Trimethoprim In Vitro Antibacterial Activity is Not Increased by Adding Sulfamethoxazole for Pediatric Escherichia coli Urinary Tract Infection

Antimicrobial pharmacokinetics and preclinical in vitro models to support optimized treatment approaches for uncomplicated lower urinary tract infections

INTRODUCTION

Urinary tract infections (UTIs) are extremely common. Millions of people, particularly healthy women, are affected worldwide every year. One-in-two women will have a recurrence within 12-months of an initial UTI. Inadequate treatment risks worsening infection leading to acute pyelonephritis, bacteremia and sepsis. In an era of increasing antimicrobial resistance, it is critical to provide optimized antimicrobial treatment.

AREAS COVERED

Literature was searched using PubMed and Google Scholar (up to 06/2020), examining the etiology, diagnosis and oral antimicrobial therapy for uncomplicated UTIs, with emphasis on urinary antimicrobial pharmacokinetics (PK) and the application of dynamic in vitro models for the pharmacodynamic (PD) profiling of pathogen response.

EXPERT OPINION

The majority of antimicrobial agents included in international guidelines were developed decades ago without well-described dose-response relationships. Microbiology laboratories still apply standard diagnostic methodology that has essentially remained unchanged for decades. Furthermore, it is uncertain how relevant standard in vitro susceptibility is for predicting antimicrobial efficacy in urine. In order to optimize UTI treatments, clinicians must exploit the urine-specific PK of antimicrobial agents. Dynamic in vitro models are valuable tools to examine the PK/PD and urodynamic variables associated with UTIs, while informing uropathogen susceptibility reporting, optimized dosing schedules, clinical trials and treatment guidelines.

[Resistance testing for urinary tract infections. A barrier to guideline implementation]

BACKGROUND

Urinary tract infections (UTI) are among the most common reasons for antibiotic prescriptions. Due to increasing resistance rates, antibiotic therapy should be targeted and based on evidence-based recommendations. Test results and recommendations by medical laboratories have a relevant impact on the choice of antibiotics. The extent to which medical laboratories consider antibiotics recommended by evidence-based treatment guidelines in microbiological testing is unclear.

OBJECTIVES

The aim of the present study is to assess whether guideline recommendations for antibiotic therapy of UTI are taken into account by medical laboratories in northern Germany.

MATERIALS AND METHODS

A standardized and piloted questionnaire was used in our telephone survey. All microbiological laboratories in northern Germany (Hamburg, Bremen, Lower Saxony, Schleswig-Holstein, and Mecklenburg-Western Pomerania; n = 82) were asked about their standards in diagnosing and microbiological testing of urine cultures.

RESULTS

A total of 71 of the 82 contacted laboratories perform microbiological tests, whereby 40 of these participated (56 %). Most of the laboratories (43 %) routinely perform microbiological testing when bacterial counts were ≥ 10(4) colony forming units per ml (CFU/ml), 15 % ≥ 10(5) CFU/ml, 17 % ≥ 10(3) CFU/ml, and 8 % ≥ 10(2) CFU/ml. Antibiotic testing includes ciprofloxacin (95 %), cotrimoxazole (87.5 %), trimethoprim (57 %), fosfomycin (85 %), and nitrofurantoin (72 %).

CONCLUSIONS

The diagnostic threshold recommended in evidence-based guidelines (10(3) CFU/ml) is used only by a few laboratories. Antibiotics recommended as a first line therapy are only partly taken into account in microbiological testing. This variance in different diagnostic thresholds and microbiological testing is a barrier to guideline implementation.

Bacterial conversion of folinic acid is required for antifolate resistance

Antifolates, which are among the first antimicrobial agents invented, inhibit cell growth by creating an intracellular state of folate deficiency. Clinical resistance to antifolates has been mainly attributed to mutations that alter structure or expression of enzymes involved in de novo folate synthesis. We identified a Mycobacterium smegmatis mutant, named FUEL (which stands for folate utilization enzyme for leucovorin), that is hypersusceptible to antifolates. Chemical complementation indicated that FUEL is unable to metabolize folinic acid (also known as leucovorin or 5-formyltetrahydrofolate), whose metabolic function remains unknown. Targeted mutagenesis, genetic complementation, and biochemical studies showed that FUEL lacks 5,10-methenyltetrahydrofolate synthase (MTHFS; also called 5-formyltetrahydrofolate cyclo-ligase; EC 6.3.3.2) activity responsible for the only ATP-dependent, irreversible conversion of folinic acid to 5,10-methenyltetrahydrofolate. In trans expression of active MTHFS proteins from bacteria or human restored both antifolate resistance and folinic acid utilization to FUEL. Absence of MTHFS resulted in marked cellular accumulation of polyglutamylated species of folinic acid. Importantly, MTHFS also affected M. smegmatis utilization of monoglutamylated 5-methyltetrahydrofolate exogenously added to the medium. Likewise, Escherichia coli mutants lacking MTHFS became susceptible to antifolates. These results indicate that folinic acid conversion by MTHFS is required for bacterial intrinsic antifolate resistance and folate homeostatic control. This novel mechanism of antimicrobial antifolate resistance might be targeted to sensitize bacterial pathogens to classical antifolates.

[Treatment of vesicoureteral reflux in childhood]

The pathophysiology, evaluation and therapy of vesicoureteral reflux (VUR) were newly illuminated over the past years through different clinical studies and basic research. Our understanding of vesicoureteral reflux and the therapeutic spectrum of its treatment should therefore consistently undergo critical revision. The Swedish Reflux Study set up three different therapy options for small children with dilated VUR: antibiotic prophylaxis, endoscopic reflux correction and surveillance were prospectively analysed in a randomized fashion. The results are discussed in this work and completed with a statement about open operative reflux therapy.