Reduced virulence of an extensively drug-resistant outbreak strain of Mycobacterium tuberculosis in a murine model

Novel Experimental Mouse Model to Study the Pathogenesis and Therapy of Actinobacillus pleuropneumoniae Infection

Actinobacillus pleuropneumoniae (APP) is a major cause of lung infections in pigs. An experimental mouse has the edge over pigs pertaining to the ease of experimental operation, disease study and therapy, abundance of genetic resources, and cost. However, it is a challenge to introduce APP into a mouse lung due to the small respiratory tract of mice and bacterial host tropism. In this study, an effective airborne transmission of APP serovar 1 (APP1) was developed in mice for lung infection. Consequently, APP1 infected BALB/c mice and caused 60% death within three days of infection at the indicated condition. APP1 seemed to enter the lung and, in turn, spread to other organs of the mice over the first 5 days after infection. Accordingly, APP1 damaged the lung as evidenced by its morphological and histological examinations. Furthermore, ampicillin fully protected mice against APP1 as shown by their survival, clinical symptoms, body weight loss, APP1 count, and lung damages. Finally, the virulence of two extra APP strains, APP2 and APP5, in the model was compared based on the survival rate of mice. Collectively, this study successfully established a fast and reliable mouse model of APP which can benefit APP research and therapy. Such a model is a potentially useful model for airway bacterial infections.

DNA supercoiling and regulation of intrinsic β-lactamase in pathogenic Escherichia coli

This review addresses the involvement of DNA supercoiling in the development of virulence and antibiotic profiles for uropathogenic Escherichia coli and the emergence of new pathotypes such as strain ST131 (serotype O25:H4). The mechanism suggests a role for topoisomerase enzymes and associated mutations in altering the chromosomal supercoiling state and introducing the required DNA twists for expression of intrinsic β-lactamase by ampC and certain virulence factors. In Escherichia coli, constitutive hyperexpression of intrinsic ampC is associated with specific mutations in the promoter and attenuator regions. However, many reports have documented the involvement of slow growth interventions in the expression of intrinsic resistance determinants. There is evidence that a stationary phase transcriptional switch protein, "BolA," is involved in the expression of the intrinsic ampC gene under starvation conditions. The process involves changes in the activity of the enzyme "gyrase," which leads to a change in the chromosomal DNA topology. Consequently, the DNA is relaxed, and the expression of the bolA gene is upregulated. The evolution of the extraintestinal pathogenic E. coli strain ST131 has demonstrated successful adaptability to various stress conditions and conferred compensatory mutations that endowed the microbe with resistance to fluoroquinolones and β-lactams. The results of this study provided new insights into the evidence for the influence of DNA topology in the expression of virulence genes and various determinants of antibiotic resistance (e.g., the intrinsic ampC gene) in Escherichia coli pathotypes.

Do B-1 cells play a role in response to Mycobacterium tuberculosis Beijing lineages?

We highlight the need to include an analysis of the B-1 B cell subset to complement the characterization of the cell-mediated immune response to the Mycobacterium tuberculosis Beijing lineage. The literature describes the B-1 cell repertoire's involvement in the cell-mediated response within granulomas, which is different from the classic antibody response B cells are generally associated with. Specifically, the B-1 B cell subset migrates from other compartments along with other cells to the infection site. We provide details to complement the reported results from Cerezo-Cortes et al.

Rv1258c acts as a drug efflux pump and growth controlling factor in Mycobacterium tuberculosis

The possible role of efflux pump as a survival mechanism in Mycobacterium tuberculosis (M. tb) is gaining an increasing attention. Previously, Rv1258c (Tap) and its certain mutations confer the clinically relevant drug resistance. In this study, we found new mutations of Rv1258c in G195C, T297P and I328T. Effect of modulating T297P and I328T on the drug resistance by knockout and complement in M. tb H37Rv showed that M. tb ΔRv1258c showed a slightly lower MIC for rifampin, ethambutol, ofloxacin, amikacin, capreomycin and streptomycin than M. tb H37Rv WT and the complement. Rv1258c T297P and Rv1258c I328T showed an increased drug resistance to ethambutol and capreomycin than the complement of Rv1258c WT. Most importantly, M. tb ΔRv1258c exhibited a slow growth in the normal culture medium. TMT-based quantitative proteomics analysis of M. tb ΔRv1258c and WT showed that the knockout of Rv1258c greatly down-regulated the expression of the ribosome system and one of the special five type VII secretion systems, ESX-3, which impaired the bacterial growth. These results indicate that the newly found T297P and I328T mutations of Rv1258c contributed to an increased resistance to ethambutol and capreomycin, and Rv1258c as growth controlling factor influencing the growth of M. tb.

