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@#Abstract: Objective To establish the duplex TaqMan RT-PCR method for detection of Entamoeba histolytica and Giardia lamblia in fecal samples. Methods Primer pairs and probes for Entamoeba histolytica and Giardia lamblia were designed and duplex TaqMan RT-PCR amplification system was constructed. PCR products were inserted into the pUC57 plasmid, and the lower limit of detection of the method was determined. Clinical stool samples were tested in order to evaluated the efficacy of the method. Results The detection limits of duplex TaqMan RT-PCR were 31.6 copies/μL for Entamoeba histolytica and 32 copies/μL for Giardia lamblia, respectively. Of the total of 212 clinical stool samples tested, all 3 samples with E. histolytica-positive patients by microscopy were positive by PCR, while 1 from 209 samples with E. histolytica-negative patients by microscopy were positive by PCR, and the remaining samples were negative. For Giardia lamblia, all 8 samples positive by microscopy were positive by PCR, and 1 from 204 sample with a microscopy-negative patient was positive by PCR, and the remaining samples were negative. The amplification product sequencing and blast analysis were used to confirm that the amplified sequence in the specimen of a patient with negative microscopy but positive PCR belongs to the targeted pathogen, supported by clinical symptoms and laboratory test results. PCR results for other diarrhea-causing pathogens were negative, indicating no cross-reactivity. Conclusions The dual TaqMan RT-PCR method developed in this study can not only detect microscopy-positive samples of Entamoeba histolytica and Giardia lamblia but also can detect samples that were missed by microscopy, with higher sensitivity than the microscopy method. Further, this detection method does not cross-react with other diarrhea-causing pathogens, including cross-react with other diarrhea-causing pathogens including Iodamoeba butschlii, Blastocystis hominis, Plesiomonas, Aeromonas, Salmonella, Shigella, Sphaerozoum fuscum, and Entamoeba hartmani, thus has a good specificity.
RESUMO
OBJECTIVE: To develop a PCR method for Entamoeba histolyticaï¼ E.histolytica) detection in fecal specimens, and to compare the performance of PCR to that of microscopy and ELISA. METHODS: Two pairs of self-designed primers and 2 pairs of primers from references based on small subunit ribosome RNA (SSU rRNA) fragment of E. histolytica standard strain were synthetized. DNA from E. histolytica reference strain were amilified by the conventional PCR using the 4 pairs of primers. 221 stool samples from diarrhea patients were collected and detected for E. histolytica by three methods: Entamoeba trophozoites and cysts detection by microscopy, E. histolytica-specific antigen detection using enzyme-linked immunosorbent assay (ELISA) kit ( E. HISTOLYTICA II), amplification of SSU rRNA fragment of E. histolytica by PCR method. Positive rate of three methods were compared by chi-square test, and Kappa test was applied to determine the concordance among the three methods. RESULTS: Specific fragments of E. histolytica were amplified by the PCR method we developed in this study. Positive rates of PCR, microscopy and ELISA were 2.26%, 0.90% and 9.50%, respectively. The positive rates of the three methods were significantly different ( χ 2 =23.34, P<0.01). The Kappa value of PCR and microscopy was 0.216, and that of PCR and ELISA method was -0.134, both of which showed a weak consistency. PCR results showed best consistency with clinical diagnosis. CONCLUSION: The PCR method we established in this study has a better performance in accuracy than microscopy and ELISA have in laboratory diagnosis of E. histolytica infection.