An update on Linezolid resistance in Mycobacterium tuberculosis and the challenges ahead

Resistance to antituberculosis drugs is an important cause of treatment failure. We evaluated the prevalence and pattern of antituberculosis drug resistance in the central region of Saudi Arabia, and reviewed previous reports from Saudi Arabia. We retrospectively examined the records of sputum smear and culture-positive pulmonary tuberculosis patients admitted consecutively from 1998 through 1999 in a main referral hospital in Riyadh, and analyzed drug sensitivity reports. We also reviewed previous reports on antituberculosis drug resistance in Saudi Arabia. Of 515 patients with pulmonary tuberculosis, 80 (15.5%) had resistance to at least one antituberculosis drug. Resistance to streptomycin was most frequent (9.7% ), followed by rifampicin (9.5%), isoniazid (4.3%), and ethambutol (0.2%). Resistance to one antituberculosis drug was found in 8.9%, resistance to two drugs in 5.2%, resistance to three drugs in 1.2%, and resistance to four drugs in 0.2%. Multidrug resistance (defined as resistance to at least isoniazid and rifampicin) was found in 1.9% of patients. A literature review including 6114 patients in Saudi Arabia showed that resistance against streptomycin was most common (8.8%), followed by rifampicin (8%), and isoniazid (7.2%). Of the 6114 patients, 6.8% patients were resistant to only one drug, 3.6% were resistant to two drugs, and 3.7% to three drugs. The high prevalence of rifampicin resistance and resistance to multiple drugs in the Riyadh region and in other parts of Saudi Arabia is a major challenge to the control of tuberculosis in this country. Efforts should be made to prevent the emergence of further antituberculosis drug resistance.

Phenotypic drug susceptibility testing (DST) is considered the gold standard for detecting linezolid (LZD) resistance in Mycobacterium tuberculosis (MTB), but it is time-consuming. Nanopore sequencing offers a potentially faster alternative approach. This study evaluated the agreement between phenotypically detected LZD resistance and mutations in the rrl and rplC genes of MTB isolates using nanopore sequencing. Consecutive drug-resistant MTB isolates from pulmonary samples collected in 2021 underwent liquid culture (LC) DST for LZD. All resistant isolates and an equal number of susceptible isolates were subjected to targeted sequencing of the rrl and rplC genes using nanopore technology. Sequencing identified a C154R mutation in the rplC gene in only one LZD-resistant isolate. No mutations were detected in the rrl gene. The agreement between sequencing and LC-DST for detecting LZD resistance was poor (Cohen's kappa: 0.03571, 95% confidence interval [CI]: -0.034-0.105). Additionally, no significant association was found between LZD resistance and clinical or microbiological outcomes at 6-month follow-up. This study revealed a considerable discrepancy between phenotypic and genotypic detection of LZD resistance in MTB. Further research is needed to better understand the genetic mechanisms underlying LZD resistance and to develop reliable molecular diagnostics for rapid resistance detection.

ObjectivesLimited data exist on clinical associations and genotypic correlates of linezolid resistance in Mycobacterium tuberculosis. We aimed to describe mutations and clinical factors associated with phenotypic linezolid resistance from patients with drug-resistant TB at two public sector facilities in South Africa.MethodsAdults and adolescents with treatment failure (culture positivity ≥4 months) on a linezolid-containing regimen were retrospectively identified. Phenotypic resistance, as defined by a linezolid MIC >1 mg/L, was assessed for retrieved isolates using broth microdilution. Targeted sequencing of rrl and rplC was performed, irrespective of growth on subculture.ResultsThirty-nine patients with linezolid-based treatment failure were identified, 13 (33%) of whom had phenotypic or genotypic linezolid resistance after a median duration of 22 months (range = 7–32) of linezolid therapy. Paired MIC testing and genotyping was performed on 55 unique isolates. All isolates with phenotypic resistance (n = 16) were associated with known resistance mutations, most frequently due to the T460C substitution in rplC (n = 10); rrl mutations included G2814T, G2270C/T and A2810C. No mutations were detected in isolates with MICs at or below the critical concentration.ConclusionsLinezolid resistance occurred in a third of patients with drug-resistant TB and treatment failure. Resistance occurred late and was predicted by a limited number of mutations in rrl and rplC. Screening for genotypic resistance should be considered for patients with a positive culture after 4 months of linezolid therapy in order to optimize treatment and avoid the toxicity of ineffective linezolid therapy.