Genetic and Virulence Characteristics of Linezolid and Pretomanid Dual Drug-Resistant Strains Induced from Mycobacterium tuberculosis in vitro

Purpose

Linezolid (LZD) and pretomanid (PA-824) are promising candidates in regimens for the treatment of drug-resistant tuberculosis. However, research on LZD and PA-824 dual drug-resistant (LPDR) strains is rarely reported. This study aimed to investigate the genotypic and virulence characteristics of LPDR strains.

Methods

To obtain the LPDR strains (marked as LP or PL strains), we used a two-way induction method, namely, we first induced LZD- or PA-824-resistant mutants from the parental Mycobacterium tuberculosis (MTB) strain H37Rv in vitro, then we obtained the LPDR strains from induction of LZD- or PA-824-resistant mutants. Mutations in rplC, rrl, or ddn and fgd1 were identified in all mutants. To investigate the virulence of these strains, six strains were selected as representative strains, including LZD-resistant strains, PA-824-resistant strains and LPDR strains. We performed the animal survival study as virulence of MTB can be measured as survival time of an animal after being infected.

Results

We induced 38 mutant strains of LZD and PA-824 mono or dual drug resistance from H37Rv in vitro. The mutation frequency of rplC (C154R) gene in LPDR strains was 100% and 86%, respectively. In the animal survival study, animals infected with different drug-resistant strains survived significantly longer than those infected with H37Rv; animals infected with LPDR strains and PA-824-resistant strains survived similarly and both of which survived significantly shorter than those infected with LZD-resistant strains.

Conclusion

Our study showed that rplC gene had a high mutation frequency in LPDR strains. The virulence of LPDR strains was similar to PA-824-resistant strains, and the virulence of the LZD-resistant strains was weaker than PA-824-resistant strains.

A Single Amino Acid Replacement in Penicillin-Binding Protein 2X in Streptococcus pyogenes Significantly Increases Fitness on Subtherapeutic Benzylpenicillin Treatment in a Mouse Model of Necrotizing Myositis

Invasive strains of Streptococcus pyogenes with significantly reduced susceptibility to β-lactam antibiotics have been recently described. These reports have caused considerable concern in the international infectious disease, medical microbiology, and public health communities because S. pyogenes has remained universally susceptible to β-lactam antibiotics for 70 years. Virtually all analyzed strains had single amino acid replacements in penicillin-binding protein 2X (PBP2X), a major target of β-lactam antibiotics in pathogenic bacteria. We used isogenic strains to test the hypothesis that a single amino acid replacement in PBP2X conferred a fitness advantage in a mouse model of necrotizing myositis. We determined that when mice were administered intermittent subtherapeutic dosing of benzylpenicillin, the strain with a Pro601Leu amino acid replacement in PBP2X that confers reduced β-lactam susceptibility in vitro was more fit, as assessed by the magnitude of colony-forming units recovered from disease tissue. These data provide important pathogenesis information that bears on this emerging global infectious disease problem.

Genetic Evolution of Mycobacterium abscessus Conferring Clarithromycin Resistance during Long-Term Antibiotic Therapy

Objectives

Clarithromycin is recommended as the core agent for treating M. abscessus infections, which usually calls for at least one year of treatment course, facilitating the development of resistance. This study aimed to identify the underlying mechanism of in vivo development of clarithromycin resistance in M. abscessus clinical isolates.

Methods

M. abscessus isolates from patients with lung infections during long-term antibiotic therapy were longitudinally collected and sequenced. PFGE DNA fingerprinting was used to confirm the genetic relationships of the isolates. Whole genome comparative analysis was performed to identify the genetic determinants that confer the clarithromycin resistance.

