Incidence and predictors of tuberculosis among HIV-infected children after initiation of antiretroviral therapy in Ethiopia: A systematic review and meta-analysis

BACKGROUND

Globally, Tuberculosis (TB) is the main cause of morbidity and mortality among infectious disease. TB and Human Immune Virus (HIV) are the two deadly pandemics which interconnected each other tragically, and jeopardize the lives of children; particularly in Sub-Saharan Africa. Therefore, this review was aimed to determine the aggregated national pooled incidence of tuberculosis among HIV- infected children and its predictors in Ethiopia.

METHODS

An electronic search engine (HINARI, PubMed, Scopus, web of science), Google scholar and free Google databases were searched to find eligible studies. Quality of the studies was checked using the Joanna Briggs Institute (JBI) quality assessment checklists for cohort studies. Heterogeneity between studies was evaluated using Cochrane Q-test and the I2 statistics.

RESULT

This review revealed that the pooled national incidence of tuberculosis among children with HIV after initiation of ART was 3.63% (95% CI: 2.726-4.532) per 100-person-years observations. Being Anemic, poor and fair ART adherence, advanced WHO clinical staging, missing of cotrimoxazole and isoniazid preventing therapy, low CD4 cell count, and undernutrition were significant predictors of tuberculosis incidence.

CONCLUSION

The study result indicated that the incidence of TB among HIV- infected children is still high. Therefore, parents/guardians should strictly follow and adjust nutritional status of their children to boost immunity, prevent undernutrition and opportunistic infections. Cotrimoxazole and isoniazid preventive therapy need to continually provide for HIV- infected children for the sake of enhancing CD4/immune cells, reduce viral load, and prevent from advanced disease stages. Furthermore, clinicians and parents strictly follow ART adherence.

Pharmacological validation of dihydrofolate reductase as a drug target in Mycobacterium abscessus

The Mycobacterium abscessus drug development pipeline is poorly populated, with particularly few validated target-lead couples to initiate de novo drug discovery. Trimethoprim, an inhibitor of dihydrofolate reductase (DHFR) used for the treatment of a range of bacterial infections, is not active against M. abscessus. Thus, evidence that M. abscessus DHFR is vulnerable to pharmacological intervention with a small molecule inhibitor is lacking. Here, we show that the pyrrolo-quinazoline PQD-1, previously identified as a DHFR inhibitor active against Mycobacterium tuberculosis, exerts whole cell activity against M. abscessus. Enzyme inhibition studies showed that PQD-1, in contrast to trimethoprim, is a potent inhibitor of M. abscessus DHFR and over-expression of DHFR causes resistance to PQD-1, providing biochemical and genetic evidence that DHFR is a vulnerable target and mediates PQD-1's growth inhibitory activity in M. abscessus. As observed in M. tuberculosis, PQD-1 resistant mutations mapped to the folate pathway enzyme thymidylate synthase (TYMS) ThyA. Like trimethoprim in other bacteria, PQD-1 synergizes with the dihydropteroate synthase (DHPS) inhibitor sulfamethoxazole (SMX), offering an opportunity to exploit the successful dual inhibition of the folate pathway and develop similarly potent combinations against M. abscessus. PQD-1 is active against subspecies of M. abscessus and a panel of clinical isolates, providing epidemiological validation of the target-lead couple. Leveraging a series of PQD-1 analogs, we have demonstrated a dynamic structure-activity relationship (SAR). Collectively, the results identify M. abscessus DHFR as an attractive target and PQD-1 as a chemical starting point for the discovery of novel drugs and drug combinations that target the folate pathway in M. abscessus.

Synthesis, antimicrobial, anti-cancer and in silico studies of new urea derivatives

The reaction of an alkyl or aryl isocyanates with some primary amines in acetonitrile at room temperature afforded the corresponding alkyl- and aryl-urea derivatives. All the prepared urea compounds have been elucidated by FTIR, NMR, and elemental analysis. The compounds 1 and 3 were confirmed by single-crystal X-ray diffraction. The 4-tolylsulfonyl isocyanate reacted with the aryl amines 1, 2, 3, and 2,4-dichloroaniline to afford the corresponding sulfonylurea derivatives 5-8. Likewise, the reaction of the isocyanates with 2,4-dichloroaniline, 5-methyl isoxazole-3-amine, and 2-aminothiazole derivatives gave the corresponding urea derivatives 9-17. All the prepared compounds 5-17 were tested in vitro as anti-microbial and anti-HepG2 agents. Moreover, analyzing gene expression of TP53-exon4 and TP53-exon7, DNA damage values, and DNA fragmentation percentages have been discussed. The compounds 5 and 8 recorded the highest activity against the tested microbial strains with maximum activity against C. albicans (50 mm) and B. mycoides (40 mm), respectively. The compounds 5 inhibited the growth of E. coli, S. aureus, and C. Albicans at the MIC level of 0.0489 µM, while the compound 8 was able to inhibit the visible growth of E. coli and C. albicans at MIC value of 3.13 µM and S. aureus at 0.3912 µM. In the same line, compound 5 showed the best cytotoxic activity against the HepG2 cell line (IC₅₀ = 4.25 µM) compared to 5 fluorouracil with IC₅₀ = 316.25 µM. Expression analysis of liver cancer related to a gene including TP53-exon4 and TP53-exon7 was used in HepG2 Liver cancer cell lines using RT-qPCR. The expression values of TP53-exon4 and TP53-exon7 genes were decreased. The DNA damage values and DNA fragmentation percentages were increased significantly (P < 0.01) in the treated HepG2 (5) sample compared with the negative control. Docking studies were performed for the synthetic compounds against 2 bacterial proteins (DNA gyrase subunit B, and penicillin binding protein 1a) that are known targets for some antibiotics, and one cell division protein kinase 2 (CDK2) as target for anticancer drugs.

