Prevalence of Epstein Barr Virus and Herpes Simplex Virus Among Human Papillomavirus Negative Oral Cancer Patients: A Cross-Sectional Study from South India.

The high incidence of oral carcinomas is due to its multifactorial etiology and the presence of various risk factors. Human Papillomavirus (HPV) has a proven role in the pathogenesis of oral carcinomas, but in the recent times there has been an increasing incidence of oral cancers who are negative for HPV infection. Also, these patients are non-smokers and non-drinkers so it could be speculated that these oral cancers are due to some other etiological factor probably of other viral infections. Therefore, this study examined the prevalence of Epstein Barr Virus (EBV) and Herpes Simplex Virus (HSV) among oral cancer patients. This cross-sectional study was conducted from January 2019 to June 2020. Biopsy samples from 47 newly diagnosed untreated patients with oral malignancies were collected along with their demographic and clinicopathological information. DNA extracted from the biopsies was processed for nested PCR for the detection of EBV and HSV. All the samples tested negative for HPV and HSV infection. Nested PCR detected 29 cases (70.7%) to be positive for EBV. The non-cancerous adjacent tissues also were negative for HPV, EBV and HSV. The prevalence of EBV was found to be more in males (62.1%) and the highest number of cases was of the left buccal mucosa compromising 34% of the total cases. From the present study it can be concluded that EBV but not HSV infection is associated with an increased risk of developing oral cancers. Although, 70.7% of the patients were found to be positive for EBV whether the viral infection played any role in the driving the malignancy needs to be further elucidated.

Balancing Routine and Pandemic: The Synergy of India's Universal Immunization Program and COVID-19 Vaccination Program.

The COVID-19 pandemic posed substantial challenges to healthcare systems globally and severely disrupted essential health services, including routine immunization programs. In India, these disruptions were exacerbated due to the sudden emergence of the pandemic and lockdown measures, leading to mass migrations and a shortage of healthcare workers. Caregivers' concerns about routine immunization sessions further compounded the problem, resulting in a sharp increase in zero-dose children. This review paper examines India's strategies for conducting one of the world's largest COVID-19 vaccination programs while effectively restoring and perpetuating its Universal Immunization Program (UIP). The UIP played a pivotal role in sustaining immunization services during the pandemic, ultimately improving immunization coverage compared to pre-pandemic levels. India's accomplishments in this regard are highlighted through key performance indicators, the reach of immunization services, a reduction in zero-dose children, and antigen-wise coverage. The paper also discusses the successful integration of COVID-19 vaccination within the UIP framework, underscoring the significance of existing infrastructure, technology, and capacity building. India's dedication to concurrently managing routine immunization and COVID-19 vaccination showcases the adaptability and resilience of its healthcare system. India's journey serves as a global example of efficient mass immunization during challenging times, emphasizing the importance of political will, healthcare infrastructure investment, skilled healthcare workforces, and comprehensive vaccination programs. In a world grappling with the dual challenge of COVID-19 and routine immunization, India's experience provides a roadmap for strengthening healthcare systems and promoting public health as the critical agenda in challenging times.

Dynamical hallmarks of cancer: Phenotypic switching in melanoma and epithelial-mesenchymal plasticity.

Phenotypic plasticity was recently incorporated as a hallmark of cancer. This plasticity can manifest along many interconnected axes, such as stemness and differentiation, drug-sensitive and drug-resistant states, and between epithelial and mesenchymal cell-states. Despite growing acceptance for phenotypic plasticity as a hallmark of cancer, the dynamics of this process remains poorly understood. In particular, the knowledge necessary for a predictive understanding of how individual cancer cells and populations of cells dynamically switch their phenotypes in response to the intensity and/or duration of their current and past environmental stimuli remains far from complete. Here, we present recent investigations of phenotypic plasticity from a systems-level perspective using two exemplars: epithelial-mesenchymal plasticity in carcinomas and phenotypic switching in melanoma. We highlight how an integrated computational-experimental approach has helped unravel insights into specific dynamical hallmarks of phenotypic plasticity in different cancers to address the following questions: a) how many distinct cell-states or phenotypes exist?; b) how reversible are transitions among these cell-states, and what factors control the extent of reversibility?; and c) how might cell-cell communication be able to alter rates of cell-state switching and enable diverse patterns of phenotypic heterogeneity? Understanding these dynamic features of phenotypic plasticity may be a key component in shifting the paradigm of cancer treatment from reactionary to a more predictive, proactive approach.