Results

Three pairs of initially clarithromycin-susceptible and subsequently clarithromycin-resistant M. abscessus isolates were obtained. We found that the clarithromycin-resistant isolates emerged relatively rapidly, after 4–16 months of antibiotic therapy. PFGE DNA fingerprinting showed that the clarithromycin-resistant isolates were identical to the initial clarithromycin-susceptible ones. Whole genome sequencing and bioinformatics analysis identified several genetic alternations in clarithromycin-resistant isolates, including genes encoding efflux pump/transporter, integral component of membrane, and the tetR and lysR family transcriptional regulators.

Conclusion

We identified genes likely encoding new factors contributing to clarithromycin-resistance phenotype of M. abscessus, which can be useful in prediction of clarithromycin resistance in M. abscessus.

Pre-detection history of extensively drug-resistant tuberculosis in KwaZulu-Natal, South Africa

Antimicrobial-resistant (AMR) infections pose a major threat to global public health. Similar to other AMR pathogens, both historical and ongoing drug-resistant tuberculosis (TB) epidemics are characterized by transmission of a limited number of predominant Mycobacterium tuberculosis (Mtb) strains. Understanding how these predominant strains achieve sustained transmission, particularly during the critical period before they are detected via clinical or public health surveillance, can inform strategies for prevention and containment. In this study, we employ whole-genome sequence (WGS) data from TB clinical isolates collected in KwaZulu-Natal, South Africa to examine the pre-detection history of a successful strain of extensively drug-resistant (XDR) TB known as LAM4/KZN, first identified in a widely reported cluster of cases in 2005. We identify marked expansion of this strain concurrent with the onset of the generalized HIV epidemic 12 y prior to 2005, localize its geographic origin to a location in northeastern KwaZulu-Natal ∼400 km away from the site of the 2005 outbreak, and use protein structural modeling to propose a mechanism for how strain-specific rpoB mutations offset fitness costs associated with rifampin resistance in LAM4/KZN. Our findings highlight the importance of HIV coinfection, high preexisting rates of drug-resistant TB, human migration, and pathoadaptive evolution in the emergence and dispersal of this critical public health threat. We propose that integrating whole-genome sequencing into routine public health surveillance can enable the early detection and local containment of AMR pathogens before they achieve widespread dispersal.

Finding New Ways to Combat Multidrug-Resistant Tuberculosis

Tuberculosis (TB) is a major issue in global health and affects millions of people each year. Multidrug-resistant tuberculosis (MDR-TB) annually causes many deaths worldwide. Development of a way to diagnose and treat patients with MDR-TB can potentially reduce the incidence of the disease. The current study reviews the risk factors, pattern of progression, mechanism of resistance, and interaction between bacteria and the host immune system, which disrupts the immune response. It also targets the components of Mycobacterium tuberculosis (Mtb) and diagnosis and treatment options that could be available for clinical use in the near future. Mutations play an important role in development of MDR-TB and the selection of appropriate mutations can help to understand the type of resistance in patients to anti-TB drugs. In this way, they can be initially treated with proper and effective therapeutic choices, which can accelerate the course of treatment and improve patient health. Targeting the components and enzymes of Mtb is necessary for understanding bacterial survival and finding a way to destroy the pathogen and allow patients to recover faster and prevent the spread of disease, especially resistant strains.

Wavelet-domain elastic net for clustering on genomes strains

We propose to evaluate genome similarity by combining discrete non-decimated wavelet transform (NDWT) and elastic net. The wavelets represent a signal with levels of detail, that is, hidden components are detected by means of the decomposition of this signal, where each level provides a different characteristic. The main feature of the elastic net is the grouping of correlated variables where the number of predictors is greater than the number of observations. The combination of these two methodologies applied in the clustering analysis of the Mycobacterium tuberculosis genome strains proved very effective, being able to identify clusters at each level of decomposition.

