Establishment Of A Mouse Model Of Otomycosis

Objective: Otomycosis is a chronic infectious disease caused by pathogenic fungi outside the body or opportunistic fungi in the external auditory canal,and it is also a common ENT disease especially in the coastal area or warm and humid areas in the South.In the recent years,the curative effect of research on the drug in the clinic,which are used in human external auditory canal can not be evaluated from the long-term side effects because of repeated use of antifungal drugs.Therefore,the establishment of a mouse model of otomycosis with sensitivity and good repeatability,and observes in different periods of the skin of external auditory canal’s pathological changes,have an important role in the defense mechanism of the host and pathogenicity of fungi.There also have a positive effect for the new anti fungi drug,including researches on its effectiveness,side-effects and pharmacokinetics.Methods: Totally,48 Wister mice were randomly and equally divided into four groups: A is high-concentration immunosuppressive mice inoculated with Aspergillus fumigatus suspension of 1*10^9 CFU conidia/ml,B is low-concentration immunosuppressive mice inoculated with Aspergillus fumigatus suspension of 1*10^6CFU conidia/ml,C is high-concentration healthy group-healthy mice inoculated with Aspergillus fumigatus suspension of 1*10^9 CFU conidia/ml,and control group-healthy mice inoculated with sodium chloride physiological solution.Group-A and group-B’s immunosuppression by abdominal injection of cyclophosphamide 200mg/Kg on the first day,On the third day,the mice’s right ears were selected as research objects,using sterile sandpaper coiled rod,scraping the skin,with principle of no bleeding.The different concentration of Aspergillus fumigatus suspension were smeared on the damaged skin of external auditory canal,with the inoculation volume being 200 ul.The control group were smeared on the damaged skin of external auditory with sodium chloride physiological solution.This operation has been repeated for 7 days.Skin appearance at the inoculation site was observed using ear endoscopy,and four mice were sacrificed in each group on day seven,fourteen and twenty-eight after inoculation.According to the scores of external auditory canal’s infection and microscopic examination and histopathology,to see weather the comparison of scores of within and between groups has statistical differences.Results: After seven days’ infection,the skin of the experimental group were swelling and thickening,and we could see ulceration,erosion,exudation and also some moist,pale yellow liquid with local crusting on the inoculated place,the edge had angiotelectasis,some of the serious ones also had bleeding and purulent secretion,stenosis of external auditory canal can be found in two cases.Around fourteen days,some moist secretions of different degrees can be observed,granular,villous,film covering of some parts,the color is black,yellow,white and green.On the 28 day after infection,the conditions of experimental mice of external auditory canal skin were gradually improved(ulceration healing,scab fall off,canal skin becomes dry),the infection rate was 100%.Significant were noted in the infective scores of skin lesions between the three time points in these experiment groups(P<0.05),and in seventh days after inoculation of infective grade was the highest.They were 10.5±0.5 point、8.9±1.3 point、9.2±0.6 point、5.5±1.3 point.Comparison between groups was not statistically significant in seventh days and fourteenth days(P>0.05),comparisons of infective scores revealed a statistical significantdifference on the day of twenty-eight(P<0.05).High-concentration immunosuppressive mice inoculated with Aspergillus fumigatus suspension of 1*10^9 CFU conidia/ml has the score up to twelve points of all.The three experimental groups were all positive for microscopic examination,and the pathology showed inflammatory cell infiltration,necrosis and granuloma formation.Meanwhile,no mice were infected in the control group.Conclusion: The mouse model of otomycosis was successfully established in both healthy mice and immunosuppressive mice.Three experimental group at the initial stage of infection was serious,but gradually improved.Considering that the host immune system gradually occupied the advantage,leading to the elimination of pathogenic bacteria and the reduction of inflammatory reaction,suggesting that the disease is self healing.