Molecular epidemiology of M. tuberculosis in Ethiopia: A systematic review and meta-analysis

Genetic diversity of Mycobacterium tuberculosis strains isolated from spiritual holy water site attendees in Northwest Ethiopia. A cross-sectional study

Background

The genetic diversity of Mycobacterium tuberculosis complex (MTBC) strains was characterized among isolates from individuals with pulmonary tuberculosis (PTB) symptoms attended holy water sites (HWSs) in the Amhara region, Ethiopia.

Methods

A cross-sectional study was done from June 2019 to March 2020 to describe the genetic diversity and drug-resistance profiles of MTBC isolates. Sputum specimens were collected and cultured in the Löwenstein-Jensen culture medium. Line Probe Assay, MTBDRplus VER 2.0, and MTBDRsl VER 2.0 were used to detect first-and second-line anti-TB drug-resistance patterns. A spoligotyping technique was utilized to characterize the genetic diversity. Statistical analysis was performed using STATA 15.

Results

Of 560 PTB-symptomatic participants, 122 (21.8%) were culture-positive cases. Spoligotyping of 116 isolates revealed diverse MTBC sublineages, with four major lineages: Euro-American (EA) (Lineage 4), East-African-Indian (EAI) (Lineage 3), Ethiopian (ETH) (Lineage 7), East Asian (EA) (Lineage 2). The majority (96.6%) of the isolates were EA (lineage 4) and EAI, with proportions of 54.3% and 42.2%, respectively. A total of 31 spoligotype patterns were identified, 26 of which were documented in the SITVIT2 database. Of these, there were 15 unique spoligotypes, while eleven were grouped with 2-17 isolates. SIT149/T3-ETH (n = 17), SIT26/CAS1-DELHI (n = 16), SIT25/CAS1-DELHI (n = 12), and SIT52/T2 (n = 11) spoligotypes were predominant. A rare spoligotype pattern: SIT41/Turkey and SIT1/Beijing, has also been identified in North Shewa. The overall clustering rate of sub-lineages with known SIT was 76.4%.Of the 122 culture-positive isolates tested, 16.4% were resistant to rifampicin (RIF) and/or isoniazid (INH). Multidrug-resistant TB (MDR-TB) was detected in 12.3% of isolates, five of which were fluoroquinolones (FLQs) resistant. SIT149/T3-ETH and SIT21/CAS1-KILI sublineages showed a higher proportion of drug resistance.

Conclusions

Diverse MTBC spoligotypes were identified, with the T and CAS families and EA (lineage 4) predominating. A high prevalence of drug-resistant TB, with SIT149/T3-ETH and CAS1-KILI sublineages comprising a greater share, was observed. A study with large sample size and a sequencing method with stronger discriminatory power is warranted to understand better the genetic diversity of circulating MTBC in this cohort of study, which would help to adopt targeted interventions.

Molecular epidemiology and drug sensitivity of Mycobacterium tuberculosis in homeless individuals in the Addis Ababa city, Ethiopia

