CN111690760A

CN111690760A - Method for accurately detecting cryptococcus neoformans

Info

Publication number: CN111690760A
Application number: CN202010159851.6A
Authority: CN
Inventors: 不公告发明人
Original assignee: Beijing Shijitan Hospital
Current assignee: Beijing Shijitan Hospital
Priority date: 2020-03-10
Filing date: 2020-03-10
Publication date: 2020-09-22
Also published as: CN112359126A; CN113999933A

Abstract

The invention belongs to the technical field of fungal etiology detection, and discloses a method for accurately detecting cryptococcus neoformans, which comprises the following steps: step 1) selecting a sample to be detected; step 2), extracting DNA; step 3) preparing a real-time fluorescent PCR reaction system; and 4) performing fluorescent PCR amplification. The detection method can quickly and accurately detect the cryptococcus neoformans.

Description

Method for accurately detecting cryptococcus neoformans

Technical Field

The invention belongs to the technical field of fungal etiology detection, and particularly relates to a method for accurately detecting cryptococcus neoformans.

Background

Cryptococcus is a pathogen that can cause cryptococcosis. The medium is generally dry pigeon feces, and reports are rarely transmitted from person to person. No specific medicine exists, and symptomatic treatment is generally carried out. Cryptococcosis is a pulmonary or disseminated infectious disease caused by cryptococci, mainly resulting in pneumonia and meningitis, and also in infections of the skin, bones or internal organs. Clinically, the diagnosis is carried out by combining the clinical manifestations and the microscopic examination results, and then the diagnosis is confirmed by fungus culture or tissue staining. The clinical therapeutic drugs comprise amphotericin B, triazole antifungal drugs and flucytosine。

Cryptococcus neoformans (Cryptococcus neoformans) belongs to the genus Cryptococcus. New hidden ballThe fungus is a yeast type fungus, a layer of pachymenia capsule consisting of polysaccharide is coated outside the fungus, and the fungus is generally stained by a staining method and is difficult to find, so the fungus is called cryptococcus. Cryptococcus neoformans is widely distributed in nature and is most common in pigeon feces. When the immunity of people is low, the people are infected by inhaling air polluted by pigeon feces, and the subacute or chronic infection of the lung and the brain is mainly caused. The lung can be used as primary focus, and spread to brain infection to cause chronic inflammation and abscess. Cryptococcus neoformans and its variants are pathogenic and mainly attack the central nervous system. The cryptococcus neoformans is an environmental saprophytic bacterium which widely lives in soil and pigeon feces. Normal people are often in an environment contaminated by cryptococcus neoformans, but the number of patients is very small. When the resistance of the body is reduced, it is easy to invade the body to cause diseases. Due to the use of tumor and chemotherapy drugs, the prevalence of AIDS, the use of immunosuppressive drugs after transplantation and other reasons, the incidence of cryptococcus neoformans is increasing, and the cryptococcus neoformans becomes one of the common complications of AIDS patients abroad and is also an important cause of death of the patients. The incidence of cryptococcus neoformans is also on the trend of increasing year by year in China.

Cryptococcus neoformans presents round yeast-like cells both in tissue and under artificial culture conditions, and has a thicker layer of glial-like capsule, called thick capsule, around its periphery. The diameter of the thallus is 4-20um, the capsule width is 3-5um, and one or more reflective particles are arranged in the thallus and are in a core structure. Some of the cells were germinated. Clinical and environmental isolates strains are typically yeast phase grown in asexual phase. Kwon-Chung discovered the sexual stage of the new variety in 1976, where hyphal formation was visible. Culture induction experiments are the main method for observing the sexual stage of cryptococcus. The nonpathogenic cryptococcus is acapsular. Cryptococcus neoformans can grow on a sand protection culture medium and a blood agar culture medium at 25 ℃ and 37 ℃, and non-pathogenic cryptococcus can not grow at 37 ℃. After culturing for several days, yeast type colonies are formed, the surface is sticky, the color is milky initially, and then the color is changed into orange. The bacteria can decompose urea, and can be distinguished from Candida.

