The impact of sample storage on molecular-based detection of Mycoplasma genitalium

Abstract

Aims: Mycoplasma genitalium causes a common, sexually transmitted bacterial infection. This study assessed the detection of M. genitalium in stored urine samples to understand the impact of sample storage on M. genitalium detection. Methods: Aliquots of M. genitalium-positive urine (n = 20 patients) were stored at either room temperature (22°C) or 4°C, without a preservative. At weekly intervals, samples were tested using the commercial test ResistancePlus MG® (SpeeDx®, Australia). We report the analysis at 1 week, an acceptable collection-to-test turnaround time, with further analysis over 5 weeks to illustrate degradation trends. Results: After storing at 4°C, the proportion of specimens that remained positive for M. genitalium was 100% after 1 week and 95% after 4 weeks. Storage at 22°C led to more rapid decline in detection in the first 4 weeks, with 95% detected after 1 week and 85% at 2 weeks onwards. At 5 weeks, samples stored at both temperatures had an 85% M. genitalium detection rate, with increase in crossing points (Cq) of 0·72 (95% confidence interval (CI) 0·01–1·43; P-trend = 0·027) at 4°C, and 1·75 ((95% CI 0·79–2·71), P-trend <0·001) at 22°C. Conclusions: Urine samples stored without preservative, and unfrozen, retained high M. genitalium detection levels over the short term (up to 5 weeks). To minimize degradation, storing at 4°C is recommended. Significance and Impact of the Study: There is little known about the stability of clinical samples for M. genitalium detection. This study found that a high proportion (85–100%) of samples are still suitable for M. genitalium detection after storage for up to 5 weeks.