MICs of ciprofloxacin and trimethoprim for Escherichia coli: influence of pH, inoculum size and various body fluids

Urinary pH and antibiotics, choose carefully. A systematic review

Uncomplicated urinary tract infection (UTI) is the most common bacterial infection in women. Since 1948, the relationship between urinary pH and antibiotics (ABs) has been established. We aimed to search for the best urinary pH for each family of antibiotics and to assess whether pH changes bacterial susceptibility to them. We included in vitro research and in vivo studies including one or more bacterial species and tested the effect of one or more ABs at different pH values. We also included randomized controlled clinical trials (RCTs) in uncomplicated UTI (EAU guidelines 2019 definition), choosing the ABs based on urinary pH or using an antibiotic plus urinary pH modifiers (L-methionine, vitamin C…) vs. an antibiotic and a placebo. Quadas-2 tool was used as a quality assessment of the studies and PRISMA set of items for systematic reviews. Two authors independently screened and evaluated the papers, while two additional authors individually repeated the search. A fifth researcher acted as an arbiter, and another author collaborated as a hospital pharmaceutical consultant. Alkaline-friendly antibiotics are most fluoroquinolones, aminoglycosides, trimethoprim. Acidic-friendly antibiotics are fosfomycin, tetracycline, nitrofurantoin and some β-lactams. We suggest performing urine cultures with antibiogram tests, in both acidic and alkaline media, to define the bacterial susceptibility profile. There is insufficient in vivo evidence to support whether choosing an antibiotic based on a patient's urinary pH or adding urinary pH modifiers will lead to a higher cure rate.

Structure-guided functional studies of plasmid-encoded dihydrofolate reductases reveal a common mechanism of trimethoprim resistance in Gram-negative pathogens

Two plasmid-encoded dihydrofolate reductase (DHFR) isoforms, DfrA1 and DfrA5, that give rise to high levels of resistance in Gram-negative bacteria were structurally and biochemically characterized to reveal the mechanism of TMP resistance and to support phylogenic groupings for drug development against antibiotic resistant pathogens. Preliminary screening of novel antifolates revealed related chemotypes that showed high levels of inhibitory potency against Escherichia coli chromosomal DHFR (EcDHFR), DfrA1, and DfrA5. Kinetics and biophysical analysis, coupled with crystal structures of trimethoprim bound to EcDHFR, DfrA1 and DfrA5, and two propargyl-linked antifolates (PLA) complexed with EcDHFR, DfrA1 and DfrA5, were determined to define structural features of the substrate binding pocket and guide synthesis of pan-DHFR inhibitors.

Critical residue variations in two of the most clinically prevalent DHFR isoforms are identified as a common structural element in trimethoprim-resistant DHFR which impose changes on enzyme catalysis and ligand-cofactor cooperativity.

Mastering the Gram-negative bacterial barrier - Chemical approaches to increase bacterial bioavailability of antibiotics

To win the battle against resistant, pathogenic bacteria, novel classes of anti-infectives and targets are urgently needed. Bacterial uptake, distribution, metabolic and efflux pathways of antibiotics in Gram-negative bacteria determine what we here refer to as bacterial bioavailability. Understanding these mechanisms from a chemical perspective is essential for anti-infective activity and hence, drug discovery as well as drug delivery. A systematic and critical discussion of in bacterio, in vitro and in silico assays reveals that a sufficiently accurate holistic approach is still missing. We expect new findings based on Gram-negative bacterial bioavailability to guide future anti-infective research.

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.