Since the cryptococcus infection is easy to misdiagnose only according to clinical manifestations, the etiology detection is the main basis for diagnosis and treatment. The main detection methods of cryptococcus in the present stage have limitations, wherein the morphology of the cryptococcus can be preliminarily observed by cerebrospinal fluid and ink staining, but the sensitivity is low; the cryptococcus antigen reagent can quickly detect cryptococcus antigens, but cannot distinguish cryptococcus neoformans from cryptococcus gatherens; cryptococcus culture identification is also difficult to identify cryptococcus neoformans and cryptococcus gatherens. The literature "multiple polymerase chain reaction identification of cryptococcus neoformans grubbs, new variants and cryptococcus gatherensis, von xiagbo, journal of china dermatology, 2012" establishes a multiple Polymerase Chain Reaction (PCR) based on ribosomal intergenic spacer region (IGS) for rapidly identifying the new variants of cryptococcus neoformans, grubbs and cryptococcus gatherens, the method needs to design primers for each bacterium, the method is complicated, and the reaction is not fast enough; the patent CN2017101725670 discloses a target gene, a primer, a probe and a kit for detecting and identifying cryptococcus, belonging to the field of medical mycology. According to the target gene of cryptococcus, the primer sequence for detecting cryptococcus gene is designed to be shown in SEQ ID No.3 and SEQ ID No.4 and/or SEQ ID No.6 and SEQ ID No.7, wherein SEQ ID No.3 and SEQ ID No.4 correspond to cryptococcus neoformans, SEQ ID No.6 and SEQ ID No.7 correspond to cryptococcus gatherens, and the method can be used for specifically detecting two cryptococcus neoformans and cryptococcus gatherens in the same system.

Therefore, new techniques and methods are needed to properly detect and identify cryptococcus neoformans.

Disclosure of Invention

The invention provides a method for accurately detecting cryptococcus neoformans, aiming at overcoming the defects of complicated operation, low sensitivity, high error rate and the like of the traditional cryptococcus neoformans detection.

In order to achieve the above object, the present invention adopts the following technical solutions.

A method for accurately detecting cryptococcus neoformans, characterized in that the method comprises the following steps

Step 1) selecting a sample to be detected;

step 2), extracting DNA;

step 3) preparing a real-time fluorescent PCR reaction system;

and 4) performing fluorescent PCR amplification.

Further, the fluorescent PCR reaction system comprises a primer and a probe.

Further, the primer consists of SEQ ID NO: 1 and the sequence shown in SEQ ID NO: 2 is shown in the specification; the probe is used for detecting cryptococcus neoformans.

Preferably, the probe is FAM 5'-TCGGATGATGATCCTCAGACCGACC-3' BHQ 1.

More preferably, the fluorescent PCR reaction system is:

Reagents	Volume (ul)
		10×ExTag Buffer	2.5ul
Original DNA	1ul
		dNTP	2ul
probe (10nmol/ml)	0.5ul
		Upstream primer (10nmol/ml)	0.5ul
Downstream primer (10nmol/ml)	0.5ul
		TaKara ExTag enzyme (5U/ul)	0.25ul
Ultrapure water	17.25ul

On the other hand, the invention also claims a real-time fluorescence PCR reaction system for simultaneously detecting cryptococcus neoformans and cryptococcus gatherens, wherein the real-time fluorescence PCR reaction system is as follows:

Reagents	Volume (ul)
		10×ExTag Buffer	2.5ul
Original DNA	1ul
		dNTP	2ul
probe 1(10nmol/ml)	0.5ul
		Probe 2(10nmol/ml)	0.5ul
Upstream primer (10nmol/ml)	0.5ul
		Downstream primer (10nmol/ml)	0.5ul
TaKara ExTag enzyme (5U/ul)	0.25ul
		Ultrapure water	17.25ul

Further, the primer consists of SEQ ID NO: 1 and the sequence shown in SEQ ID NO: 2 is shown in the specification; the probe 1 is used for detecting cryptococcus neoformans, and the probe 2 is used for detecting cryptococcus gatherens.

