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Journal of Clinical Microbiology, Dec 1996, 3072-3074, Vol 34, No. 12
RP Verkooyen, A Luijendijk, WM Huisman, WH Goessens, JA Kluytmans, JH van Rijsoort-Vos and HA Verbrugh
To determine that susceptibility of AMPLICOR Chlamydia trachomatis PCR to
inhibitory factors possibly present in cervical specimens, we obtained
cervical specimens from 200 gynecology patients attending our outpatient
clinic. The prevalence of C. trachomatis infection was 4.1%, as determined
by cell culture. All AMPLICOR specimens were tested in one procedure as
described by the manufacturer, and after the specimen was spiked with C.
trachomatis, several other pretreatment protocols were used. Complete
inhibition of the PCR was observed in 38 (19%) cervical specimens. Heat
treatment at 95 degrees C, freeze-thawing, or 10-fold dilution of the
samples reduced the initial inhibition to 9, 16, or 9%, respectively. A
combination of heat treatment and 10-fold dilution reduced the inhibition
to 4% of the samples. A second specimen type (swabs inoculated in 0.2 M
sucrose phosphate buffer [2SP]) was also evaluated. A 10-fold dilution of
the spiked 2SP specimen resulted in an inhibition rate of 6%, which was
comparable to that obtained by centrifugation of the 2SP specimen prior to
processing. Furthermore, it was shown that the inhibition was not
correlated with blood contamination. Processing the specimens on the day of
collection or the day after resulted in a higher inhibition rate than did
delayed processing (27.6 versus 15.5%, respectively). An inverse
correlation was found between the concentration of C. trachomatis added to
the sample and the rate of inhibition observed. The inhibition was partly
correlated with the pH of the cervical mucosa. Decreased inhibition was
found at pH values of > or = 7.5. The effects of blood, pH, and delay in
processing were all evaluated by using the AMPLICOR specimen. We conclude
that the susceptibility of AMPLICOR C. trachomatis PCR to inhibiting
factors in cervical specimens can be significantly reduced if the
pretreatment procedure includes heat treatment or the use of 2SP transport
medium. Also, a 10-fold dilution of the clinical specimen followed by heat
treatment will largely prevent the inhibition of this PCR.
Copyright © 1996 by the American Society for Microbiology. All rights reserved.
Detection of PCR inhibitors in cervical specimens by using the AMPLICOR Chlamydia trachomatis assay
Department of Clinical Microbiology, Academic Hospital Dijkzigt, Rotterdam, The Netherlands. Verkooyen@kmic.fgg.eur.nl
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