Fungal Culture Test Media

Microbiology fungal culture in petri dish/agar plate: Isolation of fungi, either yeast, mould or a dimorphic fungus, at 30C for four weeks

Synopsis
Purpose and Specimens: 0:00
Media: 0:21
Incubation: 1:22
Reading Plates: 2:23
Positive Workup: 3:55
Insights and thanks for watching: 6:53

Acceptable specimens: All of your usual specimens such as wounds, abscesses, respiratory specimens (bronch wash, bronch lavage) sterile body fluids (CSF, plueral fluid, pericardial, ascitic fluid etc.), tissues and bones – got incorporated into ortho protocol for fear of missing fungal growth on regular culture and having to invasively resample the patient.

Media: Two types of media required, one non-selective and one selective. We use four (two of each):
a. PD = Potato Dextrose
i. ONLY plate to determine true colour of mold!
b. SAB = Sabouraud Dextrose
c. IMA = Inhibitory Mould Agar (inhibits most bacteria and some of your contaminating or fast growing moulds)
d. BHI = Brain Heart Infusion Agar (inhibits most bacteria due to antibiotics gentamicin and chloramphenicol)

Incubation time and conditions (4 weeks at 30C) – could vary depending on institution but this is a happy medium between mould (25C) and yeast (35C) growth. Regular cultures generally are held for a few days and ortho specimens can be held for two weeks.

Reading Plates: culture can be read twice a week depending on volume.
a. Non-inhibitory plates (SAB and PD) will grow bacteria
b. Inhibitory plates (IMA and BHI) will generally grow only yeast or moulds
i. Therefore compare growth on SAB/PD to IMA/BHI to determine to easily if fungi

Positive work up dependent on yeast vs mould
a. Yeast: wet mount (link video) or visually be able to identify
i. Work up appropriate to body site if significant vs not (urine, sterile site, wound vs respiratory)
ii. Respiratory only required workup to rule out Cryptococcus neoformans otherwise report as normal flora
b. Mould: visually able to identify macroscopically
i. Sub to PD plate for isolation and to determine true colour
ii. Identification performed via Lactophenol Cotton Blue slide via a tape prep (most commonly from sub but can be performed if good growth on original plate)
iii. Mould is significant for most sites but main issue is contaminant vs not (look at growth on 1 vs 4 plates) and look to see if another pathogen is present. Objectionable to respiratory sites (e.g. sputum) but depends on site and patient – mould spores are everywhere hence the contamination even when inoculating in the BSC.


End credit mould and thumbnail mould: Penicillium species
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