Summary auto-generated
This study demonstrates the use of polymerase chain reaction (PCR) to detect Mycobacterium leprae DNA in various clinical samples for leprosy diagnosis. The researchers developed an efficient method targeting an M. leprae-specific repetitive sequence, achieving detection sensitivity of 100 attograms (ag) of target DNA, approximately one-tenth of a bacterial genome. The PCR method showed high specificity when tested against seven other mycobacterial species and human DNA. Clinical samples including skin biopsies, blood, and lymph fluid were collected from 27 untreated leprosy patients representing different disease forms. After optimizing sample processing protocols using freezing-boiling cycles with Triton X-100 and addressing PCR inhibitors through NaOH pretreatment, 25 of 27 patients (93%) yielded positive results in at least one sample type. Biopsy samples were most reliable, while blood samples showed lower positivity (43-53%) with occasional non-specific amplification. The results were confirmed by Southern blot hybridization. The study indicates PCR is significantly more sensitive than traditional microscopic examination, detecting M. leprae in samples from paucibacillary patients where bacteria were undetectable by conventional methods.
Key findings
- PCR achieved 100 ag sensitivity for M. leprae detection, representing approximately one-tenth of a bacterial genome, showing extremely high sensitivity compared to previous reports
- 25 of 27 untreated leprosy patients (93%) tested positive for M. leprae DNA in at least one clinical sample type, with biopsy showing the best results
- The simple freeze-boiling method with Triton X-100 was more efficient for DNA extraction than enzymatic protocols, and NaOH pretreatment eliminated PCR inhibitors in blood samples
- PCR detected M. leprae in paucibacillary patients where microscopic examination found no bacteria, demonstrating superior diagnostic sensitivity
- The method showed complete specificity to M. leprae, producing no positive results with seven other mycobacterial species or human DNA
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Abstract
DNA of Mycobacterium leprae, obtained by a highly efficient nucleic acid extraction procedure, was used for standardisation of the amplification of an M. leprae-specific repetitive sequence by use of the polymerase chain reaction (PCR). With pure DNA, M. leprae-specific amplification was obtained with as low as 100 ag (1 ag = 10(-18) g) of target DNA, a quantity equal to about one-tenth of the bacterial genome. Optimal processing of different types of clinical samples such as biopsy material, blood and lymph fluid, from multibacillary leprosy patients, was studied. Simple freezing-boiling cycles in the presence of Triton X100, with some additional sample-specific modifications such as pre-treatment with NaOH to eliminate PCR inhibitors, was found to be sufficient to yield amplification of bacterial DNA in samples from paucibacillary patients. Clinical samples from 27 untreated leprosy patients, covering the various clinical forms of the disease, and with a bacterial index ranging from 5+ to 0, were collected and processed for PCR analysis. After hybridisation of the amplified material with a specific sequence, 25 of 27 patients analysed gave positive results for M. leprae in at least one of the samples. The potential of PCR for the diagnosis of leprosy is discussed.