Lesson 36: Fungal Culture

Saborauds Dextrose Agar

• Primarily for isolation of dermatophytes from cutaneous samples or yeasts (Candida spp) from clinical samples

• This medium has acidic pH (5.5) which inhibits the growth of most bacteria

ii. Czepak’s Agar

• For colonial study of Aspergillus spp

iii. Sabhi Agar/Inhibitory Mould Agar

• Recommended for improved recovery of fastidious, slow-growing fungi

iv. Potato Dextrose Agar

• For isolation of mould and yeast

Selective Culture

• Addition of chloramphenicol (16µg/ml), penicillin (20 I.U/ml), streptomycin (40 U/ml), gentamicin (5 µg/ml) and cycloheximide/actidione (0.5mg/ml) increases selectivity by inhibiting contaminations by bacteria and fast growing fungi

• e.g. Zygomycetes

Enriched Media

• Brain-heart infusion agar is supplemented with 5% blood

Enriched Media

• This is used to stimulate the growth of yeast phase of dimorphic fungi • Incubation is at 37 O C

Culture Procedures

• Fungi are cultured in tubes or in plates (Petri dishes)

• Clinical samples are inoculated directly onto prepared medium and incubated aerobically

Tube

• Agar media are poured and allowed to solidify in slanting position to prevent dehydration during prolonged incubation

tubes

plugged with cotton wool or covered with screw cap

• The cap should not be screwed tightly after inoculation to allow access to oxygen

Plate

• This provides large surface area and good hydration for fungal growth

• It allows easy examination and subculture from the plate

plate

is taped round to prevent escape and dispersal of fungal spores

flat pan containing water

placed under the incubator to provide humidity

i. Condition of Growth

ii. Colonial characteristics

iii. Microscopy

iv. Biochemical Reaction of Yeasts

v. Immunological Test/Serology

vi. Molecular Identification

Criteria for identification:

vi. Molecular Identification

• Using polymerase chain reaction

• Dot blot hybridization

• Specific nucleic acid probes and other molecular characterization

v. Immunological Test/Serology

• Gel diffusion test

• Complement fixation test

• Agglutination reactions

• Delayed hypersensitivity test (purified protein derivatives)

iii. Microscopy

• Examination of sporing head for conidia

• Presence or absence of septa