Epigenetic memory acquired during long-term EMT induction governs the recovery to the epithelial state.

Epithelial-mesenchymal transition (EMT) and its reverse mesenchymal-epithelial transition (MET) are critical during embryonic development, wound healing and cancer metastasis. While phenotypic changes during short-term EMT induction are reversible, long-term EMT induction has been often associated with irreversibility. Here, we show that phenotypic changes seen in MCF10A cells upon long-term EMT induction by TGFß need not be irreversible, but have relatively longer time scales of reversibility than those seen in short-term induction. Next, using a phenomenological mathematical model to account for the chromatin-mediated epigenetic silencing of the miR-200 family by ZEB family, we highlight how the epigenetic memory gained during long-term EMT induction can slow the recovery to the epithelial state post-TGFß withdrawal. Our results suggest that epigenetic modifiers can govern the extent and time scale of EMT reversibility and advise caution against labelling phenotypic changes seen in long-term EMT induction as 'irreversible'.

National Control Laboratory Assessment of Quality of Rituximab Biosimilars in India.

In past few years many rituximab (RTX) biosimilars have been launched in India. Biosimilars are products that are similar in terms of quality, safety, and efficacy to its innovator product and are expected to offer improved affordability. The less clinical examination is a significant source of reduction in the cost of development of a biosimilar. However, this clinical relief is predicated on the assumption that there is analytical similarity between the biosimilar and the innovator product. Therefore, the role of National Control Laboratory become very important to ensure the quality of these drugs by carrying out analytical characterization at the point of drug product release level as when referred by National Regulatory Authority for quality evaluation. To assess the similarity between innovator and biosimilars, different physicochemical and biological quality attributes were assessed. A multitude of state-of-the-art analysis of N = 3 RTX biosimilars marketed in India revealed that the impurity profiles of these biosimilars measured by charge variant analysis (cation exchange chromatography-high performance liquid chromatography [HPLC], capillary zone electrophoresis, and capillary isoelectric focusing), aggregates profiling (size exclusion chromatography-HPLC), fragments analysis (capillary electrophoresis-sodium dodecyl sulfate) were found to be significantly varying as compared with the innovator product. There were significant variations in acidic variants (p = 0.023) and basic variants (p = 0.0005), isoelectric point value (p < 0.0001), aggregates (p = 0.0231), and fragments (p < 0.0001) of biosimilars were found as that of innovator product. However, these differences were not affecting the biological activity in the cell-based potency analysis by complement-dependent cytotoxicity (CDC) assay (p = 0.1026), antibody-dependent cell-mediated cytotoxicity (ADCC) (p = 0.3736), and binding assay by flow cytometer fluorescence-activated cell sorting (p = 0.4005) of these biosimilars as compared with the innovator product.

Exogenously Scavenged and Endogenously Synthesized Heme Are Differentially Utilized by Mycobacterium tuberculosis.

