknown/'other' submissions (n = 373). There were 2,711 Gram-negative isolates and 3,307 Gram-positive isolates. Prevalence of MDR for E. coli was 31.7%, Staphylococcus spp. 25.3% and > 25% for the majority of bacterial isolates from SSI/CRI/orthopaedic submissions. For Enterococcus spp. there was no readily available treatment for adult horses in the UK in 30.2% of positive submissions. MDR was significantly higher from referral hospital than first opinion submissions for the majority of pathogens (except Actinobacillus spp. and Pasteurella spp. and β-haemolytic Streptococcus spp.).

MAIN LIMITATIONS

Since culture and susceptibility results are not systematic analyses based on harmonised methods, selection bias could impact the findings.

CONCLUSIONS

Ongoing surveillance is essential to understand emerging patterns of resistance. MDR is high in SSI/CRI/orthopaedic infections, which is important for hospital biosecurity and guiding treatment decisions. Harmonisation of diagnostic procedures and interpretation of results amongst veterinary laboratories will improve AMR surveillance and data comparison among laboratories.

White Paper: Bridging the gap between surveillance data and antimicrobial stewardship in the animal sector-practical guidance from the JPIAMR ARCH and COMBACTE-MAGNET EPI-Net networks

BACKGROUND

The JPIAMR ARCH and COMBACTE-MAGNET EPI-Net networks have joined efforts to formulate a set of target actions to link the surveillance of antimicrobial usage (AMU) and antimicrobial resistance (AMR) with antimicrobial stewardship (AMS) activities in four different settings. This White Paper focuses on the veterinary setting and embraces the One Health approach.

METHODS

A review of the literature was carried out addressing research questions in three areas: AMS leadership and accountability; AMU surveillance and AMS; and AMR surveillance and AMS. Consensus on target actions was reached through a RAND-modified Delphi process involving over 40 experts in infectious diseases, clinical microbiology, AMS, veterinary medicine and public health, from 18 countries.

RESULTS/DISCUSSION

Forty-six target actions were developed and qualified as essential or desirable. Essential actions included the setup of AMS teams in all veterinary settings, building government-supported AMS programmes and following specific requirements on the production, collection and communication of AMU and AMR data. Activities of AMS teams should be tailored to the local situation and capacities, and be linked to local or national surveillance systems and infection control programmes. Several research priorities were also identified, such as the need to develop more clinical breakpoints in veterinary medicine.

CONCLUSIONS

This White Paper offers a practical tool to veterinary practitioners and policy makers to improve AMS in the One Health approach, thanks to surveillance data generated in the veterinary setting. This work may also be useful to medical doctors wishing to better understand the specificities of the veterinary setting and facilitate cross-sectoral collaborations.

Antimicrobial use in wean to market pigs in the United States assessed via voluntary sharing of proprietary data

Data on antimicrobial use were collected for the 2016 and 2017 calendar years from swine producers in the United States. Nine large systems, collectively producing over 20 million market pigs annually, voluntarily provided data to advance understanding of antimicrobial use in the industry and to support antimicrobial stewardship initiatives. The scope of the study was limited to growing pigs, and the granularity of data varied across the systems. Data were summarized both qualitatively and quantitatively by antimicrobial class, active ingredient and route of administration (injection, water and feed). Data on the purpose of administration, doses and durations of administration were not available, but some information was provided by the responsible veterinarians. Aggregate data were similar both qualitatively and quantitatively in 2016 and 2017, although marked changes between years were evident within systems for some antimicrobials. Antimicrobial use (by weight) was dominated by the tetracycline class (approximately 60% of total use). Antimicrobials in classes categorized as critically important constituted 4.5% and 5.3% of total use in 2016 and 2017, respectively. In both years, fluoroquinolone (0.23%, 0.46%) and 3rd generation cephalosporin (0.15%, 0.11%) use collectively accounted for <1% of total use. Administration was predominantly oral in feed and water, and injection comprised approximately 2% of use overall, but around 12% for critically important antimicrobials. There was considerable variability among systems in patterns of antimicrobial use. This pilot project demonstrates the feasibility of acquiring antimicrobial use data via voluntary sharing. It is currently being expanded among larger swine production systems, and further efforts to enable confidential data sharing and benchmarking for smaller producers are being pursued by the swine industry. Recognized biases in the data caution against over-interpretation of these data as an index of national use.

Detection of multidrug resistance and extended-spectrum/plasmid-mediated AmpC beta-lactamase genes in Enterobacteriaceae isolates from diseased cats in Italy

OBJECTIVES

The aim of this study was to determine the antimicrobial susceptibility of Enterobacteriaceae isolated from cats affected by diseases commonly encountered in practice, and to characterise the third-generation cephalosporin (3GC)-resistance molecular mechanisms involved.

METHODS

Clinical samples (n = 100) included 58 rectal swabs from cats with diarrhoea, 31 nasal swabs from cats with clinical signs of upper respiratory tract disease, four ear swabs from cats with otitis, three conjunctival swabs from cats with conjunctivitis, two oral swabs from cats with stomatitis, one swab from a skin abscess and one urine sample from a cat with cystitis. A total of 125 Enterobacteriaceae were isolated from 90 cats. Escherichia coli was the most frequently isolated species (n = 65), followed by Enterobacter species (n = 20), Proteus species (n = 13), Citrobacter species (n = 12) and others (n = 15). Bacterial susceptibility testing was performed with respect to eight antimicrobial classes. Beta (β)-lactamase genes were identified by PCR and nucleotide sequencing.

