Fluoroquinolone has been widely used to treat various bacterial infectious diseases. However, the misuse of FQ without proper prescription has led to a significant increase in FQ resistance. FQ are essential for treating multidrug-resistant tuberculosis (MDR-TB), and resistance to them is linked to poor treatment outcomes.13 Global prevalence data on FQ resistance is limited due to inadequate FQ testing facilities in many tuberculosis-endemic areas. Therefore, localized data is urgently needed to understand FQ resistance in MDR and non-MDR-TB, which is crucial for determining the feasibility of introducing a standardized shorter MDR-TB regimen. In our study, the overall genotypic resistance rate of fluoroquinolones among MDR-TB was 33%, 5.4% in non-MDR, and 16.5% in rifampicin mono-resistant tuberculosis patients. Sethi et al. (2020)14 reported 38.6% in RR isolates in India, and Li et al. (2024)15 reported 34.7% FQ resistance among MDR-TB patients in China. Our findings indicate a lower resistance rate than previous reports, but the 33% FQ resistance among MDR-TB in our study was significantly higher than the global rate (20.0%) of WHO (2020)16 report. The high rate of FQ resistance in MDR-TB patients in Southern India suggests that including FQ in treatment could lead to ineffective treatments and worsen treatment outcomes. These findings emphasize the urgent need for FQ resistance testing before initiating MDR-TB treatment. In our study, the detection rate for extensively drug-resistant tuberculosis (XDR-TB) was 1.33% (2 isolates), which is relatively lower than the reported global prevalence of XDR-TB and the 8.6% reported in India by Sethi et al., 2020. The resistance rate to any FQs in our cohort among non-MDR-TB was 5.4%, which is relatively higher than the 0.8% reported by Kim et al., 2018, indicating a trend that warrants comparison with the recent prevalence of FQ resistance in TB-endemic countries like India.
Among 91 fluoroquinolone (FQ) true resistant isolates, the frequency of gyrA mutations was higher than gyrB, which aligns with the findings of Kabir et al9. The most common mutations in the gyrA gene associated with FQ resistance in Mycobacterium tuberculosis are S91P, A90V, and D94A/N/Y/G/H. Most FQ-resistant isolates exhibited a mutation at codon D94G, with A90V being the most prevalent. Our study found that 49% of the FQ-resistant isolates carried the D94G mutation, a notably higher figure compared to Tania Matsui et al.'s17 (2020) report of 44% in Brazil. Our findings are further supported by a recent study in Ethiopia, which detected a gyrA/D94A gene mutation (2%) in FQ-resistant TB isolates.18 Moreover, our study identified a rare gyrA mutation at codon D94H in nine isolates, a mutation not commonly reported in other studies.14 Among the 91 FQ-true resistant isolates, 26 exhibited resistance to levofloxacin and low-level resistance to moxifloxacin, while 62 displayed resistance to levofloxacin and high-level resistance to moxifloxacin. Additionally, alanine, asparagine, and serine are nonessential amino acids that promote brain functions, remove toxins, and synthesize blood cells. Any functional changes in these nonessential amino acids resulting from mutations can lead to difficulty in producing proteins necessary for cell growth, maintenance, and repair mechanisms.19 In our study, we observed a heteroresistance mutation pattern in the gyrA gene exhibited by 39 (42.9%) isolates, characterized by the expression of MUT probe and all WT probes, including at codons 90, 91, and 94. This aligns with a recent report by Dixit et al. (2023)20, who documented a 39.3% heteroresistance mutation pattern in the gyrA gene in India. It's worth noting that heteroresistance has been linked to limited treatment options and an increasing rate of unfavorable treatment outcomes, as reported by Rigouts et al.21
The prevalence rate of fluoroquinolone (FQ) resistance among non-MDR-TB in this study is 5.4%, higher than the global estimate of 0.8%. This suggests a need to be cautious about the widespread use of FQ in the community. In this study, FQ resistance among MDR-TB and RR-TB were 32.7% and 16.5%, respectively, which is also higher than the global estimates (Dixit et al., 2023). The FQ resistance in this study among the MDR/RR-TB is 24.9%, higher than the global estimates of 18.0%22. Among newly diagnosed H-resistance cases, the FQ resistance was 6.9%, lower than the 9.8% reported in a recent study in Pakistan.23 Similarly, the FQ resistance in the previously treated cases was 3.81% compared to the previous study report of 44.6% by Sethi et al.14 Among newly diagnosed MDR/RR-TB cases, the FQ resistance was 23.4%, which was higher than the 21.82% reported in the recent study carried out in China15 and 14.2% in an Indian research.24 Similarly, the FQ resistance in the previously treated cases was 74.24% compared to the previous study report of 44.6% by Sethi et al.14 Another study in India reported 72.8% FQ resistance.10 The high FQ resistance was noted in previously newly diagnosed MDR/RR TB cases, which might be due to the high transmission of the drug-resistant strains. The high rate of FQ resistance in MDR and non-MDR-TB (H-resistance) patients could lead to ineffective treatment of H mono-resistant and unfavorable outcomes.