Bacterial interspecies interactions modulate pH-mediated antibiotic tolerance

Predicting antibiotic efficacy within microbial communities remains highly challenging. Interspecies interactions can impact antibiotic activity through many mechanisms, including alterations to bacterial physiology. Here, we studied synthetic communities constructed from the core members of the fruit fly gut microbiota. Co-culturing of Lactobacillus plantarum with Acetobacter species altered its tolerance to the transcriptional inhibitor rifampin. By measuring key metabolites and environmental pH, we determined that Acetobacter species counter the acidification driven by L. plantarum production of lactate. Shifts in pH were sufficient to modulate L. plantarum tolerance to rifampin and the translational inhibitor erythromycin. A reduction in lag time exiting stationary phase was linked to L. plantarum tolerance to rifampicin, opposite to a previously identified mode of tolerance to ampicillin in E. coli. This mechanistic understanding of the coupling among interspecies interactions, environmental pH, and antibiotic tolerance enables future predictions of growth and the effects of antibiotics in more complex communities.

Subcellular Quantification of Uptake in Gram-Negative Bacteria

Infections by Gram-negative pathogens represent a major health care issue of growing concern due to a striking lack of novel antibacterial agents over the course of the last decades. The main scientific problem behind the rational optimization of novel antibiotics is our limited understanding of small molecule translocation into, and their export from, the target compartments of Gram-negative species. To address this issue, a versatile, label-free assay to determine the intracellular localization and concentration of a given compound has been developed for Escherichia coli and its efflux-impaired ΔTolC mutant. The assay applies a fractionation procedure to antibiotic-treated bacterial cells to obtain periplasm, cytoplasm, and membrane fractions of high purity, as demonstrated by Western Blots of compartment-specific marker proteins. This is followed by an LC-MS/MS-based quantification of antibiotic content in each compartment. Antibiotic amounts could be converted to antibiotic concentrations by assuming that an E. coli cell is a cylinder flanked by two half spheres and calculating the volumes of bacterial compartments. The quantification of antibiotics from different classes, namely ciprofloxacin, tetracycline, trimethoprim, and erythromycin, demonstrated pronounced differences in uptake quantities and distribution patterns across the compartments. For example, in the case of ciprofloxacin, a higher amount of compound was located in the cytoplasm than in the periplasm (592 ± 50 pg vs 277 ± 13 pg per 3.9 × 10⁹ cells), but owing to the smaller volume of the periplasmic compartment, its concentration in the cytoplasm was much lower (37 ± 3 vs 221 ± 10 pg/μL for the periplasm). For erythromycin and tetracycline, differences in MICs between WT and ΔTolC mutant strains were not reflected by equal differences in uptake, illustrating that additional experimental data are needed to predict antibiotic efficacy. We believe that our assay, providing the antibiotic concentration at the compartment in which the drug target is expressed, constitutes an essential piece of information for a more rational optimization of novel antibiotics against Gram-negative infections.

pH plays a role in the mode of action of trimethoprim on Escherichia coli

Metabolomics-based approaches were applied to understand interactions of trimethoprim with Escherichia coli K-12 at sub-minimum inhibitory concentrations (MIC≈0.2, 0.03 and 0.003 mg L-1). Trimethoprim inhibits dihydrofolate reductase and thereby is an indirect inhibitor of nucleic acid synthesis. Due to the basicity of trimethoprim, two pH levels (5 and 7) were selected which mimicked healthy urine pH. This also allowed investigation of the effect on bacterial metabolism when trimethoprim exists in different ionization states. UHPLC-MS was employed to detect trimethoprim molecules inside the bacterial cell and this showed that at pH 7 more of the drug was recovered compared to pH 5; this correlated with classical growth curve measurements. FT-IR spectroscopy was used to establish recovery of reproducible phenotypes under all 8 conditions (3 drug levels and control in 2 pH levels) and GC-MS was used to generate global metabolic profiles. In addition to finding direct mode-of-action effects where nucleotides were decreased at pH 7 with increasing trimethoprim levels, off-target pH-related effects were observed for many amino acids. Additionally, stress-related effects were observed where the osmoprotectant trehalose was higher at increased antibiotic levels at pH 7. This correlated with glucose and fructose consumption and increase in pyruvate-related products as well as lactate and alanine. Alanine is a known regulator of sugar metabolism and this increase may be to enhance sugar consumption and thus trehalose production. These results provide a wider view of the action of trimethoprim. Metabolomics indicated alternative metabolism areas to be investigated to further understand the off-target effects of trimethoprim.

