SURVEY ON THE YEAST FLORA IN EXTERNAL EAR CANALS OF RABBIT

INTRODUCTION: The recovery of Malassezia from rodents and lagomorphs has been rarely cited in literature, and some studies have failed to demonstrate the presence of these fastidious yeasts in rabbit (Guillot et al., 1994, J. Mycol. Med., 4: 72-79). In 2011, Cabanes & Castellà (Med. Mycol., 49: 40-48) described a novel yeast species, named Malassezia cunicoli, from the skin of two rabbit from Spain. This yeast was not able to grow on Sabouraud Dextrose Agar (SDA) and modified Dixon Agar (mDA) medium but grew slowly on Leeming & Notman agar (LNA). In the course of a survey on the fungal flora in the rabbit skin, we searched for the presence of Malassezia sp. in rabbits from Emilia Romagna and Veneto regions. MATERIALS AND METHODS: The screening was performed on 168 rabbits; 70 rabbits for meat and 98 dwarf rabbits. Samples were collected from both the external ear canals of each animal using swabs soaked in phosphate buffered physiological saline containing 0.1% Tween 80, according to Cabanes & Castellà (2011 l.c.). All samples were inoculated onto SDA (BBL-BD), mDA (Gueho et al., 1996, Antonie van Leeuw. 69: 337- 355) and LNA (Leeming and Notman, 1987, J. Clin. Microbiol. 25: 2017-2019). These culture media included 0.05% cloramphenicol. Plates were incubated at 30°C and examined daily for 20 days. All swabs were also rolled over the surface of microscopic slides and the smears were stained with May Grunwald-Giemsa. Afterwards swabs collected from further 24 rabbits were used to inoculate 3 modified culture media with different composition and for slides. RESULTS: Microscopic observation of the swabs showed yeasts in one or both the external ear canals of 98 rabbit (58.3%). The yeasts were rounded, 2-4 um in diameter, with buds formed in monopolar pattern on narrow bases, like to the description of M. cunicoli according to Cabanes and Castellà (2011 l.c.). The prevalence was higher in the rabbits breeding for meat than the dwarf rabbits (X2y = 12.33; p<0.01): no statistically significant differences were observed in relation to age, gender and kind of breeding. Cultural examinations showed the presence of rare colonies of yeasts in two rabbit for meat, identified as Candida famata. All the other samples not showed any yeasts growth on all the culture media employed as screening. Also swabs from the further 24 rabbits examined, all positive at microscopic examination, were negative on the modified culture media. CONCLUSIONS: In the present survey we recovered, at the microscopic observation, the presence of yeasts morphologically similar to those described by Cabanes and Castellà (2011 l.c.), with a prevalence (58.3%) beyond all expectation. These authors observed M. cunicoli in only 2 out of 11 rabbits investigated (18.2% ), both in cultures and in microscopic examination. Previously, only Radi (Comp. Med. 2004, 54: 434-437) observed round yeast cells by direct microscopy in 20 out of 500 (4%) rabbits affected by Sarcoptes scabiei. In the present survey, the yeasts were not able to grow on the different medium used in the screening and in the modified cultural media. This observation show how the presence of yeasts in the microflora of the rabbits’ external ear canals is probably more common than you think, and that the inhibition of growth observed may be related to different nutritional requirement than the one described by Cabanes and Castellà (2011 l.c.) and Cabanes (PLOS Path. 2014, 10: e1003892).