Although homeless segment of the society could be the hotspots for tuberculosis (TB) transmission, there is little data on TB in homeless individuals in Ethiopia. The objective of this study was to investigate the molecular epidemiology and drug sensitivity of Mycobacterium tuberculosis (M. tuberculosis) isolated from homeless individuals in Addis Ababa, Ethiopia. The study was conducted on 59 M. tuberculosis isolates, which were recovered by the clinical screening of 5600 homeless individuals and bacteriological examination of 641 individuals with symptoms of pulmonary tuberculosis (PTB). Region of difference-9 (RD9) based polymerase-chain reaction (PCR), Spoligotyping and 24-loci Mycobacterial Interspersed Repetitive Unit-Variable Number Tandem Repeat (MIRU-VNTR) typing were used for genotyping of the isolates. In addition, drug sensitivity test was performed on the isolates using BD Bactec Mycobacterial Growth Inhibition Tube (MGIT) 960. Fifty-eight of the 59 isolates were positive by spoligotyping and spoligotyping International type (SIT) 53, SIT 37, and SIT 149 were the dominant spoligotypes; each consisting of 19%, 15.5%, and10.3% of the isolates, respectively. The majority of the isolates (89.7%) were members of the Euro-American (EA) major lineage. MIRU-VNTR identified Ethiopia_3, Delhi/CAS, Ethiopia_2, TUR, X-type, Ethiopia_H37Rv-like strain, Haarlem and Latin-American Mediterranean (LAM) sub lineages. The proportion of clustering was 77.6% (45/58) in spoligotyping while it was 39.7% (23/58) in 24-loci MIRU-VNTR typing. Furthermore, the proportion of clustering was significantly lowered to 10.3% (6/58) when a combination of spoligotyping and 24-loci MIRU-VNTRplus was used. The recent transmission index (RTI) recorded by spoligotyping, 24-loci MIRU-VNTR typing, and a combination of the two genotyping methods were 58.6%, 27.6% and 5.2%, respectively. Young age and living in groups were significantly associated with strain clustering (P < 0.05). The drug sensitivity test (DST) result showed 8.9% (4/58) of the isolates were resistant to one or more first line ant-TB drugs; but multidrug resistant isolate was not detected. Clustering and RTI could suggest the transmission of TB in the homeless individuals, which could suggest a similar pattern of transmission between homeless individuals and the general population. Hence, the TB control program should consider homeless individuals during the implementation of TB control program.

Genomic transmission clusters and circulating lineages of Mycobacterium tuberculosis among refugees residing in refugee camps in Ethiopia

BACKGROUND

Understanding the transmission dynamics of Mycobacterium tuberculosis (Mtb) could benefit the design of tuberculosis (TB) prevention and control strategies for refugee populations. Whole Genome Sequencing (WGS) has not yet been used to document the Mtb transmission dynamics among refugees in Ethiopia. We applied WGS to accurately identify transmission clusters and Mtb lineages among TB cases in refugee camps in Ethiopia.

METHOD AND DESIGN

We conducted a cross-sectional study of 610 refugees in refugee camps in Ethiopia presenting with symptoms of TB. WGS data of 67 isolates was analyzed using the Maximum Accessible Genome for Mtb Analysis (MAGMA) pipeline; iTol and FigTree were used to visualize phylogenetic trees, lineages, and the presence of transmission clusters.

RESULTS

Mtb culture-positive refugees originated from South Sudan (52/67, 77.6%), Somalia (9/67, 13.4%). Eritrea (4/67, 6%), and Sudan (2/67, 3%). The majority (52, 77.6%) of the isolates belonged to Mtb lineage (L) 3, and one L9 was identified from a Somalian refugee. The vast majority (82%) of the isolates were pan-susceptible Mtb, and none were multi-drug-resistant (MDR)-TB. Based on the 5-single nucleotide polymorphisms cutoff, we identified eight potential transmission clusters containing 23.9% of the isolates. Contact investigation confirmed epidemiological links with either family or social interaction within the refugee camps or with neighboring refugee camps.

CONCLUSION

Four lineages (L1, L3, L4, and L9) were identified, with the majority of strains being L3, reflecting the Mtb L3 dominance in South Sudan, where the majority of refugees originated from. Recent transmission among refugees was relatively low (24%), likely due to the short study period. The improved understanding of the Mtb transmission dynamics using WGS in refugee camps could assist in designing effective TB control programs for refugees.

Genetic diversity of Mycobacterium tuberculosis isolates from the central, eastern and southeastern Ethiopia

Introduction

The population structure of Mycobacterium tuberculosis complex (MTBC) in Ethiopia is diverse but dominated by Euro-American (Lineage 4) and East-African-Indian (Lineage 3) lineages. The objective of this study was to describe the genetic diversity of MTBC isolates in Central, Eastern and Southeastern Ethiopia.

Methods

A total of 223 MTBC culture isolates obtained from patients referred to Adama and Harar TB reference laboratories were spoligotyped. Demographic and clinical characteristics were collected.