Mutations of folC cause increased susceptibility to sulfamethoxazole in Mycobacterium tuberculosis

Previous studies showed that mutation of folC caused decreased expression of the dihydropteroate synthase encoding gene folP2 in Mycobacterium tuberculosis (M. tuberculosis). We speculated that mutation of folC in M. tuberculosis might affect the susceptibility to sulfamethoxazole (SMX). To prove this, 53 clinical isolates with folC mutations were selected and two folC mutants (I43A, I43T) were constructed based on M. tuberculosis H37Ra. The results showed that 42 of the 53 clinical isolates (79.2%) and the two lab-constructed folC mutants were more sensitive to SMX. To probe the mechanism by which folC mutations make M. tuberculosis more sensitive to SMX, folP2 was deleted in H37Ra, and expression levels of folP2 were compared between H37Ra and the two folC mutants. Although deletion of folP2 resulted in increased susceptibility to SMX, no difference in folP2 expression was observed. Furthermore, production levels of para-aminobenzoic acid (pABA) were compared between the folC mutants and the wild-type strain, and results showed that folC mutation resulted in decreased production of pABA. Taken together, we show that folC mutation leads to decreased production of pABA in M. tuberculosis and thus affects its susceptibility to SMX, which broadens our understanding of mechanisms of susceptibilities to antifolates in this bacterium.

Crystal structures of the closed form of Mycobacterium tuberculosis dihydrofolate reductase in complex with dihydrofolate and antifolates

Tuberculosis is a disease caused by Mycobacterium tuberculosis and is the leading cause of death from a single infectious pathogen, with a high prevalence in developing countries in Africa and Asia. There still is a need for the development or repurposing of novel therapies to combat this disease owing to the long-term nature of current therapies and because of the number of reported resistant strains. Here, structures of dihydrofolate reductase from M. tuberculosis (MtDHFR), which is a key target of the folate pathway, are reported in complex with four antifolates, pyrimethamine, cycloguanil, diaverdine and pemetrexed, and its substrate dihydrofolate in order to understand their binding modes. The structures of all of these complexes were obtained in the closed-conformation state of the enzyme and a fine structural analysis indicated motion in key regions of the substrate-binding site and different binding modes of the ligands. In addition, the affinities, through K_d measurement, of diaverdine and methotrexate have been determined; MtDHFR has a lower affinity (highest K_d) for diaverdine than pyrimethamine and trimethoprim, and a very high affinity for methotrexate, as expected. The structural comparisons and analysis described in this work provide new information about the plasticity of MtDHFR and the binding effects of different antifolates.

Cotrimoxazole prophylaxis decreases tuberculosis risk among Asian patients with HIV

INTRODUCTION

Cotrimoxazole (CTX) is recommended as prophylaxis against Pneumocystis jiroveci pneumonia, malaria and other serious bacterial infections in HIV-infected patients. Despite its in vitro activity against Mycobacterium tuberculosis, the effects of CTX preventive therapy on tuberculosis (TB) remain unclear.

METHODS

Adults living with HIV enrolled in a regional observational cohort in Asia who had initiated combination antiretroviral therapy (cART) were included in the analysis. Factors associated with new TB diagnoses after cohort entry and survival after cART initiation were analysed using Cox regression, stratified by site.

RESULTS

A total of 7355 patients from 12 countries enrolled into the cohort between 2003 and 2016 were included in the study. There were 368 reported cases of TB after cohort entry with an incidence rate of 0.99 per 100 person-years (/100 pys). Multivariate analyses adjusted for viral load (VL), CD4 count, body mass index (BMI) and cART duration showed that CTX reduced the hazard for new TB infection by 28% (HR 0.72, 95% CI l 0.56, 0.93). Mortality after cART initiation was 0.85/100 pys, with a median follow-up time of 4.63 years. Predictors of survival included age, female sex, hepatitis C co-infection, TB diagnosis, HIV VL, CD4 count and BMI.

CONCLUSIONS

CTX was associated with a reduction in the hazard for new TB infection but did not impact survival in our Asian cohort. The potential preventive effect of CTX against TB during periods of severe immunosuppression should be further explored.

