Trimethoprim-sulfamethoxazole for methicillin-resistant Staphylococcus aureus: a forgotten alternative?

Prediction of Synergistic Antibiotic Combinations by Graph Learning

Antibiotic resistance is a major public health concern. Antibiotic combinations, offering better efficacy at lower doses, are a useful way to handle this problem. However, it is difficult for us to find effective antibiotic combinations in the vast chemical space. Herein, we propose a graph learning framework to predict synergistic antibiotic combinations. In this model, a network proximity method combined with network propagation was used to quantify the relationships of drug pairs, and we found that synergistic antibiotic combinations tend to have smaller network proximity. Therefore, network proximity can be used for building an affinity matrix. Subsequently, the affinity matrix was fed into a graph regularization model to predict potential synergistic antibiotic combinations. Compared with existing methods, our model shows a better performance in the prediction of synergistic antibiotic combinations and interpretability.

The First Report on Pharmacokinetic/Pharmacodynamic Study of Trimethoprim/Sulfamethoxazole against Staphylococcus aureus with a Neutropenic Murine Thigh Infection Model

INTRODUCTION

With an increase in the incidence of Staphylococcus aureus infections in the healthcare settings and in the community, trimethoprim/sulfamethoxazole (TMP/SMX) has been suggested as a convenient treatment option. However, the appropriate dosage regimen of TMP/SMX is unclear.

OBJECTIVE

This study aimed to examine the pharmacokinetics/pharmacodynamics (PK/PD) of TMP/SMX against S. aureus using a neutropenic murine thigh infection model.

METHODS

Five S. aureus isolates with TMP/SMX (1:5 fixed ratio) minimum inhibitory concentrations (MICs) of 0.032-64 μg/mL were tested. The antimicrobial efficacy of TMP/SMX (1-689 mg/kg/day: dose shown as SMX dosage) was calculated as the change in bacterial density after 24 h of treatment. The plasma concentrations of TMP/SMX were detected using high-performance liquid chromatography.

RESULTS

After TMP/SMX single dose (130 mg/kg), the half-life, area under the blood concentration curve (AUC0-∞), and the protein binding ratio of SMX were 1.5 h, 718.2 μg h/mL, and 73.0 ± 8.3%, respectively. The free AUC/MIC and free %time (%T) above the MIC of SMX were better correlated with the in vivo antimicrobial activity than Cmax/MIC (free AUC/MIC, R2 = 0.69; free %T > MIC, R2 = 0.71; free Cmax/MIC, R2 = 0.53). The distributed doses (2-3 times per day) of TMP/SMX (130, 260, and 390 mg/kg/day) showed higher antimicrobial activity than the single dosage. However, TMP/SMX did not show its antimicrobial activity at <100% free %T > MIC.

CONCLUSIONS

The TMP/SMX treatment demonstrated that the free AUC/MIC of SMX was the better predictor of the PK/PD index of TMP/SMX.

Targeting fundamental pathways to disrupt Staphylococcus aureus survival: clinical implications of recent discoveries

The emergence of community-associated methicillin-resistant Staphylococcus aureus during the past decade along with an impending shortage of effective antistaphylococcal antibiotics have fueled impressive advances in our understanding of how S. aureus overcomes the host environment to establish infection. Backed by recent technologic advances, studies have uncovered elaborate metabolic, nutritional, and virulence strategies deployed by S. aureus to survive the restrictive and hostile environment imposed by the host, leading to a plethora of promising antimicrobial approaches that have potential to remedy the antibiotic resistance crisis. In this Review, we highlight some of the critical and recently elucidated bacterial strategies that are potentially amenable to intervention, discuss their relevance to human diseases, and address the translational challenges posed by current animal models.

Old antimicrobials and Gram-positive cocci through the example of infective endocarditis and bone and joint infections

The management of some serious infections such as infective endocarditis (IE) and bone and joint infections (BJIs) caused by Gram-positive cocci (GPC) is complex and requires great responsiveness and effective antimicrobials with high bioavailability in heart valves or bone tissues. Treatment of these infections requires the use of a higher dosage that may result in increased toxicity or the use of new promising antimicrobials to control the infection. However, use of these new antimicrobials could still bring about new toxicity and resistance. Another approach may be the 'comeback' of old antimicrobials, which is evaluated in this review in the treatment of IE and BJIs caused by GPC.

