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

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.

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.

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.

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.

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.