Collateral sensitivity constrains resistance evolution of the CTX-M-15 β-lactamase

Antibiotic resistance is a major challenge to global public health. Discovery of new antibiotics is slow and to ensure proper treatment of bacterial infections new strategies are needed. One way to curb the development of antibiotic resistance is to design drug combinations where the development of resistance against one drug leads to collateral sensitivity to the other drug. Here we study collateral sensitivity patterns of the globally distributed extended-spectrum β-lactamase CTX-M-15, and find three non-synonymous mutations with increased resistance against mecillinam or piperacillin-tazobactam that simultaneously confer full susceptibility to several cephalosporin drugs. We show in vitro and in mice that a combination of mecillinam and cefotaxime eliminates both wild-type and resistant CTX-M-15. Our results indicate that mecillinam and cefotaxime in combination constrain resistance evolution of CTX-M-15, and illustrate how drug combinations can be rationally designed to limit the resistance evolution of horizontally transferred genes by exploiting collateral sensitivity patterns.

Susceptibilities of MDR Mycobacterium tuberculosis isolates to unconventional drugs compared with their reported pharmacokinetic/pharmacodynamic parameters

Background

The second-line drugs recommended to treat drug-resistant TB are toxic, expensive and difficult to procure. Given increasing resistance, the need for additional anti-TB drugs has become more urgent. But new drugs take time to develop and are expensive. Some commercially available drugs have reported anti-mycobacterial activity but are not routinely used because supporting laboratory and clinical evidence is sparse.

Methods

We analysed 217 MDR M. tuberculosis isolates including 153 initial isolates from unique patients and 64 isolates from follow-up specimens during the course of treatment. The resazurin microdilution assay was performed to determine MICs of trimethoprim/sulfamethoxazole, mefloquine, thioridazine, clofazimine, amoxicillin/clavulanate, meropenem/clavulanate, nitazoxanide, linezolid and oxyphenbutazone. Isoniazid was used for validation. We calculated the MIC 50 and MIC 90 as the MICs at which growth of 50% and 90% of isolates was inhibited, respectively.

Results

The MIC 50 s, in mg/L, for initial isolates were as follows: trimethoprim/sulfamethoxazole, 0.2/4; mefloquine, 8; thioridazine, 4; clofazimine, 0.25; amoxicillin/clavulanate, 16/8; meropenem/clavulanate, 1/2.5; nitazoxanide, 16; linezolid, 0.25; and oxyphenbutazone, 40. The MIC 90 s, in mg/L, for initial isolates were as follows: trimethoprim/sulfamethoxazole, 0.4/8; mefloquine, 8; thioridazine, 8; clofazimine, 0.5; amoxicillin/clavulanate, 32/16; meropenem/clavulanate, 8/2.5; nitazoxanide, 16; linezolid, 0.25; and oxyphenbutazone, 60. By comparison, the MIC 90 of isoniazid was >4 mg/L, as expected. There was no evidence that previous treatment affected susceptibility to any drug.

Conclusions

Most drugs demonstrated efficacy against M. tuberculosis . When these MICs are compared with the published pharmacokinetic/pharmacodynamic profiles of the respective drugs in humans, trimethoprim/sulfamethoxazole, meropenem/clavulanate, linezolid, clofazimine and nitazoxanide appear promising and warrant further clinical investigation.

Antimycobacterial Metabolism: Illuminating Mycobacterium tuberculosis Biology and Drug Discovery

Bacteria are capable of performing a number of biotransformations that may activate or deactivate xenobiotics. Recent efforts have utilized metabolomics techniques to study the fate of small-molecule antibacterials within the targeted organism. Examples involving Mycobacterium tuberculosis are reviewed and analyzed with regard to the insights they provide as to both activation and deactivation of the antibacterial. The studies, in particular, shed light on biosynthetic transformations performed by M. tuberculosis while suggesting avenues for the evolution of chemical tools, highlighting potential areas for drug discovery, and mechanisms of approved drugs. A two-pronged approach investigating the metabolism of antibacterials within both the host and bacterium is outlined and will be of value to both the chemical biology and drug discovery fields.

Old antibiotics for emerging multidrug-resistant/extensively drug-resistant tuberculosis (MDR/XDR-TB)

Recently, multidrug-resistant tuberculosis (MDR-TB) has become a therapeutic challenge. In addition to drug resistance, drug adverse events, intravenous delivery, cost and availability of some antibiotics in low-income countries have led to a look back to old drugs, especially those efficient against closely related organisms such as Mycobacterium leprae. Here we review the available drugs that respect the conditions above and could be upgraded to first-line therapy for treating MDR-TB and extensively drug-resistant tuberculosis (XDR-TB).