Heme is both an essential cofactor and an abundant source of nutritional iron for the human pathogen Mycobacterium tuberculosis. While heme is required for M. tuberculosis survival and virulence, it is also potentially cytotoxic. Since M. tuberculosis can both synthesize and take up heme, the de novo synthesis of heme and its acquisition from the host may need to be coordinated in order to mitigate heme toxicity. However, the mechanisms employed by M. tuberculosis to regulate heme uptake, synthesis, and bioavailability are poorly understood. By integrating ratiometric heme sensors with mycobacterial genetics, cell biology, and biochemistry, we determined that de novo-synthesized heme is more bioavailable than exogenously scavenged heme, and heme availability signals the downregulation of heme biosynthetic enzyme gene expression. Ablation of heme synthesis does not result in the upregulation of known heme import proteins. Moreover, we found that de novo heme synthesis is critical for survival from macrophage assault. Altogether, our data suggest that mycobacteria utilize heme from endogenous and exogenous sources differently and that targeting heme synthesis may be an effective therapeutic strategy to treat mycobacterial infections. IMPORTANCE Mycobacterium tuberculosis infects ~25% of the world's population and causes tuberculosis (TB), the second leading cause of death from infectious disease. Heme is an essential metabolite for M. tuberculosis, and targeting the unique heme biosynthetic pathway of M. tuberculosis could serve as an effective therapeutic strategy. However, since M. tuberculosis can both synthesize and scavenge heme, it was unclear if inhibiting heme synthesis alone could serve as a viable approach to suppress M. tuberculosis growth and virulence. The importance of this work lies in the development and application of genetically encoded fluorescent heme sensors to probe bioavailable heme in M. tuberculosis and the discovery that endogenously synthesized heme is more bioavailable than exogenously scavenged heme. Moreover, it was found that heme synthesis protected M. tuberculosis from macrophage killing, and bioavailable heme in M. tuberculosis is diminished during macrophage infection. Altogether, these findings suggest that targeting M. tuberculosis heme synthesis is an effective approach to combat M. tuberculosis infections.

Stochastic population dynamics of cancer stemness and adaptive response to therapies.

Intratumoral heterogeneity can exist along multiple axes: Cancer stem cells (CSCs)/non-CSCs, drug-sensitive/drug-tolerant states, and a spectrum of epithelial-hybrid-mesenchymal phenotypes. Further, these diverse cell-states can switch reversibly among one another, thereby posing a major challenge to therapeutic efficacy. Therefore, understanding the origins of phenotypic plasticity and heterogeneity remains an active area of investigation. While genomic components (mutations, chromosomal instability) driving heterogeneity have been well-studied, recent reports highlight the role of non-genetic mechanisms in enabling both phenotypic plasticity and heterogeneity. Here, we discuss various processes underlying phenotypic plasticity such as stochastic gene expression, chromatin reprogramming, asymmetric cell division and the presence of multiple stable gene expression patterns ('attractors'). These processes can facilitate a dynamically evolving cell population such that a subpopulation of (drug-tolerant) cells can survive lethal drug exposure and recapitulate population heterogeneity on drug withdrawal, leading to relapse. These drug-tolerant cells can be both pre-existing and also induced by the drug itself through cell-state reprogramming. The dynamics of cell-state transitions both in absence and presence of the drug can be quantified through mathematical models. Such a dynamical systems approach to elucidating patterns of intratumoral heterogeneity by integrating longitudinal experimental data with mathematical models can help design effective combinatorial and/or sequential therapies for better clinical outcomes.

A Cloud-Based Machine Learning Approach to Reduce Noise in ECG Arrhythmias for Smart Healthcare Services.

ECG (electrocardiogram) identifies and traces targets and is commonly employed in cardiac disease detection. It is necessary for monitoring precise target trajectories. Estimations of ECG are nonlinear as the parameters TDEs (time delays) and Doppler shifts are computed on receipt of echoes where EKFs (extended Kalman filters) and electrocardiogram have not been examined for computations. ECG, certain times, results in poor accuracies and low SNRs (signal-to-noise ratios), especially while encountering complicated environments. This work proposes to track online filter performances while using optimization techniques to enhance outcomes with the removal of noise in the signal. The use of cost functions can assist state corrections while lowering costs. A new parameter is optimized using IMCEHOs (Improved Mutation Chaotic Elephant Herding Optimizations) by linearly approximating system nonlinearity where multi-iterative function (Optimized Iterative UKFs) predicts a target's unknown parameters. To obtain optimal solutions theoretically, multi-iterative function takes less iteration, resulting in shorter execution times. The proposed multi-iterative function provides numerical approximations, which are derivative-free implementations. Signals are updated in the cloud environment; the updates are received by the patients from home. The simulation evaluation results with estimators show better performances in terms of reduced NMSEs (normalized mean square errors), RMSEs (root mean squared errors), SNRs, variances, and better accuracies than current approaches. Machine learning algorithms have been used to predict the stages of heart disease, which is updated to the patient in the cloud environment. The proposed work has a 91.0% accuracy rate with an error rate of 0.05% by reducing noise levels.

