Investigation of the Development of Dermatitis in Hypotrichotic Rats

—Microbiological Study—

Abstract

The hereditary hypotrichotic (WBN/Ila-Ht) rat is affected by dermatitis characterized by erosions and crust formation on dorsal skin areas. The bacterial flora of this dermatitis and the normal skin of the hypotrichotic rat was examined. As controls the cutaueous flora of atrichotic and Wistar rats was examined, and the results compared with those in hypotrichotic rats. The total number of bacterial colonies from the lesions and normal skin of hypotrichotic rats were 3.9×10⁵ to 1.16×10⁸ CFU/cm² and 1.6×10³ to 1.8×10⁴CFU/cm², respectively. In the lesions, overwhelming numbers of S. aureus were detected as almost pure cultures. In the normal skin, S. aureus was predominant, accounting for about 90% of all bacteria. The total number of bacterial colonies in the atrichotic rats was the same as in the hypotrichotic rats. The majority of the isolates were Staphylococcus sp., and about half of them were identified as S. aureus. The total number of bacterial colonies from the skin of individual Wistar rats varied extremely, ranging from 64 to 2.98×10⁵ CFU/cm². The flora mainly consisted of coagulase-negative Staphylococcus (CNS), S. aureus, and α-hemolytic Streptococcus sp., and CNS was isolated most frequently. Histopathological examination of the eroded portions in hypotrichotic rats revealed many clusters of coccoid bacteria and neutrophilic cell infiltration of the epidermis. These findings suggest that the dermatitis in hypotrichotic rats was caused by S. aureus and affected by unknown traits of these rats.