Procedure: Fungal Culture
Posted by: Azhar Hamdan (0503269C)
In this post, I am focusing on the fungal culture procedure for clinical specimens.
Purpose
Fungal cultures on clinical specimens are done to detect the presence of:
• Yeast
• Yeast-like fungi
• Hyaline or dematiaceous filamentous fungi
• Aerobic actinomycetes
Common specimens received
• Cerebrospinal Fluid (CSF)
• Blood
• Vaginal/Cervical Swabs
• Skin
• Hair
• Nail
Media Used
• Sabouraud Dextrose Agar (SDA)
• Sabouraud Dextrose Agar with Chloramphenicol (SDC)
• Brain Heart Infusion Agar with Chloramphenicol and Gentamicin (BHICGA)
• Brain Heart Infusion Agar (BHIA)
• Mycobiotic agar with Actidione (AA)
Chloramphenicol, Gentamicin & Actidione are antibiotics. The purpose of adding antibiotics to media is to suppress normal flora and thus to allow for the multiplication and detection of the pathogenic organisms
Okay, maybe all the media looks the same, but just to point something out, different media have different corresponding coloured covers. This prevents accidental mix up.
(Left to right; SDA, SDC, BHICGA, BHIA & AA)
General Procedures
• The ideal temperature for the recovery of fungi is 30°C
• Cultures are kept for 2-4 weeks depending on the specimen and the suspected organism before cultures are reported as negative and then discarded
• Media is preferably prepared as a slant in a tube as opposed to being prepared in a Petri-dish
Reasons for preference of slant:
• Potentially less hazardous for staff to work on ( e.g. due to the vertical tubes, aerosols produced would less likely escape)
• Less prone to contamination and dehydration
• Easier to store in racks
Pictures were taken with permisson from the supervisor.Thats all for this post. Say HELLO to week 10
6 comments:
Hey azhar,
how do you inoculate the specimen on/in the medium?
do you streak on the surface of the slant?
does it appears white on the surface when there is fungus growth?
boonching
tg01
Hey,
Interesting and weird agar names..
Anyway you mentioned in the 2nd last table, SDA:"...pathogenic and non-pathogenic fungi.."
If the agar medium can detect both, can it still be used as a diagnostic indicator then?
Tanx.
Nisha
TG02
hello =)
As u mentioned, different media has different colored covers..so are these covers still labelled? coz there might be a chance that the covers are switched in the midst of preparing the media right? Any way to prevent it?
Thanks!
Kangting 0503331A
TG02
Kangting
0503331A
hi Azhar,
Why need to use india ink for CSF microscopy? Thanks
Ci Liang
TG01
Hi Rina,
What is the purpose of testing the presence of fungal on skin, hair and nails?
To test on CSF, blood and vaginal/cervical swabs is to test for infection right?
Tang Jiaxin
Tg01
0503257H
Hello, Im sorry bout this late reply for the questions
So without further delay, here goes:
To Boon Ching;
Yes we only streak on the surface, we do not stab the agar unlike some other media. And yes the colonies appear white and there may even be filamentous growth.
To Nisha;
SDA is still an important diagnostic tool and its partly due to its ability to grow both pathogenic and non-pathogenic organisms.
The reason for this is that there must always be a combination of media with at least one being non-selective(SDA) and another being made selective through the addition of antibiotics (SDC)
After incubation, we can then identitify and distinguish the organism(s) by comparing the two media.
Think of it this way, SDA shows you a growth which you suspect to be organism A but you are not sure, you thus refer to SDC to confirm.
To Kangting;
Actually the tubes are not labelled at all. The only labels that can be found are on the racks that the tubes are placed in. The tubes are placed in separate racks with one rack filled with just SDA, another rack filled with just SDC, and so on and so forth.
To Ci Liang;
Normally for other samples, we do not do microscopy. However, since CSF is supposed to be a sterile site, the presence of any pathogen indicates a serious infection.
Thus we perform India Ink, which stains the background and leaves the bacterial cells clear, and Microscopy as a precaution.
To Jiaxin;
Firstly, I apologise for previoulsy not elaborating on what a dermatophyte is.
Dermatophytes are parasitic fungus that causes skin infections, with an example being ringworms.
And as mentioned in my post, skin, hair or nail cultures are done to recover and identify dermatophytes, non-dermatophytes and yeasts responsible for infection.
So, for the case of dermatophytes, we test these samples so that we can can identify the organisms that is causing the skin infections.
Anyways we rarely receive skin samples therefore, I am not too sure why we tests the samples for non-dermatophytes and yeasts.
And yes to test on CSF, blood and vaginal/cervical swabs is to test for infection, with vaginal/cervical swabs being more specific forvaginal yeast infection.
Thanks for your questions,
Azhar
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