THE GROWTH RATE PHENOTYPIC PROPERTY OF MYCOBACTERIUM TUBERCULOSIS CLINICAL STRAINS: DEPENDENCE ON TUBERCULOSIS LOCALIZATION, TREATMENT, DRUG SUSCEPTIBILITY

The phenotypic properties of the M. tuberculosis strains obtained from patients with pulmonary or extra-pulmonary tuberculosis are  determined by a complex set of factors: the genetic characteristics  of the pathogen, its ability to adapt in vivo and in vitro, the influence of the host’s immune system and chemotherapy. The growth rate as  the phenotypic property is the most accessible for the study of the  host-pathogen relationships at the level of host/strain population  interactions. The aim of the study is to assess in vitro of the growth  rate of M. tuberculosis strains isolated from patients with pulmonary  and extra-pulmonary tuberculosis: untreated and treated (with  surgical and non-surgical treatment) and also sensitive and resistant isolates in comparison with the reference strain H37Rv. To estimate  the growth rate of 116 clinical isolates we have used the modified  method originally developed by von Groll and co-authors: to get the  bacteria growth curve the fluorescence intensity of growing strains  (with indicator resazurin) has been measured daily for 8 days in 96- well plate. The growth rate is determined as the slope of the growth  curve. The mean values of the growth rate have been calculated in  the following groups of patients: 1 — untreated patients with  pulmonary tuberculosis (PT), respiratory material; 2 — non-surgical  treated PT patients, respiratory material; 3 — surgical treated PT  patients (mainly with chronic and hyperchronic process), respiratory  material; 4 — patients like in 3rd group, surgical material; 5 — bone  and joint tuberculosis (BJT), surgical material. In addition, groups of  sensitive and resistant strains have been examined, but there are no  significant differences in growth rates. It has been obtained that  the growth rate of strains isolated from the PT patients is higher than in BJT patients: it can be explained less favorable  conditions for the pathogen vegetation in the BJT. In the case of a  closed tuberculous lesion where the pathogen transmission to  another host is impossible, then the selection of strains with the  property to survive in the tissues of the osteoarticular system is  impossible too, therefor it should be observed only an adaptation of  the pathogen strain population to the individual host. The growth  rate of isolates from untreated PT patients is higher than that of the  treated ones. Comparison of the growth parameters of only MDR  strains 1–5 groups to eliminate the influence of the  sensitivity/resistance has resulted in the same conclusions. We  suggest that the decrease in the growth rate of strains from the  treated PT patients is in not only result of the treatment, but also is  conditioned by adaptation of the pathogen to its external  environment, which is the internal environment of the  macroorganism. To confirm this assumption, the bacterial load of  1,083 diagnostic specimens grouped in a similar manner has been  estimated, taking into account only MDR/XDR strains. In the group  of treated patients the frequency of high bacterial load (CFU ≥ 100)  reached 52.5–63.8% that shows the conserved fitness of bacteria in  such patients. The mean values of the growth rate of the strain  H37Rv non-adapted to the macroorganism (due to numerous  passages on artificial media) are higher than in all groups of clinical  strains. Thus, heterogeneity of phenotypic properties of M.  tuberculosis clinical strains on the basis of growth rate has been  obtained. The growth rate of M. tuberculosis clinical strains is  depended on the tuberculosis localization (PT, BJT) and on the joint  effect of patient treatment and pathogen adaptation to the host. 

Mycobacterium tuberculosis strains induce strain-specific cytokine and chemokine response in pulmonary epithelial cells

