Synergistic Effect of SOS Response and GATC Methylome Suppression on Antibiotic Stress Survival in Escherichia coli

The suppression of the SOS response has been shown to enhance the in vitro activity of quinolones. Furthermore, Dam-dependent base methylation has an impact on susceptibility to other antimicrobials affecting DNA synthesis. Here, we investigated the interplay between these two processes, alone and in combination, in terms of antimicrobial activity. A genetic strategy was used employing single- and double-gene mutants for the SOS response (recA gene) and the Dam methylation system (dam gene) in isogenic models of Escherichia coli both susceptible and resistant to quinolones. Regarding the bacteriostatic activity of quinolones, a synergistic sensitization effect was observed when the Dam methylation system and the recA gene were suppressed. In terms of growth, after 24 h in the presence of quinolones, the Δdam ΔrecA double mutant showed no growth or delayed growth compared to the control strain. In bactericidal terms, spot tests showed that the Δdam ΔrecA double mutant was more sensitive than the ΔrecA single mutant (about 10- to 102-fold) and the wild type (about 103- to 104-fold) in both susceptible and resistant genetic backgrounds. Differences between the wild type and the Δdam ΔrecA double mutant were confirmed by time-kill assays. The suppression of both systems, in a strain with chromosomal mechanisms of quinolone resistance, prevents the evolution of resistance. This genetic and microbiological approach demonstrated the enhanced sensitization of E. coli to quinolones by dual targeting of the recA (SOS response) and Dam methylation system genes, even in a resistant strain model.

Effect of RecA inactivation and detoxification systems on the evolution of ciprofloxacin resistance in Escherichia coli

Background

Suppression of SOS response and overproduction of reactive oxygen species (ROS) through detoxification system suppression enhance the activity of fluoroquinolones.

Objectives

To evaluate the role of both systems in the evolution of resistance to ciprofloxacin in an isogenic model of Escherichia coli.

Methods

Single-gene deletion mutants of E. coli BW25113 (wild-type) (ΔrecA, ΔkatG, ΔkatE, ΔsodA, ΔsodB), double-gene (ΔrecA-ΔkatG, ΔrecA-ΔkatE, ΔrecA-ΔsodA, ΔrecA-ΔsodB, ΔkatG-ΔkatE, ΔsodB-ΔsodA) and triple-gene (ΔrecA-ΔkatG-ΔkatE) mutants were included. The response to sudden high ciprofloxacin pressure was evaluated by mutant prevention concentration (MPC). The gradual antimicrobial pressure response was evaluated through experimental evolution and antibiotic resistance assays.

Results

For E. coli BW25113 strain, ΔkatE, ΔsodB and ΔsodB/ΔsodA mutants, MPC values were 0.25 mg/L. The ΔkatG, ΔsodA, ΔkatG/katE and ΔrecA mutants showed 2-fold reductions (0.125 mg/L). The ΔkatG/ΔrecA, ΔkatE/ΔrecA, ΔsodA/ΔrecA, ΔsodB/ΔrecA and ΔkatG/ΔkatE/ΔrecA strains showed 4–8-fold reductions (0.03–0.06 mg/L) relative to the wild-type. Gradual antimicrobial pressure increased growth capacity for ΔsodA and ΔsodB and ΔsodB/ΔsodA mutants (no growth in 4 mg/L) compared with the wild-type (no growth in the range of 0.5–2 mg/L). Accordingly, increased growth was observed with the mutants ΔrecA/ΔkatG (no growth in 2 mg/L), ΔrecA/ΔkatE (no growth in 2 mg/L), ΔrecA/ΔsodA (no growth in 0.06 mg/L), ΔrecA/ΔsodB (no growth in 0.25 mg/L) and ΔrecA/ΔkatG/ΔkatE (no growth in 0.5 mg/L) compared with ΔrecA (no growth in the range of 0.002–0.015 mg/L).

Conclusions

After RecA inactivation, gradual exposure to ciprofloxacin reduces the evolution of resistance. After suppression of RecA and detoxification systems, sudden high exposure to ciprofloxacin reduces the evolution of resistance in E. coli.

Role of low-level quinolone resistance in generating tolerance in Escherichia coli under therapeutic concentrations of ciprofloxacin

BACKGROUND

Tolerance (including persistence) and resistance result in increased survival under antibiotic pressure.

OBJECTIVES

We evaluated the interplay between resistance and tolerance to ciprofloxacin under therapeutic and killing conditions to determine the contribution of low-level quinolone resistance (LLQR) mechanisms to tolerance. We also determined how the interaction between resistance (LLQR phenotypes) and tolerance was modified under SOS response suppression.

