Primary Multidrug Resistant Tuberculosis and Utility of Line Probe Assay for Its Detection in Smear-Positive Sputum Samples in a Tertiary Care Hospital in South India

Abstract

In a high tuberculosis burdened country like India, rapid, cost-effective, and reliable diagnostic tools for tuberculosis are an urgent need of the hour to prevent inappropriate treatment strategies and further spread of resistance. This study aimed to estimate the proportion of new smear-positive tuberculosis cases with primary resistance to rifampicin and/or isoniazid as well as identify the common mutations associated with it. Sputum of 200 newly diagnosed smear-positive cases of 1+ score and above was directly subjected to Line Probe Assay using the GenoType MTBDRplus assay kit. All samples were inoculated onto solid media and 61 samples were inoculated in automated liquid culture also. The Line Probe Assay gave hundred percent interpretable results with 2.5% of the study population showing resistant pattern. Only 1% of the cases were primary multidrug resistant tuberculosis and 1.5% showed isoniazid monoresistance. S531L and C15T were the most common genetic mutations seen for rifampicin and isoniazid resistance, respectively. 40% had absent rpoB wild type 8 band indicating probable silent mutation after clinical correlation. The average turnaround time for Line Probe Assay was far less (3.8 days) as compared to solid and liquid cultures (35.6 days and 13.5 days, resp.).

Figure 1

Negative control with CC and AC bands. The red band is reference marker to align the strip.

Figure 2

Patient with MDR TB showing presence of rpoB MUT3 band and inhA MUT1 band along with the wild type bands indicating rifampicin resistance and INH heteroresistance, respectively.

Figure 3

(From left to right) Lane 1: sensitive pattern. Lane 2: MDR TB patient with rpoB MUT3 band indicating rifampicin resistance and katG MUT1 band and inhA MUT3A band along with wild type band indicating INH heteroresistance. Lane 3: reference strip.

Figure 4

Patient with inhA MUT1 band along with wild type bands indicating low level INH heteroresistance.

Figure 5

Patient showing low level INH monoresistance with absent inhA WT1 band and presence of inhA MUT1 band.

Figure 6

(From left to right) Lane 1: faint rpoB WT8 band interpreted as sensitive pattern. Lanes 2 and 3: sensitive pattern. Lane 4: sensitive pattern with absent rpoB WT8 band.

Figure 7

Age and gender distribution of the study population. The majority of the patients are of the age group between 41 and 50 with male preponderance.