for this entry, i will blog on one of the test that is carried out in microbiogy section.
the test is STOOL CULTURE
Principle Analysis
Acute infectious diarrhoea is caused by a number of different agents: bacteria, viruses and protozoa. Each bacterial agent of infectious diarrhoea has unique pathogenic mechanism that cause a specific symptoms. These symptoms and an adequate patient history are clues that will help the physician catergorise the patient's disease. Antimicorbial therapy can alter the host's normal protective microbiota and thus predispose the patient to bacterail overgrowth that result in diarrhoeal disease caused by organism such as Clostridium difficile, staphylococcus aureus, Candida spp. and Pseudomonas aeruginosa.
For our lab, we routinely cultures stools only for the presence of Salmonella, Shingela and Vibro spp. because of their role as causative agents of bacterial diarrhoea and other enteric diseases.
Organism such as Aeromonas spp., Plesiomonas shigelloides and Yersinia spp. are identified only wen they are present in pure or heavy growth or upon request.
Specimen
stool
- collect the specimen in a sterile, dry, leak-proof container
- select portion containing pus, blood or mucus for culture
- 1 to 2 g of sample is sufficient
Reagents
media
- Alkaline Peptone Broth, AP
- MacConkey Agar, MAC
- Selenite-F Broth, SF
- Thiosulphate-Citrate-Bile salts-Sucrose Agar, TCBS
- TSA with 5% Sheep Blood, BA
- XLD
supplies
- Sterile cotton swabs
- Applicator sticks
- Inoculating loop/straight wire
storage requirements
- store all media (agar plates and broth) at 2 to 8 degree celcius
- leave the media at room temperature overnight before use
primary inoculation
- note the appearance of the stools i.e watery, loose, bloody, semi-formed and form
- inoculate stools according to Table 1
- subculture selective broth after 18 to 24 hours of incubation as in Table 2
Culture examination
After incubation, examine all primary and subculture plates for the growth of enteric pathogens.
For Salmonella/Shigella/Vibrio cholerae screenig, examine all the primary and subculture plates for the growth of Salmonella, Shigella and V. cholerae.
For the Vibrio cholerae screening, examine all the primary and subculture plates for the growth of V. cholerae.
Reporting of results
dats all...i hope you guys learnt something from my posting.
thanks for reading..
sutiana
TG01
0604651J
11 comments:
Hello sutiana..
Got a question to ask u.. why is subculturing performed on selective broth only?
thanks!
Shihui
0607135A
Hi Sutiana
May I know more about XLD medium? as my lab doesnt use this medium for stool culture. Is it mainly used to detect Salmonella & Shigella spp.?
Thanks!
LeeJin
TG02
Hey Sutiana!
In my lab I handle stool too! But only to test for fecal occult blood.. didnt do much on stool culture before :P
Anw can i ask is all type of stool suitable for culturing? Eg. if stool is too hard do u need to add any reagents to liquefy it before peforming plating?
Thanks!
Cheers,
HuiMin
TG01=)
Heys:D
u mentioned 'note the appearance of the stools i.e watery, loose, bloody, semi-formed and form'.
were you guys taught to predict the type of organism that has infected the person based on the appearence of the stool?
like if the stool is watery, den do you like kind of noe wad kind of organism could it be?
Thanks:D
Neela
Tg02
Hey sutiana,
Ask u arh, how do u determine if an organism is pure or not? And also, when u examine the primary and subculture plates for the growth of pathogens right, what do u normally look out for or obeserve to see if they are positive or negative?
Thanks alot
Zhenling
TG02
Hi there Sutiana!
Boy, reading your entry makes me feel like i'm taking a tour of what i was doing in the lab two weeks ago - Stool sample handling too. And yes, we made use of all six of the type of cultures you'd mentioned - XLD, TCBS, BA, MAC, Selenite broth, and AP. On top of that, we also include a Campylobacter Agar if the stools are watery, or if the patient is less than 6 months old, to determine if Campylobacter bacteria is present in the stools.
Took me a week to get use to it all. Boy, all the best to you there! hahs(=
Alrights. Thanks for your entry!Outta here.
Alexander Soo TG02
0608122H
Hi Sutiana!
I did microbiology in my 1st 3 weeks of SIP. Regarding the dection of salmonella and shigella, if i rmb correctly, my company used Macconkey agar to see any presence of black microorganisms.