More preferably, the probe 1 is FAM 5'-TCGGATGATGATCCTCAGACCGACC-3' BHQ1, and the probe 2 is HEX 5'-TCGGATGATGATCCTGAGACCGACG-3' BHQ 1.

Compared with the prior art, the invention mainly has the following advantages that:

according to the invention, by comparing the genomic sequence difference of logarithmic ten cryptococcus neoformans and cryptococcus gatherensis through a genomics method, a conserved sequence and a difference sequence are selected, and a primer and a probe are designed, so that the primers have the characteristics of high sensitivity and strong specificity in the process of detecting and identifying the cryptococcus neoformans and the cryptococcus gatherens. In addition, the kit has the characteristics of simple operation, short detection time and strong applicability when the kit is used for detecting cryptococcus neoformans and cryptococcus gatherensis, the raw materials required for detecting the cryptococcus neoformans and the cryptococcus gatherens are placed in the same reaction system, the cryptococcus neoformans and the cryptococcus gatherens can be simultaneously detected and identified, the types of pathogenic bacteria are determined, the rapid and accurate clinical early diagnosis is facilitated, the drug abuse is reduced, and the precious time is won for the disease treatment.

Drawings

FIG. 1: amplification curves of cryptococcus neoformans at different concentrations of DNA (50ng, 5ng, 0.5ng, 0.05 ng);

FIG. 2: amplification curves of Cryptococcus gatherens at different concentrations of DNA (50ng, 5ng, 0.5ng, 0.05 ng);

FIG. 3: specific amplification curves of the neocryptococcus repeat three reactions;

FIG. 4: a specific amplification curve of three repeated reactions of Cryptococcus gatherensis;

FIG. 5: detecting Escherichia coli, Staphylococcus aureus, Streptococcus pneumoniae, Candida albicans, Candida glabrata, Saccharomyces cerevisiae, and Trichosporon assamici by parallel test according to a specific amplification curve of cryptococcus neoformans;

FIG. 6: the specific amplification curve of the Cryptococcus gatherensis, and a parallel test are used for detecting Escherichia coli, staphylococcus aureus, streptococcus pneumoniae, Candida albicans, Candida glabrata, Saccharomyces cerevisiae and Trichosporon assamici.

Detailed Description

Those skilled in the art can modify the process parameters appropriately to achieve the desired results with reference to the disclosure herein. It is expressly intended that all such similar substitutes and modifications which would be obvious to one skilled in the art are deemed to be included in the invention. While the products and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations and modifications, or appropriate alterations and combinations, of the products and methods described herein may be made and utilized without departing from the spirit, scope, and spirit of the invention. For a further understanding of the present invention, reference will now be made in detail to the following examples.

Example 1

Target gene, primer, probe and kit for detecting and identifying cryptococcus neoformans and cryptococcus gatherer

Dozens of genome sequences of cryptococcus neoformans and cryptococcus gatherensis are obtained by a high-throughput sequencing technology, a CAP59 sequence is selected as a target gene by comparing the difference of the genomic sequences of the cryptococcus gatherens with the dozens of cryptococcus logens through a genomics method, the gene segment is relatively conserved in two cryptococcus species, and the difference exists between the cryptococcus neoformans and the cryptococcus gatherens. The nucleotide sequence for detecting the target genes of cryptococcus neoformans and cryptococcus gatherens is shown as SEQ ID NO: 5 and SEQ ID NO: and 6.