Methylfolate Trap Promotes Bacterial Thymineless Death by Sulfa Drugs

The methylfolate trap, a metabolic blockage associated with anemia, neural tube defects, Alzheimer’s dementia, cardiovascular diseases, and cancer, was discovered in the 1960s, linking the metabolism of folate, vitamin B₁₂, methionine and homocysteine. However, the existence or physiological significance of this phenomenon has been unknown in bacteria, which synthesize folate de novo. Here we identify the methylfolate trap as a novel determinant of the bacterial intrinsic death by sulfonamides, antibiotics that block de novo folate synthesis. Genetic mutagenesis, chemical complementation, and metabolomic profiling revealed trap-mediated metabolic imbalances, which induced thymineless death, a phenomenon in which rapidly growing cells succumb to thymine starvation. Restriction of B₁₂ bioavailability, required for preventing trap formation, using an “antivitamin B₁₂” molecule, sensitized intracellular bacteria to sulfonamides. Since boosting the bactericidal activity of sulfonamides through methylfolate trap induction can be achieved in Gram-negative bacteria and mycobacteria, it represents a novel strategy to render these pathogens more susceptible to existing sulfonamides.

Sulfonamides were the first agents to successfully treat bacterial infections, but their use later declined due to the emergence of resistant organisms. Restoration of these drugs may be achieved through inactivation of molecular mechanisms responsible for resistance. A chemo-genomic screen first identified 50 chromosomal loci representing the whole-genome antifolate resistance determinants in Mycobacterium smegmatis. Interestingly, many determinants resembled components of the methylfolate trap, a metabolic blockage exclusively described in mammalian cells. Targeted mutagenesis, genetic and chemical complementation, followed by chemical analyses established the methylfolate trap as a novel mechanism of sulfonamide sensitivity, ubiquitously present in mycobacteria and Gram-negative bacterial pathogens. Furthermore, metabolomic analyses revealed trap-mediated interruptions in folate and related metabolic pathways. These metabolic imbalances induced thymineless death, which was reversible with exogenous thymine supplementation. Chemical restriction of vitamin B₁₂, an important molecule required for prevention of the methylfolate trap, sensitized intracellular bacteria to sulfonamides. Thus, pharmaceutical promotion of the methylfolate trap represents a novel folate antagonistic strategy to render pathogenic bacteria more susceptible to available, clinically approved sulfonamides.

Pharmacokinetic Evaluation of Sulfamethoxazole at 800 Milligrams Once Daily in the Treatment of Tuberculosis

For treatment of multidrug-resistant tuberculosis (MDR-TB), there is a scarcity of antituberculosis drugs. Co-trimoxazole is one of the available drug candidates, and it is already frequently coprescribed for TB-HIV-coinfected patients. However, only limited data are available on the pharmacokinetic (PK) and pharmacodynamic (PD) parameters of co-trimoxazole in TB patients. The objective of this study was to evaluate the PK parameters and in vitro PD data on the effective part of co-trimoxazole: sulfamethoxazole. In a prospective PK study in patients infected with drug-susceptible Mycobacterium tuberculosis (drug-susceptible TB patients) (age, >18), sulfamethoxazole-trimethoprim (SXT) was administered orally at a dose of 960 mg once daily. One-compartment population pharmacokinetic modeling was performed using MW\Pharm 3.81 (Mediware, Groningen, The Netherlands). The area under the concentration-time curve for the free, unbound fraction of a drug (ƒAUC)/MIC ratio and the period in which the free concentration exceeded the MIC (fT > MIC) were calculated. Twelve patients received 960 mg co-trimoxazole in addition to first-line drugs. The pharmacokinetic parameters of the population model were as follows (geometric mean ± standard deviation [SD]): metabolic clearance (CLm), 1.57 ± 3.71 liters/h; volume of distribution (V), 0.30 ± 0.05 liters · kg lean body mass(-1); drug clearance/creatinine clearance ratio (fr), 0.02 ± 0.13; gamma distribution rate constant (ktr_po), 2.18 ± 1.14; gamma distribution shape factor (n_po), 2.15 ± 0.39. The free fraction of sulfamethoxazole was 0.3, but ranged between 0.2 and 0.4. The median value of the MICs was 9.5 mg/liter (interquartile range [IQR], 4.75 to 9.5), and that of theƒAUC/MIC ratio was 14.3 (IQR, 13.0 to 17.5). The percentage of ƒT > MIC ranged between 43 and 100% of the dosing interval. The PK and PD data from this study are useful to explore a future dosing regimen of co-trimoxazole for MDR-TB treatment. (This study has been registered at ClinicalTrials.gov under registration no. NCT01832987.).

The potential role of trimethoprim-sulfamethoxazole in the treatment of drug-resistant tuberculosis

Tuberculosis (TB) remains a serious public health threat worsened by emerging drug resistance. Mycobacterium tuberculosis has become resistant not only to front-line drugs but also to second-line antimicrobials directed at drug-resistant TB. Renewed efforts are devoted for the development of new antibiotics active against TB. Also, repurposing of other antibiotics is being explored to shorten the time to develop new drugs against M. tuberculosis. As a result, trimethoprim-sulfamethoxazole (SXT) has emerged as a potential new option to treat drug-resistant TB. SXT has been found to be surprisingly active against drug-resistant M. tuberculosis, not only in vitro but also in vivo. The potential role of SXT for the treatment of multidrug resistant/extensively drug resistant TB might be explored in further clinical evaluations.