Rapid, sensitive, and low-cost detection of Escherichia coli bacteria in contaminated water samples using a phage-based assay.

Inadequate drinking water quality is among the major causes of preventable mortality, predominantly in young children. Identifying contaminated water sources remains a significant challenge, especially where resources are limited. The current methods for measuring Escherichia coli (E. coli), the WHO preferred indicator for measuring fecal contamination of water, involve overnight incubation and require specialized training. In 2016, UNICEF released a Target Product Profile (TPP) to incentivize product innovations to detect low levels of viable E. coli in water samples in the field in less than 6 h. Driven by this challenge, we developed a phage-based assay to detect and semi-quantify E. coli. We formulated a phage cocktail containing a total of 8 phages selected against an extensive bacterial strain library and recombined with the sensitive NanoLuc luciferase reporter. The assay was optimized to be processed in a microfluidic chip designed in-house and was tested against locally sourced sewage samples and on drinking water sources in Nairobi, Kenya. With this assay, combined with the microfluidic chip platform, we propose a complete automated solution to detect and semi-quantify E. coli at less than 10 MPN/100 mL in 5.5 h by minimally trained personnel.

Population Dynamics of Epithelial-Mesenchymal Heterogeneity in Cancer Cells.

Phenotypic heterogeneity is a hallmark of aggressive cancer behaviour and a clinical challenge. Despite much characterisation of this heterogeneity at a multi-omics level in many cancers, we have a limited understanding of how this heterogeneity emerges spontaneously in an isogenic cell population. Some longitudinal observations of dynamics in epithelial-mesenchymal heterogeneity, a canonical example of phenotypic heterogeneity, have offered us opportunities to quantify the rates of phenotypic switching that may drive such heterogeneity. Here, we offer a mathematical modeling framework that explains the salient features of population dynamics noted in PMC42-LA cells: (a) predominance of EpCAMhigh subpopulation, (b) re-establishment of parental distributions from the EpCAMhigh and EpCAMlow subpopulations, and (c) enhanced heterogeneity in clonal populations established from individual cells. Our framework proposes that fluctuations or noise in content duplication and partitioning of SNAIL-an EMT-inducing transcription factor-during cell division can explain spontaneous phenotypic switching and consequent dynamic heterogeneity in PMC42-LA cells observed experimentally at both single-cell and bulk level analysis. Together, we propose that asymmetric cell division can be a potential mechanism for phenotypic heterogeneity.

Multiplexed and Extraction-Free Amplification for Simplified SARS-CoV-2 RT-PCR Tests.

The rapid onset of the global COVID-19 pandemic has led to challenges for accurately diagnosing the disease, including supply shortages for sample collection, preservation, and purification. Currently, most diagnostic tests require RNA extraction and detection by RT-PCR; however, extraction is expensive and time-consuming and requires technical expertise. With these challenges in mind, we report extraction-free, multiplexed amplification of SARS-CoV-2 RNA from 246 clinical samples, resulting in 86% sensitivity and 100% specificity. The multiplex RT-PCR uses the CDC singleplex targets and has an LoD of 2 c/µL. We also report on amplification using a range of master mixes in different transport media. This work can help guide which combinations of reagents will enable accurate results when availability of supplies changes throughout the pandemic. Implementing these methods can reduce complexity and cost, minimize reagent usage, expedite time to results, and increase testing capacity.

A student centric method for calculation of fatty acid energetics: Integrated formula and web tool.