In 2018, shorter treatment regimens (STR) for people with drug-resistant tuberculosis (DR-TB) were introduced in Tanzania and included kanamycin, high-dose moxifloxacin, prothionamide, high-dose isoniazid, clofazimine, ethambutol and pyrazinamide. We describe treatment outcomes of people diagnosed with DR-TB in a cohort initiating treatment in 2018 in Tanzania. This was a retrospective cohort study conducted at the National Centre of Excellence and decentralised DR-TB treatment sites for the 2018 cohort followed from January 2018 to August 2020. We reviewed data from the National Tuberculosis and Leprosy Program DR-TB database to assess clinical and demographic information. The association between different DR-TB regimens and treatment outcome was assessed using logistic regression analysis. Treatment outcomes were described as treatment complete, cure, death, failure or lost to follow-up. A successful treatment outcome was assigned when the patient achieved treatment completion or cure. A total of 449 people were diagnosed with DR-TB of whom 382 had final treatment outcomes: 268 (70%) cured; 36 (9%) treatment completed; 16 (4%) lost to follow-up; 62 (16%) died. There was no treatment failure. The treatment success rate was 79% (304 patients). The 2018 DR-TB treatment cohort was initiated on the following regimens: 140 (46%) received STR, 90 (30%) received the standard longer regimen (SLR), 74 (24%) received a new drug regimen. Normal nutritional status at baseline [adjusted odds ratio (aOR)=6.57, 95% CI (3.33-12.94), p < 0.001] and the STR [aOR=2.67, 95% CI (1.38-5.18), p=0.004] were independently associated with successful DR-TB treatment outcome. The majority of DR-TB patients on STR in Tanzania achieved a better treatment outcome than on SLR. The acceptance and implementation of STR at decentralised sites promises greater treatment success. Assessing and improving nutritional status at baseline and introducing new shorter DR-TB treatment regimens may strengthen favourable treatment outcomes.

Tuberculosis (TB) is a disease associated with poverty. Moreover, a significant proportion of TB patients face a substantial financial burden before and during TB care. One of the top targets in the End TB strategy was to achieve zero catastrophic costs due to TB by 2020. To assess patient costs related to TB care and the proportion of TB-affected households that faced catastrophic costs, the Philippines National TB Programme (NTP) conducted a national TB patient cost survey in 2016-2017. A cross-sectional survey of 1,912 TB patients taking treatment in health facilities engaged with the NTP. The sample consists of 786 drug-sensitive TB (DS-TB) patients in urban facilities, 806 DS-TB patients in rural facilities, and 320 drug-resistant TB (DR-TB) patients. Catastrophic cost due to TB is defined as total costs, consisting of direct medical and non-medical costs and indirect costs net of social assistance, exceeding 20% of annual household income. The overall mean total cost including pre- and post-diagnostic costs was US$601. The mean total cost was five times higher among DR-TB patients than DS-TB patients. Direct non-medical costs and income loss accounted for 42.7% and 40.4% of the total cost of TB, respectively. More than 40% of households had to rely on dissaving, taking loans, or selling their assets to cope with the costs. Overall, 42.4% (95% confidence interval (95% CI): 40.2-44.6) of TB-affected households faced catastrophic costs due to TB, and it was significantly higher among DR-TB patients (89.7%, 95%CI: 86.3-93.0). A TB enabler package, which 70% of DR-TB patients received, reduced catastrophic costs by 13.1 percentage points (89.7% to 76.6%) among DR-TB patients, but only by 0.4 percentage points (42.4% to 42.0%), overall. TB patients in the Philippines face a substantial financial burden due to TB despite free TB services provided by the National TB Programme. The TB enabler package mitigated catastrophic costs to some extent, but only for DR-TB patients. Enhancing the current social and welfare support through multisectoral collaboration is urgently required to achieve zero catastrophic costs due to TB.