METHODS

Twelve isogenic Escherichia coli strains harbouring quinolone resistance mechanisms combined with SOS response deficiency and six clinical E. coli isolates (LLQR or non-LLQR) were evaluated. Survival (tolerance or persistence) assays were used to measure surviving bacteria after a short period (up to 4 h) of bactericidal antibiotic treatment under therapeutic and killing concentrations of ciprofloxacin [1 mg/L, EUCAST/CLSI breakpoint for resistance; and 2.5 mg/L, peak serum concentration (Cmax) of this drug].

RESULTS

QRDR substitutions (S83L in GyrA alone or combined with S80R in ParC) significantly increased the fraction of tolerant bacteria (2-4 log10 cfu/mL) after exposure to ciprofloxacin at clinically relevant concentrations. The impact on tolerant bacteria due to SOS response suppression (including persistence mediated by the tisB gene) was reversed by LLQR mechanisms at therapeutic concentrations. Furthermore, no reduction in the fraction of tolerant bacteria due to SOS response suppression was observed when S83L in GyrA plus S80R in ParC were combined.

CONCLUSIONS

Tolerance and quinolone resistance mutations interact synergistically, giving LLQR mechanisms an additional role in allowing bacterial survival and evasion of therapeutic antimicrobial conditions by a combination of the two strategies. At clinically relevant concentrations, LLQR mechanisms reverse further impact of SOS response suppression in reducing bacterial tolerance.

Effect of RecA inactivation on quinolone susceptibility and the evolution of resistance in clinical isolates of Escherichia coli

BACKGROUND

SOS response suppression (by RecA inactivation) has been postulated as a therapeutic strategy for potentiating antimicrobials against Enterobacterales.

OBJECTIVES

To evaluate the impact of RecA inactivation on the reversion and evolution of quinolone resistance using a collection of Escherichia coli clinical isolates.

METHODS

Twenty-three E. coli clinical isolates, including isolates belonging to the high-risk clone ST131, were included. SOS response was suppressed by recA inactivation. Susceptibility to fluoroquinolones was determined by broth microdilution, growth curves and killing curves. Evolution of quinolone resistance was evaluated by mutant frequency and mutant prevention concentration (MPC).

RESULTS

RecA inactivation resulted in 2-16-fold reductions in fluoroquinolone MICs and modified EUCAST clinical category for several isolates, including ST131 clone isolates. Growth curves and time-kill curves showed a clear disadvantage (up to 10 log10 cfu/mL after 24 h) for survival in strains with an inactivated SOS system. For recA-deficient mutants, MPC values decreased 4-8-fold, with values below the maximum serum concentration of ciprofloxacin. RecA inactivation led to a decrease in mutant frequency (≥103-fold) compared with isolates with unmodified SOS responses at ciprofloxacin concentrations of 4×MIC and 1 mg/L. These effects were also observed in ST131 clone isolates.

CONCLUSIONS

While RecA inactivation does not reverse existing resistance, it is a promising strategy for increasing the effectiveness of fluoroquinolones against susceptible clinical isolates, including high-risk clone isolates.

Suppression of the SOS response modifies spatiotemporal evolution, post-antibiotic effect, bacterial fitness and biofilm formation in quinolone-resistant Escherichia coli

Background

Suppression of the SOS response has been proposed as a therapeutic strategy for potentiating quinolones against susceptible, low-level quinolone-resistant (LLQR) and resistant Enterobacteriaceae.

Objectives

To monitor the functionality of the SOS response in the evolution towards clinical quinolone resistance and study its impact on the evolution of spatiotemporal resistance.

Methods

An isogenic collection of Escherichia coli (derived from the strain ATCC 25922) carrying combinations of chromosomally and plasmid-mediated quinolone resistance mechanisms (including susceptible, LLQR and resistant phenotypes) and exhibiting a spectrum of SOS activity was used. Relevant clinical parameters such as mutation rate, mutant prevention concentration (MPC), bacterial fitness, biofilm formation and post-antibiotic effect (PAE) were evaluated.

Results

Inactivating the SOS response (recA deletion) led to a decrease in mutation rate (∼103 fold) in LLQR compared with WT strains at ciprofloxacin concentrations of 1 mg/L (the EUCAST breakpoint for resistance) and 2.5 mg/L (Cmax), as well as a remarkable delay in the spatiotemporal evolution of quinolone resistance. For all strains, there was an 8-fold decrease in MPC in RecA-deficient strains, with values for LLQR strains decreasing below the Cmax of ciprofloxacin. Inactivation of the SOS response reduced competitive fitness by 33%-50%, biofilm production by 22%-80% and increased the PAE by ∼3-4 h at sub-MIC concentrations of ciprofloxacin.

Conclusions

Our data indicate that suppression of the SOS response affects key bacterial traits and is a promising strategy for reversing and tackling the evolution of antibiotic resistance in E. coli, including low-level and resistant phenotypes at therapeutic quinolone concentrations.

