Plasma and ear tissue concentrations of enrofloxacin and its metabolite ciprofloxacin in dogs with chronic end-stage otitis externa after intravenous administration of enrofloxacin

The purpose of this study was to measure the concentrations of enrofloxacin and its metabolite ciprofloxacin following intravenous administration of enrofloxacin in the plasma and ear tissue of dogs with chronic end-stage otitis undergoing a total ear canal ablation and lateral bulla osteotomy. The goals were to determine the relationship between the dose of enrofloxacin and the concentrations of enrofloxacin and ciprofloxacin, and determine appropriate doses of enrofloxacin for treatment of chronic otitis externa and media. Thirty dogs were randomized to an enrofloxacin-treatment group (5, 10, 15 or 20 mg kg⁻¹) or control group (no enrofloxacin). After surgical removal, ear tissue samples (skin, vertical ear canal, horizontal ear canal, middle ear) and a blood sample were collected. Concentrations of enrofloxacin and ciprofloxacin in the plasma and ear tissue were measured by high performance liquid chromatography. Repeated measures models were applied to log-transformed data to assess dosing trends and Pearson correlations were calculated to assess concentration associations. Ear tissue concentrations of enrofloxacin and ciprofloxacin were significantly ( P  < 0.05) higher than plasma concentrations. Each 5 mg kg⁻¹ increase in the dose of enrofloxacin resulted in a 72% and 37% increase in enrofloxacin and ciprofloxacin concentrations, respectively. For bacteria with an minimal inhibitory concentration of 0.12–0.15 or less, 0.19–0.24, 0.31–0.39 and 0.51–0.64 µg mL⁻¹, enrofloxacin should be dosed at 5, 10, 15 and 20 mg kg⁻¹, respectively. Treatment with enrofloxacin would not be recommended for a bacterial organism intermediate or resistant in susceptibility to enrofloxacin since appropriate levels of enrofloxacin would not be attained.     

FC-46 Methicillin-resistant Staphylococcus intermedius organisms from the vertical ear canal of dogs with end-stage otitis externa

Different mite species generally found on animals may temporarily also infest humans. Consequently, these arthropods may be responsible for pruritic skin reactions that are often misdiagnosed. Mite dermatitis caused by the tropical rat mite Ornithonyssus bacoti occurs in several small mammals and rodents under tropical and temperate climatic conditions. According to various observations in Germany, O. bacoti appears in wild rodents more frequently than previously thought. In most cases, symptoms of mites are recognized only when they attack humans, but the diagnosis of rat mite dermatitis requires identification of the parasite, which is more likely to be found in the environment than on the hosts' skin itself. Here, five different outbreaks from Bavaria are reported. A clinical example is the case of a 23-year-old medical student and several other residents inhabiting a rat- and mouse-infested house in Munich. The arthropods originally came from an Italian restaurant and surrounding facilities. Mites were found in large numbers in the students' flat. The patient was suffering from severe itching and papular urticaria. He consulted a dermatology clinic complaining of a pruritic dermatitis of 2-weeks duration. Dermatitis was misdiagnosed as allergy and treatment with an anti-inflammatory agent was unsuccessful. Eradication of rodents and treatment of the house with a pyrethroid were performed to prevent reinfestation. Ornithonyssus bacoti is a periodic haematophageous parasite and spends a relatively short time on the host. Causal therapy with antiparasitic agents on human patients is not necessary. If indicated, treatment should be symptomatic.
Funding: Self-funded.     

Antimicrobial susceptibility of Pseudomonas aeruginosa isolates from dogs with otitis externa

Pseudomonas aeruginosa is a common cause of otitis externa in dogs, and treatment of these infections is becoming problematic because of the increasing number of multiresistant strains. The aim of the present study was to compare the in vitro activities of cefepime, ceftazidime, enrofloxacin, ciprofloxacin, gentamicin and ticarcillin/clavulanic acid against 104 strains of P aeruginosa isolated from dogs with otitis externa. Antimicrobial susceptibility and minimum inhibitory concentrations, in μg/ml, were evaluated by the E test (bioMérieux). The most active compound was ceftazidime, with 100 per cent efficiency. The majority of tested strains were susceptible to ticarcillin/clavulanic acid (89.4 per cent), followed by ciprofloxacin (88.5 per cent) and cefepime (60.6 per cent). The highest resistance was observed to enrofloxacin (51.9 per cent) and gentamicin (43.3 per cent). Large numbers of strains were intermediately susceptible to antibiotics registered for use in veterinary medicine in Croatia--enrofloxacin (47.1 per cent) and gentamicin (41.3 per cent).     

