Using minimum inhibitory concentration values of common topical antibiotics to investigate emerging antibiotic resistance: A retrospective study of 134 dogs and 20 horses with ulcerative keratitis

Prevalence and antibiotic resistance in bacterial isolates of dogs with ulcerative keratitis in São Paulo State, Brazil

OBJECTIVE

Identify microorganisms present in canine eyes affected by ulcerative keratitis and assess its resistance profile to available antimicrobial drugs.

METHODS

Samples were collected from 88 canine eyes that exhibited ulcerative keratitis. They were identified using MALDI-TOF and subjected to antimicrobial susceptibility testing by disk diffusion.

RESULTS

Among the assessed subjects, brachycephalic dogs accounted for 74.48% (50/83) of the evaluated canines. Among the 88 evaluated eyes, 90.9% (80/88) showed positive cultures, with 11.33% (10/88) of the samples isolating more than one species of bacteria. Of all bacterial isolates identified (90), Gram-positive bacteria accounted for 63.33% (57/90), while Gram-negative bacteria constituted 36.66% (33/90), with predominance of Staphylococcus spp. at 35.55% (32/90) being, Staphylococcus pseudintermedius at 68.75% (22/32), and Pseudomonas aeruginosa at 15.55% (14/90), respectively. Staphylococcus spp. exhibited resistance to penicillin (89.29%), sulfadiazine and trimethoprim (60.71%), and tetracycline (67.86%), while doxycycline (88.89%), cefotaxime (85.71%), chloramphenicol (82.14%), gentamicin, and moxifloxacin (78.57%) showed the highest sensitivity rates. Pseudomonas aeruginosa displayed sensitivity (100%) to gentamicin and imipenem, and resistance (8.33%) to norfloxacin, ciprofloxacin, and cefepime. Similarly, the Enterobacteriaceae family showed higher sensitivity to amikacin and gentamicin (88.89%), imipenem (88.24%), and levofloxacin (87.5%), with pronounced resistance to amoxicillin-clavulanate (50%) and cefazolin (47.06%). This highlights multiresistance in 23.33% (21/90) of the isolates.

CONCLUSIONS

The most isolated species in canine ulcerative keratitis are S. pseudintermedius and P. aeruginosa. However, other species were also isolated, demonstrating diversity in ocular microbiota infection. There is a high-rate multidrug resistance associated with canine ulcerative keratitis. Nevertheless, these strains exhibited sensitivity to antimicrobials commonly used in veterinary ophthalmology.

Equine ulcerative keratitis in the Netherlands (2012-2021): Bacterial and fungal isolates and antibiotic susceptibility

BACKGROUND

Ulcerative keratitis is a common ophthalmic disease in horses which can be complicated by microbial infection and requires immediate, accurate treatment to prevent loss of visual function or the eye.

OBJECTIVES

To report the results of microbial cultures, antibiotic susceptibility tests and corneal cytology in horses with ulcerative keratitis presented to a referral clinic, to assess agreement between cytology and culture results, to investigate whether previous topical treatment affected microbial culture results and whether the incidence of antimicrobial resistance changed during the study period.

STUDY DESIGN

Retrospective analysis.

METHODS

Case characteristics and results of cytology and microbial cultures were retrieved. Statistical analyses included descriptive statistics, χ2 or Fisher's exact test and McNemar test.

RESULTS

Samples for bacterial culturing (n = 187), fungal culturing (n = 153) and cytology (n = 153) were collected from 178 horses. Bacterial and fungal cultures were positive in 36% (n = 67) and 20% (n = 30), respectively. Staphylococcus (n = 35/67; 48%), Streptococcus (n = 12/67; 16%) and Aspergillus species (n = 22/30; 81%) were most frequently found. Microorganisms were observed in 14% of cytology samples (n = 22/153). Acquired antibiotic resistance was commonly observed amongst Streptococcus and Staphylococcus species. Acquired antibiotic resistance to gentamicin was more common in cases previously treated with gentamicin (p < 0.001). The incidence of acquired antibiotic resistance did not increase significantly between Cohort 2012-2017 and Cohort 2018-2021. Neither bacterial nor fungal culturing results were in agreement with cytology findings (p < 0.001 and p = 0.02, respectively). In 6 of 104 samples that were negative on fungal culturing, cytology revealed fungal elements.

MAIN LIMITATIONS

Due to the retrospective nature of this study, some case characteristics and test results were unavailable.