Molecular insights into fosfomycin resistance in Escherichia coli

Objectives

Fosfomycin activity in Escherichia coli depends on several genes of unknown importance for fosfomycin resistance. The objective was to characterize the role of uhpT , glpT , cyaA and ptsI genes in fosfomycin resistance in E. coli.

Methods

WT E. coli BW25113 and null mutants, Δ uhpT , Δ glpT , Δ cyaA , Δ ptsI , Δ glpT-uhpT , Δ glpT-cyaA , Δ glpT-ptsI , Δ uhpT-cyaA , Δ uhpT-ptsI and Δ ptsI-cyaA , were studied. Susceptibility to fosfomycin was tested using CLSI guidelines. Fosfomycin mutant frequencies were determined at concentrations of 64 and 256 mg/L. Fosfomycin in vitro activity was tested using time-kill assays at concentrations of 64 and 307 mg/L (human C max ).

Results

Fosfomycin MICs were: WT E. coli BW25113 (2 mg/L), Δ glpT (2 mg/L), Δ uhpT (64 mg/L), Δ cyaA (8 mg/L), Δ ptsI (2 mg/L), Δ glpT-uhpT (256 mg/L), Δ glpT-cyaA (8 mg/L), Δ glpT-ptsI (2 mg/L), Δ uhpT-cyaA (512 mg/L), Δ uhpT-ptsI (64 mg/L) and Δ ptsI-cyaA (32 mg/L). In the mutant frequency assays, no mutants were recovered from BW25113. Mutants appeared in Δ glpT , Δ uhpT , Δ cyaA and Δ ptsI at 64 mg/L and in Δ uhpT and Δ cyaA at 256 mg/L. Δ glpT-ptsI , but not Δ glpT-cyaA , Δ uhpT-cyaA or Δ uhpT-ptsI , increased the mutant frequency compared with the highest frequency found in each single mutant. In time-kill assays, all mutants regrew at 64 mg/L. Initial bacterial reductions of 2-4 log 10 cfu/mL were observed for all strains, except for Δ uhpT-ptsI , Δ glpT-uhpT and Δ uhpT-cyaA . Only Δ glpT and Δ ptsI mutants were cleared using 307 mg/L.

Conclusions

Fosfomycin MIC may not be a good efficacy predictor, as highly resistant mutants may appear, depending on other pre-existing mutations with no impact on MIC.

Pharmacodynamics of vancomycin for CoNS infection: experimental basis for optimal use of vancomycin in neonates

OBJECTIVES

CoNS are the most common cause of neonatal late-onset sepsis. Information on the vancomycin pharmacokinetics/pharmacodynamics against CoNS is limited. The aim of this study was to characterize vancomycin pharmacokinetic/pharmacodynamic relationships for CoNS and investigate neonatal optimal dosage regimens.

METHODS

A hollow fibre and a novel rabbit model of neonatal central line-associated bloodstream CoNS infections were developed. The results were then bridged to neonates by use of population pharmacokinetic techniques and Monte Carlo simulations.

RESULTS

There was a dose-dependent reduction in the total bacterial population and C-reactive protein levels. The AUC/MIC and Cmax/MIC ratios were strongly linked with total and mutant resistant cell kill. Maximal amplification of resistance was observed in vitro at an fAUC/MIC of 200 mg · h/L. Simulations predicted that neonates <29 weeks post-menstrual age are underdosed with standard regimens with respect to older age groups.

CONCLUSIONS

The AUC/MIC and Cmax/MIC ratios are the pharmacodynamic indices that best explain total and resistant cell kill in CoNS infection. This suggests that less-fractionated regimens are appropriate for clinical use and continuous infusions may be associated with increased risk of emergence of antimicrobial resistance. This study has provided the pharmacodynamic evidence to inform an optimized neonatal dosage regimen to take into a randomized controlled trial.

Impact of qnrA1, qnrB1 and qnrS1 on the efficacy of ciprofloxacin and levofloxacin in an experimental pneumonia model caused by Escherichia coli with or without the GyrA mutation Ser83Leu

OBJECTIVES

The aim of this study was to evaluate the impact of qnrA1, qnrB1 and qnrS1 on the in vivo efficacies of ciprofloxacin and levofloxacin in an experimental model of pneumonia caused by Escherichia coli.

METHODS

Two isogenic groups of E. coli transformants, based on two ATCC 25922 strains, with or without the GyrA mutation Ser83Leu, and carrying qnrA1, qnrB1 or qnrS1, were used in an experimental pneumonia model. The efficacies of ciprofloxacin (40 mg/kg/day) and levofloxacin (50 and 150 mg/kg/day) were evaluated.