M. tuberculosis F15/LAM4/KZN has been associated with high transmission rates of drug resistant tuberculosis in the KwaZulu-Natal province of South Africa. The current study elucidated the cytokine/chemokine responses induced by representatives of the F15/LAM4/KZN and other dominant strain families in pulmonary epithelial cells. Multiplex cytokine analyses were performed at 24, 48 and 72h post infection of the A549 pulmonary epithelial cell line with the F15/LAM4/KZN, F28, F11, Beijing, Unique and H37Rv strains at an MOI of ∼10:1. Twenty-three anti- and pro-inflammatory cytokines/chemokines were detected at all-time intervals. Significantly high concentrations of IL-6, IFN-γ, TNF-α and G-CSF at 48h, and IL-8, IFN-γ, TNF-α, G-CSF and GM-CSF at 72h, were induced by the F28 and F15/LAM4/KZN strains, respectively. Lower levels of cytokines/chemokines were induced by either the Beijing or Unique strains at all three time intervals. All strains induced up-regulation of pathogen recognition receptors (PRRs) (TLR3 and TLR5) while only the F15/LAM4/KZN, F11 and F28 strains induced significant differential expression of TLR2 compared to the Beijing, Unique and H37Rv strains. The low induction of cytokines in epithelial cells by the Beijing strain correlates with its previously reported hypervirulent properties. High concentrations of cytokines and chemokines required for early protection against M. tuberculosis infections induced by the F15/LAM4/KZN and F28 strains suggests a lower virulence of these genotypes compared to the Beijing strain. These findings demonstrate the high diversity in host cytokine/chemokine response to early infection of pulmonary epithelial cells by different strains of M. tuberculosis.

A Nonsynonymous SNP Catalog of Mycobacterium tuberculosis Virulence Genes and Its Use for Detecting New Potentially Virulent Sublineages

Mycobacterium tuberculosis is divided into several distinct lineages, and various genetic markers such as IS-elements, VNTR, and SNPs are used for lineage identification. We propose an M. tuberculosis classification approach based on functional polymorphisms in virulence genes. An M. tuberculosis virulence genes catalog has been established, including 319 genes from various protein groups, such as proteases, cell wall proteins, fatty acid and lipid metabolism proteins, sigma factors, toxin–antitoxin systems. Another catalog of 1,573 M. tuberculosis isolates of different lineages has been developed. The developed SNP-calling program has identified 3,563 nonsynonymous SNPs. The constructed SNP-based phylogeny reflected the evolutionary relationship between lineages and detected new sublineages. SNP analysis of sublineage F15/LAM4/KZN revealed four lineage-specific mutations in cyp125, mce3B, vapC25, and vapB34. The Ural lineage has been divided into two geographical clusters based on different SNPs in virulence genes. A new sublineage, B0/N-90, was detected inside the Beijing-B0/W-148 by SNPs in irtB, mce3F and vapC46. We have found 27 members of B0/N-90 among the 227 available genomes of the Beijing-B0/W-148 sublineage. Whole-genome sequencing of strain B9741, isolated from an HIV-positive patient, was demonstrated to belong to the new B0/N-90 group. A primer set for PCR detection of B0/N-90 lineage-specific mutations has been developed. The prospective use of mce3 mutant genes as genetically engineered vaccine is discussed.

In vitro and in vivo fitness costs associated with Mycobacterium tuberculosis RpoB mutation H526D

AIM

There is controversy regarding the potential fitness costs of rifampicin (RIF) resistance-conferring mutations in the Mycobacterium tuberculosis (Mtb) rpoB gene. We characterized the pathogenicity of an Mtb RpoB H526D mutant.

MATERIALS & METHODS

A mutant containing the RpoB H526D mutation was isolated from wild-type Mtb grown on RIF-containing plates and complemented for determination of in vitro and in vivo fitness costs.

RESULTS

The RpoB H526D mutant showed reduced survival relative to control strains during progressive hypoxia and delayed growth following resuscitation from nutrient starvation (p < 0.05), which was associated with reduced expression of the resuscitation-promoting factor genes rpfB, rpfC and rpfE. Relative to the isogenic wild-type strain, the mutant showed significantly attenuated growth and long-term survival as well as reduced inflammation in mouse lungs. Conclusion & future perspective: Our data suggest that RpoB H526D mutation confers a fitness cost during growth-limiting conditions in vitro and in mouse lungs.

Tradeoffs in Introduction Policies for the Anti-Tuberculosis Drug Bedaquiline: A Model-Based Analysis

BACKGROUND

New drugs for the treatment of tuberculosis (TB) are becoming available for the first time in over 40 y. Optimal strategies for introducing these drugs have not yet been established. The objective of this study was to compare different strategies for introducing the new TB drug bedaquiline based on patients' resistance patterns.

