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Journal of Clinical Microbiology, October 1998, p. 2877-2881, Vol. 36, No. 10
Liverpool School of Tropical Medicine,
Liverpool L3 5QA, United Kingdom,1 and
Health Net International, University Town, Peshawar,
Pakistan2
Received 21 January 1998/Returned for modification 27 April
1998/Accepted 1 July 1998
A nested PCR was developed to amplify the variable region of the
kinetoplast minicircles of all Leishmania species which
infect mammals. Each Leishmania parasite contains
approximately 10,000 kinetoplast DNA minicircles, which are unequally
distributed among approximately 10 minicircle classes. The PCR primers
were designed to bind within the 120-bp conserved region which is
common to all minicircle classes; the remaining approximately 600 bp of each minicircle is highly conserved within each minicircle class but
highly divergent between classes. The nested PCR generated a strong
signal from a minimum of 0.1 fg of Leishmania DNA.
Restriction digests of the amplicons from the highest dilutions
suggested that minicircles from only a limited number of minicircle
classes had acted as template in the reaction. One PCR product was
directly sequenced and found to be derived from only one minicircle
class. Since the primers amplify all minicircle classes, this indicated that as little as 1/10 of one Leishmania parasite was
present in the PCR template. This demonstrated that the nested PCR
achieved very nearly the maximum theoretically possible sensitivity and is therefore a potentially useful method for diagnosis. The nested PCR
was tested for sensitivity on 20 samples from patients from the
Timargara refugee camp, Pakistan. Samples were collected by scraping
out a small amount of tissue with a scalpel from an incision at the
edge of the lesion; the tissue was smeared on one microscope slide and
placed in a tube of 4 M guanidine thiocyanate, in which the sample was
stable for at least 1 month. DNA for PCR was prepared by being bound to
silica in the presence of 6 M guanidine thiocyanate; washed in
guanidine thiocyanate, ethanol, and acetone; and eluted with 10 mM
Tris-HCl. PCR products of the size expected for Leishmania tropica were obtained from 15 of the 20 samples in at least one of three replicate reactions. The negative samples were from lesions that had been treated with glucantime or were over 6 months old, in
which parasites are frequently scanty. This test is now in routine use
for the detection and identification of Leishmania parasites in our clinical laboratory. Fingerprints produced by restriction digests of the PCR products were defined as complex or
simple. There were no reproducible differences between the complex
restriction patterns of the kinetoplast DNA of any of the parasites
from Timargara camp with HaeIII and HpaII. The
simple fingerprints were very variable and were interpreted as being the product of PCR on a limited subset of minicircle classes, and
consequently, it was thought that the variation was determined by the
particular minicircle classes that had been represented in the
template. The homogeneity of the complex fingerprints suggests that the
present epidemic of cutaneous leishmaniasis in Timargara camp may be
due to the spread of a single clone of L. tropica.
0095-1137/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
A Nested-PCR-Based Schizodeme Method for
Identifying Leishmania Kinetoplast Minicircle Classes
Directly from Clinical Samples and Its Application to the Study
of the Epidemiology of Leishmania tropica in
Pakistan
*
Corresponding author. Mailing address: Liverpool School
of Tropical Medicine, Pembroke Place, Liverpool L3 5QA, United Kingdom. Phone: 151-708-9393. Fax: 151-708-8733. E-mail:
harry{at}liv.ac.uk.
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