Species distribution and antimicrobial susceptibility of staphylococci isolated from canine otitis externa

The diversity of species of the genus Staphylococcus sp. and the antimicrobial resistance of isolates from 151 unmedicated dogs of both sexes with a clinical diagnosis of otitis were recorded. Ninety‐one isolates of Staphylococcus spp. were identified by biochemical reactions and tested for susceptibility to 15 antimicrobials. Coagulase‐positive species were most common; S. pseudintermedius (38.4%), S. schleiferi schleiferi (15.4%), S. aureus (14.3%), S. epidermidis (11%), S. simulans (11%), S. schleiferi coagulans (8.8%) and S. saprophyticus (1.1%). All the isolates showed resistance to at least one drug and 89% were multiresistant. Amoxicillin combined with clavulanic acid and oxacillin were the most effective, while resistance was widely observed for neomycin and erythromycin. The results highlight the recognition and the potential need for bacterial culture with species identification and antimicrobial susceptibility tests for appropriate antimicrobial therapy.     

New combination for the therapy of canine otitis externa I Microbiology of otitis externa

In order to compound a new drug comblnatlon agalnst canlne otitis externa (OE), 515 dogs affected wlth OE were subjected to physical examlnatlon and mlcroblologlcal analysis of their ear exudates. OE was erythematous-cerumlnous In 83 per cent and suppurative In 17 per cent of the patlent material. Erythematous-cerumlnous lnflammatlons were characterlsed by severe prurltus and accumulatlon of brownlsh, greasy cerumen In the audltory canal. The yeast Malassezla jmchydermat/s was Isolated from the ears of 76 per cent of the dogs, often In comblnatlon wlth Staphylococcus lntermedlus bacterla. M pachydermatls showed the most sensltlvlty, In decreasing order of efflcacy, to ketoconazole, econazole, clotrlmazole, mlconazole and nystatln. S lntermedlus Isolates were most sensltlve to amoxyclllln-clavulanlc acld, enrofloxacln, cephalexln and gentamlcln. The mlcroorganlsm most frequently Isolatcbd from dogs wlth suppurative OE was Pseudomonas aewglnosa; In some cases Proteus, Streptococcus and Pasteurella were also Isolated. The P aeruglnosa Isolates showed the highest sensltlvlty to gentamlcln, polymyxln B and tobramycln.     

Update on antimicrobial susceptibilities of bacterial isolates from canine and feline otitis externa

The in vitro susceptibility of a total of 1819 bacterial isolates from canine and 103 isolates from feline otitis externa cases to 13 antimicrobial drugs over a 5-year period was evaluated. Among topically used drugs, 90% of isolates were susceptible to gentamicin. Susceptibility of Pseudomonas aeruginosa to gentamicin was 85%, and to polymyxin B 100%. For isolates other than the Pseudomonas sp., susceptibility was highest to amoxicillin-clavulanic acid.     

Comparative study of the microbial profile from bilateral canine otitis externa

Fifty dogs with bilateral otitis externa were studied over a 10-month period. The exudates of both external ears were obtained, using sterile swabs, and microorganisms were isolated according to standard microbiological techniques. Antimicrobial susceptibility testing of Staphylococcus intermedius was done by the agar diffusion method. There was bacterial and/or fungal growth in all of the samples. These were all polymicrobial infections. Anaerobic bacteria were not isolated in any sample. The most common pathogens isolated were S. intermedius and Malassezia pachydermatis. A statistically significant difference (P < 0.05) was observed in the isolation pattern between the right and left ears in 34 of the 50 animals (68%). High resistance rates of S. intermedius strains to penicillin, ampicillin, erythromycin, tetracycline, and clindamycin were found. The results suggest that in bilateral canine otitis externa, each ear should be cultured separately and considered as separate units.     

Treatment of canine otitis externa using video otoscopy

Otitis externa in 27 toy poodles and 40 miniature dachshunds was treated using a video otoscope. A distinct concavity (external tympanic concavity) was observed at the junction between the ventral part of the external surface of the tympanum and the ear canal to which a considerable amount of hair and debris had adhered. All hair and debris adhering to the external tympanic concavity were removed, and systemic antibiotic and antifungal agents were administered, after which all of the dogs recovered. The pattern of hair growth observed in the external tympanic concavity could be characterized according to the breed of dog. All of the toy poodles presented with curly hairs, while the miniature dachshunds had upright or flat-lying hairs.     

Aetiology of canine otitis externa: a retrospective study of 100 cases

The objective of this retrospective study was to investigate in 100 dogs with otitis externa (OE) the possible associations between signalment, history, clinical and laboratory findings and the various primary, secondary and perpetuating causative factors of ear canal inflammation. The age of the dogs ranged from 3 months to 14 years (median: 4.75 years) and they included 45 males and 55 females. Cocker spaniels, Jura des Alpes and Brittany spaniels were significantly overrepresented among dogs with OE when compared to the hospital canine population. In the majority of the cases, OE was chronic-recurrent (63%) or bilateral (93%). Allergic dermatitis (43/100 dogs), grass awns (12/100) and otoacariasis (7/100) were the most common primary causative factors; no primary factor could be incriminated in 32 cases and more than one was found in three dogs. Malassezia spp. (66/100 dogs), cocci (38/100) and rods (22/100) were the secondary causative factors, while ear canal stenosis (38/100) and tympanic membrane perforation-otitis media (25/100) were the most important perpetuating factors. Atopic dermatitis and adverse food reactions-associated OE was more common in females and dogs with a history of pruritic skin disease, while grass awn-induced OE occurred in cocker spaniels and acute cases. Tympanic membrane perforation was less frequent in atopic dermatitis and adverse food reactions-associated OE, but more common when otoscopic and ear canal cytological examination revealed the presence of grass awns and rods, respectively. Finally, cocci overgrowth was positively associated with ear canal stenosis.     