Is Trimethoprim-Sulfamethoxazole a Valid Alternative in the Management of Infections in Children in the Era of Community-Acquired Methicillin-Resistant Staphylococcus aureus? A Comprehensive Systematic Review

Objective. To evaluate the use of TMP-SMX compared with other options available for the treatment of children with community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections. Data Sources. The following databases were searched: Medline and PreMedline (OivdSP interface); Excerpta Medica Database (EMBASE; Elsevier interface); Cumulative Index to the Nursing and Allied Health Literature (CINAHL; EbscoHost interface); Sciences Citation Index Expanded (SCI-EXPANDED; Web of Science interface); Cochrane Library (Wiley interface); Scopus (Elsevier interface), and DARE, HTA (CRD interface). The search strategy was the one developed by SIGN to identify randomized clinical trials and systematic reviews. Also, we conducted a hand review of all reference lists of included studies. No language or data limits were added. The last search was done on October 1, 2015. Main key words were trimethoprim or trimethoprim-sulfamethoxazole combination and Staphylococcus aureus. Study Selection. Only randomized controlled trials comparing TMP-SMX versus any other antibiotic as the first-line treatment in CA-MRSA infections in children were included. Articles were reviewed by 2 reviewers, and in case of discrepancy, the final decision was made by the study coordinator. Data Extraction. Only 27 out of 364 articles identified were randomized controlled trials and only 4 fulfilled the eligibility criteria (Jadad score >3). Data Synthesis. Evidence found only referred to use of TMP-SMX in soft tissue infections. Heterogeneity among studies precluded meta-analysis. Conclusions. Available evidence is not conclusive to promote or refuse TMP-SMX as first-line treatment in CA-MRSA infections in children. Additional well-designed studies are required to fsurther elucidate this issue.

Binding Isotope Effects for para-Aminobenzoic Acid with Dihydropteroate Synthase from Staphylococcus aureus and Plasmodium falciparum

Dihydropteroate synthase is a key enzyme in folate biosynthesis and is the target of the sulfonamide class of antimicrobials. Equilibrium binding isotope effects and density functional theory calculations indicate that the substrate binding sites for para-aminobenzoic acid on the dihydropteroate synthase enzymes from Staphylococcus aureus and Plasmodium falciparum present distinct chemical environments. Specifically, we show that para-aminobenzoic acid occupies a more sterically constrained vibrational environment when bound to dihydropteroate synthase from P. falciparum relative to that of S. aureus. Deletion of a nonhomologous, parasite-specific insert from the plasmodial dihydropteroate synthase abrogated the binding of para-aminobenzoic acid. The loop specific to P. falciparum is important for effective substrate binding and therefore plays a role in modulating the chemical environment at the substrate binding site.

Trimethoprim-sulfamethoxazole versus vancomycin for severe infections caused by meticillin resistant Staphylococcus aureus: randomised controlled trial

OBJECTIVE

To show non-inferiority of trimethoprim-sulfamethoxazole compared with vancomycin for the treatment of severe infections due to meticillin resistant Staphylococcus aureus (MRSA).

DESIGN

Parallel, open label, randomised controlled trial.

SETTING

Four acute care hospitals in Israel.

PARTICIPANTS

Adults with severe infections caused by MRSA susceptible to trimethoprim-sulfamethoxazole and vancomycin. Patients with left sided endocarditis, meningitis, chronic haemodialysis, and prolonged neutropenia were excluded.

INTERVENTIONS

Trimethoprim-sulfamethoxazole 320 mg/1600 mg twice daily versus vancomycin 1 g twice daily for a minimum of seven days and then by indication.

MAIN OUTCOME MEASURES

The primary efficacy outcome was treatment failure assessed at day 7, consisting of death, persistence of haemodynamic instability or fever, stable or worsening Sequential Organ Failure Assessment score, and persistence of bacteraemia. The primary safety outcome was all cause mortality at day 30. Non-inferiority was defined by a difference of less than 15% for treatment failure.

