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.

Septic keratitis in dogs, cats, and horses in Switzerland: associated bacteria and antibiotic susceptibility.

OBJECTIVE: To evaluate the most common bacterial pathogens associated with septic keratitis in veterinary patients from Switzerland. The second objective was to analyze antibiotic susceptibility test results of the identified bacterial pathogens. The third objective was to evaluate potential breed predispositions to septic keratitis. PROCEDURES: Two hundred and fifty-five cultures and antibiotic susceptibility reports from dogs, cats, and horses with septic keratitis that were presented to the University of Zurich Veterinary Medical Teaching Hospital between 2009 and 2013 were reviewed. Odds ratios for the risk of having a septic keratitis were estimated for all dog and cat breeds compared to the general nonbrachycephalic hospital population. RESULTS: Ninety-six, 29, and 31 positive cultures were obtained from 89 canine, 28 feline, and 29 equine eyes, respectively. Repeat sampling accounted for the differences in numbers. Negative culture results were obtained in 50, 31, and 18 cases. Staphylococci and streptococci accounted for 66% of the isolates in dogs and 80% of the isolates in cats and horses. Staphylococcus spp. had a higher percentage of fluoroquinolone-resistant isolates compared to previous reports. Brachycephalic breeds had elevated odds ratios for the presence of septic keratitis. CONCLUSION: Identified bacterial pathogens and their prevalence as well as the elevated odds ratios for septic keratitis in brachycephalics are roughly consistent with previous studies. Based on systemic breakpoint data, resistance to commonly used topical antibiotics, including the second-generation fluoroquinolones, was found.

Biofilms of Candida spp. from the ocular conjunctiva of horses with reduced azole susceptibility: a complicating factor for the treatment of keratomycosis?

OBJECTIVES: This study aimed to assess the biofilm-forming ability of Candida spp. from the ocular conjunctiva of horses and to investigate the antifungal susceptibility of these biofilms. PROCEDURES: Initially, the biofilm-forming ability of 15 strains was assessed by crystal violet staining, which reveals the fungal biomass adhered to the polystyrene plates, and scanning electron microscopy. Then, the minimum inhibitory concentrations (MICs) of amphotericin B, fluconazole, itraconazole, and caspofungin were initially determined against strains in planktonic form. Afterward, antifungal susceptibility of mature biofilms was evaluated by exposing them to 10 × MIC and 50 × MIC of the tested drugs, followed by the assessment of their metabolic activity, using the oxidoreduction indicator XTT. Results were analyzed through ANOVA and Tukey's post-test, and P-values below 5% led to significant conclusions. RESULTS: Eight strains produced biofilms and were classified as strong (1/15), moderate (3/15) and weak (4/15) producers, according to the amount of crystal violet retained by the adhered fungal biomass. Biofilm metabolic activity of one C. tropicalis did not decrease after exposure to the tested antifungals, while biofilm metabolic activity of five strains was reduced by amphotericin B, but not the other drugs. One C. parapsilosis sensu stricto and one C. glabrata showed significant reduction in biofilm metabolic activity after exposure to fluconazole, itraconazole, and caspofungin, but not amphotericin B. CONCLUSIONS: The results demonstrate that Candida from the ocular conjunctiva of horses can pose as a risk to animal health as they are capable of forming biofilms, which are commonly involved in fungal keratitis.

Bacterial isolates, antimicrobial susceptibility, and clinical characteristics of bacterial keratitis in dogs presenting to referral practice in Australia.

OBJECTIVE: To identify clinical characteristics, bacterial isolates, and their antimicrobial susceptibility patterns in a prospective study of dogs presenting with suspected bacterial keratitis to aid selection of appropriate therapy. ANIMALS: Seventy-one client-owned dogs presenting to two referral hospitals in Australia. PROCEDURE: Corneal swabs and clinical information were collected from dogs presenting with suspect bacterial keratitis from April 2012 to December 2014. Cytology and bacteriologic culture were performed on samples with in vitro antimicrobial susceptibility performed on bacterial isolates. RESULTS: Positive cultures were obtained from 42 of the 71 ulcers sampled (59%), with 45 bacteria isolated. The most commonly isolated bacteria were ß-hemolytic Streptococcus (14/45, 31%), Pseudomonas (14/45, 31%), and Staphylococcus species (8/45, 18%). ß-Hemolytic Streptococcus spp. were resistant to neomycin, polymyxin B, gentamicin, framycetin and fusidic acid and >80% were resistant to ciprofloxacin but remained susceptible to chloramphenicol and cephalexin. Pseudomonas aeruginosa isolates were resistant to chloramphenicol, cephalexin, and fusidic acid; however, >90% were susceptible to ciprofloxacin, polymyxin B, and gentamicin. Brachycephalic breed (34/42, 81%), previous ocular surgery (15/42, 36%), prior use of a topical corticosteroid (13/42, 31%), and concurrent ocular surface disease (10/42, 24%) were common in dogs with bacterial keratitis. CONCLUSION: Our study identified ß-hemolytic Streptococcus and Pseudomonas spp. as the most common bacterial pathogens in canine bacterial keratitis presenting for referral. Many cases exhibited clinical factors known to influence corneal integrity that may predispose them to ulceration and infection. Based on in vitro antimicrobial susceptibility patterns and clinical outcomes, monotherapy with a fluoroquinolone may be ineffective in ulcers caused by ß-hemolytic Streptococcus spp.