A population genomics approach to exploiting the accessory 'resistome' of Escherichia coli

The emergence of antibiotic resistance is a defining challenge, and Escherichia coli is recognized as one of the leading species resistant to the antimicrobials used in human or veterinary medicine. Here, we analyse the distribution of 2172 antimicrobial-resistance (AMR) genes in 4022 E. coli to provide a population-level view of resistance in this species. By separating the resistance determinants into 'core' (those found in all strains) and 'accessory' (those variably present) determinants, we have found that, surprisingly, almost half of all E. coli do not encode any accessory resistance determinants. However, those strains that do encode accessory resistance are significantly more likely to be resistant to multiple antibiotic classes than would be expected by chance. Furthermore, by studying the available date of isolation for the E. coli genomes, we have visualized an expanding, highly interconnected network that describes how resistances to antimicrobials have co-associated within genomes over time. These data can be exploited to reveal antimicrobial combinations that are less likely to be found together, and so if used in combination may present an increased chance of suppressing the growth of bacteria and reduce the rate at which resistance factors are spread. Our study provides a complex picture of AMR in the E. coli population. Although the incidence of resistance to all studied antibiotic classes has increased dramatically over time, there exist combinations of antibiotics that could, in theory, attack the entirety of E. coli, effectively removing the possibility that discrete AMR genes will increase in frequency in the population.

Urinary Tract Physiological Conditions Promote Ciprofloxacin Resistance in Low-Level-Quinolone-Resistant Escherichia coli

Escherichia coli isolates carrying chromosomally encoded low-level-quinolone-resistant (LLQR) determinants are frequently found in urinary tract infections (UTIs). LLQR mutations are considered the first step in the evolutionary pathway producing high-level fluoroquinolone resistance. Therefore, their evolution and dissemination might influence the outcome of fluoroquinolone treatments of UTI. Previous studies support the notion that low urine pH decreases susceptibility to ciprofloxacin (CIP) in E. coli However, the effect of the urinary tract physiological parameters on the activity of ciprofloxacin against LLQR E. coli strains has received little attention. We have studied the activity of ciprofloxacin under physiological urinary tract conditions against a set of well-characterized isogenic E. coli derivatives carrying the most prevalent chromosomal mutations (ΔmarR, gyrA-S83L, gyrA-D87N, and parC-S80R and some combinations). The results presented here demonstrate that all the LLQR strains studied became resistant to ciprofloxacin (according to CLSI guidelines) under physiological conditions whereas the control strain lacking LLQR mutations did not. Moreover, the survival of some LLQR E. coli variants increased up to 100-fold after challenge with a high concentration of ciprofloxacin under UTI conditions compared to the results seen with Mueller-Hinton broth. These selective conditions could explain the high prevalence of LLQR mutations in E. coli Furthermore, our data strongly suggest that recommended methods for MIC determination produce poor estimations of CIP activity against LLQR E. coli in UTIs.

Urinary concentrations and antibacterial activities of nitroxoline at 250 milligrams versus trimethoprim at 200 milligrams against uropathogens in healthy volunteers