Mycobacterium tuberculosis folate metabolism and the mechanistic basis for para-aminosalicylic acid susceptibility and resistance

para-Aminosalicylic acid (PAS) entered clinical use in 1946 as the second exclusive drug for the treatment of tuberculosis (TB). While PAS was initially a first-line TB drug, the introduction of more potent antitubercular agents relegated PAS to the second-line tier of agents used for the treatment of drug-resistant Mycobacterium tuberculosis infections. Despite the long history of PAS usage, an understanding of the molecular and biochemical mechanisms governing the susceptibility and resistance of M. tuberculosis to this drug has lagged behind that of most other TB drugs. Herein, we discuss previous studies that demonstrate PAS-mediated disruption of iron acquisition, as well as recent genetic, biochemical, and metabolomic studies that have revealed that PAS is a prodrug that ultimately corrupts one-carbon metabolism through inhibition of the formation of reduced folate species. We also discuss findings from laboratory and clinical isolates that link alterations in folate metabolism to PAS resistance. These advancements in our understanding of the basis of the susceptibility and resistance of M. tuberculosis to PAS will enable the development of novel strategies to revitalize this and other antimicrobial agents for use in the global effort to eradicate TB.

Sulfamethoxazole susceptibility of Mycobacterium tuberculosis isolates from HIV-infected Ugandan adults with tuberculosis taking trimethoprim-sulfamethoxazole prophylaxis

Additional drugs are needed for the treatment of multidrug-resistant tuberculosis (TB). Sulfamethoxazole has been shown to have in vitro activity against Mycobacterium tuberculosis; however, there is concern about resistance given the widespread use of trimethoprim-sulfamethoxazole prophylaxis among HIV-infected patients in sub-Saharan Africa. Thirty-eight of 40 Mycobacterium tuberculosis isolates (95%) from pretreatment sputum samples from Ugandan adults with pulmonary TB, including HIV-infected patients taking trimethoprim-sulfamethoxazole prophylaxis, were susceptible with MICs of ≤38.4 μg/ml.

Co-trimoxazole prophylaxis in adults, including pregnant women, with HIV: a systematic review and meta-analysis

INTRODUCTION

Co-trimoxazole prophylaxis is used to reduce morbidity and mortality in people with HIV. We systematically reviewed three topics related to co-trimoxazole prophylaxis to update WHO guidelines: initiation, discontinuation, and dose.

METHODS

We searched PubMed, Embase, WHO Global Index Medicus, and clinical trial registries in November, 2013, for randomised controlled trials and observational studies including co-trimoxazole prophylaxis and a comparator group. Studies were eligible if they reported death, WHO clinical stage 3 or 4 events, admittance to hospital, severe bacterial infections, tuberculosis, pneumonia, diarrhoea, malaria, or treatment-limiting adverse events. Infant mortality, low birthweight, and placental malaria were additional outcomes for the comparison of co-trimoxazole prophylaxis and intermittent preventive treatment for malaria in pregnant women (IPTp). We compared a dose of 480 mg co-trimoxazole once a day with one of 960 mg co-trimoxazole once a day. We used a 10% margin for non-inferiority and equivalence analyses. We used random-effects models for all meta-analyses. This study is registered with PROSPERO, number CRD42014007163.

FINDINGS

19 articles, published from 1995 to 2014 and including 35 328 participants, met the inclusion criteria. Co-trimoxazole prophylaxis reduced rates of death (hazard ratio [HR] 0·40, 95% CI 0·26-0·64) when started at CD4 counts of 350 cells per μL or lower with antiretroviral therapy (ART) worldwide. Co-trimoxazole prophylaxis started at higher than 350 cells per μL without ART reduced rates of death (0·50, 0·30-0·83) and malaria (0·25, 0·10-0·57) in Africa. Co-trimoxazole prophylaxis was non-inferior to IPTp with respect to infant mortality (risk difference [RD] -0·05, 95% CI -0·12 to 0·02), low birthweight (0·00, -0·07 to 0·07), and placental malaria (0·00, -0·10 to 0·10). Co-trimoxazole prophylaxis continuation after ART-induced recovery with CD4 counts higher than 350 cells per μL reduced admittances to hospital (HR 0·42, 95% CI 0·22-0·80), pneumonia (0·73, 0·61-0·88), malaria (0·03, 0·01-0·10), and diarrhoea (0·61, 0·48-0·78) in Africa. A dose of 480 mg co-trimoxazole prophylaxis once a day did not reduce treatment-limiting adverse events compared with 960 mg once a day (RD -0·07, 95% CI -0·52 to 0·39).

INTERPRETATION

Co-trimoxazole prophylaxis should be given with ART in people with CD4 counts of 350 cells per μL or lower in low-income and middle-income countries. Co-trimoxazole prophylaxis should be provided irrespective of CD4 count in settings with a high burden of infectious diseases. Pregnant women with HIV in Africa should use co-trimoxazole rather than IPTp to prevent malaria complications in infants. Further research is needed to inform dose optimisation and co-trimoxazole use in the context of expanded ART in different epidemiological settings.