Successful treatment of distichiasis in a cat using transconjunctival electrocautery.

A 2-year-old male castrated Domestic Short-haired cat presented to the Ophthalmology Service at the Matthew J. Ryan Veterinary Hospital at the University of Pennsylvania for evaluation of chronic bilateral ocular discharge and blepharospasm. Initial ophthalmic examination revealed severe conjunctivitis and keratitis and the presence of upper eyelid distichiae bilaterally. Initial therapy for suspected feline herpesviral infection provided moderate, but not complete, resolution of the clinical signs. Over the subsequent year, the cat suffered from recurrent, severe, ulcerative keratitis in both eyes despite appropriate medical therapy. Approximately 13 months after the initial presentation, the distichiae were surgically removed using transconjunctival electrocautery, which resulted in complete resolution of the clinical signs. This report documents bilateral distichiasis in a cat, a condition that is considered rare in this species.

In vitro efficacy of a buffered chelating solution as an antimicrobial potentiator for antifungal drugs against fungal pathogens obtained from horses with mycotic keratitis.

OBJECTIVE: To determine whether a novel third-generation chelating agent (8 mM disodium EDTA dehydrate and 20 mM 2-amino-2-hydroxymethyl-1, 3-propanediol) would act as an antimicrobial potentiator to enhance in vitro activity of antifungal medications against fungal isolates obtained from horses with mycotic keratitis. SAMPLE POPULATION: Fungal isolates (3 Aspergillus isolates, 5 Fusarium isolates, 1 Penicillium isolate, 1 Cladosporium isolate, and 1 Curvularia isolate) obtained from horses with mycotic keratitis and 2 quality-control strains obtained from the American Type Culture Collection (ATCC; Candida albicans ATCC 90028 and Paecilomyces variotii ATCC 36257). PROCEDURE: Minimum inhibitory concentrations (MICs) against fungal isolates for 4 antifungal drugs (miconazole, ketoconazole, itraconazole, and natamycin) were compared with MICs against fungal isolates for the combinations of each of the 4 antifungal drugs and the chelating agent. The Clinical and Laboratory Standards Institute microdilution assay method was performed by use of reference-grade antifungal powders against the fungal isolates and quality-control strains of fungi. RESULTS: Values for the MIC at which the antifungal drugs decreased the growth of an organism by 50% (MIC50) and 90% (MIC90) were decreased for the control strains and ophthalmic fungal isolates by 50% to 100% when the drugs were used in combination with the chelating agent at a concentration of up to 540 microg/mL. CONCLUSIONS AND CLINICAL RELEVANCE: The chelating agent increased in vitro activity of antifungal drugs against common fungal pathogens isolated from eyes of horses with mycotic keratitis.

Evaluation of clinical characteristics and bacterial isolates in dogs with bacterial keratitis: 97 cases (1993-2003).

OBJECTIVE: To evaluate clinical characteristics and breeds affected with bacterial keratitis and compare patterns of resistance in bacterial isolates over time in dogs. DESIGN: Retrospective cross-sectional study. ANIMALS: 97 dogs with bacterial keratitis. PROCEDURE: Dogs with bacterial keratitis were identified from teaching hospital medical records at the Universities of Tennessee and Florida during the years 1993 to 2003. Data were collected pertaining to breed, Schirmer tear test results, treatments administered at the time of initial examination, bacterial species isolated, and resistance to selected antimicrobials. RESULTS: 66% of the dogs were brachycephalic, 54% had tear production < 15 mm/min, and 29% were receiving a corticosteroid at the time of initial examination. The most common bacteria isolated were Staphylococcus intermedius (29%), beta-hemolytic Streptococcus spp (17%), and Pseudomonas aeruginosa (21%). Staphylococcus intermedius isolates had limited resistance to certain antimicrobials. More than 80% of beta-hemolytic Streptococcus spp isolates were resistant to neomycin, polymyxin B, and tobramycin. Isolates of P aeruginosa were susceptible to tobramycin and gentamicin and had limited resistance to ciprofloxacin and enrofloxacin. Among bacterial species isolated, there was no evidence of development of antimicrobial resistance over time. CONCLUSIONS AND CLINICAL RELEVANCE: Data suggested that administration of ciprofloxacin or a combination of a first-generation cephalosporin and tobramycin may be used in the treatment of bacterial keratitis while awaiting results of bacterial culture and susceptibility testing. Evidence suggests that current methods of medical management of bacterial keratitis are not associated with increased antimicrobial resistance.

Enhancement of Moraxella bovis-induced keratitis of mice by exposure of the eye to ultraviolet radiation and ragweed extract.

Effects of a ragweed extract and ultraviolet (UV) radiation on Moraxella bovis-induced keratitis of DBA/2J mice were investigated. Mouse eyes were exposed to ragweed extract and/or UV radiation during induction of keratitis. Pathogenesis was enhanced by exposure to ragweed extract alone and by exposure to UV radiation alone. It was enhanced most when eyes were exposed to ragweed extract and UV radiation.