Because of the increasing bacterial resistance of uropathogens against standard antibiotics, such as trimethoprim (TMP), older antimicrobial drugs, such as nitroxoline (NTX), should be reevaluated. This randomized crossover study investigated the urinary concentrations of parent drugs and their metabolites and their antibacterial activities (urinary inhibitory titers [UITs] and urinary bactericidal titers [UBTs]) against uropathogens at three different urinary pH values within 24 h in six healthy volunteers after a single oral dose of NTX at 250 mg versus TMP at 200 mg. In three additional volunteers, urinary bactericidal kinetics (UBK) were studied after oral administration of NTX at 250 mg three times a day. The mean urinary concentrations of NTX and NTX sulfate in 24 h were 0.012 to 0.507 mg/liter and 0.28 to 27.83 mg/liter, respectively. The mean urinary concentrations of TMP were 18.79 to 41.59 mg/liter. The antibacterial activity of NTX was higher in acidic urine than in alkaline urine, and that of TMP was higher in alkaline urine than in acidic urine. The UITs and UBTs of NTX were generally lower than those of TMP except for a TMP-resistant Escherichia coli strain, for which NTX showed higher UITs/UBTs than did TMP. UBK showed mainly bacteriostatic activity of NTX in urine. NTX exhibits mainly bacteriostatic activity and TMP also shows bactericidal activity in urine against susceptible strains. NTX is a more active antibacterial in acidic urine, and TMP is more active in alkaline urine. The cumulative effects of multiple doses or inhibition of bacterial adherence could not be evaluated. (This study has been registered at EudraCT under registration no. 2009-015631-32.).

Antimicrobial therapy for chronic bacterial prostatitis

BACKGROUND

Chronic bacterial prostatitis (CBP) is frequently diagnosed in men of fertile age, and is characterized by a disabling array of symptoms, including pain in the pelvic area (for example, perineum, testicles), voiding symptoms (increased frequency and urgency, also at night; pain or discomfort at micturition), and sexual dysfunction. Cure of CBP can be attempted by long-term therapy with antibacterial agents, but relapses are frequent. Few antibacterial agents are able to distribute to the prostatic tissue and achieve sufficient concentrations at the site of infection. These agents include fluoroquinolones, macrolides, tetracyclines and trimethoprim. After the introduction of fluoroquinolones into clinical practice, a number of studies have been performed to optimize the antimicrobial treatment of CBP, and to improve eradication rates and symptom relief.

OBJECTIVES

To assess and compare the efficacy and harm of antimicrobial treatments for chronic bacterial prostatitis.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (PubMed), EMBASE, other national or international databases and abstracts from conference proceedings on 8 August 2012.

SELECTION CRITERIA

We included all randomized controlled comparisons of one antimicrobial agent versus placebo or one or more comparator antimicrobial agents, combined or not with non-antimicrobial drugs. We also included trials comparing different doses, treatment durations, dosing frequencies, or routes of administration of antimicrobial agents. We excluded studies in which patients were not diagnosed according to internationally recommended criteria, or were not subjected to lower urinary tract segmented tests.

DATA COLLECTION AND ANALYSIS

Study data were extracted independently by two review authors. Study outcomes were microbiological efficacy (pathogen eradication), clinical efficacy (symptom cure or improvement, or symptom scores) at test-of-cure visits or at follow-up, or both, and adverse effects of therapy. Secondary outcomes included microbiological recurrence rates.Statistical analysis was performed using a fixed-effect model for microbiological outcomes and a random-effects model for clinical outcomes and adverse effects. The results were expressed as risk ratios for dichotomous outcomes (with 95% confidence intervals) or as standardized mean differences for continuous or non-dichotomous variables.

MAIN RESULTS

We identified 18 studies, enrolling a total of 2196 randomized patients. The oral fluoroquinolones ciprofloxacin, levofloxacin, lomefloxacin, ofloxacin and prulifloxacin were compared. There were no significant differences in clinical or microbiological efficacy or in the rate of adverse effects between these fluoroquinolones. In chlamydial prostatitis, (i) azithromycin showed improved eradication rates and clinical cure rates compared to ciprofloxacin, with no significant differences regarding adverse effects; (ii) azithromycin was equivalent to clarithromycin, both microbiologically and clinically; (iii) prulifloxacin appeared to improve clinical symptoms, but not eradication rates, compared to doxycycline. In ureaplasmal prostatitis, the comparisons ofloxacin versus minocycline and azithromycin versus doxycycline showed similar microbiological, clinical and toxicity profiles.