CONCLUSIONS

Acquired resistance was commonly observed amongst Streptococcus and Staphylococcus species, and in bacteria previously exposed to topical gentamicin. The incidence of acquired antibiotic resistance did not increase over time. When fungal cultures prove negative, cytology may have some added benefit in identifying keratomycosis.

Corneal stromal ulcerations in a referral population of dogs and cats in the Netherlands (2012-2019): Bacterial isolates and antibiotic resistance

OBJECTIVE

To evaluate bacterial isolates from corneal stromal ulcerations in dogs and cats in the Netherlands, review their antibiotic susceptibility, determine whether recent topical treatment affected bacterial culture results, and investigate whether (multi-drug) resistance patterns changed over time.

ANIMALS STUDIED

Client-owned dogs and cats were diagnosed with corneal stromal ulceration at the Utrecht University Clinic for Companion Animals between 2012 and 2019.

PROCEDURES

Retrospective analysis.

RESULTS

In total, 163 samples were collected from 122 dogs (130 samples) and 33 cats. Positive cultures were obtained from 76 canine and 13 feline samples (59% and 39%, respectively) and included Staphylococcus (42 in dogs, 8 in cats), Streptococcus (22 in dogs, 2 in cats), and Pseudomonas (9 in dogs, 1 in cats) species. Significantly fewer positive cultures were found in dogs and cats previously treated with topical antibiotics (χ2  = 6.52, p = .011 and χ2  = 4.27, p = .039, respectively). Bacterial resistance to chloramphenicol was more common in dogs previously treated with chloramphenicol (χ2  = 5.24, p = .022). The incidence of acquired antibiotic resistance did not increase significantly over time. In dogs, the incidence of multi-drug-resistant isolates increased significantly between 2012-2015 and 2016-2019 (9.4% vs. 38.6%, p = .0032).

CONCLUSIONS

Staphylococcus, Streptococcus, and Pseudomonas species were the most common bacteria associated with canine and feline corneal stromal ulcerations. Previous treatment with antibiotics affected bacterial culture results and antibiotic sensitivity. Although the overall incidence of acquired antibiotic resistance did not change over time, the incidence of multi-drug-resistant isolates in dogs increased over an 8-year period.

Progressive ulcerative keratitis in dogs in the United Kingdom: Microbial isolates, antimicrobial sensitivity, and resistance patterns

OBJECTIVES

The objective of the study was to identify bacterial pathogens and their antimicrobial sensitivity profile associated with cases of canine progressive ulcerative keratitis.

MATERIALS AND METHODS

Analysis of microbial culture and sensitivity results from dogs with progressive ulcerative keratitis presenting to a UK referral practice between December 2018 and August 2020.

RESULTS

Positive bacterial cultures were obtained from 80/148 (54%) of the canine ulcers sampled with 99 bacterial isolates cultured. Streptococcus canis (n = 29), Pseudomonas aeruginosa (n = 19), and Staphylococcus pseudintermedius (n = 16) were the most common isolates. Pseudomonas aeruginosa was more likely to be isolated whether the ulcer was clinically malacic at the time of sampling (OR = 10.1, p < .001). Ulcers treated prior to culture with fusidic acid were 7.6 times more likely to be positive than those treated with any other antimicrobial(s). Bacterial isolates demonstrated resistance against neomycin (85%), fusidic acid (78%), and tetracycline (68%). Conversely, isolates were most likely to be sensitive to gentamicin (88%), ofloxacin (77%), ciprofloxacin (73%), and chloramphenicol (64%). Antimicrobial combinations of chloramphenicol or gentamicin with a fluoroquinolone (ofloxacin or ciprofloxacin) or chloramphenicol combined with gentamicin were the most effective on in vitro analysis (over 90% susceptibility of all isolates).

CONCLUSION

The most common bacterial species associated with canine progressive ulcerative keratitis in a UK referral population were S. canis, P. aeruginosa, and S. pseudintermedius. Combination antimicrobial therapy is recommended pending culture and sensitivity results given the varied antimicrobial susceptibility profiles and significant bacterial in vitro resistance to antimicrobial monotherapy.

In vitro antibacterial efficacy of autologous conditioned plasma and amniotic membrane eye drops

OBJECTIVE

To determine the in vitro antibacterial efficacy of equine and canine autologous conditioned plasma (ACP) and amniotic membrane extract eye drops (AMEED) against aerobic bacteria common to the corneal surface.