Results

Six major lineages: Euro-American (Lineage 4), East-African-Indian (Lineage 3), East Asian (Lineage 2), Indo-Oceanic (Lineage 1), Mycobacterium africanum (Lineage 5 and Lineage 6) and Ethiopian (Lineage 7) were identified. The majority (94.6 %) of the isolates were Euro-American and East-African-Indian, with proportions of 75.3 % and 19.3 %, respectively. Overall, 77 different spoligotype patterns were identified of which 42 were registered in the SITVIT2 database. Of these, 27 spoligotypes were unique, while 15 were clustered with 2-49 isolates. SIT149/T3_ETH (n = 49), SIT53/T1 (n = 33), SIT21/CAS1_Kili (n = 24) and SIT41/Turkey (n = 11) were the dominant spoligotypes. A rare Beijing spoligotype pattern, SIT541, has also been identified in Eastern Ethiopia. The overall clustering rate of sub-lineages with known SIT was 71.3 %. Age group (25-34) was significantly associated with clustering.

Conclusion

We found a heterogeneous population structure of MTBC dominated by T and CAS families, and the Euro-American lineage. The identification of the Beijing strain, particularly the rare SIT541 spoligotype in Eastern Ethiopia, warrants a heightened surveillance plan, as little is known about this genotype. A large-scale investigation utilizing a tool with superior discriminatory power, such as whole genome sequencing, is necessary to gain a thorough understanding of the genetic diversity of MTBC in the nation, which would help direct the overall control efforts.

Molecular epidemiology and transmission dynamics of multi-drug resistant tuberculosis strains using whole genome sequencing in the Amhara region, Ethiopia

BACKGROUND

Drug resistant Mycobacterium tuberculosis prevention and care is a major challenge in Ethiopia. The World health organization has designated Ethiopia as one of the 30 high burden multi-drug resistant tuberculosis (MDR-TB) countries. There is limited information regarding genetic diversity and transmission dynamics of MDR-TB in Ethiopia.

OBJECTIVE

To investigate the molecular epidemiology and transmission dynamics of MDR-TB strains using whole genome sequence (WGS) in the Amhara region.

METHODS

Forty-five MDR-TB clinical isolates from Amhara region were collected between 2016 and 2018, and characterized using WGS and 24-loci Mycobacterium Interspersed Repetitive Units Variable Number of Tandem Repeats (MIRU-VNTR) typing. Clusters were defined based on the maximum distance of 12 single nucleotide polymorphisms (SNPs) or alleles as the upper threshold of genomic relatedness. Five or less SNPs or alleles distance or identical 24-loci VNTR typing is denoted as surrogate marker for recent transmission.

RESULTS

Forty-one of the 45 isolates were analyzed by WGS and 44% (18/41) of the isolates were distributed into 4 clusters. Of the 41 MDR-TB isolates, 58.5% were classified as lineage 4, 36.5% lineage 3 and 5% lineage 1. Overall, TUR genotype (54%) was the predominant in MDR-TB strains. 41% (17/41) of the isolates were clustered into four WGS groups and the remaining isolates were unique strains. The predominant cluster (Cluster 1) was composed of nine isolates belonging to lineage 4 and of these, four isolates were in the recent transmission links.

CONCLUSIONS

Majority of MDR-TB strain cluster and predominance of TUR lineage in the Amhara region give rise to concerns for possible ongoing transmission. Efforts to strengthen TB laboratory to advance diagnosis, intensified active case finding, and expanded contact tracing activities are needed in order to improve rapid diagnosis and initiate early treatment. This would lead to the interruption of the transmission chain and stop the spread of MDR-TB in the Amhara region.

Comparative whole-genome sequence analysis of Mycobacterium tuberculosis isolated from pulmonary tuberculosis and tuberculous lymphadenitis patients in Northwest Ethiopia

Background

Tuberculosis (TB), caused by the Mycobacterium tuberculosis complex (MTBC), is a chronic infectious disease with both pulmonary and extrapulmonary forms. This study set out to investigate and compare the genomic diversity and transmission dynamics of Mycobacterium tuberculosis (Mtb) isolates obtained from tuberculous lymphadenitis (TBLN) and pulmonary TB (PTB) cases in Northwest Ethiopia.

