Direct amplification and detection of viral and bacterial pathogens
Provided herein are methods for identifying the presence or absence of a target nucleic acid from a microorganism using direct amplification without a step of extraction of the nucleic acids, but retaining substantially the same specificity and sensitivity of methods assaying extracted nucleic acids.
1. A method for identifying the presence or absence of a target nucleic acid from a microorganism in a biological sample obtained from a human, said method comprising:
(a) contacting the biological sample with a reaction mixture containing a DNA polymerase and a buffer to form a sample mixture under conditions suitable for amplification of the target nucleic acid from the biological sample without extracting the target nucleic acid from the biological sample;
(b) thermocycling the sample mixture from step (a) such that the target nucleic acid, if present, is amplified; and
(c) detecting the amplified target nucleic acid, if present, produced from step (b),
wherein the biological sample is selected from the group consisting of whole blood, plasma, serum, and cerebrospinal fluid (CSF),
wherein the nucleic acid in the biological sample is not extracted from the biological sample prior to amplification;
wherein the biological sample is not diluted prior to contacting the biological sample with the reaction mixture;
wherein 20-30% of the total volume of the sample mixture following step (a) is the biological sample;
wherein the target nucleic acid is not present in a biological sample that does not contain the microorganism; and
wherein the reaction mixture contains a cationic surfactant.
2. The method of claim 1 , wherein the sample is heated prior to step (b).
3. The method of claim 2 , wherein the sample is heated prior to step (a).
4. The method of claim 1 , wherein the sample is heated prior to step (b) for at least 2 minutes at a temperature of at least 70° C.
5. The method of claim 1 , wherein the buffer comprises potassium chloride (KCl).
6. The method of claim 5 , wherein the KCl is present in a concentration of about 5 mM to about 50 mM.
7. The method of claim 1 , wherein the DNA polymerase is a Taq polymerase.
8. The method of claim 1 , wherein the target nucleic acid is DNA.
9. The method of claim 1 , wherein the target nucleic acid is RNA.
10. The method of claim 9 , wherein the sample is further contacted with a reverse transcriptase prior to amplification.
11. The method of claim 10 , wherein the sample is simultaneously contacted with the DNA polymerase and the reverse transcriptase.
12. The method of claim 1 , wherein the microorganism is a virus.
13. The method of claim 12 , wherein the virus is selected from the group consisting of an influenza virus, a respiratory syncytial virus, a varicella zoster virus, a herpes simplex virus, and an enterovirus.
14. The method of claim 1 , wherein the microorganism is a bacterium.
15. The method of claim 14 , wherein the bacterium is Clostridium or Streptococcus.
16. The method of claim 1 , wherein the buffer comprises albumin.
17. The method of claim 16 , wherein the albumin is bovine serum albumin (BSA).
18. A method for identifying the presence or absence of a target nucleic acid from a microorganism in a biological sample obtained from a human, said method comprising:
(a) contacting the biological sample with a reaction mixture containing a DNA polymerase and a buffer to form a sample mixture under conditions suitable for amplification of the target nucleic acid from the biological sample without extracting the target nucleic acid from the biological sample;
(b) thermocycling the sample mixture from step (a) such that the target nucleic acid, if present, is amplified; and
(c) detecting the amplified target nucleic acid, if present, produced from step (b),
wherein nucleic acid in the sample is not extracted from the biological sample prior to amplification,
wherein the biological sample is selected from the group consisting of whole blood, plasma, serum, and CSF,
wherein the nucleic acid in the biological sample is not extracted from the biological sample prior to amplification;
wherein the biological sample is not diluted prior to contacting the biological sample with the reaction mixture;
wherein 20-30% of the total volume of the sample mixture following step (a) is the biological sample;
wherein the target nucleic acid is not present in a biological sample that does not contain the microorganism; and
wherein the reaction mixture comprises KCl, bovine serum albumin and a cationic surfactant.
19. The method of claim 18 , further comprising heating the sample prior to step (a) or step (b).
20. A method for identifying the presence or absence of a target nucleic acid from a microorganism in a biological sample obtained from a human, said method comprising:
(a) contacting the biological sample with a reaction mixture containing a DNA polymerase and a buffer to form a sample mixture under conditions suitable for amplification of the target nucleic acid from the biological sample without extracting the target nucleic acid from the biological sample;
(b) thermocycling the sample mixture from step (a) such that the target nucleic acid, if present, is amplified; and
(c) detecting the amplified target nucleic acid, if present, produced from step (b),
wherein the biological sample is a stool sample,
wherein the nucleic acid in the biological sample is not extracted from the biological sample prior to amplification;
wherein 20-30% of the total volume of the sample mixture following step (a) is the biological sample;
wherein the target nucleic acid is not present in a biological sample that does not contain the microorganism; and
wherein the reaction mixture contains a cationic surfactant.
21. The method of claim 20 , wherein the stool sample is prepared by swabbing a mixed stool specimen and mixing the swabbed stool specimen in a buffer to produce the stool sample.
22. The method of claim 20 , wherein the biological sample is heated prior to step (a) or step (b).
23. The method of claim 20 , wherein the reaction mixture comprises potassium chloride.
24. The method of claim 20 , wherein the reaction mixture comprises albumin.
25. The method of claim 20 , wherein the microorganism is a virus.
26. The method of claim 25 , wherein the virus is selected from the group consisting of an influenza virus, a respiratory syncytial virus, a varicella zoster virus, a herpes simplex virus, and an enterovirus.
27. The method of claim 20 , wherein the microorganism is a bacterium.
28. The method of claim 27 , wherein the bacterium is Clostridium or Streptococcus.