PROCEDURES

Canine (n = 4) and equine (n = 4) anticoagulated whole blood samples were sterilely collected, pooled for each species, and processed using the Arthrex ACP® Double-Syringe System. Platelet counts were performed on ACP and pooled blood. AMEED were obtained from a commercial source. An electronic medical records search (2013-2022) identified aerobic bacteria cultured from canine and equine corneal ulcers at Mississippi State University College of Veterinary Medicine (MSU-CVM). Ten commonly isolated bacteria for each species were collected from cultures submitted to the MSU-CVM Microbiology Diagnostic Service and frozen at -80°C. The Kirby-Bauer disk diffusion method was used to determine the sensitivities of these isolates to ACP and AMEED. Bacterial isolates were plated onto Mueller-Hinton +5% sheep blood agar and blank sterile discs saturated with 20 μL of ACP or AMEED were tested in duplicate. Imipenem discs served as positive controls and blank discs as negative controls. Zones of inhibition were measured at 18 h.

RESULTS

ACP platelet counts were 1.06 and 1.65 times higher than blood for equine and canine samples, respectively. Growth of a multi-drug resistant Enterococcus faecalis was partially inhibited by canine and equine ACP. AMEED did not inhibit growth of any examined bacteria.

CONCLUSIONS

Canine and equine ACP partially inhibited E. faecalis growth in vitro. Further studies using varying concentrations of ACP against bacterial isolates from corneal ulcers are warranted.

Susceptibility pattern of bacterial isolates in equine ulcerative keratitis: Implications for empirical treatment at a university teaching hospital in Sydney

Corneal ulceration is a common ophthalmic condition in horses. It is frequently caused by trauma to the corneal surface, followed by secondary infection by commensal or pathogenic organisms including Streptococcus equi subspecies zooepidemicus, Pseudomonas aeruginosa and Staphylococcus spp. Emerging antimicrobial resistance amongst these organisms has raised the need for appropriate antimicrobial therapy selection, to optimise treatment efficacy while minimising further antimicrobial resistance. Medical records of 38 horses presented at the University Veterinary Teaching Hospital Camden for ulcerative keratitis between 2010 and 2020 were reviewed to identify those with positive bacterial cultures and antimicrobial susceptibility profiles (13/38). Common susceptibility patterns were identified and used to guide the empirical treatment of equine bacterial corneal ulcers. Pseudomonas spp. (64.3%), Streptococcus equi subspecies zooepidemicus (14.3%) and Actinobacillus spp. (14.3%) were most commonly identified. Susceptibility to amikacin, gentamicin and ciprofloxacin was observed in 100%, 66.7% and 85.7% Pseudomonas spp. isolates respectively. Resistance to polymyxin B and neomycin occurred in 85.7% and 71.4% of Pseudomonas spp., respectively. All Streptococcus equi subspecies zooepidemicus organisms in this study were susceptible to ceftiofur, cephalexin, penicillin and ampicillin, while they were all resistant to gentamicin, neomycin, enrofloxacin and marbofloxacin. Predominating in this study, Pseudomonas spp. maintained overall aminoglycoside susceptibility despite some emerging resistance, and good fluoroquinolone susceptibility. High resistance to Polymyxin B could have arisen from its common use as first-line therapy for bacterial corneal ulcers. Although further research is required, these new findings about predominant bacteria in equine corneal ulceration in the Camden region and their antimicrobial susceptibility patterns can be used to guide the empirical treatment of bacterial corneal ulcers in horses.

Antibiotic Recommendations for Treatment of Canine Stromal Corneal Ulcers

The aim of the study was to identify the aerobic bacterial isolates and determine corresponding antibiotic susceptibility profiles in vitro in canine clinical specimens with stromal corneal ulcers, with the goal of providing recommendations for first-line treatment with antibiotics. A total of 198 canine corneal stromal ulcer samples were studied between 2018 and 2021. A corneal swab was collected and cultured under aerobic conditions. Bacterial organisms were identified at the species level by MALDI-TOF mass spectrometry. Antibiotic susceptibility testing for commonly used topical and systemic antibiotics was performed by disk diffusion. Bacterial growth was obtained from 80% of samples. A variety of bacterial species were identified wherein the most common specimens were represented by Staphylococcus pseudintermedius (22%), Staphylococcus epidermidis (12%), Staphylococcus capitis (11%), and Pseudomonas aeruginosa (10%). Based on the overall antibiotic susceptibility data, neopolybac alone (96%) or a combination of neopolybac with either ofloxacin or amikacin (each 99%) showed the best coverage for commonly isolated bacterial organisms from canine corneal stromal ulcers. Results of this study support the use of the combined antibiotics as the first-line response for the treatment of canine corneal stromal ulcers. A statically significant increase in acquired bacterial resistance was detected during the longitudinal data observation.