Methods

A facility-based cross-sectional study was conducted using two groups of samples collected between February 2021 and June 2022 (Group 1) and between June 2020 and June 2022 (Group 2) in Northwest Ethiopia. Deoxyribonucleic acid (DNA) was extracted from 200 heat-inactivated Mtb isolates. Whole-genome sequencing (WGS) was performed from 161 isolates having ≥1 ng DNA/μl using Illumina NovaSeq 6000 technology.

Results

From the total 161 isolates sequenced, 146 Mtb isolates were successfully genotyped into three lineages (L) and 18 sub-lineages. The Euro-American (EA, L4) lineage was the prevailing (n = 100; 68.5%) followed by Central Asian (CAS, L3, n = 43; 25.3%) and then L7 (n = 3; 2.05%). The L4.2.2.ETH sub-lineage accounted for 19.9%, while Haarlem estimated at 13.7%. The phylogenetic tree revealed distinct Mtb clusters between PTB and TBLN isolates even though there was no difference at lineages and sub-lineages levels. The clustering rate (CR) and recent transmission index (RTI) for PTB were 30 and 15%, respectively. Similarly, the CR and RTI for TBLN were 31.1 and 18 %, respectively.

Conclusion and recommendations

PTB and TBLN isolates showed no Mtb lineages and sub-lineages difference. However, at the threshold of five allelic distances, Mtb isolates obtained from PTB and TBLN form distinct complexes in the phylogenetic tree, which indicates the presence of Mtb genomic variation among the two clinical forms. The high rate of clustering and RTI among TBLN implied that TBLN was likely the result of recent transmission and/or reactivation from short latency. Hence, the high incidence rate of TBLN in the Amhara region could be the result of Mtb genomic diversity and rapid clinical progression from primary infection and/or short latency. To validate this conclusion, a similar community-based study with a large sample size and better sampling technique is highly desirable. Additionally, analysis of genomic variants other than phylogenetic informative regions could give insightful information. Combined analysis of the host and the pathogen genome (GXG) together with environmental (GxGxE) factors could give comprehensive co-evolutionary information.

Lack of methoxy-mycolates characterizes the geographically restricted lineage 7 of Mycobacterium tuberculosis complex

Lineage 7 (L7) emerged in the phylogeny of the Mycobacterium tuberculosis complex (MTBC) subsequent to the branching of 'ancient' lineage 1 and prior to the Eurasian dispersal of 'modern' lineages 2, 3 and 4. In contrast to the major MTBC lineages, the current epidemiology suggests that prevalence of L7 is highly confined to the Ethiopian population, or when identified outside of Ethiopia, it has mainly been in patients of Ethiopian origin. To search for microbiological factors that may contribute to its restricted distribution, we compared the genome of L7 to the genomes of globally dispersed MTBC lineages. The frequency of predicted functional mutations in L7 was similar to that documented in other lineages. These include mutations characteristic of modern lineages - such as constitutive expression of nitrate reductase - as well as mutations in the VirS locus that are commonly found in ancient lineages. We also identified and characterized multiple lineage-specific mutations in L7 in biosynthesis pathways of cell wall lipids, including confirmed deficiency of methoxy-mycolic acids due to a stop-gain mutation in the mmaA3 gene that encodes a methoxy-mycolic acid synthase. We show that the abolished biosynthesis of methoxy-mycolates of L7 alters the cell structure and colony morphology on selected growth media and impacts biofilm formation. The loss of these mycolic acid moieties may change the host-pathogen dynamic for L7 isolates, explaining the limited geographical distribution of L7 and contributing to further understanding the spread of MTBC lineages across the globe.

