Page 270 - The Veterinary Laboratory and Field Manual 3rd Edition

Microbiology 239

2 Sabouraud dextrose agar alone and/or other fungal pathogens
Sabouraud dextrose agar with cyclohexamide
0.5 mg per ml, penicillin 20 units per ml, and A number of fungal species have the potential
streptomycin 40 mg per ml. to cause systemic disease in animals although
The specimen should be pressed into the this is more common when fungal infections
centre of the agar plate (or slope), using ster- occur secondary to other debilitating disease(s).
ile forceps, and incubated in the dark at a For example, Candida albicans, a yeast, can cause
temperature of 24–26°C. The culture should a range of diseases in debilitated animals, for
be examined at intervals of a few days over a example, ‘canker’ in the horse’s foot and inflam-
period of 4 weeks. Identification of the fungus mation of the crop in birds (‘sour crop’). Thrush
involved is based on microscopic examination (or candidiasis) is especially common in people
of stained slides of the cultured colonies and and animals after prolonged treatment with
the recorded macroscopic characteristics. In broad spectrum antibiotics, which destroy the
most cases lactophenol cotton blue (LPCB) normal flora of the gastrointestinal and repro-
(see box) stain is used. ductive tracts, allowing an overgrowth of yeast.
Candida sp. yeasts can be readily seen in smears
prepared from lesions, identification can be con-
Lactophenol cotton blue stain (for staining firmed by culture at 37 C for up to 4 days.
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fungal elements in wet preparation) Aspergillus fumigatus can be readily seen in
Phenol crystals 20 g smears and histological sections prepared from
Glycerine 40 ml lung and air sac lesions collected from birds with
Lactic acid 20 ml aspergillosis. Culture of material from lesions
Distilled water 20 ml should be done at 37ºC with samples incubated

The ingredients are dissolved by gently heat- for 1–4 days. Aspergillus species fungi can also
ing over a steam bath. When in solution, cause guttural pouch infections in horses, nasal
0.05 g of cotton blue dye is added. The solu- granulomas in a range of species and Mycotic
tion should be mixed thoroughly. abortion in cattle.
Dimorphic fungi include Blastomyces derma-
titidis (blastomycosis), Histoplasma capsulatum
(histoplasmosis) and Coccidioides immitis (coccidi-
Fungi that are commonly isolated oidomycosis). The spores of these fungi, which
from cases of ringworm and other can cause systemic disease, usually enter the body
skin conditions in animals via the respiratory route. Culture requires incuba-
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tion at 37 C over 1–4 weeks for the yeast phase
• Cattle: Trichophyton verrucosum, Trichophyton and at 25 C for 1–4 weeks for the mould phase.
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mentagrophytes There are a range of antifungal drugs avail-
• Horses: Trichophyton equinium, Trichophyton ver- able to treat fungal diseases but it is usually just
rucosum, Microsporum equinum as important to treat the underlying problem.
• Dogs and cats: Microsporum canis (some A full evaluation of the animal’s health and accu-
infected hairs may fluoresce green under a rate identification of the fungal species involved
Wood’s UV lamp). Trichophyton mentagrophytes. is essential. Each case of fungal infection, other
than ringworm, should be discussed with the
All the above fungi form arthrospores outside nearest veterinary officer so that its significance
the hair shaft. can be determined.

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