Phenotypic characterization of non-dermatophyte moulds from companion animals with mycotic dermatitis

Introduction

Mycotic dermatitis is an important fungal skin disease of companion animals characterized by alopecia, erythema, scaling, crust formation, variable pruritus, hyperpigmentation and malodour (Scott et al., 2001; Bond et al., 2020) [1,2] . The disease poses significant diagnostic challenges as its clinical manifestations often resemble those of several infectious and noninfectious dermatological conditions (Outerbridge, 2006) [3] . Accurate identification of the etiological agent is therefore essential for effective treatment and prevention of recurrent infections (Chakrabarti and Singh, 2011) [4] . Dermatophytes are traditionally regarded as the principal fungal pathogens associated with superficial mycoses in dogs and cats (Ivaskiene et al., 2016) [5] . However, increasing reports have documented the recovery of nondermatophyte moulds (NDM) from companion animals with fungal dermatitis, highlighting their growing clinical significance (Kumar et al., 2011; Zenad et al., 2015; Hassanien et al., 2021) [6,7,8] [6,8] . Recent investigations have reported the occurrence of Aspergillus spp. in dogs and cats with mycotic dermatitis (Padala et al., 2026) [9] . Diagnosis of NDMassociated dermatitis is often difficult because lesions frequently mimic dermatophytosis, bacterial pyoderma and allergic skin diseases (Bond et al., 2020) [2] . Although molecular techniques have enhanced fungal identification, conventional mycological methods based on culture characteristics and microscopic morphology remain valuable tools for routine diagnosis and characterization of fungal isolates (Borman and Johnson, 2014; Rudramurthy and Shaw, 2018) [10,11] . Therefore, the present study was undertaken to characterize non-dermatophyte moulds isolated from dogs and cats with mycotic dermatitis based on their cultural and microscopic characteristics.

Materials and methods

The present study was conducted at the Department of Veterinary Microbiology, NTR College of Veterinary Science, Gannavaram, (Andhra Pradesh, India). Skin scrapings and hair samples were collected from dogs and cats exhibiting skin lesions suggestive of mycotic dermatitis, including alopecia, scaling, crusting, erythema, malodour and pruritus. Samples were obtained aseptically from the site of active lesions using sterile scalpel blades and forceps after cleansing the affected area with 70% alcohol to reduce surface contaminants. The collected specimens were transferred to sterile labelled containers and transported to the laboratory for mycological examination (Dworecka-Kaszak et al., 2020; Hassanien et al., 2021; Patel et al., 2024) [12,8,13] . The collected samples were inoculated onto Sabouraud Dextrose Agar (SDA) and incubated at 28 ± 2 °C for 2 days to a week (Quinn et al., 2011; Padala et al., 2026) [14, 9] . The culture plates were examined periodically for fungal growth, and distinct colonies were subcultured onto fresh SDA plates to obtain pure cultures. Identification of the recovered non-dermatophyte moulds was carried out based on their cultural characteristics and microscopic morphology following standard mycological procedures (Larone, 2011; Procopet et al., 2020) [15,16] . Pure cultures of the recovered non-dermatophyte moulds were examined for their macroscopic characteristics on SDA. Colony morphology was assessed based on colony colour, texture, growth rate, surface topography, margin characteristics and reverse pigmentation following standard fungal identification procedures (Larone, 2011; Samson et al., 2014) [15,17] . The observed cultural features were recorded and utilized for characterization of the fungal isolates. Microscopic characterization of the fungal isolates was performed using Lactophenol Cotton Blue (LPCB) staining as described by Benson (2001) [18] and Procopet et al. (2020) [16] . A small portion of fungal growth was mounted in LPCB stain on a clean glass slide and examined under a light microscope. Morphological features including hyphal characteristics, conidiophores or sporangiophores, arrangement of reproductive structures and spore morphology were evaluated for identification and characterization of the isolates following the keys of Larone (2011) [15] and de Hoog et al. (2020) [19] .

Results and Discussion

Fungal culture yielded diverse fungal isolates comprising dermatophytes, yeasts and non-dermatophyte moulds. Among the recovered fungal isolates, non-dermatophyte moulds predominated, with Aspergillus spp. representing the most frequently encountered genus, followed by Penicillium spp. The remaining isolates comprised Mucor spp., Rhizopus spp., Alternaria spp., Curvularia spp. and Fusarium spp. The predominance of Aspergillus spp. observed in the present study is in accordance with earlier reports by Kumar et al. (2011) [6] , Zenad et al. (2015) [7] and Padala et al. (2026) [9] , who documented a higher occurrence of Aspergillus species among fungal isolates recovered from companion animals with dermatological lesions. The cultural and microscopic characteristics of the recovered non-dermatophyte mould isolates are presented in Tables 1 and2. Broad aseptate hyphae with well-developed rhizoids, sporangiophores and spherical sporangia. Alternaria spp.

Septate hyphae with brown muriform conidia having transverse and longitudinal septa. Curvularia spp.

Septate hyphae with geniculate conidiophores and curved multicellular conidia. Fusarium spp.

Septate hyphae with characteristic sickle-shaped multicellular macroconidia. Aspergillus spp. and Penicillium spp. were the predominant non-dermatophyte moulds recovered in the present study and exhibited rapid growth on SDA (Fig. 1). Isolates of Aspergillus spp. produced characteristic colonies ranging from black granular growth in A. niger and yellowish-green powdery colonies in A. flavus to blue-green velvety colonies in A. fumigatus, whereas Penicillium spp. developed greenish velvety colonies. Microscopically, both genera exhibited septate hyphae and abundant conidial structures (Fig. 2); however, Aspergillus spp. were distinguished by prominent conidiophores terminating in vesicles bearing phialides and chains of conidia, while Penicillium spp. exhibited characteristic brush-like conidiophores with branched phialides. The observed cultural and microscopic features were consistent with the descriptions of Klich (2002) [20] , Geiser et al. (2007) [21] , Larone (2011) [15] and Padala et al. (2026) [9] . Mucor spp. and Rhizopus spp. were characterized by rapidly growing cottony colonies and broad aseptate hyphae (Figs. 1 and2). The presence of rhizoids in Rhizopus spp. and their absence in Mucor spp. facilitated differentiation between the two genera. Similar findings have been reported by de Hoog et al. (2020) [19] . The dematiaceous fungi, including Alternaria spp. and Curvularia spp., exhibited pigmented colonies and characteristic multicellular conidia, whereas Fusarium spp. produced cottony colonies with distinctive sickle-shaped macroconidia. The observed cultural and microscopic features were consistent with standard descriptions reported in the literature (Larone, 2011; Samson et al., 2014) [15,17] .

Conclusion

The present study demonstrated the occurrence of diverse non-dermatophyte moulds in dogs and cats with mycotic dermatitis. Among the recovered isolates, Aspergillus spp. and Penicillium spp. were the predominant moulds, whereas Alternaria spp., Curvularia spp. and Fusarium spp. were encountered less frequently. The distinct cultural and microscopic characteristics exhibited by the isolates facilitated their identification and differentiation. Conventional mycological techniques based on culture isolation and microscopic examination continue to serve as the gold standard for routine characterization of fungal isolates and remain valuable tools in veterinary diagnostic laboratories.

Acknowledgement

AcknowledgementThe authors are thankful to the Department of Veterinary Microbiology, NTR College of Veterinary Science, Gannavaram, Sri Venkateswara Veterinary University (SVVU), Andhra Pradesh, for providing the necessary facilities and financial support to carry out this research work.

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