An optimal processing method for recovery of tuberculosis in the tongue swab using the Mycobacterium growth indicator tube method

Effective diagnosis for pulmonary tuberculosis (TB) remains challenging, especially in the face of no symptom and no sputum. A tongue swab has become a promising alternative to sputum collection. We aimed to optimize the tongue swab processing method for culture and evaluate the diagnostic value of tongue swab culture. We compared the contamination rate and the growth of bacilli in Mycobacterium Growth Indicator Tube (MGIT) after different digestion times using tongue swab samples spiked with Mycobacterium bovis BCG strain. After enrolling 119 individuals with symptoms suggestive of active TB, the predictive potential of optimized tongue swab culture method for TB was compared with other sputum testing approaches. We established an optimized method for tongue swab MGIT culture through 4% NaOH digestion for 10 min. Compared with sputum culture, tongue swab culture exhibited diagnostic accuracy with a sensitivity of 81.43% (95% confidence interval [CI] 72.80%–91.06%) and a specificity of 81.63% (95% CI 71.60%–93.47%). When utilizing sputum culture and sputum Xpert Ultra as the combinational reference standard, the sensitivity and specificity of tongue swab culture were 75.29% (95% CI 64.90%–84.00%) and 94.12% (95% CI 80.00%–99.60%). Furthermore, the positive detection rates of tongue swab culture varied when stratified by results of sputum smear and sputum Xpert Ultra, which depended on bacterial loads in specimens. This study constructed a well-optimized tongue swab MGIT culture method with great diagnostic value, thus providing a non-invasive and highly accurate strategy for non-sputum pulmonary TB patients. IMPORTANCE Tuberculosis (TB), caused by Mycobacterium tuberculosis , remains the leading global cause of death from a single infectious pathogen. It is noteworthy that nearly half of TB patients could not timely receive accurate diagnosis and effective treatment, particularly when confronted with no clinical symptom and no sputum production. Tongue swab tests have become a promising strategy for active TB case finding because of their non-invasive specimen collection and high accuracy. However, effective methods for bacilli release from tongue swab samples still remained warranted. This study optimized the tongue swab processing method for Mycobacterium Growth Indicator Tube culture to ensure better recovery of bacilli and a lower contamination rate. Under this optimized method, tongue swab culture exhibited diagnostic accuracy with the sensitivity of 81.43% and the specificity of 81.63% in comparison with sputum culture. This advancement supports the timely and efficient TB diagnosis based on non-invasive tongue swab specimens.