Development of resistant bacteria isolated from dogs with otitis externa or urinary tract infections after exposure to enrofloxacin in vitro

Minimum inhibitory concentrations for enrofloxacin were determined for 63 bacterial isolates from dogs with otitis externa or urinary tract infections. Development of resistant mutants was determined after exposing the isolates to enrofloxacin in vitro for up to five serial passages. Results indicated that Pseudomonas aeruginosa and Enterococcus spp isolates exposed to enrofloxacin developed resistance rapidly, whereas Klebsiella, Proteus, and Streptococcus spp were less likely to develop resistance. Despite the presence of enrofloxacin pressure, no resistant bacteria developed in the Escherichia coli and staphylococcal isolates. In many isolates, susceptibility patterns changed from susceptible to intermediate.     

Identification and antimicrobial susceptibility of bacteria and yeasts isolated from healthy dogs and dogs with otitis externa

The bacterial and fungal flora of the external ear canal of dogs with otitis externa and of healthy dogs were studied. The most frequently isolated microorganism from otitic ears was Staphylococcus intermedius (58.8%), followed by Malassezia pachydermatis (30.9%), Streptococcus canis (29.9%), Proteus spp. (14.4%) and Escherichia coli (10.3%). A statistical analysis of our results showed that the prevalence of these microorganisms is significant in dogs with otitis externa. Furthermore, the antimicrobial susceptibility patterns of isolated strains were determined. Majority of all bacterial isolates were most susceptible to gentamicin. Malassezia pachydermatis, the most prevalent yeast in this study, showed an excellent level of susceptibility to all antifungal agents tested.     

Comparison of microbial isolates and susceptibility patterns from the external ear canal of dogs with otitis externa

Otic exudate was obtained from 33 dogs with otitis externa for cytopathology and culture. Two samples were taken from the same location in the external ear canal, for a total of 100 samples. Thirty-six (36%) samples isolated only a single organism, of which 21 (21%) were Malassezia spp. Two organisms were present in 23 (23%) of the samples. Cultures of the two samples agreed in 40 (80%) of the 50 pairs. Cytopathology agreed with culture results only 68% of the time. Cytopathology and culture may not be as definitive as previously assumed because of apparent variability of the microbial population within the external canal.     

Identification and antimicrobial susceptibility patterns of bacteria causing otitis externa in dogs

Bacterial agents are considered important pathogens causing external otitis in dogs. It is essential to carry out bacterial culture and antimicrobial susceptibility test in the case of otitis externa, particularly for chronic or recurring cases. Sterile swab samples were obtained from terminal part of vertical ear canals of 74 dogs with otitis externa for cytology, bacterial culture and antimicrobial susceptibility test. Cytologic smears were stained using Gram and Giemsa staining methods. Aerobic bacterial culture performed on blood agar and MacConkey agar. Among total number of 92 isolated bacteria, 68 were Staphylococcus intermedius. Other isolated bacteria included: Pseudomonas aeruginosa, Proteus mirabilis, Escherichia coli, Pasteurella canis, and six other species of coagulase-negative Staphylococcus. Antimicrobial susceptibility test were performed for all isolated bacteria using 14 antibiotics. Based on the results of this study, all isolated Staphylococcus spp. were sensitive to amikacin, enrofloxacin, and rifampin, and had low resistance to gentamicin, cephalothin and ceftriaxone. More than half of gram-positive isolates were resistant to penicillin and ampicillin. Generally, all isolated gram-negative bacteria, were sensitive to amikacin and enrofloxacin, and had low resistance to ceftriaxone and gentamicin. They were highly resistant to penicillin, eythromycin, and cephalothin. Regarding the results of this study, in cases of uncomplicated otitis externa, it is possible to select antimicrobial drugs merely based on cytology, but it is recommended to perform bacterial culture and antimicrobial susceptibility test. However, in complicated or refractory cases, antimicrobials should be selected based on bacterial culture and antimicrobial susceptibility test.     

Identification and antimicrobial susceptibility of coagulase positive staphylococci isolated from healthy dogs and dogs suffering from otitis externa

A total of 67 strains of coagulase positive staphylococci isolated from healthy dogs and dogs suffering from otitis externa were studied. Twenty-two isolates were from healthy dogs (five from hound dogs and 17 from companion dogs) and 45 from dogs suffering otitis externa (14 from hound dogs and 31 from companion dogs). Presumptive identification was attempted using the following tests: production of acetoin, anaerobic utilization of mannitol, acid production from mannitol, presence of beta-galactosidase, and growth on P agar supplemented with different concentrations of acriflavine. Susceptibility of staphylococci to 16 antibiotics was determined. Most effective antibiotics were imipenem, amoxycillin/clavulanic acid, ciprofloxacin, tobramycin, gentamicin and marbofloxacin. Penicillin, ampicillin and polymyxin B showed the lowest activity. There were no significant differences in antimicrobial susceptibility among isolates from healthy dogs and dogs suffering from otitis externa.     

