Drug-resistant tuberculosis (TB) kills approximately 200,000 people every year. A contributing factor is the slow turnaround time of TB drug susceptibility testing. Current tests take at least two weeks to perform due to the slow growth of the pathogen M. tuberculosis. In a new study that was recently published in Nature Communications, we used Mycobacterium tuberculosis variant bovis BCG (M. bovis BCG) and Mycobacterium smegmatis as models for tuberculous and nontuberculous pathogens. The bacteria were loaded into microchambers on a microfluidic chip and exposed to antibiotics used for treating (multidrug-resistant) TB - i.e. rifampicin (RIF), isoniazid (INH), ethambutol (EMB), linezolid (LZD), streptomycin (STR), bedaquiline (BDQ), and levofloxacin (LFX). The bacteria’s reaction to the drugs was observed via time-lapse phase contrast microscopy. A deep neural network-based image segmentation algorithm was used to quantify the growth rate over time and to determine how the strains responded to the drugs compared to the untreated reference. M. bovis BCG strains susceptible to INH, EMB, and LZD were significantly impacted by these antibiotics within 3 hours when treated at the respective minimum inhibitory concentration (MIC). A panel of susceptible and resistant M. bovis BCG was tested at the critical concentrations for TB for INH, RIF, STR, and LFX. The results show that growth-based phenotypic drug susceptibility testing can be conducted in less than 12 hours for M. bovis BCG, a strain that shares 99.96% genetic identity with M. tuberculosis. This work could pave the way for a pDST for TB in less than 12 hours.

Figure: Testing susceptible and resistant M. bovis BCG Russia at critical drug concentrations. pDST profiles of M. bovis BCG Russia WT (a.) and M. bovis BCG Russia INHR  (b.) in INH 0.5 mg/L; M. bovis BCG Russia WT (c.) and M. bovis BCG Russia RIFR  (d.) in RIF 1 mg/L; M. bovis BCG Russia WT (e.) and M. bovis BCG Russia STRR  (f.) in STR 1 mg/L; and M. bovis BCG Russia WT (g.) and M. bovis BCG Russia FQR  (h.) in LFX 1 mg/L.

Read more in Nature Communications!