Mitochondrial beta-oxidation is one of the most common modes of fatty acids' oxidation in most organisms, particularly mammals. Biochemistry undergraduate curriculum often contains the description of the process, with emphasis on ATP calculations for various types of fatty acids. During our decade long teaching experience in biochemistry, we observed the difficulty faced by students in calculating energetics of several fatty acids beyond palmitic acid. We developed a canonical formula by mathematical transformations and logical derivation to aid the calculation in a much simpler manner to ease both teaching and learning experience. ATP yield of even-numbered fatty acids may be calculated using a formula [(7C - 6 - 1.5 D) - 2(D-2)], andadenosine triphosphate (ATP) yield for odd-numbered fatty acids can be calculated using [(7C - 19 - 1.5 D) - 2(D-2)], where C is the number of carbon atoms in fatty acids, D is the number of double bonds. The unbold part of the formulae is limited to polyunsaturated fatty acids. Moreover, we integrated these formulae into an HTML based web-interface for handily calculations, which is likely to augment fatty acids oxidation learning-teaching processes easier. This tool has been recently tested in our classroom programs on biochemistry and received an excellent feedback from the learners. Also, the mathematical formula is ready for being incorporated into standard biochemistry textbooks. The webtool as an opensource biochemical calculator can be effectively used in classrooms by both instructors and students while solving comprehension based questions on lipid metabolism.

Nanoluciferase Reporter Mycobacteriophage for Sensitive and Rapid Detection of Mycobacterium tuberculosis Drug Susceptibility.

Phenotypic testing for drug susceptibility of Mycobacterium tuberculosis is critical to basic research and managing the evolving problem of antimicrobial resistance in tuberculosis management, but it remains a specialized technique to which access is severely limited. Here, we report on the development and validation of an improved phage-mediated detection system for M. tuberculosis We incorporated a nanoluciferase (Nluc) reporter gene cassette into the TM4 mycobacteriophage genome to create phage TM4-nluc. We assessed the performance of this reporter phage in the context of cellular limit of detection and drug susceptibility testing using multiple biosafety level 2 drug-sensitive and -resistant auxotrophs as well as virulent M. tuberculosis strains. For both limit of detection and drug susceptibility testing, we developed a standardized method consisting of a 96-hour cell preculture followed by a 72-hour experimental window for M. tuberculosis detection with or without antibiotic exposure. The cellular limit of detection of M. tuberculosis in a 96-well plate batch culture was ≤102 CFU. Consistent with other phenotypic methods for drug susceptibility testing, we found TM4-nluc to be compatible with antibiotics representing multiple classes and mechanisms of action, including inhibition of core central dogma functions, cell wall homeostasis, metabolic inhibitors, compounds currently in clinical trials (SQ109 and Q203), and susceptibility testing for bedaquiline, pretomanid, and linezolid (components of the BPaL regimen for the treatment of multi- and extensively drug-resistant tuberculosis). Using the same method, we accurately identified rifampin-resistant and multidrug-resistant M. tuberculosis strains.IMPORTANCEMycobacterium tuberculosis, the causative agent of tuberculosis disease, remains a public health crisis on a global scale, and development of new interventions and identification of drug resistance are pillars in the World Health Organization End TB Strategy. Leveraging the tractability of the TM4 mycobacteriophage and the sensitivity of the nanoluciferase reporter enzyme, the present work describes an evolution of phage-mediated detection and drug susceptibility testing of M. tuberculosis, adding a valuable tool in drug discovery and basic biology research. With additional validation, this system may play a role as a quantitative phenotypic reference method and complement to genotypic methods for diagnosis and antibiotic susceptibility testing.

Genome Sequences of 38 Bacteriophages Infecting Escherichia coli, Isolated from Raw Sewage.

Here, we report the complete genome sequences of 38 novel bacteriophages infecting Escherichia coli, isolated from a raw sewage source in Washington. Of these phages, 26 are under 100 kb, 11 are near 170 kb, and 1 352-kb jumbo phage was discovered.

A Type IA DNA/RNA Topoisomerase with RNA Hydrolysis Activity Participates in Ribosomal RNA Processing.