Quantifying topical antimicrobial use before and during participation in an antimicrobial stewardship programme in Dutch companion animal clinics

The emergence of bacterial strains resistant to topical antimicrobials in both human and veterinary medicine has raised concerns over retaining the efficacy of these preparations. Yet, little information is available regarding the use of topical antimicrobials in either sector for planning targeted interventions. This study aims to quantify the use of topical antimicrobials in 44 Dutch companion animal clinics before and during their participation in an antimicrobial stewardship programme (ASP), to explore the effect of the intervention on topical antimicrobial use (AMU). Hence, prescription and clinic animal population data, collected from July 2012 until June 2018 were used. Specifically, the period from July 2012 until June 2015 was defined as pre-intervention period, whereas clinics started to participate in the ASP from March 2016 onwards. As quantification metric, the Defined Daily Dose for Animals (DDDA) was used and a mixed effect times series model with auto-regression was applied to monthly topical AMU data. The intervention effect was modelled using a step function with a change in (linear) time trend and clinic characteristics, as potential determinants of topical AMU, were assessed using a multivariable regression model. A seasonal pattern was identified, in the pre-intervention period, where topical AMU was highest in July-August and lowest in February-March. In addition, total topical AMU appeared to significantly decrease over time in the pre-intervention period and the proportion of dogs in the clinic was positively associated with topical AMU. The intervention effect was significant only for second line and for skin product AMU. This study demonstrates that during participation in an ASP, second line and skin product AMU decreased in Dutch companion animal clinics. Additionally, this study demonstrates the existence of a seasonal effect and a decrease in topical AMU over time already before introduction of a targeted intervention.

An eye on the Shih Tzu dog: Ophthalmic examination findings and ocular surface diagnostics

OBJECTIVE

To characterize the ocular surface parameters and determine the prevalence of ocular pathology in Shih Tzu dogs.

ANIMAL STUDIED

Fifty Shih Tzu dogs (28 male, 22 female).

PROCEDURES

Each dog underwent a complete ophthalmic examination (recording any pathology) and a series of diagnostics, allowing for a 10 min-interval between tests: intraocular pressure (IOP), blink rate, palpebral fissure length (PFL), corneal tactile sensation (CTS), Schirmer tear test, and nasolacrimal reflex without (STT-1, NL-STT1) and with topical anesthesia (STT-2, NL-STT2), tear ferning, strip meniscometry test (SMT), tear film breakup time (TFBUT), and punctate fluorescein staining (PFS) of the cornea.

RESULTS

Mean ± SD test values were as follows: IOP (17.9 ± 3.7 mmHg), blink rate (2.4 ± 1.4 blinks/min), PFL (23.8 ± 1.8 mm), CTS (1.8 ± 0.7 cm), STT-1 (22.0 ± 5.5 mm/min), NL-STT1 (24.2 ± 4.7 mm/min), STT-2 (16.9 ± 6.5 mm/min), NL-STT2 (18.5 ± 7.5 mm/min), SMT (7.5 ± 3.5 mm/5 s), TFBUT (5.3 ± 2.4 s), tear ferning (1.3 ± 0.7), and PFS (1.6 ± 0.6). PFL was significantly greater in male vs. female Shih Tzus (p< .001). Age was negatively correlated with TFBUT results (r = -0.31, p = .027). Lagophthalmos was observed in 82% eyes. Ocular surface pathology was common, including adnexal abnormalities (100% eyes with caruncular trichiasis and medial lower lid entropion) and corneal opacification (27% pigmentation, 20% fibrosis, 12% neovascularization).

CONCLUSIONS

Qualitative tear film deficiency (low TFBUT), along with several anatomical abnormalities that promote ocular irritation and reduce globe protection, together help explain the concerningly high prevalence of ocular surface disease in the Shih Tzu breed. Prophylactic measures (e.g., medial canthoplasty, topical lubrication) could be considered to improve ocular health in Shih Tzus.