And designing a primer by using primer software according to the sequence information of the selected target gene. Through repeated contrast analysis, a real-time fluorescent PCR detection primer and a probe which can be used for detecting and identifying cryptococcus neoformans and cryptococcus gatherens are finally designed; the specific oligonucleotide primer sequence for specifically detecting and identifying cryptococcus neoformans and cryptococcus gatherens is shown as SEQ ID NO: 1 and SEQ ID NO: 2, the primer pair is a universal primer for detecting cryptococcus neoformans and cryptococcus gatherens. The sequence of the probe for detecting cryptococcus neoformans is shown as SEQ ID NO: 3, the sequence of the probe for detecting the cryptococcus gatherer is shown as SEQ ID NO: 4, the 3 'end of the probe is connected with a fluorescence quenching group, and the 5' end of the probe is connected with a fluorescence reporter group.

The primer sequence is shown as SEQ ID NO: 1, and the following components: 5'-GTATTCGATACGGTGGTTGAACAGA-3' (Tm =62.4 ℃) and SEQ ID NO: 2, as shown in the figure: 5'-GGTTCCAACGACCAGACAAAGG-3' (Tm =63.2 ℃); the probe sequences are respectively SEQ ID NO: 3, showing: FAM 5'-TCGGATGATGATCCTCAGACCGACC-3' BHQ1 was used to detect cryptococcus neoformans (Tm =70.2 ℃), and SEQ ID NO: 4, and (2) is as follows: HEX 5'-TCGGATGATGATCCTGAGACCGACG-3' BHQ1 was used to detect cryptococcus gatherensis (Tm =71.1 ℃).

The primer specifically recognizes the sequence shown by SEQ ID NO: 5 and seq id NO: 6. The kit for detecting cryptococcus can be used for simultaneously detecting cryptococcus neoformans and cryptococcus gatherensis, comprises a pair of universal primers, probes for detecting the cryptococcus neoformans and the cryptococcus gatherens respectively, and also comprises buffer solution, dNTPs, MgCl2, Taq DNA polymerase and the like.

Firstly, test materials: the experimental materials are shown in Table 1

Second, main reagent and instrument

The DNA extraction adopts a yeast gene extraction kit of Tiangen company; the synthesis of primers and probes was performed by bioengineering, Inc.; DNA polymerase and dNTPs were purchased from Takara; fluorescent quantitative PCR instruments were purchased from Roche.

Third, Experimental methods

DNA extraction and concentration determination: DNA was extracted according to the DNA extraction kit instructions, and the OD260/OD280 ratio was determined by measuring the DNA content in the sample using a spectrophotometer.

The real-time fluorescent PCR reaction system is shown in Table 1. The amplification conditions were: pre-denaturation at 95 ℃ for 10 min; amplification results were obtained at 95 ℃ for 10s, 60 ℃ for 60s, and 45 cycles.

TABLE 1 real-time fluorescent PCR amplification reaction System (25ul)

Reagents	Volume (ul)
		10×ExTag Buffer	2.5ul
Original DNA	1ul
		dNTP	2ul
FAM Probe(10nmol/ml)	0.5ul
		HEX Probe(10nmol/ml)	0.5ul
Upper primer(10nmol/ml)	0.5ul
		Lower primer(10nmol/ml)	0.5ul
TaKara ExTag enzyme (5U/ul)	0.25ul
		Ultrapure water	17.25ul

Fourthly, analyzing and judging the amplification result

In a real-time fluorescence PCR reaction system of the sample, FAM fluorescence has fluorescence logarithm increase, and when the Ct value is less than or equal to 30.0, the detection result of cryptococcus neoformans is positive; and if the HEX fluorescence has fluorescence logarithm increase and the Ct value is less than or equal to 30.0 in the real-time fluorescence PCR reaction system of the sample, the detection result of the Cryptococcus gatherensis is positive.

Fifth, sensitivity, specificity and reproducibility assays

Sensitivity detection: the extracted template DNA of cryptococcus neoformans and cryptococcus gatherens was diluted to the following concentrations: 50 ng/ul, 5 ng/ul, 0.5 ng/ul and 0.05 ng/ul, and the lowest detectable concentration of cryptococcus neoformans and cryptococcus gatherens is obtained by detecting through a fluorescence quantitative PCR method, as shown in figure 1-2, the lowest detectable concentration of cryptococcus neoformans and cryptococcus gatherens is 0.05 ng/ul, and the sensitivity is high.

