I am working on the prevalence of asymptomatic carriers of group A streptococci (GAS)among school children of 5-15 years. Culture yield was very low for GAS, but with the use of qPCR (spy1258 gene) i could pick up more positives. what should be the actual bacterial load in throat swabs to confirm as carriers?If the ct value is between 36 and 40 can we take as positives?
We serially diluted the sample of known DNA concentration. ct value of 24.45 corresponded to DNA concentration of 37.6ng/µl (apprximately1.5 x 10^8 cfu/ml). ct value of 38.56 corresponded to DNA concentration of 37.6fg/µl (apprximately1.5 x 10^4 cfu/ml).
What concentration of DNA/ bacteria should be there in throat swabs to be interpreted as asymptomatic colonization?
Hello Tintu,
obviously, you want to use your PCR for the discrimination between asymptomatic carriers and ill patients.
I would suggest that, first, you try to define a cutoff between these two groups based on your culture. I would expect that asymptomatic carriere have lower cfus than patients.
Than you can define a cutoff (ct value) for your PCR, again saymptomatic carriers versus patients.
And then you can correlate the number of cfu of asymptomatic carriers and patients with the ct value of these two grops.
To cut a long story short: I would expect the cutoff to be somewhere around ct value 32-35.
By the way: how many circles to you use?
Best wishes
Dirk
Thank you Dirk Schmidt.
For patients the ct values ranged between 20 and 30.
Is there any guidelines about detection GAS asymptomatic carriers (especially about the bacterial /DNA load)
If the qPCR flags positive at 36 to 40 is it really carrier state positive, since group A streptococcus won't be present as normal flora of upper respiratory tract.
- Badges
- Science topic
- Similar topics
- Biological Science
- Molecular Biology