FUNDING

None.

The expanding role of co-trimoxazole in developing countries

Co-trimoxazole is an inexpensive, broad-spectrum antimicrobial drug that is widely used in developing countries. Before antiretroviral therapy (ART) scale-up, co-trimoxazole prophylaxis reduced morbidity and mortality in adults and children with HIV by preventing bacterial infections, diarrhoea, malaria, and Pneumocystis jirovecii pneumonia, despite high levels of microbial resistance. Co-trimoxazole prophylaxis reduces early mortality by 58% (95% CI 39-71) in adults starting ART. Co-trimoxazole provides ongoing protection against malaria and non-malaria infections after immune reconstitution in ART-treated individuals in sub-Saharan Africa, leading to a change in WHO guidelines, which now recommend long-term co-trimoxazole prophylaxis for adults and children in settings with a high prevalence of malaria or severe bacterial infections. Co-trimoxazole prophylaxis is recommended for HIV-exposed infants from age 4-6 weeks; however, the risks and benefits of co-trimoxazole during infancy are unclear. Co-trimoxazole prophylaxis reduces anaemia and improves growth in children with HIV, possibly by reducing inflammation, either through direct immunomodulatory activity or through effects on the intestinal microbiota leading to reduced microbial translocation. Ongoing trials are now assessing the ability of adjunctive co-trimoxazole to reduce mortality in children after severe anaemia or severe acute malnutrition. In this Review, we discuss the mechanisms of action, benefits and risks, and clinical trials of co-trimoxazole in developing countries.

Collateral Resistance and Sensitivity Modulate Evolution of High-Level Resistance to Drug Combination Treatment in Staphylococcus aureus

As drug-resistant pathogens continue to emerge, combination therapy will increasingly be relied upon to treat infections and to help combat further development of multidrug resistance. At present a dichotomy exists between clinical practice, which favors therapeutically synergistic combinations, and the scientific model emerging from in vitro experimental work, which maintains that this interaction provides greater selective pressure toward resistance development than other interaction types. We sought to extend the current paradigm, based on work below or near minimum inhibitory concentration levels, to reflect drug concentrations more likely to be encountered during treatment. We performed a series of adaptive evolution experiments using Staphylococcus aureus. Interestingly, no relationship between drug interaction type and resistance evolution was found as resistance increased significantly beyond wild-type levels. All drug combinations, irrespective of interaction types, effectively limited resistance evolution compared with monotreatment. Cross-resistance and collateral sensitivity were found to be important factors in the extent of resistance evolution toward a combination. Comparative genomic analyses revealed that resistance to drug combinations was mediated largely by mutations in the same genes as single-drug-evolved lineages highlighting the importance of the component drugs in determining the rate of resistance evolution. Results of this work suggest that the mechanisms of resistance to constituent drugs should be the focus of future resistance evolution work.

Tuberculosis treatment and drug regimens

Tuberculosis is an airborne infectious disease treated with combination therapeutic regimens. Adherence to long-term antituberculosis therapy is crucial for maintaining adequate blood drug level. The emergence and spread of drug-resistant Mycobacterium tuberculosis strains are mainly favored by the inadequate medical management of the patients. The therapeutic approach for drug-resistant tuberculosis is cumbersome, because of the poor, expensive, less-effective, and toxic alternatives to the first-line drugs. New antituberculosis drugs (bedaquiline and delamanid) have been recently approved by the health authorities, but they cannot represent the definitive solution to the clinical management of drug-resistant tuberculosis forms, particularly in intermediate economy settings where the prevalence of drug resistance is high (China, India, and former Soviet Union countries). New research and development activities are urgently needed. Public health policies are required to preserve the new and old therapeutic options.

A new strategy to fight antimicrobial resistance: the revival of old antibiotics

The increasing prevalence of hospital and community-acquired infections caused by multidrug-resistant (MDR) bacterial pathogens is limiting the options for effective antibiotic therapy. Moreover, this alarming spread of antimicrobial resistance has not been paralleled by the development of novel antimicrobials. Resistance to the scarce new antibiotics is also emerging. In this context, the rational use of older antibiotics could represent an alternative to the treatment of MDR bacterial pathogens. It would help to optimize the armamentarium of antibiotics in the way to preserve new antibiotics and avoid the prescription of molecules known to favor the spread of resistance (i.e., quinolones). Furthermore, in a global economical perspective, this could represent a useful public health orientation knowing that several of these cheapest “forgotten” antibiotics are not available in many countries. We will review here the successful treatment of MDR bacterial infections with the use of old antibiotics and discuss their place in current practice.