And (3) repeatability detection: the cryptococcus neoformans and cryptococcus gatherens were respectively tested repeatedly, as shown in fig. 3-4, the results of the respective three reactions were consistent, and the repeatability was excellent.

And (3) specific detection: the designed primers are used for respectively carrying out specific amplification on cryptococcus neoformans and cryptococcus gatherer, and the designed probes can identify the cryptococcus neoformans and the cryptococcus gatherer. Parallel tests were performed to detect Escherichia coli, Staphylococcus aureus, Streptococcus pneumoniae, Candida albicans, Candida glabrata, Saccharomyces cerevisiae, and Trichosporon axacuminatum, as shown in FIGS. 5-6, and the results were all negative without non-specific amplification curve.

The real-time fluorescence PCR detection method for identifying the template through specific hybridization of the primer, the probe and the template has high specificity and low false positive. The fluorescence after PCR amplification is detected, the reaction signal is amplified, and the sensitivity is greatly improved. The method skillfully utilizes the DNA high-efficiency amplification of the PCR technology, the specificity of nucleic acid hybridization and the rapidness and the sensitivity of the fluorescence detection technology, has the advantages of simple operation, time and labor saving, reliable and accurate result, high sensitivity and the like, and is used for treating cryptococcus neoformans and cryptococcus gatus

The lowest limit detectable concentration is 0.05 ng/ul, the two cryptococcus infections can be accurately distinguished, and the sensitivity is far superior to that of the existing kit. The invention is used for clinical treatment, can be beneficial to doctors to quickly distinguish and diagnose cryptococcus neoformans and cryptococcus gatherens infection diseases in early stage, improves treatment schemes and reduces abuse of drugs. The technical scheme of the invention is convenient to operate, easy to popularize and has better application prospect.

Although the present invention has been described in detail with respect to the general description and the specific embodiments, it will be apparent to those skilled in the art that modifications and improvements can be made based on the present invention. Accordingly, it is intended that all such modifications and variations as fall within the true spirit of this invention be included within the scope thereof.

Sequence listing

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Claims

1. A method for accurately detecting cryptococcus neoformans, characterized in that the method comprises the following steps

Step 1) selecting a sample to be detected;

step 2), extracting DNA;

step 3) preparing a real-time fluorescent PCR reaction system;

and 4) performing fluorescent PCR amplification.

2. The method of claim 1, wherein the fluorescent PCR reaction system comprises primers and probes.

3. The method of claim 2, wherein the primer consists of SEQ ID NO: 1 and the sequence shown in SEQ ID NO: 2 is shown in the specification; the probe is used for detecting cryptococcus neoformans.

4. The method of claim 3, wherein the probe is FAM 5'-TCGGATGATGATCCTCAGACCGACC-3' BHQ 1.

5. The method of claim 3, wherein the fluorescent PCR reaction system is:

。

6. A real-time fluorescence PCR reaction system for simultaneously detecting cryptococcus neoformans and cryptococcus gatherens is characterized in that the real-time fluorescence PCR reaction system is as follows:

。

7. The real-time fluorescent PCR reaction system for simultaneously detecting cryptococcus neoformans and cryptococcus gatherens according to claim 6, wherein the primers consist of the sequences shown in SEQ ID NO: 1 and the sequence shown in SEQ ID NO: 2 is shown in the specification; the probe 1 is used for detecting cryptococcus neoformans, and the probe 2 is used for detecting cryptococcus gatherens.

8. The real-time fluorescent PCR reaction system for simultaneously detecting cryptococcus neoformans and cryptococcus gatherer according to claim 7, wherein the probe 1 is FAM 5'-TCGGATGATGATCCTCAGACCGACC-3' BHQ1, and the probe 2 is HEX 5'-TCGGATGATGATCCTGAGACCGACG-3' BHQ 1.