Whole Genome Sequencing of Drug Resistant and Drug Susceptible Mycobacterium tuberculosis Isolates From Tigray Region, Ethiopia

Background: Tuberculosis, mainly caused by Mycobacterium tuberculosis (Mtb), is an ancient human disease that gravely affects millions of people annually. We wanted to explore the genetic diversity and lineage-specific association of Mtb with drug resistance among pulmonary tuberculosis patients. Methods: Sputum samples were collected from pulmonary tuberculosis patients at six different healthcare institutions in Tigray, Ethiopia, between July 2018 and August 2019. DNA was extracted from 74 Mtb complex isolates for whole-genome sequencing (WGS). All genomes were typed and screened for mutations with known associations with antimicrobial resistance using in silico methods, and results were cross-verified with wet lab methods. Results: Lineage (L) 4 (55.8%) was predominant, followed by L3 (41.2%); L1 (1.5%) and L2 (1.5%) occurred rarely. The most frequently detected sublineage was CAS (38.2%), followed by Ural (29.4%), and Haarlem (11.8%). The recent transmission index (RTI) was relatively low. L4 and Ural strains were more resistant than the other strains to any anti-TB drug (P < 0.05). The most frequent mutations to RIF, INH, EMB, SM, PZA, ETH, FLQs, and 2nd-line injectable drugs occurred at rpoB S450L, katG S315T, embB M306I/V, rpsL K43R, pncA V139A, ethA M1R, gyrA D94G, and rrs A1401G, respectively. Disputed rpoB mutations were also shown in four (16%) of RIF-resistant isolates. Conclusion: Our WGS analysis revealed the presence of diverse Mtb genotypes. The presence of a significant proportion of disputed rpoB mutations highlighted the need to establish a WGS facility at the regional level to monitor drug-resistant mutations. This will help control the transmission of DR-TB and ultimately contribute to the attainment of 100% DST coverage for TB patients as per the End TB strategy.

Lipid droplets and the transcriptome of Mycobacterium tuberculosis from direct sputa: a literature review

Mycobacterium tuberculosis (Mtb), the main etiology of tuberculosis (TB), is predominantly an intracellular pathogen that has caused infection, disease and death in humans for centuries. Lipid droplets (LDs) are dynamic intracellular organelles that are found across the evolutionary tree of life. This review is an evaluation of the current state of knowledge regarding Mtb-LD formation and associated Mtb transcriptome directly from sputa.Based on the LD content, Mtb in sputum may be classified into three groups: LD positive, LD negative and LD borderline. However, the clinical and evolutionary importance of each state is not well elaborated. Mounting evidence supports the view that the presence of LD positive Mtb bacilli in sputum is a biomarker of slow growth, low energy state, towards lipid degradation, and drug tolerance. In Mtb, LD may serve as a source of chemical energy, scavenger of toxic compounds, prevent destruction of Mtb through autophagy, delay trafficking of lysosomes towards the phagosome, and contribute to Mtb persistence. It is suggest that LD is a key player in the induction of a spectrum of phenotypic and metabolic states of Mtb in the macrophage, granuloma and extracellular sputum microenvironment. Tuberculosis patients with high proportion of LD positive Mtb in pretreatment sputum was associated with higher rate of poor treatment outcome, indicating that LD may have a clinical application in predicting treatment outcome.The propensity for LD formation among Mtb lineages is largely unknown. The role of LD on Mtb transmission and disease phenotype (pulmonary TB vs extra-pulmonary TB) is not well understood. Thus, further studies are needed to understand the relationships between LD positivity and Mtb lineage, Mtb transmission and clinical types.

Mycobacterial Lineages Associated with Drug Resistance in Patients with Extrapulmonary Tuberculosis in Addis Ababa, Ethiopia

BACKGROUND

In Ethiopia, tuberculosis (TB) is one of the most common causes of illness and death. However, there is limited information available on lineages associated with drug resistance among extrapulmonary tuberculosis patients in Ethiopia. In this study, researchers looked into Mycobacterium tuberculosis lineages linked to drug resistance in patients with extrapulmonary tuberculosis in Addis Ababa, Ethiopia.

METHODS

On 151 Mycobacterium tuberculosis isolates, a cross-sectional analysis was performed. Spoligotyping was used to characterize mycobacterial lineages, while a phenotypic drug susceptibility test was performed to determine the drug resistance pattern. Data were analyzed using SPSS version 23.