Topoisomerases maintain topological homeostasis of bacterial chromosomes by catalysing changes in DNA linking number. The resolution of RNA entanglements occurring in the cell would also require catalytic action of topoisomerases. We describe RNA topoisomerase and hydrolysis activities in DNA topoisomerase I (topo I) from mycobacteria. The interaction of topo I with mRNA, tRNA and rRNA suggested its role in some aspect of RNA metabolism; the enzyme participates in rRNA maturation via its RNA hydrolysis activity. Accumulation of rRNA precursors in a topo I knockdown strain and the rescue of rRNA processing deficiency in RNaseE knockdown cells by topo I expression indicated the enzyme's back-up support to RNases involved in rRNA processing. We demonstrate that the active-site tyrosine of the enzyme mediates catalytic reactions with both DNA/RNA substrates, and RNA topoisomerase activity can follow two reaction paths in contrast to its DNA topoisomerase activity. Mutation in the canonical proton relay pathway impacts DNA topoisomerase activity whilst retaining activity on RNA substrates. The mycobacterial topo I thus exemplifies the resourcefulness and parsimony of biological catalysis in harnessing the limited chemical repertoire at its disposal to find common solutions to mechanistically related challenges of phosphodiester breakage/exchange reactions in DNA and RNA that are essential for cell survival.

A Syringe-Based Biosensor to Rapidly Detect Low Levels of Escherichia Coli (ECOR13) in Drinking Water Using Engineered Bacteriophages.

A sanitized drinking water supply is an unconditional requirement for public health and the overall prosperity of humanity. Potential microbial and chemical contaminants of drinking water have been identified by a joint effort between the World Health Organization (WHO) and the United Nations Children's Fund (UNICEF), who together establish guidelines that define, in part, that the presence of Escherichia coli (E. coli) in drinking water is an indication of inadequate sanitation and a significant health risk. As E. coli is a nearly ubiquitous resident of mammalian gastrointestinal tracts, no detectable counts in 100 mL of drinking water is the standard used worldwide as an indicator of sanitation. The currently accepted EPA method relies on filtration, followed by growth on selective media, and requires 24-48 h from sample to results. In response, we developed a rapid bacteriophage-based detection assay with detection limit capabilities comparable to traditional methods in less than a quarter of the time. We coupled membrane filtration with selective enrichment using genetically engineered bacteriophages to identify less than 20 colony forming units (CFU) E. coli in 100 mL drinking water within 5 h. The combination of membrane filtration with phage infection produced a novel assay that demonstrated a rapid, selective, and sensitive detection of an indicator organism in large volumes of drinking water as recommended by the leading world regulatory authorities.

Differential seminal plasma proteome signatures of acute lymphoblastic leukemia survivors.

With advances in therapeutic methods, there is a high survival rate among leukemia patients, of an extent more than 80%. However, chemotherapeutic drugs used to treat these patients have adverse effects on their overall health profile including fertility. The primary aim of this study was to identify differentially expressed proteins in seminal plasma of acute lymphoblastic leukemia (ALL) survivors compared to age-matched healthy controls, which can provide molecular basis of idiopathic infertility in such survivors. Differential proteome profiling was performed by 2D-differential in-gel electrophoresis, protein spots were identified by mass spectrometry and selective differentially expressed proteins (DEPs) were validated by western blotting and ELISA method. Out of eight DEPs identified, five proteins (isocitrate dehydrogenase 1, semenogelin 1, lactoferrin, prolactin-inducible protein, and human serum albumin) were upregulated and three (pepsinogen, prostate specific antigen and prostatic acid phosphatase) were downregulated. Expression profiles of these proteins are suggestive of reduction in semen quality in ALL survivors and can further be explored to determine their fertility status.

Early Detection of Emergent Extensively Drug-Resistant Tuberculosis by Flow Cytometry-Based Phenotyping and Whole-Genome Sequencing.