Intra- and extracellular activities of trimethoprim-sulfamethoxazole against susceptible and multidrug-resistant Mycobacterium tuberculosis

We investigated the activity of trimethoprim-sulfamethoxazole (SXT) against Mycobacterium tuberculosis, the pathogen that causes tuberculosis (TB). The MIC distribution of SXT was 0.125/2.4 to 2/38 mg/liter for the 100 isolates tested, including multi- and extensively drug-resistant isolates (MDR/XDR-TB), whereas the intracellular MIC90 of sulfamethoxazole (SMX) for the pansusceptible strain H37Rv was 76 mg/liter. In an exploratory analysis using a ratio of the unbound area under the concentration-time curve from 0 to 24 h over MIC (fAUC0-24/MIC) using ≥ 25 as a potential target, the cumulative fraction response was ≥ 90% at doses of ≥ 2,400 mg of SMX. SXT is a potential treatment option for MDR/XDR-TB.

Co-trimoxazole prophylaxis is associated with reduced risk of incident tuberculosis in participants in the Swiss HIV Cohort Study

Co-trimoxazole reduces mortality in HIV-infected adults with tuberculosis (TB), and in vitro data suggest potential antimycobacterial activity of co-trimoxazole. We aimed to evaluate whether prophylaxis with co-trimoxazole is associated with a decreased risk of incident TB in Swiss HIV Cohort Study (SHCS) participants. We determined the incidence of TB per 1,000 person-years from January 1992 to December 2012. Rates were analyzed separately in participants with current or no previous antiretroviral treatment (ART) using Poisson regression adjusted for CD4 cell count, sex, region of origin, injection drug use, and age. A total of 13,431 cohort participants contributed 107,549 person-years of follow-up: 182 patients had incident TB-132 (73%) before and 50 (27%) after ART initiation. The multivariable incidence rate ratios for cumulative co-trimoxazole exposure per year for persons with no previous ART and current ART were 0.70 (95% confidence interval [CI], 0.55 to 0.89) and 0.87 (95% CI, 0.74 to 1.0), respectively. Co-trimoxazole may prevent the development of TB among HIV-positive persons, especially among those with no previous ART.

Cotrimoxazole prophylaxis and tuberculosis risk among people living with HIV

Objectives

Many randomized and cohort studies have reported a survival benefit with cotrimoxazole prophylaxis without detecting a difference in tuberculosis (TB) incidence by cotrimoxazole status. However, several in vitro studies have reported that cotrimoxazole possesses anti-TB activity. We sought to compare TB incidence and TB diagnostic yield by cotrimoxazole use among participants in a well characterized cohort of HIV-infected adults living in a high TB prevalence region.

Methods

We analyzed prospective data from a long-term longitudinal cohort of adults receiving HIV care and TB investigations in Soweto, South Africa. Using longitudinal analysis, we compared total and laboratory confirmed TB incidence by cotrimoxazole status as well as all-cause mortality. In addition, we compared TB culture results by cotrimoxazole status.

Results

In a multivariable analysis, adjusted for sex, body mass index, WHO clinical stage, time-updated CD4 count, and antiretroviral therapy status, we observed an association between cotrimoxazole and an increase in TB incidence (hazard ratio 1.7, 95% CI: 1.2, 2.2). However, when restricted to laboratory-confirmed TB, there was no association between cotrimoxazole and TB incidence (hazard ratio: 0.97, 95% CI: 0.39, 2.4). In TB cases, we found no difference in the proportion of positive sputum cultures or days to culture positivity by cotrimoxazole status. Cotrimoxazole was associated with a reduction in mortality.

Conclusions

In this cohort with a mortality benefit from cotrimoxazole, we found an increased risk of all TB among individuals using cotrimoxazole, likely a result of residual confounding, but no association between use of cotrimoxazole and laboratory-confirmed TB. Cotrimoxazole did not compromise TB diagnosis.

Characterization of pure cultures isolated from sulfamethoxazole-acclimated activated sludge with respect to taxonomic identification and sulfamethoxazole biodegradation potential

Background

Sulfamethoxazole (SMX, sulfonamide antibiotic) biodegradation by activated sludge communities (ASC) is still only partly understood. The present work is focusing on nine different bacteria species capable of SMX biodegradation that were isolated from SMX-acclimated ASC.

Results

Initially 110 pure cultures, isolated from activated sludge, were screened by UV-absorbance measurements (UV-AM) for their SMX biodegradation potential. Identification via almost complete 16S rRNA gene sequencing revealed five Pseudomonas spp., one Brevundimonas sp., one Variovorax sp. and two Microbacterium spp.. Thus seven species belonged to the phylum Proteobacteria and two to Actinobacteria. These cultures were subsequently incubated in media containing 10 mg L^-1 SMX and different concentrations of carbon (sodium-acetate) and nitrogen (ammonium-nitrate). Different biodegradation patterns were revealed with respect to media composition and bacterial species. Biodegradation, validated by LC-UV measurements to verify UV-AM, occurred very fast with 2.5 mg L^-1 d^-1 SMX being biodegraded in all pure cultures in, for UV-AM modified, R2A-UV medium under aerobic conditions and room temperature. However, reduced and different biodegradation rates were observed for setups with SMX provided as co-substrate together with a carbon/nitrogen source at a ratio of DOC:N – 33:1 with rates ranging from 1.25 to 2.5 mg L^-1 d^-1.