RESULTS

Among 151 Mycobacterium tuberculosis complex (MTBC) genotyped isolates, four lineages (L1-L4), and Mycobacterium bovis were identified. The predominantly identified lineage was Euro-American (73.5%) followed by East-African-Indian (19.2%). Any drug resistance (RR) and multidrug-resistant (MDR) tuberculosis was identified among 16.2% and 7.2% of the Euro-American lineage, respectively, while it was 30.8% and 15.4% among the East-African-Indian lineages. Among all three preextensively drug-resistance (pre-XDR) cases identified, two isolates belong to T3-ETH, and the other one strain was not defined by the database. There was no statistically significant association between any type of drug resistance and either lineage or sublineages of Mycobacterium tuberculosis.

CONCLUSION

A higher proportion of any type of drug resistance and MDR was detected among the East-African-Indian lineage compared to others. However, there was no statistically significant association between any type of drug resistance and either lineages or sublineages. Thus, the authors recommend a large-scale study.

Epidemiology of Mycobacterium tuberculosis lineages and strain clustering within urban and peri-urban settings in Ethiopia

Background

Previous work has shown differential predominance of certain Mycobacterium tuberculosis (M. tb) lineages and sub-lineages among different human populations in diverse geographic regions of Ethiopia. Nevertheless, how strain diversity is evolving under the ongoing rapid socio-economic and environmental changes is poorly understood. The present study investigated factors associated with M. tb lineage predominance and rate of strain clustering within urban and peri-urban settings in Ethiopia.

Methods

Pulmonary Tuberculosis (PTB) and Cervical tuberculous lymphadenitis (TBLN) patients who visited selected health facilities were recruited in the years of 2016 and 2017. A total of 258 M. tb isolates identified from 163 sputa and 95 fine-needle aspirates (FNA) were characterized by spoligotyping and compared with international M.tb spoligotyping patterns registered at the SITVIT2 databases. The molecular data were linked with clinical and demographic data of the patients for further statistical analysis.

Results

From a total of 258 M. tb isolates, 84 distinct spoligotype patterns that included 58 known Shared International Type (SIT) patterns and 26 new or orphan patterns were identified. The majority of strains belonged to two major M. tb lineages, L3 (35.7%) and L4 (61.6%). The observed high percentage of isolates with shared patterns (n = 200/258) suggested a substantial rate of overall clustering (77.5%). After adjusting for the effect of geographical variations, clustering rate was significantly lower among individuals co-infected with HIV and other concomitant chronic disease. Compared to L4, the adjusted odds ratio and 95% confidence interval (AOR; 95% CI) indicated that infections with L3 M. tb strains were more likely to be associated with TBLN [3.47 (1.45, 8.29)] and TB-HIV co-infection [2.84 (1.61, 5.55)].

Conclusion

Despite the observed difference in strain diversity and geographical distribution of M. tb lineages, compared to earlier studies in Ethiopia, the overall rate of strain clustering suggests higher transmission and warrant more detailed investigations into the molecular epidemiology of TB and related factors.

Drug Resistance Conferring Mutation and Genetic Diversity of Mycobacterium tuberculosis Isolates in Tuberculosis Lymphadenitis Patients; Ethiopia

Background

Tuberculosis lymphadenitis (TBLN) is a growing public health concern in Ethiopia. However, there is limited information available on gene mutations conferring drug resistance and genetic diversity of M. tuberculosis isolates from TBLN patients.

Methods

Drug resistance and genetic diversity analysis were done on 91 M. tuberculosis isolates from culture positive TBLN patients collected between 2016 and 2017. Detection of mutations conferring resistance was carried out using GenoType MTBDRplus VER 2.0. Thereafter, isolates were typed using spoligotyping.