BackgroundTuberculosis (TB) is a disease associated with poverty. Moreover, a significant proportion of TB patients face a substantial financial burden before and during TB care. One of the top targets in the End TB strategy was to achieve zero catastrophic costs due to TB by 2020. To assess patient costs related to TB care and the proportion of TB-affected households that faced catastrophic costs, the Philippines National TB Programme (NTP) conducted a national TB patient cost survey in 2016–2017.MethodsA cross-sectional survey of 1,912 TB patients taking treatment in health facilities engaged with the NTP. The sample consists of 786 drug-sensitive TB (DS-TB) patients in urban facilities, 806 DS-TB patients in rural facilities, and 320 drug-resistant TB (DR-TB) patients. Catastrophic cost due to TB is defined as total costs, consisting of direct medical and non-medical costs and indirect costs net of social assistance, exceeding 20% of annual household income.ResultsThe overall mean total cost including pre- and post-diagnostic costs was US$601. The mean total cost was five times higher among DR-TB patients than DS-TB patients. Direct non-medical costs and income loss accounted for 42.7% and 40.4% of the total cost of TB, respectively. More than 40% of households had to rely on dissaving, taking loans, or selling their assets to cope with the costs. Overall, 42.4% (95% confidence interval (95% CI): 40.2–44.6) of TB-affected households faced catastrophic costs due to TB, and it was significantly higher among DR-TB patients (89.7%, 95%CI: 86.3–93.0). A TB enabler package, which 70% of DR-TB patients received, reduced catastrophic costs by 13.1 percentage points (89.7% to 76.6%) among DR-TB patients, but only by 0.4 percentage points (42.4% to 42.0%), overall.ConclusionsTB patients in the Philippines face a substantial financial burden due to TB despite free TB services provided by the National TB Programme. The TB enabler package mitigated catastrophic costs to some extent, but only for DR-TB patients. Enhancing the current social and welfare support through multisectoral collaboration is urgently required to achieve zero catastrophic costs due to TB.

Antimycobacterial activity of Citrullus colocynthis (L.) Schrad. against drug sensitive and drug resistant Mycobacterium tuberculosis and MOTT clinical isolates

The emergence of antimicrobial resistance (AMR) across bacterial pathogens presents a serious threat to global health. This threat is further exacerbated in tuberculosis (TB), mainly due to a protracted treatment regimen involving a combination of drugs. A diversity of factors contributes to the emergence of drug resistance in TB, which is caused by the pathogen Mycobacterium tuberculosis (Mtb). While the traditional genetic mutation-driven drug resistance mechanisms operate in Mtb, there are also several additional unique features of drug resistance in this pathogen. Research in the past decade has enriched our understanding of such unconventional factors as efflux pumps, bacterial heterogeneity, metabolic states, and host microenvironment. Given that the discovery of new antibiotics is outpaced by the emergence of drug resistance patterns displayed by the pathogen, newer strategies for combating drug resistance are desperately needed. In the context of TB, such approaches include targeting the efflux capability of the pathogen, modulating the host environment to prevent bacterial drug tolerance, and activating the host anti-mycobacterial pathways. In this review, we discuss the traditional mechanisms of drug resistance in Mtb, newer understandings and the shaping of a set of unconventional approaches to target both the emergence and treatment of drug resistance in TB.

Background & objectives:Linezolid (LZD) is increasingly being used in tuberculosis (TB) treatment. However, LZD resistance has already been reported, which is highly alarming, given its critical therapeutic role. This study was aimed to phenotypically and genotypically assess LZD resistance in Mycobacterium tuberculosis (MTB) isolates at a laboratory in a tertiary care centre in Mumbai, India.Methods:A sample of 32 consecutive LZD-resistant MTB isolates identified by liquid culture susceptibility testing was subjected to whole-genome sequencing (WGS) on the Illumina NextSeq platform. Sequences were analyzed using BioNumerics software to predict resistance for 12 antibiotics within 15 min.Results:Sixty eight of the 2179 isolates tested for LZD resistance by MGIT-based susceptibility testing (June 2015 to June 2016) were LZD-resistant. Thirty two consecutive LZD-resistant isolates were analyzed by WGS to screen for known mutations conferring LZD resistance. WGS of 32 phenotypically LZD-resistant isolates showed that C154R in the rplC gene and G2814T in the rrl gene were the major resistance determinants.Interpretation & conclusions:LZD resistance poses an important risk to the success of treatment regimens, especially those designed for resistant isolates; such regimens are extensively used in India. As LZD-containing regimens increase in prominence, it is important to support clinical decision-making with an improved understanding of the common mutations conferring LZD resistance and their frequency in different settings.