Conclusions

Media containing only SMX as carbon and nitrogen source proved the organisms’ ability to use SMX as sole nutrient source where biodegradation rates decreased to 1.0 – 1.7 mg L^-1 d^-1. The different taxonomically identified species showed specific biodegradation rates and behaviours at various nutrient conditions. Readily degradable energy sources seem to be crucial for efficient SMX biodegradation.

In vitro susceptibility of Mycobacterium tuberculosis to trimethoprim and sulfonamides in France

Five type strains and 55 Mycobacterium tuberculosis complex clinical isolates were found resistant to trimethoprim with a MIC of >200 mg/liter and susceptible to both sulfadiazine and cotrimoxazole with a MIC90 of 10 mg/liter. Two M. canettii isolates uniquely yielded silent mutations C156 → T and G238 → C in the folP1 gene. Combined with scarce published data, these data indicate that sulfamides could be considered alternative antituberculous antibiotics.

siRNA Genome Screening Approaches to Therapeutic Drug Repositioning

Bridging high-throughput screening (HTS) with RNA interference (RNAi) has allowed for rapid discovery of the molecular basis of many diseases, and identification of potential pathways for developing safe and effective treatments. These features have identified new host gene targets for existing drugs paving the pathway for therapeutic drug repositioning. Using RNAi to discover and help validate new drug targets has also provided a means to filter and prioritize promising therapeutics. This review summarizes these approaches across a spectrum of methods and targets in the host response to pathogens. Particular attention is given to the utility of drug repurposing utilizing the promiscuous nature of some drugs that affect multiple molecules or pathways, and how these biological pathways can be targeted to regulate disease outcome.

Para-aminosalicylic acid acts as an alternative substrate of folate metabolism in Mycobacterium tuberculosis

Folate biosynthesis is an established anti-infective target, and the antifolate para-aminosalicylic acid (PAS) was one of the first anti-infectives introduced into clinical practice on the basis of target-based drug discovery. Fifty years later, PAS continues to be used to treat tuberculosis. PAS is assumed to inhibit dihydropteroate synthase (DHPS) in Mycobacterium tuberculosis by mimicking the substrate p-aminobenzoate (PABA). However, we found that sulfonamide inhibitors of DHPS inhibited growth of M. tuberculosis only weakly because of their intracellular metabolism. In contrast, PAS served as a replacement substrate for DHPS. Products of PAS metabolism at this and subsequent steps in folate metabolism inhibited those enzymes, competing with their substrates. PAS is thus a prodrug that blocks growth of M. tuberculosis when its active forms are generated by enzymes in the pathway they poison.

Strategies for potentiation of ethionamide and folate antagonists against Mycobacterium tuberculosis

Antifolates inhibit de novo folate biosynthesis, whereas ethionamide targets the mycolate synthetic pathway in Mycobacterium tuberculosis. These antibiotics are effective against M. tuberculosis but their use has been hampered by concerns over toxicity and low therapeutic indexes. With the increasing spread of drug-resistant forms, interest in using old drugs for tuberculosis treatment has been renewed. Specific inhibitors targeting resistance mechanisms could sensitize M. tuberculosis to these available, clinically approved drugs. This review discusses recently developed strategies to boost the antituberculous activity of ethionamide and antifolates. These approaches might help broaden the currently limited chemotherapeutic options of not only drug-resistant but also drug-susceptible tuberculosis, which still remains one of the most common infectious diseases in the developing world.

The combination of sulfamethoxazole, trimethoprim, and isoniazid or rifampin is bactericidal and prevents the emergence of drug resistance in Mycobacterium tuberculosis

The challenges of developing new drugs to treat tuberculosis (TB) are indicated by the relatively small number of candidates entering clinical trials in the past decade. To overcome these issues, we reexamined two FDA-approved antibacterial drugs, sulfamethoxazole (SMX) and trimethoprim (TMP), for use in TB treatment. SMX and TMP inhibit folic acid biosynthesis and are used in combination to treat infections of the respiratory, urinary, and gastrointestinal tracts. The MICs of SMX and TMP, alone and in combination, were determined for drug-susceptible, multidrug-resistant (MDR), and extensively drug-resistant Mycobacterium tuberculosis strains. While TMP alone was not effective against M. tuberculosis, the combination of TMP and SMX was bacteriostatic against M. tuberculosis. Surprisingly, the combination of SMX and TMP was also active against a subset of MDR M. tuberculosis strains. Treatment of M. tuberculosis with TMP-SMX and a first-line anti-TB drug, either isoniazid or rifampin, was bactericidal, demonstrating that the combination of TMP and SMX with isoniazid or rifampin was not antagonistic. Moreover, the addition of SMX-TMP in combination with either isoniazid or rifampin also prevented the emergence of drug resistance in vitro. In conclusion, this study further illustrates the opportunity to reevaluate the activity of TMP-SMX in vivo to prevent the emergence of drug-resistant M. tuberculosis.