Objective To detect traces of microRNAs (miRNAs) in plasma and assess the expression stability of two common reference genes by stem-loop and poly A polymerase (PAP) real-time quantitative polymerase chain reaction (PCR) method, as miRNAs are the new bio-markers of tumor diagnosis and molecular targeted therapy, and its quantitative research is very important. Methods We extracted miRNAs from plasma of adult Sprague Dawley (SD) rats’ plasma, and detected the expressions of rno-miR-200b-3p and rno-miR-126-3p with stem-loop and PAP real-time PCR quantitative method, with rno-miR-103a-3p and U6 as internal controls. All the results were evaluated by 2△Ct method. Results Compared with PAP method, the stem-loop method reduced Ct value by 2-4 cycles and improved sensitivity by 10 times. In PAP method, the melting curve showed two peaks, a main peak and a small non-specific peak. Yet the melting curve of stem-loop method demonstrated a single specific peak. Furthermore, we validated the stability of internal references in the two real time PCR methods. U6 presented a more stable Ct value than rno-miR-103 in adult SD rats’ plasma samples. Conclusions Stem-loop real-time PCR is recommended as a major way to detect some samples with a low concentration of miRNAs, owing to its high accuracy and sensitivity. However, if a large number of tissue samples is going to be detected, PAP real-time PCR is more suitable and convenient than stem-loop method. U6 is more stable and repeatable than rno-miR-103a-3p as the reference gene to evaluate the semi-quantitative consequence of miRNAs.
ObjectiveTo establish a method that can eliminate the pollution of endogenous nucleic acid in the real-time quantitative polymerase chain reaction (PCR) reaction system, which can be used to reduce or eliminate the false positive rate of real-time PCR assay in detection of postoperative intracranial bacteria infection.MethodsAt first, eliminated the pollution of endogenous nucleic acid in the real-time PCR reaction system. Then, with mixed bacteria DNA as a template, multiple PCR was used to specifically identify the gram-negative bacteria. Meanwhile, evaluated the text line and sensitivity of the multiple PCR after eliminating pollution in detecting the DNA of the mixed bacteria.ResultsThe method established could quickly eliminate the pollution of endogenous nucleic acid in the real-time PCR reaction system, and it didn’t affect the Taq enzyme activity and the amplification efficiency in PCR system, with the minimum detection limit of 102 CFU/mL (Staphylococcus aureus and Pseudomonas aeruginosa), which was the same to the culture method. The enzyme cutting method had no significant effect on the activity and amplification efficiency of the enzyme in PCR system, It had no effect on PCR reaction system and primer specificity (Ct=32, ΔRn=200). However, the filtration method significantly reduced the PCR amplification efficiency (Ct=32, ΔRn=150).ConclusionsThis method can easily and rapidly eliminate the pollution of endogenous nucleic acid in the real-time PCR reaction system, and greatly reduce the false positive of PCR detection. It is able to timely and accurately diagnose the intracranial bacteria infection, which is significant for clinical testing.