METHODS AND FINDINGS

We created a Markov decision model to follow a hypothetical cohort of multidrug-resistant (MDR) TB patients under different bedaquiline use strategies. The explored strategies included making bedaquiline available to all patients with MDR TB, restricting bedaquiline usage to patients with MDR plus additional resistance and withholding bedaquiline introduction completely. We compared these strategies according to life expectancy, risks of acquired resistance, and the expected number and health outcomes of secondary cases. For our simulated cohort, the mean (2.5th, 97.5th percentile) life expectancy from time of initiation of MDR TB treatment at age 30 was 36.0 y (33.5, 38.7) assuming all patients with MDR TB received bedaquiline, 35.1 y (34.4, 35.8) assuming patients with pre-extensively drug-resistant (PreXDR) and extensively drug-resistant (XDR) TB received bedaquiline, and 34.9 y (34.6, 35.2) assuming only patients with XDR TB received bedaquiline. Although providing bedaquiline to all MDR patients resulted in the highest life expectancy for our initial cohort averaged across all parameter sets, for parameter sets in which bedaquiline conferred high risks of added mortality and only small reductions in median time to culture conversion, the optimal strategy would be to withhold use even from patients with the most extensive resistance. Across all parameter sets, the most liberal bedaquiline use strategies consistently increased the risk of bedaquiline resistance but decreased the risk of resistance to other MDR drugs. In almost all cases, more liberal bedaquiline use strategies reduced the expected number of secondary cases and resulting life years lost. The generalizability of our results is limited by the lack of available data about drug effects among individuals with HIV co-infection, drug interactions, and other sources of heterogeneity, as well as changing recommendations for MDR TB treatment.

CONCLUSIONS

If mortality benefits can be empirically verified, our results provide support for expanding bedaquiline access to all patients with MDR TB. Such expansion could improve patients' health, protect background MDR TB drugs, and decrease transmission, but would likely result in greater resistance to bedaquiline.

Epidemiology and Clinical Characteristics of Pediatric Drug-Resistant Tuberculosis in Chongqing, China

To gain insight into the epidemiology of childhood drug resistant tuberculosis (DR-TB) in China that has the second largest burden of TB and the largest number of multidrug resistant (MDR) TB cases in the world, we performed the cross-sectional study to investigate drug resistance of four first-line anti-TB drugs (isoniazid, rifampicin, streptomycin and ethambutol) using Mycobacterium tuberculosis isolates from 196 culture-confirmed pediatric TB cases diagnosed in the Children's Hospital of Chongqing Medical University, China during 2008-2013. Univariate and multivariate logistic regression analyses were performed to assess the associations between patient demographic and clinical characteristics and DR-and MDR-TB, respectively. Twenty-eight percent (56/196) of the study patients exhibited resistance to at least one of the four first-line anti-TB drugs tested. MDR was found in 4.6% (9/196) of the study patients. More than half (5/9, 55.6%) of the MDR cases were from a single county of Chongqing. A significant association was found between being acid-fast bacilli-smear negative and DR-TB (adjusted OR, 2.33; 95% CI, 1.13-4.80) and between having concurrent thoracic-extrathoracic involvement and MDR-TB (adjusted OR, 9.49; 95% CI, 1.05-85.92), respectively. The findings of this study indicate that the rate of DR is high among pediatric TB patients in Chongqing and suggest an urgent need for studies to identify MDR transmission hotspots in Chongqing, thereby contributing to the control DR- and MDR-TB epidemics in China. The study also generates new insight into the pathogenesis of DR and MDR M. tuberculosis strains and highlights the importance of studying childhood TB to the goal of global TB control.

CLARITY and PACT-based imaging of adult zebrafish and mouse for whole-animal analysis of infections