Any presence of black microorganisms signfies salmonella and shigella.
So do you guys use the same agar or different? You mentioned various agar plates but didn mention which agar plate is for which test.
Thanks,
Lloyd
Hi Sutiana,
Got some questions here...
1)"Each bacterial agent of infectious diarrhoea has unique pathogenic mechanism that cause a specific symptoms."
What do you mean by unique? How unique? Can you describe the mechanism?
2)"Organism such as Aeromonas spp., Plesiomonas shigelloides and Yersinia spp. are identified only wen they are present in pure or heavy growth or upon request."
Can you describe what do you mean by pure growth?
3)What are the functions of Selenite-F Broth,
Thiosulphate-Citrate-Bile salts-Sucrose Agar,
TSA with 5% Sheep Blood and XLD? And which microorgansims do these media support?
Thankz!
Han Yang
TG01
Hey Nana!!
How does antimicrobial theraphy alter host's normal protective microbiodata?
Why do you have to note the appearance of the stool? Do you have to cross-refer with the results of your culture?
AMiR
TG02
sorry for the late response..
i was very busy these days..
aniways,here are the answers to the questions-
t0 shi hui:
the main purpose for doing subculturing on selective broth is to identify the organism that cause food poisoning. we are only interested in those organism not the others.
t0 lee jin:
Xylose lysine deoxycholate agar(XLD agar) is a selective growth medium. It is low in nutrients and contains a small amount of sodium desoxycholate for selectivity. It has a pH of approximately 7.4. And yes, it is mainly used in isolation of both Salmonella and Shigella spp..
t0 huimin:
yes, all type of stool are suitable for culturing. we can add sterile saline if we want to but we usually don't.
t0 neela:
yes, i did mentioned that. and yes, we are taught to predict the type of organism that has infected the person based on the appearence of the stool.
for example, when we notice a watery(rice water) kind of stool, we would know that the likely organism that is present is Vibrio. For bloody, mucus stool it would indicate EHEC, which is a type of E.coli that contain toxin.
t0 zhenling:
the organism would be pure if only one type of colony is seen on the culturing plate.
IN microbiology, we don't have positive or negative results. We focus more on the significance of bacteria growth. We take into account the no. of growth, whether it is a significant growth or not, whether it is sterile or non-sterile. Based on these factors, then a report of the organism that is present can be made.
t0 alex:
thanks for the comment. it took me awhile to get use to the procedures too. all the best to u too..
t0 lloyd:
All the plates that i have mentioned in my entry are used to detect organism that cause food poisoning. WE used all the plates when a stool culture is ordered. And MacConnkey is one of them. FOr us here, we rely on MacConkey, XLD, Selenite-F broth and DC to signifies the presence of Salmonella and Shigella spp.
t0 hanyang:
1)how unique? i do not know. but i do know that specific organism do bring about symptons that signify their existance.
For example:
Salmonella- cause an intestinal infection usually accompanied by diarrhea, fever and abdominal pain which often lasts for 1 week or longer.
Shigella- Usually begins with watery diarrhea accompanied by fever and abdominal cramps. It may progress ti classic dysentery with scant stools containing blood, mucus and pus.
Vibrio- cause either diarrhea(rice water) kind or extraintestinal infections.
2) pure growth means the presence of only one type of colony on the culturing plate.
3)Selenite-F Broth is used as an enrichment medium for the isolation of Salmonella from feces, urine, water, foods and other materials of sanitary importance.
Thiosulfate Citrate Bile Sucrose Agar is used for the isolation and selective cultivation of Vibrio cholerae and other enteropahtogenic vibrios (V. parahaemolyticus, NAG vibrios).
TSA with 5% Sheep Blood is used for cultivating fastidious microorganisms and for the visualization of hemolytic reactions produced by many bacterial species.
XLD is a selective and differential medium for the recovery of Salmonella and Shigella species.
t0 amir:
1) antimicrobial therapy is basically giving antibiotics to the patient. By having this therapy the host normal microbiota is cahnged and thus the patient is protected against the organism.
2) it is to determine waht sort of plate to use. as well as to give us the indication of the organism that is present.
i hope i have answered to your questions. i tried to be as clear as possible. if there is still any queries, do let me know..
till then...
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