RESULTS

Overall, the higher frequency of resistance was to amoxicillin-clavulanate (61.3%), trimethoprim/sulfamethoxazole (33.6%) and cefotaxime (32.8%). Thirty-six percent of the isolates (n = 45) were resistant to 3GCs. Of these isolates, 34 were tested by PCR and nucleotide sequencing and 23 were confirmed as encoding β-lactamase genes. Fourteen 3GC-resistant isolates harboured extended-spectrum β-lactamases (ESBLs) belonging to groups CTX-M-1 (n = 12, two of which were CTX-M-79), CTX-M-2 (n = 1) and CTX-M-9 (n = 1), as well as SHV-12 (n = 1) and TEM-92 (n = 1). Nine isolates had CMY-2 plasmid-mediated AmpC β-lactamases (pAmpC). Thirty-one percent (n = 39) of the isolates were multidrug resistant (MDR) and were isolated from 34% (n = 31/90) of the cats.

CONCLUSIONS AND RELEVANCE

A high frequency of MDR and ESBL/pAmpC β-lactamase-producing Enterobacteriaceae were detected among bacteria isolated from a feline population in southern Italy with a variety of common clinical conditions, which poses limitations on therapeutic options for companion animals. We describe the first detection of CTX-M-79 and TEM-92 ESBL genes in isolates from cats.

Antimicrobial Resistance in Veterinary Medicine: An Overview

Antimicrobial resistance (AMR) represents one of the most important human- and animal health-threatening issues worldwide. Bacterial capability to face antimicrobial compounds is an ancient feature, enabling bacterial survival over time and the dynamic surrounding. Moreover, bacteria make use of their evolutionary machinery to adapt to the selective pressure exerted by antibiotic treatments, resulting in reduced efficacy of the therapeutic intervention against human and animal infections. The mechanisms responsible for both innate and acquired AMR are thoroughly investigated. Commonly, AMR traits are included in mobilizable genetic elements enabling the homogeneous diffusion of the AMR traits pool between the ecosystems of diverse sectors, such as human medicine, veterinary medicine, and the environment. Thus, a coordinated multisectoral approach, such as One-Health, provides a detailed comprehensive picture of the AMR onset and diffusion. Following a general revision of the molecular mechanisms responsible for both innate and acquired AMR, the present manuscript focuses on reviewing the contribution of veterinary medicine to the overall issue of AMR. The main sources of AMR amenable to veterinary medicine are described, driving the attention towards the indissoluble cross-talk existing between the diverse ecosystems and sectors and their cumulative cooperation to this warning phenomenon.

Antimicrobial stewardship in equine practice

The veterinary profession's use of critically important antimicrobials is a One Health issue that has come under the scrutiny of the World Health Organization and the European Parliament. Failure by the veterinary profession to demonstrate the ability to self-regulate may result in restriction on the freedom to dispense antimicrobials, in an effort to protect human health. The implementation of such legislation would have a considerable impact on veterinary practices and would likely impair our ability to treat some conditions. These concerns, and the increasing frequency of multi-resistant bacterial infections in equine patients, should prompt implementation and audit of antimicrobial stewardship practices and measures to limit the development and spread of multi-resistant bacteria.

In vitro antimicrobial activity of seven adjuvants against common pathogens associated with canine otitis externa

BACKGROUND

An antibiotic adjuvant is a chemical substance used to modify or augment the effectiveness of primary antimicrobial agents against drug-resistant micro-organisms. Its use provides an alternative approach to address the global issue of antimicrobial resistance and enhance antimicrobial stewardship.

HYPOTHESIS/OBJECTIVES

To determine the antimicrobial activity of a panel of potential antimicrobial adjuvants against common pathogens associated with canine otitis externa (OE).

ANIMALS/ISOLATES

A number of type strains and clinical isolates (n = 110) from canine OE were tested including Staphylococcus pseudintermedius, β-haemolytic Streptococcus spp., Pseudomonas aeruginosa, Proteus mirabilis and Malassezia pachydermatis.

METHODS AND MATERIALS

Antimicrobial activities of monolaurin, monocaprin, N-acetylcysteine (NAC), polymyxin B nonapeptide, Tris-EDTA, Tris-HCL and disodium EDTA were tested using microdilution methodology according to CLSI guidelines.

RESULTS

N-acetylcysteine, Tris-EDTA and disodium EDTA had antimicrobial activity against both type strains and otic pathogens. The other adjuvants tested had limited to no efficacy. NAC had a minimal inhibitory concentration (MIC) range of 2,500-10,000 μg/mL for the various organisms. Pseudomonas aeruginosa isolates were eight times more susceptible to disodium EDTA in the presence of Tris-HCL in comparison to disodium EDTA alone. Malassezia pachydermatis isolates were most susceptible to Tris-EDTA (MIC₉₀  = 190/60 μg/mL) and disodium EDTA (MIC₉₀  = 120 μg/mL).

CONCLUSIONS AND CLINICAL RELEVANCE

N-acetylcysteine, Tris-EDTA and disodium EDTA have intrinsic antimicrobial activity and represent promising adjuvants that could be used to enhance the efficacy of existing antibiotics against Gram-negative and multidrug-resistant bacterial infections. These agents could be combined with other antimicrobial agents in a multimodal approach for mixed ear infections in dogs.