Resistance to Second-Line Anti-TB Drugs in Cambodia: A Phenotypic and Genetic Study

Abstract

Background: Due to the emergence of Mycobacterium tuberculosis (M.tb) clinical isolates resistant to most potent first-line drugs (FLD), second-line drugs (SLD) are being prescribed more frequently. We explore the genetic characteristics and molecular mechanisms of M.tb isolates phenotypically resistant to SLD, including pre-extensively drug-resistant (pre-XDR) and extensively drug-resistant (XDR) isolates. Methods: Drug-resistant (DR) M.tb isolates collected from 2012 to 2017 were tested using sequencing and phenotypic drug susceptibility testing. Genotypes were determined to explore their links with SLD resistance patterns. Results: Of the 272 DR M.tb isolates, 6 non-multidrug resistant (non-MDR) isolates were fluoroquinolones (FQ)-resistant, 3 were XDR and 16 were pre-XDR (14 resistant to FQ and 2 to second-line injectable drugs). The most frequent mutations in FQ-resistant and secondline injectable drugs resistant isolates were gyrA D94G (15/23) and rrs a1401g (3/5), respectively. Seventy-five percent of pre-XDR isolates and 100% of XDR isolates harbored mutations conferring resistance to pyrazinamide. All XDR isolates belonged to the Beijing genotype, of which one, named XDR+, was resistant to all drugs tested. One cluster including pre-XDR and XDR isolates was observed. Conclusion: This is the first description of SLD resistance in Cambodia. The data suggest that the proportion of XDR and pre-XDR isolates remains low but is on the rise compared to previous reports. The characterization of the XDR+ isolate in a patient who refused treatment underlines the risk of transmission in the population. In addition, genotypic results show, as expected, that the Beijing family is the main involved in pre-XDR and XDR isolates and that the spread of the Beijing pre-XDR strain is capable of evolving into XDR strain. This study strongly indicates the need for rapid interventions in terms of diagnostic and treatment to prevent the spread of the pre-XDR and XDR strains and the emergence of more resistant ones.

Molecular characterisation of second-line drug resistance among drug resistant tuberculosis patients tested in Uganda: a two and a half-year’s review

“…Consistent with studies done elsewhere, among patients resistant to FQ in our study, resistance was mostly conferred by the gyrA [ 16 , 28 , 29 ] locus whereas resistance to second-line IA was mainly conferred by the rrs gene at codon A1401G [ 30 ]. Additionally, five eis C14T mutations were detected in the eis gene locus and led to low-level resistance to KAN [ 31 ], of which four occurred independent of mutations in the rrs gene.…”

Pre-extensively drug-resistant tuberculosis among multidrug-resistant tuberculosis patients in Ethiopia: a laboratory-based surveillance study

“…According to our analysis, the most common rrs gene mutation was in A1401G (45.5%). Similar studies have reported high frequencies of mutation in codon A1401G ( Cheng et al., 2021 ; Jian et al., 2018 ; Rufai et al., 2020 ). The gyrB and eis genes were found to be mutation free in the MDR strains in our study.…”

“…The most frequently observed mutations were in codons A90V, D94N / D94Y , and S91P (77.3%, 4.5%, and 4.5%, respectively). According to several studies, the majority of mutations linked with FQ resistance occurred in codons A90V and D94N / D94Y in the gyrA gene ( Brossier et al., 2016 ; Chen et al., 2012 ; Cheng et al., 2021 ; Jian et al., 2018 ). According to our analysis, the most common rrs gene mutation was in A1401G (45.5%).…”

Novel mutations detected from drug resistant Mycobacterium tuberculosis isolated from North East of Thailand

“…Our report showed that katG gene mutation was found at the rate of 79.7%, in which 95.7% had mutations in katG315 codon and 4.3% harbored mutation in katG365 codon. The percentage of 79.7% for the katG gene mutation was consistent with earlier studies in Thailand (Boonaiam et al 2010) (Suthum et al 2020) and other Southeast Asian Countries (Ismail et al 2016) (Caws et al 2006) (Valvatne et al 2009) (Liu et al 2018) (Cheng et al 2021). The prevalence of katG315 mutation varied according to the geographical region: Southeast Asia (78.4%) (Seifert et al 2015), Vietnam (85.3%) (Hang et al 2019), China (59.4%) (Wu et al 2006), the Netherlands (53%) (Van Soolingen et al 2000), Japan (22%) (Ando et al 2010) and Singapore (26%) (Lee et al 1999).…”