Background In almost all diagnostic studies, stored samples are used. This is also the case in Chlamydia trachomatis research. The performance of diagnostic assays, such as nucleic acid amplification tests, is dependent on the preservation of C trachomatis DNA. However, the influence of different storage conditions on C trachomatis DNA has not been thoroughly explored yet. Therefore, we have studied the impact of temperature, type of medium and duration of storage on the preservation of C trachomatis DNA.
Methods Phosphate buffered saline (PBS), 2-sucrose-phosphate medium (2-SP), COBAS Amplicor medium and urine samples were spiked with C trachomatis serovar D elementary bodies and stored at room temperature, 4°C, −20°C and −80°C. DNA was isolated using the Qiagen DNA mini kit (Qiagen GmbH, Hilden, Germany). Samples were tested in triplicate with a TaqMan PCR at day 0, 1, 7, 14 and 30. Furthermore, clinical C trachomatis positive urine samples were collected and pooled, and stored and tested in triplicate, at the same temperatures and time intervals. This same procedure was executed with pooled C trachomatis positive swab samples.
Results C trachomatis was detected in all samples, irrespective of the different storage temperature conditions, different types of medium and the different durations of storage. Regarding storage time, the cycle threshold (ct) overall did not increase, in fact it tended to decrease within 30 days. If there was an increase in ct over time, this occurred in <10% of the experiments, it did not outreach three (corresponding to a decline in load of 1 log). This mainly occurred in the spiked COBAS samples which were frozen.
Conclusions All samples tested positive for C trachomatis in our experiments, with on average no decrease in cycle threshold over time. We can therefore conclude that PBS, 2-SP, COBAS Amplicor medium and urine are all excellent media to preserve C trachomatis DNA for a longer period of time, independent of storage temperature.
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