Tuberculosis (TB) remains one of the leading public health problems worldwide. Declared as a global emergency in 1993 by the WHO, its control is hampered by the emergence of multidrug resistance (MDR), defined as resistance to at least rifampicin and isoniazid, two key drugs in the treatment of the disease. More recently, severe forms of drug resistance such as extensively drug-resistant (XDR) TB have been described. After the discovery of several drugs with anti-TB activity, multidrug therapy became fundamental for control of the disease. Major advances in molecular biology and the availability of new information generated after sequencing the genome of Mycobacterium tuberculosis increased our knowledge of the mechanisms of resistance to the main anti-TB drugs. Better knowledge of the mechanisms of drug resistance in TB and the molecular mechanisms involved will help us to improve current techniques for rapid detection and will also stimulate the exploration of new targets for drug activity and drug development. This article presents an updated review of the mechanisms and molecular basis of drug resistance in M. tuberculosis. It also comments on the several gaps in our current knowledge of the molecular mechanisms of drug resistance to the main classical and new anti-TB drugs and briefly discusses some implications of the development of drug resistance and fitness, transmission and pathogenicity of M. tuberculosis.

Background: The diagnosis and treatment of drug resistant tuberculosis (TB) has presented a unique challenge to the control of TB in Nigeria. Various studies have reported the presence of drug resistant TB, and some treatment centres have been established to treat cases. This study sought to establish the prevalence of rifampicin-resistant TB in our state with a view to advocating for more commitment to efforts toward the treatment and control of drug-resistant TB, including establishment of more treatment centres in the geopolitical zone. Materials and Methods: A retrospective review of laboratory records of 1882 patients whose sputum samples were sent to the Gene Xpert Laboratory of our facility between January 2014 and April 2015 for Mycobacterium tuberculosis (MTB) and rifampicin resistance assay was done using the Gene Xpert MTB/RIF assay. The patients were presumptive TB cases, suspected TB treatment failures, and suspected drug resistant cases from various health facilities in the state. Results: Of the 1882 patients, 68.4% were females and 36.6% were males; patients were aged between 1 and 70 years. MTB was detected in 18.8% (355/1882) of the patients. Forty-three of the 355 MTB positive patients were rifampicin resistant giving a prevalence of RIF resistance of 12.1%. A total of 62.8% of the RIF resistant cases were males whereas 37.2% were females. Forty-one percent of the RIF Resistant cases were aged between 21 and 30 years, 51.2% were human immunodeficiency (HIV) positive, 44.2% were HIV negative, whereas 4.6% had unknown HIV status. A higher number (62.8%) of those with RIF resistance were referred from other facilities compared to 37.2% from the host facility. There was significant association between RIF Resistance and sex, HIV status, and the facility. Conclusion: This study has established that there is a high prevalence of rifampicin resistance in the state. There is need to increase commitment to efforts being made towards treatment and control of DRTB in this zone.

In this retrospective study in China, we aimed to: (1) determine the prevalence of linezolid (LZD) resistance among multidrug-resistant tuberculosis (MDR-TB)-infected patients; (2) monitor for dynamic LZD susceptibility changes during anti-TB treatment; and (3) explore molecular mechanisms conferring LZD resistance. A total of 277 MDR-TB patients receiving bedaquiline (BDQ)-containing regimens in 13 TB specialized hospitals across China were enrolled in the study. LZD and BDQ susceptibility rates were determined using the minimum inhibitory concentration (MIC) method, then DNA sequences of patient isolates were analyzed using Sanger sequencing to detect mutations conferring LZD resistance. Of 277 patients in our cohort, 115 (115/277, 41.5%) with prior LZD exposure yielded 19 (19/277, 6.9%) isolates exhibiting LZD resistance. The LZD resistance rate of LZD-exposed group isolates significantly exceeded the corresponding rate for non-exposed group isolates (P = 0.047). Genetic mutations were observed in 10 (52.6%, 10/19) LZD-resistant isolates, of which a Cys154Arg (36.8%, 7/19) substitution within ribosomal protein L3 was most prevalent. Analysis of sequential positive cultures obtained from 81 LZD-treated patients indicated that cultured organisms obtained from most patients (85.2%, 69/81) retained original LZD MIC values; however, organisms cultured later from two patients exhibited significantly increased MIC values that were attributed to the rplC substitution T460C. Overall, LZD resistance was detected in 6.9% of patients of an MDR-TB cohort in China. Low rate of acquired LZD resistance was noted in MDR-TB treated with BDQ-LZD combination.