Increase in infected corneal ulcerations in dogs during the northern Colorado's 2020 wildfire season

OBJECTIVE

In the fall of 2020, Colorado experienced the two largest wildfires in state history. The smoke blanketed the college town of Fort Collins, Colorado, the location of the Veterinary Teaching Hospital at Colorado State University (CSU-VTH). The objective for this cross-sectional observational study was to evaluate how these wildfires and the corresponding elevated air quality index (AQI)) was associated with infected corneal ulcerations in dogs when compared to the two previous years.

ANIMALS

Seventeen dogs were included in this study.

PROCEDURES

Medical records from dogs presented to the CSU-VTH ophthalmology service with infected corneal ulcerations in August, September, and October of 2020, 2019, and 2018 were evaluated. Only corneal ulcerations with growth on their microbial cultures were included in this study.

RESULTS

The study revealed a significant increase in prevalence of infected corneal ulcerations in dogs presented to the CSU-VTH during the three wildfire months of 2020 that is, 3.5% (9/255) when compared with the two previous years, 2019: 1.0% (4/383, p = 0.04), and 2018: 0.9% (4/457) (p = .01). The AQI (mean ± standard error) was also significantly elevated for dogs that presented with infected corneal ulcerations in 2020 (70.2 ± 5.8) compared with 2019 (19.7 ± 8.7) and 2018 (45.6 ± 8.7) (p < .01).

CONCLUSIONS AND CLINICAL RELEVANCE

Elevation of AQI from wildfires seems to be correlated with an increased prevalence of infected corneal ulceration in dogs. As the duration and frequency of wildfires continues to rise globally, the effects of these wildfires on animal health should be investigated further.

Ocular Microbiome in a Group of Clinically Healthy Horses

The ocular microbiome in horses is poorly described compared to other species, and most of the information available in the literature is based on traditional techniques, which has limited the depth of the knowledge on the subject. The objective of this study was to characterize and predict the metabolic pathways of the ocular microbiome of a group of healthy horses. Conjunctival swabs were obtained from both eyes of 14 horses, and DNA extraction was performed from the swabs, followed by next generation sequencing and bioinformatics analyses employing DADA2 and PICRUSt2. A total of 17 phyla were identified, of which Pseudomonadota (Proteobacteria) was the most abundant (59.88%), followed by Actinomycetota (Actinobacteria) (22.44%) and Bacteroidota (Bacteroidetes) (16.39%), totaling an average of 98.72% of the communities. Similarly, of the 278 genera identified, Massilia, Pedobacter, Pseudomonas, Sphingomonas, Suttonella and Verticia were present in more than 5% of the samples analyzed. Both Actinobacteria and Bacteroides showed great heterogeneity within the samples. The most abundant inferred metabolic functions were related to vital functions for bacteria such as aerobic respiration, amino acid, and lipid biosynthesis.

Equine ulcerative keratitis in Belgium: Associated bacterial isolates and in vitro antimicrobial resistance in 200 eyes

PURPOSE

To describe bacterial isolates and associated antibiotic resistance from horses with ulcerative keratitis in Belgium.

METHODS

Medical records from horses with ulcerative keratitis presented to the ophthalmology service of the Veterinary teaching hospital of Liege, Belgium, between 2014 and 2021 were evaluated. Bacterial isolates were identified and VITEK^® 2 (Biomérieux) provided antimicrobial susceptibility testing and resistance detection.

RESULTS

Two hundred eyes of 196 horses were sampled. Ninety-seven eyes had a positive bacterial culture (48.5%) and 139 bacterial isolates were identified. Staphylococcus (63/139: 45.3%) and Streptococcus (33/139: 23.7%) were the most frequent genus isolated. Staphylococcus aureus (21/139: 15.1%) was the most frequent species isolated of which half were methicillin-resistant (MRS). Streptococcus equi subsp. zooepidemicus (19/139: 13.7%) was the second most identified bacterial isolate. Only two Pseudomonas species were isolated (2/139: 1.4%). The overall resistance of all bacterial isolates against chloramphenicol (12.4%) and fluoroquinolones (14.3%) was low. Resistance against tobramycin, polymyxin B, gentamicin, fusidic acid, tetracycline, and neomycin ranged from 40.8% to 58.6%. When separating the MRS from the other staphylococci, a significant difference was noted in percentage of resistance to gentamicin (p = .00026) and tetracycline (p = .00015). MRS were highly resistant to gentamicin (75%) and tetracycline (100%), whereas the remaining staphylococci were significantly less resistant to gentamicin (17%) and tetracycline (40.4%).

