Department of Pathogen Molecular Biology, Faculty of Infectious & Tropical Diseases, LSHTM, Keppel St., London WC1E 7HT, United Kingdom.
J Clin Microbiol. 2010 Dec;48(12):4512-8. doi: 10.1128/JCM.01683-10. Epub 2010 Oct 20.
The occurrence of mixed infections of Mycobacterium tuberculosis is no longer disputed. However, their frequency, and the impact they may have on our understanding of tuberculosis (TB) pathogenesis and epidemiology, remains undetermined. Most previous studies of frequency applied genotyping techniques to cultured M. tuberculosis isolates and found mixed infections to be rare. PCR-based techniques may be more sensitive for detecting multiple M. tuberculosis strains and can be applied to sputum. To date, one study in South Africa has used a PCR approach and suggested that mixed infection could be common. We investigated mixed infections in northern Malawi using two lineage-specific PCR assays targeting the Latin American-Mediterranean (LAM) and Beijing lineages. Compared with spoligotyping, the specificity and sensitivity of both assays was 100%. From 160 culture-positive sputa, mixed LAM and non-LAM strains were detected in 4 sputa belonging to 2 (2.8%) patients. Both patients were HIV positive, with no history of TB. Cultured isolates from both patients showed only LAM by PCR and spoligotyping. In a set of 377 cultured isolates, 4 were mixed LAM and non-LAM. Only one showed evidence of more than one M. tuberculosis strain using IS6110-based restriction fragment length polymorphism (IS6110-RFLP) and spoligotyping analyses. Corresponding sputa for the 4 isolates were unavailable. Mixed Beijing and non-Beijing strains were not detected in this study. Mixed infections appear to be rare in our setting and are unlikely to affect findings based on DNA fingerprinting data. Molecular methods, which avoid the selective nature of culture and target distinct strains, are well suited to detection of mixed infections.
结核分枝杆菌混合感染的发生已不再有争议。然而，其频率及其对我们理解结核病（TB）发病机制和流行病学的影响仍未确定。以前大多数关于频率的研究都应用基因分型技术对培养的结核分枝杆菌分离株进行了研究，发现混合感染很少见。基于 PCR 的技术可能更敏感地检测多种结核分枝杆菌株，并可应用于痰液。迄今为止，南非的一项研究使用了 PCR 方法，表明混合感染可能很常见。我们使用针对拉丁美洲-地中海（LAM）和北京谱系的两种谱系特异性 PCR 检测方法在马拉维北部调查了混合感染。与 spoligotyping 相比，两种检测方法的特异性和敏感性均为 100％。从 160 份培养阳性的痰液中，在属于 2 名（2.8％）患者的 4 份痰液中检测到混合 LAM 和非 LAM 菌株。这两名患者均为 HIV 阳性，无 TB 病史。来自两名患者的培养分离物通过 PCR 和 spoligotyping 仅显示 LAM。在 377 份培养分离物中，有 4 份是混合的 LAM 和非 LAM。只有一个使用基于 IS6110 的限制性片段长度多态性（IS6110-RFLP）和 spoligotyping 分析显示有超过一种结核分枝杆菌株的证据。无法获得这 4 株的相应痰液。在本研究中未检测到混合的北京和非北京菌株。混合感染在我们的环境中似乎很少见，不太可能影响基于 DNA 指纹图谱数据的发现。避免培养选择性并针对不同菌株的分子方法非常适合检测混合感染。