The objective: to evaluate main parameters of cellular, humoral immunity and natural resistance in tuberculosis patients with primary and acquired multiple drug resistance; to study the correlation of these parameters with clinical and radiological manifestations.Subjects and Methods. A prospective study was conducted which included 169 patients with pulmonary tuberculosis, 80 of them were new cases of drug susceptible pulmonary tuberculosis and they made the Comparison Group (CG), and 89 patients suffered from multiple drug resistant tuberculosis and they made the Main Group (MG). The Main Group was divided into 2 subgroups: MG-1 – 40 patients with primary multiple drug resistant tuberculosis; MG-2 ‒ 49 patients who acquired drug resistance of Mycobacterium tuberculosis during treatment of tuberculosis.The immune assays included the lymphocyte blast transformation reaction (LBTR) to phytohemagglutinin and tuberculin (PPD), immunophenotyping of CD3+ and CD19+ cells; phagocytic index and phagocytic number were calculated; nitro blue tetrazolium test was used, concentrations of immunoglobulins and antimycobacterial antibodies were determined.Results. The clinical laboratory data demonstrated a more severe course of the disease in patients with multiple drug resistant tuberculosis, especially in those with acquired multiple drug resistant tuberculosis which was confirmed by the severity of immune deficiencies of the cellular immunity and innate resistance as well as by the overactivity of humoral immunity. The levels of CD3+ and LBTR reaction to PPD had a negative correlation with clinical manifestations and radiological features demonstrating the severity of pulmonary tuberculosis in patients with multiple drug resistance, especially in those with acquired multiple drug resistance; and CD19+ and antimycobacterial antibodies positively correlated with clinical manifestations and radiological signs.Conclusions. Parameters of cellular immunity and natural resistance were the lowest in the patients with acquired multiple drug resistance of Mycobacterium tuberculosis versus primary multiple drug resistance and drug susceptible Mycobacterium tuberculosis. Parameters of humoral immunity demonstrated the increased activity to compensate for the insufficiency of cellular immunity regardless of the type of resistance of Mycobacterium tuberculosis.

Objective To explore the value of the genotype assays detection of the resistance of Mycobacterium tuberculosis to isoniazid and rifampin.Methods Seventy-eight clinical isolates susceptible of harboring Mycobacterium tuberculosis were subject to the mutation assay of katG gene S315T,inhA gene C-15Tand rpoB genes D516V,H526Y,H526D,S531L by using multiplex polymerase chain reaction-based linear probe membrane hybridization for analysis of isoniazid and rifampin resistance.These results were compared with the L-J solid medium culture,the gold standard,and MGIT BACTEC 960 drug sensitivity test.Results Genotype assay was associated with shorter time for the detection compared with routine drug sensitivity test (6 hours vs 3 months).The genotype assay yielded the sensitivity and specificity of 89％ (16/18) and 99％ (77/78) for isoniazid and 100％ and 100％ (13/13 and 78/78) for rifampin.Conclusion Genotype assay of Mycobacterium tuberculosis offers a rapid and accurate approach for the early diagnosis and treatment of drug-resistant tuberculosis,rendering it a promising technique to be extensively applied in clinical laboratories. Key words: Mycobacterium tuberculosis; Microbial sensitivity tests; Extensively drug-resistant tuberculosis ; Linear probe reverse membrane hybridization ; Genotype

Molecular epidemiology of tuberculosis in selected sites across Papua New Guinea