Mycoplasma pneumoniae detection in throat swabs and bronchoalveolar lavage fluid in children with mycoplasmal pneumonia by real-time PCR and culture

ObjectiveTo understand the performance of clinical nucleic acid detection, bacteria load detection and laboratory isolation/culture of Mycoplasma pneumoniae (MP) in throat swab and bronchoalveolar lavage fluid (BALF) samples and evaluate the significance of using throat swab in the nucleic acid detection and isolation/culture and whether the nucleic acid load of MP in throat swabs in children with MP pneumonia could predict the nucleic acid load of MP in BALF.

MethodsTwenty-nine hospitalized children with MP pneumonia were enrolled, and throat swabs and BALF samples were collected from them, simultaneously. The quality of the specimens and nucleic acid extraction were controlled by human β-globin internal reference gene. Qualified specimens were used for quantitative detection of MP with real-time PCR, and the nucleic acid load was calculated. At the same time, culture was performed for all the specimens, and positive culture rate and the bacteria contamination rate of the two kinds of specimens were compared.

ResultsThe positive rate of β-globin reference gene detection in all the specimens was 100%. The positive rate of real-time PCR detection in throat swabs and BALF samples were all 86.2% (25/29), and the quantitative range of MP nucleic acid was 3.2×10² copies/ml−1.8×10⁷ copies/ml in the throat swabs and 6.8×10² copies/ml–5.4×10⁸ copies/ml in BALF samples. The consistent rate of the detection results of two kinds of specimens was 93.1% (27/29). Ranking the MP load in BALF samples showed an increase trend, but no similar trend was found for positive throat swabs. The positive rate and contamination rate of throat swabs were 51.7% (15/29) and 51.7% (15/29), and these of BALF samples were 65.5% (19/29) and 6.9% (2/29), respectively.

ConclusionThroat swab can be used as qualitative test specimen for MP real-time PCR, but it is not suitable for quantitative study, indicating that there was no significant correlation in MP load between throat swab and BALF. Compared with throat swab specimen, BALF has a higher positive culture rate and lower contamination rate, which makes it more suitable for MP isolation research.