RESULTS

252 patients were included in the trial, of whom 91 (36%) had bacteraemia. No significant difference in treatment failure was seen for trimethoprim-sulfamethoxazole (51/135, 38%) versus vancomycin (32/117, 27%)-risk ratio 1.38 (95% confidence interval 0.96 to 1.99). However, trimethoprim-sulfamethoxazole did not meet the non-inferiority criterion-absolute difference 10.4% (95% confidence interval -1.2% to 21.5%). For patients with bacteraemia, the risk ratio was 1.40 (0.91 to 2.16). In a multivariable logistic regression analysis, trimethoprim-sulfamethoxazole was significantly associated with treatment failure (adjusted odds ratio 2.00, 1.09 to 3.65). The 30 day mortality rate was 32/252 (13%), with no significant difference between arms. Among patients with bacteraemia, 14/41 (34%) treated with trimethoprim-sulfamethoxazole and 9/50 (18%) with vancomycin died (risk ratio 1.90, 0.92 to 3.93).

CONCLUSIONS

High dose trimethoprim-sulfamethoxazole did not achieve non-inferiority to vancomycin in the treatment of severe MRSA infections. The difference was particularly marked for patients with bacteraemia. Trial registration Clinical trials NCT00427076.

Alternating antibiotic treatments constrain evolutionary paths to multidrug resistance

Alternating antibiotic therapy, in which pairs of drugs are cycled during treatment, has been suggested as a means to inhibit the evolution of de novo resistance while avoiding the toxicity associated with more traditional combination therapy. However, it remains unclear under which conditions and by what means such alternating treatments impede the evolution of resistance. Here, we tracked multistep evolution of resistance in replicate populations of Staphylococcus aureus during 22 d of continuously increasing single-, mixed-, and alternating-drug treatment. In all three tested drug pairs, the alternating treatment reduced the overall rate of resistance by slowing the acquisition of resistance to one of the two component drugs, sometimes as effectively as mixed treatment. This slower rate of evolution is reflected in the genome-wide mutational profiles; under alternating treatments, bacteria acquire mutations in different genes than under corresponding single-drug treatments. To test whether this observed constraint on adaptive paths reflects trade-offs in which resistance to one drug is accompanied by sensitivity to a second drug, we profiled many single-step mutants for cross-resistance. Indeed, the average cross-resistance of single-step mutants can help predict whether or not evolution was slower in alternating drugs. Together, these results show that despite the complex evolutionary landscape of multidrug resistance, alternating-drug therapy can slow evolution by constraining the mutational paths toward resistance.

Minocycline, often forgotten but preferred to trimethoprim-sulfamethoxazole or doxycycline for the treatment of community-acquired meticillin-resistant Staphylococcus aureus skin and soft-tissue infections

Treatment of uncomplicated skin and soft-tissue abscesses caused by meticillin-sensitive Staphylococcus aureus or meticillin-resistant S. aureus (MRSA) is problematic. Incision and drainage aside, oral antibiotic therapy for uncomplicated community-acquired MRSA (CA-MRSA) is limited and frequent choices include clindamycin, doxycycline or trimethoprim-sulfamethoxazole (TMP-SMX). The most common oral antibiotics used for CA-MRSA are doxycycline or TMP-SMX, which often fail to eradicate the infection. With MRSA, in vitro susceptibilities do not always predict in vivo effectiveness. In situations where doxycycline or TMP-SMX fails in the treatment of uncomplicated cutaneous abscesses due to CA-MRSA, minocycline is reliably effective.

Catalysis and sulfa drug resistance in dihydropteroate synthase

The sulfonamide antibiotics inhibit dihydropteroate synthase (DHPS), a key enzyme in the folate pathway of bacteria and primitive eukaryotes. However, resistance mutations have severely compromised the usefulness of these drugs. We report structural, computational, and mutagenesis studies on the catalytic and resistance mechanisms of DHPS. By performing the enzyme-catalyzed reaction in crystalline DHPS, we have structurally characterized key intermediates along the reaction pathway. Results support an S(N)1 reaction mechanism via formation of a novel cationic pterin intermediate. We also show that two conserved loops generate a substructure during catalysis that creates a specific binding pocket for p-aminobenzoic acid, one of the two DHPS substrates. This substructure, together with the pterin-binding pocket, explains the roles of the conserved active-site residues and reveals how sulfonamide resistance arises.