Results

Out of the 91 strains, mutations conferring resistance to rifampicin (RIF) and isoniazid (INH) were observed in two (2.2%) and six (6.6%) isolates, respectively. The two RIF resistant isolates displayed a mutation at codon 531 in the rpoB gene with amino acid change of S531L. Among the six INH resistant strains, four isolates had shown mutation at the KatG gene at codon 315 with amino acid change of S315T, one isolate had a mutation at the inhA gene at codon 15 with amino acid change of C15T and one isolate had a mutation at the inhA gene with unknown amino acid change. All drug resistant isolates were from treatment naive TBLN patients. The dominantly identified Spoligo International Types (SITs) were SIT25, SIT149, and SIT53, respectively; these accounted for 43% of the total number of strains. The isolates were grouped into four main lineages; Lineage 1 (2, 2.2%), Lineage 3 (38, 41.7%), Lineage 4 (49, 53.8%) and Lineage 7 (2, 2.2%). Four out of six (66.7%) isolates with drug resistance conferring mutations belonged to clustered strains (strains with shared SIT).

Conclusion

The detection of drug resistant conferring mutation in treatment naïve TBLN patients together with detection of drug resistant isolates among clustered strains might suggest resistant strains' transmission in the community. This needs to be carefully considered to prevent the spread of drug resistant clones in the country.

Genetic diversity and drug resistance pattern of Mycobacterium tuberculosis strains isolated from pulmonary tuberculosis patients in the Benishangul Gumuz region and its surroundings, Northwest Ethiopia

Introduction

Tuberculosis (TB) remains a major global public health problem and is the leading cause of death from a single bacterium, Mycobacterium tuberculosis (MTB) complex. The emergence and spread of drug-resistant strains aggravate the problem, especially in tuberculosis high burden countries such as Ethiopia. The supposedly high initial cost of laboratory diagnosis coupled with scarce financial resources has limited collection of information about drug resistance patterns and circulating strains in peripheral and emerging regions of Ethiopia. Here, we investigated drug susceptibility and genetic diversity of mycobacterial isolates among pulmonary tuberculosis patients in the Benishangul Gumuz region and its surroundings in northwest Ethiopia.

Methods and material

In a cross-sectional study, 107 consecutive sputum smear-positive pulmonary tuberculosis (PTB) patients diagnosed at two hospitals and seven health centers were enrolled between October 2013 and June 2014. Sputum samples were cultured at Armauer Hansen Research Institute (AHRI) TB laboratory, and drug susceptibility testing (DST) was performed against Isoniazid, Rifampicin, Ethambutol, and Streptomycin using the indirect proportion method. Isolates were characterized using polymerase chain reaction (PCR)based Region of Difference 9 (RD9) testing and spoligotyping. Statistical analysis was performed using Statistical Package for the Social Sciences (SPSS) for Windows version 24.0.

Results

Of 107 acid-fast-bacilli (AFB) smear-positive sputum samples collected, 81.3% (87/107) were culture positive. A PCR based RD9 testing revealed that all the 87 isolates were M. tuberculosis. Of these isolates, 16.1% (14/87) resistance to one or more drugs was observed. Isoniazid monoresistance occurred in 6.9% (6/87). Multidrug resistance (MDR) was observed in two isolates (2.3%), one of which was resistant to all the four drugs tested. Spoligotyping revealed that the majority, 61.3% (46/75) of strains could be grouped into ten spoligotype patterns containing two to 11 isolates each while the remaining 38.7% (29/75) were unique. SIT289 (11 isolates) and SIT53 (nine isolates) constituted 43.5% (20/46) among clustered isolates while 29.3% (22/75) were ‘‘New” to the database. The dominant families were T, 37% (28/75), CAS, 16.0% (12/75), and H, 8% (6/75), adding up to 51.3% (46/75) of all isolates identified.

Conclusion and recommendations

The current study indicates a moderate prevalence of MDR TB. However, the observed high monoresistance to Isoniazid, one of the two proxy drugs for MDR-TB, reveals the hidden potential threat fora sudden increase in MDR-TB if resistance to Rifampicin would increase. Clustered spoligotype patterns suggest ongoing active tuberculosis transmission in the area. The results underscore the need for enhanced monitoring of TB drug resistance and epidemiological studies in this and other peripheral regions of the country using robust molecular tools with high discriminatory power such as the Mycobacterial Interspersed Repetitive Units -Variable Number of Tandem Repeats (MIRU-VNTR) typing and whole-genome sequencing (WGS).