Therapeutic effects of beta-thujaplicin eardrops on canine Malassezia-related otitis externa

An eardrop solution of beta-thujaplicin was examined for therapeutic effects on canine Malassezia-related otitis externa. Half to one ml of beta-thujaplicin solution of 100 microg/ml including DMSO 2% was injected everyday into both external ear canals of 31 cases for test-of-cure agreement. Fifteen score phases were established from the symptoms and cerumen smear biopsy findings, and score changes were recorded at least once a week. The means of the second and the third inspection day scores decreased significantly more than the previous value of each. In addition, the numbers of yeast-like organisms clearly decreased. These results suggest that beta-thujaplicin eardrops are effective for Malassezia-related otitis externa in dogs.     

Biofilm production by pathogens associated with canine otitis externa,and the antibiofilm activity of ionophores and antimicrobial adjuvants

Otitis externa (OE) is a frequently reported disorder in dogs associated with secondary infections by Staphylococcus, Pseudomonas and yeast pathogens. The presence of biofilms may play an important role in the resistance of otic pathogens to antimicrobial agents. Biofilm production of twenty Staphylococcus pseudintermedius and twenty Pseudomonas aeruginosa canine otic isolates was determined quantitatively using a microtiter plate assay, and each isolate was classified as a strong, moderate, weak or nonbiofilm producer. Minimum biofilm eradication concentration (MBEC) of two ionophores (narasin and monensin) and three adjuvants (N‐acetylcysteine (NAC), Tris‐EDTA and disodium EDTA) were investigated spectrophotometrically (OD_570nm) and quantitatively (CFU/ml) against selected Staphylococcus and Pseudomonas biofilm cultures. Concurrently, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of planktonic cultures were assessed. 16/20 of the S. pseudintermedius clinical isolates were weak biofilm producers. 19/20 P. aeruginosa clinical isolates produced biofilms and were distributed almost equally as weak, moderate and strong biofilm producers. While significant antibiofilm activity was observed, no MBEC was achieved with narasin or monensin. The MBEC for NAC ranged from 5,000–10,000 µg/ml and from 20,000–80,000 µg/ml against S. pseudintermedius and P. aeruginosa, respectively. Tris‐EDTA eradicated P. aeruginosa biofilms at concentrations ranging from 6,000/1,900 to 12,000/3,800 µg/ml. The MBEC was up to 16‐fold and eightfold higher than the MIC/MBC of NAC and Tris‐EDTA, respectively. Disodium EDTA reduced biofilm growth of both strains at concentrations of 470 µg/ml and higher. It can be concluded that biofilm production is common in pathogens associated with canine OE. NAC and Tris‐EDTA are effective antibiofilm agents in vitro that could be considered for the treatment of biofilm‐associated OE in dogs.     

Optimum incubation conditions for the isolation of yeasts from canine otitis externa

Samples from otitis externa in the dog were cultured on a variety of media under different conditions of incubation in order to assess the most suitable conditions, especially for the isolation of Malassezia pachydermatis. Columbia blood and MacConkey agar at 37 degrees C for 24 h with air and Sabouraud glucose agar under microaerophilic conditions for 48 h at 37 degrees C were considered the ideal combination.     

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.     

Effects of beta-thujaplicin on anti-Malassezia pachydermatis remedy for canine otitis externa

The antifungal activity of beta-thujaplicin was evaluated against 51 Malassezia pachydermatis strains isolated from canine ear canals with or without otitis externa. For comparison, sensitivity tests were performed on M. pachydermatis isolates for nystatin, ketoconazole, and terbinafine HCl, all clinically available antifungal agents. The minimal inhibition concentrations over 50% of the tested isolates (MIC50) were 3.13 microg/ml for beta-thujaplicin and nystatin, 0.016 microg/ml for ketoconazole, and 1.56 microg/ml for terbinafine HCl. The antifungal effect for M. pachydermatis of beta-thujaplicin compared favorably with commercial antifungal agents. None of the 51 M. pachydermatis isolates showed resistance against any of the tested antibiotics investigated in this study. Ten representative isolates of M. pachydermatis were subcultured for 30 generations at concentrations close to the MIC levels of beta-thujaplicin, nystatin, ketoconazole, and terbinafine HCl, and examined to determine whether they had acquired resistance to each drug. As a result, M. pachydermatis was found to achieve resistance more easily for ketoconazole and terbinafine HCl than for beta-thujaplicin or nystatin. The MIC50 of beta-thujaplicin did not change during the course of subculture, and it is thought that the potential development of a resistant strain is low, even with continuous infusion for otitis externa therapy. beta-Thujaplicin is an inexpensive and safe treatment with anti-inflammatory and deodorant effects that can be recommended as an effective remedy for canine otitis externa.