A critical gap in tuberculosis (TB) treatment is detection of emergent drug resistance. We hypothesized that advanced phenotyping with whole-genome sequencing (WGS) will detect low-frequency Mycobacterium tuberculosis drug resistance. We assessed a reporter mycobacteriophage (Φ2GFP10) in vitro to detect drug-resistant subpopulations and predict M. tuberculosis bactericidal activity in this pilot study. Subsequently, we prospectively studied 20 TB patients with serial Φ2GFP10, Xpert MTB/RIF, and M. tuberculosis culture through end of treatment. WGS was performed, and single nucleotide polymorphisms (SNPs) were examined to detect mixed infection in selected M. tuberculosis isolates. Resistant M. tuberculosis isolates were detected at 1:100,000, and changes in cytometry-gated events were predictive of in vitroM. tuberculosis bactericidal activity using the Φ2GFP10 assay. Emergent drug resistance was detected in one patient by Φ2GFP10 at 3 weeks but not by conventional testing (M. tuberculosis culture and GeneXpert). WGS revealed a phylogeographically distinct extensively drug-resistant tuberculosis (XDR-TB) genome, identical to an XDR-TB isolate from the patient's spouse. Variant lineage-specific SNPs were present early, suggesting mixed infection as the etiology of emergent resistance with temporal trends providing evidence for selection during treatment. Φ2GFP10 can detect low-frequency drug-resistant M. tuberculosis and with WGS characterize emergent M. tuberculosis resistance. In areas of high TB transmission and drug resistance, rapid screening for heteroresistance should be considered.

Rational Design of Biosafety Level 2-Approved, Multidrug-Resistant Strains of Mycobacterium tuberculosis through Nutrient Auxotrophy.

Multidrug-resistant (MDR) tuberculosis, defined as tuberculosis resistant to the two first-line drugs isoniazid and rifampin, poses a serious problem for global tuberculosis control strategies. Lack of a safe and convenient model organism hampers progress in combating the spread of MDR strains of Mycobacterium tuberculosis We reasoned that auxotrophic MDR mutants of M. tuberculosis would provide a safe means for studying MDR M. tuberculosis without the need for a biosafety level 3 (BSL3) laboratory. Two different sets of triple auxotrophic mutants of M. tuberculosis were generated, which were auxotrophic for the nutrients leucine, pantothenate, and arginine or for leucine, pantothenate, and methionine. These triple auxotrophic strains retained their acid-fastness, their ability to generate both a drug persistence phenotype and drug-resistant mutants, and their susceptibility to plaque-forming mycobacterial phages. MDR triple auxotrophic mutants were obtained in a two-step fashion, selecting first for solely isoniazid-resistant or rifampin-resistant mutants. Interestingly, selection for isoniazid-resistant mutants of the methionine auxotroph generated isolates with single point mutations in katG, which encodes an isoniazid-activating enzyme, whereas similar selection using the arginine auxotroph yielded isoniazid-resistant mutants with large deletions in the chromosomal region containing katG These M. tuberculosis MDR strains were readily sterilized by second-line tuberculosis drugs and failed to kill immunocompromised mice. These strains provide attractive candidates for M. tuberculosis biology studies and drug screening outside the BSL3 facility.IMPORTANCE Elimination of Mycobacterium tuberculosis, the bacterium causing tuberculosis, requires enhanced understanding of its biology in order to identify new drugs against drug-susceptible and drug-resistant M. tuberculosis as well as uncovering novel pathways that lead to M. tuberculosis death. To circumvent the need for a biosafety level 3 (BSL3) laboratory when conducting research on M. tuberculosis, we have generated drug-susceptible and drug-resistant triple auxotrophic strains of M. tuberculosis suitable for use in a BSL2 laboratory. These strains originate from a double auxotrophic M. tuberculosis strain, H37Rv ΔpanCD ΔleuCD, which was reclassified as a BSL2 strain based on its lack of lethality in immunocompromised and immunocompetent mice. A third auxotrophy (methionine or arginine) was introduced via deletion of metA or argB, respectively, since M. tuberculosis ΔmetA and M. tuberculosis ΔargB are unable to survive amino acid auxotrophy and infect their host. The resulting triple auxotrophic M. tuberculosis strains retained characteristics of M. tuberculosis relevant for most types of investigations.