AUTHORS' CONCLUSIONS

The microbiological and clinical efficacy, as well as the adverse effect profile, of different oral fluoroquinolones are comparable. No conclusions can be drawn regarding the optimal treatment duration of fluoroquinolones in the treatment of CBP caused by traditional pathogens.Alternative antimicrobial agents tested for the treatment of CBP caused by traditional pathogens are co-trimoxazole, beta-lactams and tetracyclines, but no conclusive evidence can be drawn regarding the role of non-fluoroquinolone antibiotics in the treatment of CBP caused by traditional pathogens.In patients with CBP caused by obligate intracellular pathogens, macrolides showed higher microbiological and clinical cure rates compared to fluoroquinolones.

Comparative in vitro activities of the novel antibacterial finafloxacin against selected Gram-positive and Gram-negative bacteria tested in Mueller-Hinton broth and synthetic urine

Kill kinetics and MICs of finafloxacin and ciprofloxacin against 34 strains with defined resistance mechanisms grown in cation-adjusted Mueller-Hinton broth (CAMHB) at pH values of 7.2 and 5.8 and in synthetic urine at pH 5.8 were determined. In general, finafloxacin gained activity at low pH values in CAMHB and remained almost unchanged in artificial urine. Ciprofloxacin MICs increased and bactericidal activity decreased strain dependently in acidic CAMHB and particularly in artificial urine.

Protein binding of antimicrobials: methods for quantification and for investigation of its impact on bacterial killing

Plasma protein binding of antimicrobial agents is considered to be a key characteristic of antibiotics as it affects both their pharmacokinetics and pharmacodynamics. However, up to the present, no standard methods for measuring protein binding or for quantification of the influence of protein binding on antimicrobial activity exist. This short-coming has previously led to conflicting results on antibacterial activity of highly protein-bound antibiotics. The present review, therefore, set out to summarize (1) methods for quantification of protein binding, (2) microbiological growth media used for determination of the impact of protein binding on antimicrobial activity of antibiotics, and (3) different pharmacodynamic in vitro studies that are used in this context. The advantages and disadvantages of a wide range of different approaches are discussed and compared. The urgent call for international standardization by microbiological societies and laboratories may be considered as a logical consequence of the presented data.

Influences of urinary pH on ciprofloxacin pharmacokinetics in humans and antimicrobial activity in vitro versus those of sparfloxacin

The impact of acidification and alkalinization of urine on the pharmacokinetics of ciprofloxacin was investigated after single 200-mg oral doses were administered to nine healthy male volunteers. In addition, the effect of human urine on the MICs of ciprofloxacin and sparfloxacin against some common urinary tract pathogens such as Escherichia coli and Pseudomonas aeruginosa was investigated. Acidic and alkaline conditions were achieved by repeated oral doses of ammonium chloride or sodium bicarbonate, respectively. Plasma ciprofloxacin levels in all subjects were adequately described in terms of two-compartment model kinetics with first-order absorption. Acidification and alkalinization treatments had no effect on ciprofloxacin absorption, distribution, or elimination. The total amount of unchanged ciprofloxacin excreted over 24 h under acidic conditions was 88.4 +/- 14.5 mg (mean +/- standard deviation) (44.2% of the oral dose) and 82.4 +/- 16.5 mg (41.2% of the oral dose) under alkaline conditions, while the total amount of unchanged drug excreted over 24 h in volunteers receiving neither sodium bicarbonate nor ammonium chloride was 90.53 +/- 9.8 mg (45.2% of the oral dose). The mean renal clearance of ciprofloxacin was 16.78 +/- 2.67, 16.08 +/- 3.2, and 16.31 +/- 2.67 liters/h with acidification, alkalinization, and control, respectively. Renal clearance and concentrations of ciprofloxacin in urine were not correlated with urinary pH. The antibacterial activity of ciprofloxacin and sparfloxacin against E. coli NIHJ JC-2 and P. aeruginosa ATCC 27853 was affected by human urine and in particular by its pH. The activities of both quinolones against E. coli NIHJ JC-2 were lower at lower urinary pH and rather uniform, while in the case of P. aeruginosa ATCC 27853 ciprofloxacin was more active than sparfloxacin.