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A clinical study of otitis externa with bacterial isolation, antimicrobial susceptibility and therapeutic management in 44 dogs.


Otitis externa is the most common disease of ear canal in canines with a multifactorial etiology, including fungi, yeasts, parasites and bacteria, mainly from Staphylococcus genus (Kiss et al., 1997). In recent days, due to development of antimicrobial resistance, isolation and antibiogram of pathogen is highly important together with judicious use of antimicrobials in treating bacterial diseases. The purpose of present study was to determine the prevalence of bacterial otitis externa in canines and analyse the antimicrobial susceptibility.

Materials and Methods

The study included 44 dogs from both sexes, different breeds and 1 year-12 years old with clinical signs specific for otitis externa. By using the sterile disposable cotton swabs, 44 samples were aseptically collected from external auditory canal of canines with otitis externa (signs of erythema, swelling, otorrhoea, pain, itch, lesions of the ear tegument) from March' 2014-February' 2015 in a private clinic. These samples were sent to bacteriological laboratory for isolation and identification. Out of 44 samples, S. aureus has been isolated from 35 samples.

Antimicrobial susceptibility testing was performed by Kirby-Bauer disk diffusion method, as outlined by Quinn et al (1994). The antibiogram included 15 antibiotic agents viz., Amoxicillin, Amoxicillin--Clavulinic acid, Azithromycin, Cephalexin, Cefuroxime, Chloromphenicol, Ciprofloxacin, Co-Trimaxozole, Erythromycin, Gatifloxacin, Ofloxacin, Penicillin, Tetracycline, Piperacillin and Vancomycin.

Results and discussion

The microbiological tests conducted on 44 samples showed that 35 isolates with typical characteristic of genus S. aureus (79%). No isolate from 4 samples and isolate of gram negative bacteria and yeast from 5 dogs were eliminated from this study.

Out of 44 samples, 35 (79%) were positive for Staphylococcus aureus. Resistance to antibiotics was frequently observed with 77.77% of isolates showing resistance to at least one drug (Love et al., 1981). The most active antimicrobial agents against Staphylococci isolated from otitis externa of dogs were Cephalexin and Penicillin. The organism is highly resistant to Azithromycin (77.78%), Ciprofloxacin (55.56%), Gatifloxacin (44.44%) and Piperacillin (55.56%) (Table 1 and Fig. 1).

Ear canals were carefully flushed with sterile saline solution using sterile bulb syringe. Based on antimicrobial susceptibility all the animals were treated with Tab. Cephalexin 25mg/kg b.wt BID orally, Tab. Wysolone (a) 1mg/kg b.wt orally for seven days and Ear drops (Pomisol (b)) was applied twice daily for 7 days. After a week, all animals showed marked clinical improvement and reduction in signs of erythema, swelling, otorrhoea, pain and itch.


Otitis externa is an acute or chronic inflammation of external ear canal. Dogs with long pendulous ears are most commonly affected. Now a days the cases are not responding to treatment with antimicrobials (August et al., 1988). This may be due to the indiscriminate use of some antibiotics and indicates the importance of sensitivity testing for effective treatment of chronic otitis externa (Senthilkumar et al., 2010). Systematically administered glucocorticods may help control the primary cause of inflammation, subsequent swelling or ceruminous gland hyperplasia that may occur with otitis externa (Morris, 2004).

As a conclusion, coagulase positive Staphylococci was the commonest bacterial agent isolated from canine otitis externa. Microbiological tests are recommended for isolation and identification of antimicrobial agents and its chemotherapeutic use.


August, J.R. (1988). Otitis externa: a disease of multifactorial etiology. Vet. Clin. North Am. Small. Anim. Pract. 18: 731-42.

Kiss, G., Radvanyi, S.Z. and Szigeti, G. (1997). New combination for the therapy of canine otitis externa- I. Microbiology of otitis externa. J. Small Anim. Pract. 38: 51-56.

Love, D.N., Lomas, G., Bailey, M., Jones, R.F. and Weston, I. (1981). Characterization of strains of Staphylococci from infections in dogs and cats. J. Small Anim. Pract. 22: 195-99.

Morris, D.O. (2004). Medical therapy of otitis externa and otitis media. Vet. Clin. North Am. Small Anim. Pract. 34: 541-55.

Quinn, P.J., Carter, M.E., Markey, B. and Carter, G.R. (1994). Clinical Veterinary Microbiology, London: Wolfe/ Mosby. p. 95-101.

SenthilKumar, K., Selvaraj, P., Vairamuthu, S., Mala Shammi and Kathiresan, D. (2010). Antibiogram patterns of microbes isolated from otitis externa of dogs. Tamil Nadu J. Vet. Anim. Sci. 6: 145-47.

(1.) Assistant Professor, University Research Farm, Madhavaram Milk Colony and Corresponding author. E-mail:

(a)--Brand of GSK Pharma Ltd., Mumbai

(b)--Brand of Intas Animal Health, Ahmedabad

S. Selvakumar, M.G. Mohamed Ali and P. Pothiappan (1)

Emergency and Critical Care Unit

Madras Veterinary College

Tamil Nadu Veterinary and Animal Sciences University (TANUVAS)

Chennai--600007 (Tamil Nadu)
Table 1: In vitro antimicrobial drug
susceptibility pattern of S. aureus

Antibiotic         Highly     Moderately
used              Sensitive   sensitive    Resistant
clavulinic acid     66.67         0          33.33
Amoxicillin         44.44       22.22        33.33
Azithromycin        22.22         0          77.78
Cephalexin          88.89       11.11          0
Cefuroxime          11.11       88.89          0
Chloromphenicol     55.56       11.11        33.33
Ciprofloxacin       33.33       11.11        55.56
Co-Trimoxazole      44.44       22.22        33.33
Erythromycin          0         88.89        11.11
Gatifloxacin        33.33       22.22        44.44
Ofloxacin           55.56       11.11        33.33
Penicillin          88.89         0          11.11
Tetracycline        33.33       55.56        11.11
Piperacillin        11.11       33.33        55.56
Vancomycin          33.33       33.33        33.33
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Title Annotation:Clinical Article
Author:Selvakumar, S.; Ali, M.G. Mohamed; Pothiappan, P.
Publication:Intas Polivet
Article Type:Report
Date:Jul 1, 2015
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