External Ear Canal Evaluation in Dogs with Chronic Suppurative Otitis Externa: Comparison of Direct Cytology, Bacterial Culture and 16S Amplicon Profiling

Abstract

A discrepancy between cytology and bacterial culture methods is sometimes observed in canine otitis externa. The objective of this study was to compare results from cytology, bacterial culture and 16S amplicon profiling. Twenty samples from 16 dogs with chronic suppurative otitis externa were collected. A direct cytological evaluation was carried out during the consultations. Aerobic bacterial culture and susceptibility were performed by an external laboratory used in routine practice. For 16S amplicon profiling, DNA was extracted and the hypervariable segment V1–V3 of the 16S rDNA was amplified and then sequenced with a MiSeq Illumina sequence carried out by the Mothur software using the SILVA database. A good correlation between cytology and bacterial culture was observed in 60% of the samples. Some bacterial species revealed by bacterial culture were present with low relative abundance (<10%) in 16S amplicon profiling. Some bacterial species revealed by the 16S amplicon profiling analysis were not identified with culture; most of the time, the offending species was a Corynebacterium. To conclude, a careful interpretation of the results of bacterial culture should be made and always be in agreement with the cytology. The 16S amplicon profiling method appears to be a more sensitive method for detecting strains present in suppurative otitis but does not provide information on bacterial susceptibility.

Microbiological Survey and Evaluation of Antimicrobial Susceptibility Patterns of Microorganisms Obtained from Suspect Cases of Canine Otitis Externa in Gran Canaria, Spain

“…Similarly, other canine otitis prevalence studies did not report this microorganism [ 32 , 40 ]. Interestingly, in a report studying the correlation between cytology, bacterial culture and 16S amplicon profiling for the diagnoses of cases of canine otitis externa [ 44 ], the majority of the culture-negative results were diagnosed as Corynebacterium spp. based on 16S sequencing, suggesting a more prevalent role of this bacteria in cases of otitis, and the need for adapting isolation protocols to improve Corynebacterium spp.…”

“…These results are in accordance with those described by Nocera et al [ 15 ], where the authors observed a 16% rate of coinfections in cases of pyoderma and otitis of dogs. However, other authors have described much higher coinfection rates, ranging from 61.7% [ 43 ] to 80% [ 44 ]. M. pachydermatis (61/85; 71.8%) and S. pseudintermedius (39/85; 45.9%) were found in most of the coinfection cases observed, in agreement with previous studies [ 43 ].…”

Pseudomonas spp. in Canine Otitis Externa

“…Microorganisms in the ear are characterised using three main techniques: cytological examination, bacterial culture, and deep sequencing [16][17][18]. The cytological examination of otic discharge/cerumen is mostly used in the clinical setting as a quick, convenient test.…”

Antibacterial effects of chitosan-based hydrogels containing Trachyspermum ammi essential oil on pathogens isolated from dogs with otitis externa

“…is the most frequently isolated bacterial species from the ear canals of dogs with OE. However, other bacteria, such as Streptococcus spp., Pseudomonas spp., Corynebacterium spp., Escherichia coli , and other Enterobacteriaceae , can also be involved [ 16 , 17 ]. Diagnosis of OE typically involves palpation of the ear canal, visual inspection, and Otoscope examination.…”

“…Cytology and bacterial culture are commonly used diagnostic tools. In cases of colonization by opportunistic bacteria, veterinarians may face therapeutic challenges [ 16 , 18 ].…”