Molecular characterization and antibiotic susceptibility of Staphylococcus aureus from a multidisciplinary hospital in Romania

From 2004 to 2005, 60%-72% of invasive Staphylococcus aureus isolates from Romanian hospitals were resistant to methicillin (methicillin-resistant S. aureus [MRSA]), the highest frequency for any European nation. Few reports, however, have addressed the molecular characteristics of S. aureus in Romania. In this study, we utilized spa typing, multilocus sequence typing, staphylococcal cassette chromosome mec (SCCmec) typing, dru typing, pulsed-field gel electrophoresis, and detection of virulence factors to characterize 146 S. aureus strains isolated from 2004 to 2005 at the Clinic County Hospital in Braşov. Antibiotic susceptibility patterns for all MRSA isolates and patient demographic data were also obtained. Fifty-six strains (38.4%) were determined to be MRSA by susceptibility testing and SCCmec typing. All MRSA strains were resistant to beta-lactams and tetracycline, but susceptible to nitrofurans, vancomycin, and clindamycin, with inducible clindamycin resistance in 23/28 clindamycin-sensitive/erythromycin-resistant isolates. Molecular typing identified 15 clonal backgrounds (CC 1, 5, 8, 8/239, 9, 15, 20, 22, 25, 30, 45, 80, 97, 101, and 121), only 4 of which were associated with MRSA (CC 1, 8/239, 30, and 80). Spa types 35 (t127, CC 1) and 351 (t030, CC 8/239) accounted for 27.4% and 21.9% of all S. aureus strains, respectively, and 19.6% and 57.1% of all MRSA strains. Both hospital-associated (SCCmec type III) and community-associated (SCCmec type IV) elements were identified within MRSA strains, whereas Panton-Valentine leukocidin was detected in 10 MRSA and 12 methicillin-sensitive S. aureus strains. These results demonstrate the presence of various endemic S. aureus clones within the Clinic County Hospital in Braşov, suggestive of ongoing nosocomial and community transmission.

A randomized controlled trial of intermittent compared with daily cotrimoxazole preventive therapy in HIV-infected children

OBJECTIVE

Cotrimoxazole preventive therapy (CPT) reduces morbidity and mortality in HIV-infected children. The WHO recommends prolonged daily CPT for HIV-infected infants and children. In adults, intermittent CPT has been associated with less adverse events than daily, with increased tolerability and equal efficacy. We investigated the efficacy and tolerability of intermittent CPT compared with daily CPT in HIV-infected children over a 5-year period.

DESIGN

A prospective randomized controlled study.

METHODS

HIV-infected children aged at least 8 weeks were randomized to thrice weekly or daily CPT. Outcome measures were mortality, bacterial infections, hospitalizations and adverse events.

RESULTS

Three hundred and twenty-four children (median age 23 months) were followed for 672 child-years; 165 (51%) were randomized to intermittent CPT. Most children (287, 89%) were Centers for Disease Control and Prevention clinical category B or C; 207 (64%) received HAART during the study. Mortality (53 deaths, 16%) was similar in the intermittent CPT compared with the daily CPT group {24 (14%) vs. 29 (18%), hazard ratio 0.75 [95% confidence interval (CI) 0.44-1.29]}. The predominant causes of death in both groups were sepsis (17, 32%), pneumonia (13, 25%) or diarrhoea (8, 15%). Intermittent CPT was associated with more bacteraemias [incidence rate ratio 2.36 (95% CI 1.21-4.86)]. Children receiving intermittent CPT also spent more days in hospital [incidence rate ratio 1.15 (95% CI 1.04-1.28)]. The rate of serious adverse events was similar between groups [incidence rate ratio 1.07 (95% CI 0.58-2.02)].

CONCLUSION

Intermittent CPT was associated with more invasive bacterial disease than daily CPT, but survival was similar. Both regimens were well tolerated. On balance, daily CPT remains preferable to intermittent therapy for HIV-infected children.