Variability of laboratory identification and antibiotic susceptibility reporting of Pseudomonas spp. isolates from dogs with chronic otitis externa

The purpose of this study was to evaluate interlaboratory variation in isolation and antibiotic susceptibility pattern of Pseudomonas spp. as reported to veterinarians for cases of canine chronic bacterial otitis externa. Twenty-six dogs with unilateral or bilateral bacterial otitis externa from multiple referral practices were included in this prospective study. Triplicate samples collected simultaneously from the same location in the external ear canal were randomly submitted to three laboratories for culture and susceptibility testing. Pseudomonas spp. were isolated from 18 of 34 (53%) ears. All three laboratories agreed on the presence of Pseudomonas spp. in 15 (83.3%) ears sampled. However, two laboratories agreed on two (11.1%) occasions, and on one occasion (5.5%) Pseudomonas spp. were identified in only one laboratory. Minimum inhibitory concentration (MIC) susceptibilities to 11 antibiotics were compared between laboratories B and C. Using laboratory-defined susceptibility of sensitive (S), intermediate (I) and resistant (R), none of the 16 Pseudomonas spp. with MIC data reported had identical patterns of antibiotic susceptibility. Agreement in susceptibility to individual antibiotics was observed in 13 of 16 (81%) occasions for amikacin and gentamicin, 10 of 16 (63%) occasions for ticarcillin, and nine of 16 (56%) for enrofloxacin. These results indicate that Pseudomonas spp. were identified by all three laboratories chosen for this study in 83% of the time. Moreover, antibiotic susceptibility patterns and MIC values reported to veterinarians may not agree between laboratories. Veterinarians should interpret bacterial culture and susceptibility results with multiple caveats including variability between laboratories.     

In vitro activity of an ear rinse containing tromethamine, EDTA, benzyl alcohol and 0.1% ketoconazole on Malassezia organisms from dogs with otitis externa

The purpose of this study was to evaluate the in vitro activity of an ear rinse containing tromethamine, EDTA, benzyl alcohol and 0.1% ketoconazole in purified water on Malassezia organisms from dogs with otitis externa. Malassezia organisms were collected from ear swab samples from the external ear canal of 19 dogs with otitis externa plus one control strain of Malassezia pachydermatis. Three test solutions were evaluated: ER (EDTA, tromethamine, benzyl alcohol), ER + keto (EDTA, tromethamine, benzyl alcohol, ketoconazole), and H2O (purified water). Ten-millilitre aliquots of each test solution was transferred into 20 tubes and inoculated with one of the isolates (1 tube per isolate: 19 clinical and 1 control strain). Samples were retrieved from each tube at five time points (0, 15, 30, 45 and 60 min), transferred to Petri dishes, mixed with Sabouraud dextrose agar supplemented with 0.5% Tween 80 and incubated. Following incubation, the plates were examined for growth and colonies counted as colony-forming units per millilitre. The data were analysed using a repeated measures analysis, with pair-wise comparisons of solution-time combinations. There was a significant reduction in Malassezia growth in ER + keto at all time points (P < 0.0001) compared to time zero. Neither ER nor H2O had any effect on the growth of Malassezia. ER + keto was significantly more effective in reducing Malassezia growth (P < 0.0001) at all time points compared to both ER and H2O. ER + keto may be useful in the treatment of Malassezia otitis externa. Future studies should be performed to evaluate the in vivo efficacy of ER + keto as treatment for otic infections caused by Malassezia.     

Evaluation of an ear cleanser for the treatment of infectious otitis externa in dogs

Thirty-one ears (16 dogs) with otitis externa originating from bacterial or yeast infections were enrolled in a study to evaluate the in vivo efficacy of an ear cleanser containing 2.5% lactic acid and 0.1% salicylic acid for the treatment of infectious otitis externa. The affected ears were treated with the ear cleanser twice daily for 2 weeks and evaluated after 1 and 2 weeks of treatment. The ear cleanser was effective in resolution of infection in 67.7% of the ears, and clinical signs of infectious otitis externa were significantly reduced within 2 weeks.     

Comparison of bacterial organisms and their susceptibility patterns from otic exudate and ear tissue from the vertical ear canal of dogs undergoing a total ear canal ablation

The purpose of this prospective study was to compare bacterial organisms and their susceptibility patterns from otic exudate and ear tissue from the vertical ear canal of six dogs with end-stage otitis undergoing a total ear canal ablation. Twenty-six organisms, 13 from the exudate and 13 from the tissue, were morphologically and biochemically similar, and their susceptibility patterns were compared. There were discrepancies for only 5 antibiotics for 4 organisms from 3 dogs. Culture of otic exudate from the vertical ear canal of dogs with chronic end-stage otitis externa provides an accurate reflection of the bacterial species present and the antimicrobial susceptibility patterns of these infections.