Of the 289 MDR/RR –TB isolates, 53% exhibited a mutation at codon S450L of the rpoB gene, which is lower than the previously reported rate of 77% by Tania Matsui et al.17 Among 1230 H-mono-resistant isolates, 65% showed a mutation at codon S315T of the katG gene, resulting in high-level isoniazid resistance - a rate lower than the previously reported 72%. Notably, out of the 53% with a mutation at the S450L codon of the rpoB gene and the 65% with a mutation at the S315T codon of the katG gene, 27.9% and 5.9% were at an increased risk for FQ-resistant, a previously unreported finding. This information will be valuable for policymakers and decision-makers, providing timely evidence. Additionally, this study offers crucial insights for physicians in their daily treatment practices and serves as essential baseline information for researchers.
The study found that the rates of unfavorable outcomes were 42.9% for MDR/RR tuberculosis patients and 20.4% for non-MDR-TB patients. Our study showed a higher rate of unfavorable outcomes (42.9%) for MDR/RR tuberculosis patients compared to a previous study in Ethiopia by Bogale et al.(2023)25, which reported a rate of 23.68%. Nair et al. (2017)26 reported a 40% unfavorable outcome rate in India. Aaina et al. (2022)19 reported rates of 29.4% for MDR-TB and 14.5% for non-MDR-TB cases in India. The unfavorable outcome for non-MDR (H-resistance) patients in our study was 20%, lower than the 29.4% reported by Aaina et al. (2021)19 in India. These unsuccessful treatment outcomes were significantly associated with FQ resistance. The increasing percentage of unfavorable outcomes could pose a risk of transmitting tuberculosis-resistant forms and negatively impact the country's GDP.
The study has significant strengths, such as recruiting a large sample size and using various diagnostic methods. However, our study has several limitations to our study. We relied on secondary data for patient characteristics, and only patients with a laboratory diagnosis of tuberculosis were included. Our study used a cross-sectional design and only identified associated factors, not risk factors, for FQ-resistant transmission. We were unable to determine if FQ resistance resulted from previous treatment exposure because data on previous FQ use before DR-TB diagnosis were not available. Additionally, drug susceptibility tests for DS tuberculosis are not routinely conducted, although FQ resistance among DS-TB could lead to unfavorable treatment outcomes. FQ resistance is higher in regions where these drugs are widely prescribed and sometimes misused as fluoroquinolones.
This text highlights the concerning rise of FQ (fluoroquinolone) resistance in India due to the unregulated prescription of these drugs. The study found a higher proportion of MDR/RR (multidrug-resistant/rifampicin-resistant) TB cases with FQ-resistant genotypes, even in isolates with resistance to a single drug. The high FQ resistance rate identified in the study is alarming for the National Tuberculosis Elimination Programme and underscores the need for reasonable use of fluoroquinolone drugs. This report also describes specific mutations related to high FQ resistance in TB patients from India, which could inform the development of a new algorithm for rapid drug-resistant TB diagnosis, leading to better treatment outcomes. Around one-third of FQ-resistant cases were presumed to be transmitted, indicating the urgent need for policymakers to address the higher rate of FQ resistance in India among DR-TB (drug-resistant tuberculosis) patients. The findings suggest implementing the diagnosis of FQ resistance, preferably at the initial diagnosis stage, to identify all resistance-promoting mutations and ensure effective treatment and resistance control.