Is there any published observations regarding how long bacterial DNA can remain/circulate in a patient? I.e. how long we can expect DNA from a pathogen following pathogen death in a recently infected patient? How long it would take for the DNA to disappear in a patient? Would appreciate any comments/references! Thanks!
Olena,
I think that alive bacterial cells in latent form (L-form maybe?), as biofim, or intracellular infection (which is 10-100 folds more resistant to antibiotics) will exist in organism much longer comparing to DNA of dead bacteria.
Alex Ignatov has a point. It is not nessessary the DNA, that persist, but it could be the dormant stadium of bacteria. However depending on whats is your actual scientific problem you could get rid of extracellular DNA (DNA from dead cells) by using propidium monoazide which makes extracellular DNA inaccesible for DNA polymerase when performing PCR detection or simply by DNaze treatment of the sample before DNA extraction.
Jan Tkadlec Jan, thank you for support. We worked with propidium monoazide - it gives still quantitative reduction of PCR signal, very difficut to make a final decision. Really, some short bacterial DNA fragments can form stable complexes with proteins and other metabolites - their PCR reaction capability will depend on DNA extraction method.
Dear colleagues, thank you for joining the discussion! No doubt, you are both right: eDNA derived from both biofilm matrix and dead cells as well as persistors and L-forms are all present. But that is exactly a point: when we do have a positive PCR product is it enough to be absolutely sure that it is because of active bacterial colonisation? If there is a bacterial-specific PCR signal is detected in an atheromatous plaque, but no bacteria can be isolated from the same material, I personally have no problem to be sure that it is enough to say about persitors/biofilms etc. But we have classical clinicians, who believe that this bacterial DNA might be a remaining of bacteria which might contaminate sample long before, were eradicated and "left" their DNA in patient's tissue. Following their point, this specific DNA in a sample is not enough to be sure in bacetrial persistence. Thus, I wonder is there any publications about that?
Dear Olena, we are using exactly for this reason UMD (also known as SepsiTest) 16S PCR detection kit (Molzym). The isolation of the DNA includes enzymatic treatment to remove extracellular DNA.
There is our recent publication using the technology (for some time it could be freeely downloaded):
Article The use of broad-range bacterial PCR in the diagnosis of inf...
However, it is not probably the answer for your current problem.
Dear Jan Tkadlec, thanks for your response! It is not exactly what I need indeed, but your paper might anyway help me a lot , thank you!
Dear Traci L Testerman, that is exactly my point: can we consider a positive DNA signal from an atherosclerotic plaque clinically relevant? I have no doubt, but cannot find any data. It seems many years ago I have seen a paper where it was proved that DNA from dead bacteria could not survive longer than two weeks in a patient. But cannot find it now.
Traci L Testerman I fully agree with you, I just need some references. Do you know, are there any CLSI recommendations to use PCR for atheroma? Perhaps, not as it is irrelevant to a treatment strategy. However, is there any CLSI/ESCMID recommendations following endocarditis diagnostics with PCR?
Olena, I think you should look for the information you are interested in into the articles devoted to the problems of DNA vaccine preservation, or contact the researchers specializing in it development. They should know a lot about intracellular endonucleases and their activity.
Perhaps they will tell you more about the mechanisms of degradation of foreign DNA into the human body. As far as I know, the person involved in the development of DNA vaccines worked at your institute.
Perhaps she would help you in finding the answer to your question.
From other point of view, presence of microbial DNA in blood but not positive blood culture was found to be associated with increased mortality.
Article The detection of microbial DNA but not cultured bacteria is ...
Also in case of endocarditis I think it was proposed that PCR detection of patogen from heart valve should be one of the Duke´s criteria for definitive diagnosis of IE. Culture itself is poor method for microbial detection in case of IE as was shown in multiple studies, including our paper.
Dear Traci,
Traci L Testerman you are right. I confuse the key message of the study. Still as you sum it up better than me, PCR positivity=presence of DNA is better predictor of sepsis, than culture.
Dear Traci L Testerman and Jan Tkadlec , thank you so much for your contribution to the discussion! These two papers are helpful very much!
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