Evaluation of the molecular bacterial load assay for detecting viable Mycobacterium tuberculosis in cerebrospinal fluid before and during tuberculous meningitis treatment

Hoang Thanh Hai,Wilber Sabiiti,Do Dang Anh Thu,Nguyen Hoan Phu,Stephen H Gillespie,Guy E Thwaites,Nguyen Thuy Thuong Thuong

doi:10.1016/j.tube.2021.102084

Abstract

New tools to monitor treatment response and predict outcome from tuberculous meningitis (TBM) are urgently required. We retrospectively evaluated the 16S rRNA-based molecular bacterial load assay (MBLA) to quantify viable Mycobacterium tuberculosis in serial cerebrospinal fluid (CSF) from adults with TBM. 187 CSF samples were collected before and during the first two months of treatment from 99 adults TBM, comprising 56 definite, 43 probable or possible TBM, and 18 non-TBM and preserved at −80°C prior to MBLA. We compared MBLA against MGIT culture, GeneXpert MTB/RIF (Xpert) and Ziehl-Neelsen (ZN) smear. Before treatment, MBLA was positive in 34/99 (34.3%), significantly lower than MGIT 47/99 (47.5%), Xpert 51/99 (51.5%) and ZN smear 55/99 (55.5%). After one month of treatment, MBLA and MGIT were positive in 3/38 (7.9%) and 4/38 (10.5%), respectively, whereas Xpert and ZN smear remained positive in 19/38 (50.0%) and 18/38 (47.4%). In summary, MBLA was less likely to detect CSF bacteria before the start of treatment compared with MGIT culture, Xpert and ZN smear. MBLA and MGIT positivity fell during treatment because of detecting only viable bacteria, whereas Xpert and ZN smear remained positive for longer because of detecting both live and dead bacteria. Sample storage and processing may have reduced MBLA-detectable viable bacteria; and sampling earlier in treatment may yield more useful results. Prospective studies with CSF sampling after 1–2 weeks are warranted.

Highlights

Tuberculous meningitis (TBM) is the most severe form of tubercu losis (TB)
187 stored cerebrospinal fluid (CSF) samples from 117 suspected TBM participants were used for molecular bacterial load assay (MBLA)
Deaths from TBM are prevented by the effective killing of Mycobacterium tuberculosis (Mtb) by anti-tuberculosis drugs and the control of the intracerebral inflamma tory response [18]

Summary

Introduction

Tuberculous meningitis (TBM) is the most severe form of tubercu losis (TB). Caused by dissemination of Mycobacterium tuberculosis (Mtb) to the brain, it results in death or neurological disability in half of all cases. In pulmonary tuberculosis (PTB), monitoring Mtb bacil lary load before and during treatment has been found to be useful for examining treatment response, evaluating therapy efficiency and pre dicting outcome [4]. Numbers of Mtb in cerebrospinal fluid (CSF) of TBM patients are normally much lower than in PTB sputum samples, which may make it challenging to assess viable bacterial load during treatment [5,6]. Using GeneXpert MTB/RIF (Xpert) among 692 adults with TBM, we showed previously that pre-treatment bacterial load correlated with neurological severity at presentation and with the appearance of new neurological events after starting treatment [6]. Whether pre-treatment bacterial load and bacterial clearance affect early treatment response, and in turn treatment outcome, is still unknown due to the limitations of current methods for measuring viable Mtb in TBM. A new rapid assay is needed for TBM patients, during the early phases of treatment [7,8]

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