Visualization of infection and the associated host response has been challenging in adult vertebrates. Owing to their transparency, zebrafish larvae have been used to directly observe infection in vivo; however, such larvae have not yet developed a functional adaptive immune system. Cells involved in adaptive immunity mature later and have therefore been difficult to access optically in intact animals. Thus, the study of many aspects of vertebrate infection requires dissection of adult organs or ex vivo isolation of immune cells. Recently, CLARITY and PACT (passive clarity technique) methodologies have enabled clearing and direct visualization of dissected organs. Here, we show that these techniques can be applied to image host-pathogen interactions directly in whole animals. CLARITY and PACT-based clearing of whole adult zebrafish and Mycobacterium tuberculosis-infected mouse lungs enables imaging of mycobacterial granulomas deep within tissue to a depth of more than 1 mm. Using established transgenic lines, we were able to image normal and pathogenic structures and their surrounding host context at high resolution. We identified the three-dimensional organization of granuloma-associated angiogenesis, an important feature of mycobacterial infection, and characterized the induction of the cytokine tumor necrosis factor (TNF) within the granuloma using an established fluorescent reporter line. We observed heterogeneity in TNF induction within granuloma macrophages, consistent with an evolving view of the tuberculous granuloma as a non-uniform, heterogeneous structure. Broad application of this technique will enable new understanding of host-pathogen interactions in situ.

Risk Factors for Multidrug-Resistant Tuberculosis among Patients with Pulmonary Tuberculosis at the Central Chest Institute of Thailand

There are limited data available on the risk factors for multidrug-resistant tuberculosis (MDR-TB). Therefore, we here conducted a retrospective matched case-control study among adults with pulmonary TB who received treatment at the Central Chest Institute of Thailand (CCIT) between January 2007 and December 2013, in order to determine the risk factors associated with MDR-TB among patients with pulmonary TB. We identified 145 patients with pulmonary MDR-TB (cases) and 145 patients with drug-sensitive pulmonary TB (controls). Multivariate analysis identified the independent risk factors for MDR-TB as follows: (1) ≥ 2 episodes of prior pulmonary TB (odds ratio [OR] 39.72, 95% confidence interval (95% CI) 7.86-200.66), (2) duration of illness > 60 days (OR 3.08, 95% CI 1.52-6.22), (3) sputum acid fast bacilli smear 3+ (OR 13.09, 95% CI 4.64-36.91), (4) presence of lung cavities (OR 3.82, 95% CI 1.89-7.73), and (5) presence of pleural effusion (OR 2.75, 95% CI 1.06-7.16). Prior pulmonary TB management with a non-category I regimen (P = 0.012) and having treatment failure or default as treatment outcomes (P = 0.036) were observed in a higher proportion among patients with MDR-TB. Particular characteristics of lung cavities, including the maximum diameter ≥ 30 mm (P < 0.001), the number of cavities ≥ 3 (P = 0.001), bilateral involvement (P < 0.001), and ≥ 2 lung zones involved (P = 0.001) were more commonly observed in patients with MDR-TB. In conclusion, these clinical factors and chest radiographic findings associated with MDR-TB among patients with pulmonary TB may help physicians to provide proper management of cases for prevention of the development and spread of MDR-TB in future.

Search for microRNAs expressed by intracellular bacterial pathogens in infected mammalian cells

MicroRNAs are expressed by all multicellular organisms and play a critical role as post-transcriptional regulators of gene expression. Moreover, different microRNA species are known to influence the progression of a range of different diseases, including cancer and microbial infections. A number of different human viruses also encode microRNAs that can attenuate cellular innate immune responses and promote viral replication, and a fungal pathogen that infects plants has recently been shown to express microRNAs in infected cells that repress host cell immune responses and promote fungal pathogenesis. Here, we have used deep sequencing of total expressed small RNAs, as well as small RNAs associated with the cellular RNA-induced silencing complex RISC, to search for microRNAs that are potentially expressed by intracellular bacterial pathogens and translocated into infected animal cells. In the case of Legionella and Chlamydia and the two mycobacterial species M. smegmatis and M. tuberculosis, we failed to detect any bacterial small RNAs that had the characteristics expected for authentic microRNAs, although large numbers of small RNAs of bacterial origin could be recovered. However, a third mycobacterial species, M. marinum, did express an ∼23-nt small RNA that was bound by RISC and derived from an RNA stem-loop with the characteristics expected for a pre-microRNA. While intracellular expression of this candidate bacterial microRNA was too low to effectively repress target mRNA species in infected cultured cells in vitro, artificial overexpression of this potential bacterial pre-microRNA did result in the efficient repression of a target mRNA. This bacterial small RNA therefore represents the first candidate microRNA of bacterial origin.