CONCLUSION

Although Pseudomonas species has been rarely cultured, our results are roughly consistent with previous studies. Multiple drug resistance was high and resistance to first-choice antibiotics in ulcerative keratitis was noted. These results warrant continued monitoring of susceptibility profile.

Analysis of Virulence and Antimicrobial Resistance Gene Carriage in Staphylococcus aureus Infections in Equids Using Whole-Genome Sequencing

While Staphylococcus aureus is associated with significant morbidity and mortality in equids (horses, donkeys, and mules), few studies have performed whole-genome sequencing to fully categorize large collections of equine isolates. Such sequencing allows for a comprehensive analysis of the genetic lineage and relationships of isolates, as well as the virulence genes present in each, which can be important for understanding the epidemiology of strains and their range of infections. Seventy-two clinical Staphylococcus aureus isolates from equids were collected at the Texas A&M University Veterinary Medical Teaching Hospital between 2007 and 2017. Whole-genome sequencing was performed to characterize the isolates according to sequence typing, biofilm association, antimicrobial resistance, and toxin gene carriage. Of the 72 isolates, 19% were methicillin resistant, of which the majority belonged to clonal complex 8. Eighteen distinct sequence types (STs) were represented, with the most common being ST1, ST133, ST8, and ST97. Most isolates had weak or negative overall biofilm production. Toxin and antimicrobial resistance gene carriage was varied; of note, this study revealed that a large proportion of North American equine isolates carry the leucocidin PQ toxin (66% of isolates). One isolate (17-021) carried genes imparting lincosamide and high-level mupirocin resistance, a combination not previously reported in equine-derived S. aureus isolates.

IMPORTANCE This is one of the first studies to perform whole-genome sequencing (WGS) of a large collection of Staphylococcus aureus isolates, both methicillin resistant and susceptible, collected from horses. A large proportion of the isolates carry leucocidin PQ (LukPQ), making this one of the first reports of such carriage in the United States. The presence of lincosamide and high-level mupirocin resistance in a methicillin-susceptible S. aureus (MSSA) isolate highlights the importance of MSSA as a reservoir of important antimicrobial resistance genes. As microbial resistance genes on mobile genetic elements can pass between S. aureus strains and livestock-associated strains can be transferred to humans, these findings have important public health implications.

Prevalence and Antibiotic Susceptibility of Bacterial Isolates From Dogs With Ulcerative Keratitis in Midwestern United States

The objective of this study was to describe bacterial culture and antibiotic susceptibility results in 476 dogs presenting with suspected bacterial keratitis in Iowa and surrounding Midwestern states, further detailing trends in patient characteristics, seasonality, and antimicrobial resistance. Corneal swabs yielded 465 bacterial isolates and 220 cultures (46.2%) with no apparent growth (0–5 isolates per culture). The most frequent bacterial genera were Staphylococcus (32.3%), Streptococcus (19.1%), and Pseudomonas (12.5%), while the most common bacterial species were Staphylococcus pseudintermedius (26.7%), Streptococcus canis (12%), and Pseudomonas aeruginosa (7.5%). Compared to mixed-breed dogs, canine breeds most likely to be examined for ulcerative keratitis included Boston terrier, Cavalier King Charles spaniel, miniature pinscher, pug, rat terrier, Saint Bernard, shih tzu, and silky terriers. In summer, the likelihood to yield a negative culture was reduced while the likelihood to culture Pseudomonas species was increased. Bacteria considered multidrug resistant (MDR, resistant to ≥ 3 antibiotic classes) represented 20% of all canine isolates and were most prevalent for Staphylococcus species (33%). An alarming, escalating trend of MDR prevalence was noted between 2016 (5%) and 2020 (34%). Individual ophthalmic preparations (i.e., single antibiotics or commercially available antibiotic combinations) with highest efficacy against all bacterial isolates included chloramphenicol (83%), ceftiofur (79%), amikacin (77%), neomycin-polymyxin B-bacitracin (77%), and gentamicin (74%). Efficacy of systemic antibiotics and combinations of ophthalmic preparations was also evaluated. Based on the present findings, triple antibiotic (Neo-Poly-Bac) is recommended as empirical monotherapy for prophylactic antibiotic therapy in dogs with simple corneal ulcers, while a chloramphenicol-ciprofloxacin combination is empirically recommended for therapeutic management of infected corneal ulcers. Pending culture and susceptibility results, appropriate selection of empiric antibiotic therapy is important to enhance therapeutic outcome and reduce antibacterial resistance in dogs with corneal ulceration.