RESULTS

For the pneumonia caused by the parental strains lacking qnr genes, both fluoroquinolones significantly (P<0.05) reduced the bacterial lung concentration by >7 log10 cfu/g against E. coli ATCC/pBK and between 5.09 and 6.34 log10 cfu/g against E. coli ATCC-S83L/pBK. The presence of any qnr genes in the strains of both isogenic groups diminished the reduction of bacterial lung concentration with any therapy (P<0.05). Furthermore, all therapeutic schemes reduced the percentage of positive blood cultures in both isogenic groups (P<0.05). Finally, the survival results suggest a higher mortality with the strains expressing qnr genes.

CONCLUSIONS

The presence of qnrA1, qnrB1 and qnrS1 in E. coli reduced the efficacy of ciprofloxacin and levofloxacin in a murine pneumonia model.

Efficacy of cecropin A-melittin peptides on a sepsis model of infection by pan-resistant Acinetobacter baumannii

Pan-resistant Acinetobacter baumannii have prompted the search for therapeutic alternatives. We evaluate the efficacy of four cecropin A-melittin hybrid peptides (CA-M) in vivo. Toxicity was determined in mouse erythrocytes and in mice (lethal dose parameters were LD(0), LD(50), LD(100)). Protective dose 50 (PD(50)) was determined by inoculating groups of ten mice with the minimal lethal dose of A. baumannii (BMLD) and treating with doses of each CA-M from 0.5 mg/kg to LD(0). The activity of CA-Ms against A. baumannii was assessed in a peritoneal sepsis model. Mice were sacrificed at 0 and 1, 3, 5, and 7-h post-treatment. Spleen and peritoneal fluid bacterial concentrations were measured. CA(1-8)M(1-18) was the less haemolytic on mouse erythrocytes. LD(0) (mg/kg) was 32 for CA(1-8)M(1-18), CA(1-7)M(2-9), and Oct-CA(1-7)M(2-9), and 16 for CA(1-7)M(5-9). PD(50) was not achieved with non-toxic doses (≤ LD(0)). In the sepsis model, all CA-Ms were bacteriostatic in spleen, and decreased bacterial concentration (p < 0.05) in peritoneal fluid, at 1-h post-treatment; at later times, bacterial regrowth was observed in peritoneal fluid. CA-Ms showed local short-term efficacy in the peritoneal sepsis model caused by pan-resistant Acinetobacter baumannii.

Efficacy of rifampin, in monotherapy and in combinations, in an experimental murine pneumonia model caused by panresistant Acinetobacter baumannii strains

The objective of this work was to evaluate the efficacy of rifampin, and its combinations with imipenem or sulbactam, in an experimental pneumonia model caused by two panresistant Acinetobacter baumannii strains (HUVR99 and HUVR113). Minimum inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) (μg/ml) of the strains were rifampin 128/>128 for both strains, imipenem 128/>256 and 256/>256 for HUVR99 and HUVR113, respectively, and sulbactam >256/>256 for both strains. In time-kill studies, at MICs, rifampin was bactericidal for both strains and sulbactam against the HUVR99 strain. Rifampin plus imipenem or sulbactam, at the MIC or mice C (max), were synergistic. In vivo, against HUVR99 and HUVR113, rifampin (73% and 40%) and its combinations improved the survival with respect to the control group (20% and 0%, p < 0.05), respectively. Rifampin (87% and 46%) and its combinations improved the sterilization of blood cultures with respect to the control groups (0%, p < 0.05). In regard to the bacterial clearance from lungs, rifampin (2.57 ± 2.47 and 5.35 ± 3.03 log(10) cfu/g) and its combinations with imipenem or sulbactam diminished the bacterial lung concentration with respect to the control group (10.89 ± 3.00 and 11.86 ± 0.49, p < 0.05) with both strains. In conclusion, rifampin alone or associated to imipenem or sulbactam were effective for the treatment of murine pneumonia caused by selected panresistant A. baumannii strains.

Clinical relevance and prevalence of polymorphisms in CYP3A5 and MDR1 genes that encode tacrolimus biotransformation enzymes in liver transplant recipients

OBJECTIVES

To study the prevalence and clinical significance of polymorphisms in the CYP3A5 and MDR1 genes in liver transplant patients and their donors; to determine the relative importance of genes from the donor and the recipient; to assess the relationship of polymorphisms with the variability of concentration/dose of tacrolimus for optimization and individualization regimens.

MATERIALS AND METHODS

This prospective study included 53 liver transplant recipients who received tacrolimus de novo. CYP3A5 and MDR1 gene polymorphisms were identified in the donors and recipients using polymerase chain reaction. We collected indicator variables of graft function and the patient for 3 months after the transplantation: days 0, 1, 3, 7, 14, 30, 60, and 90.

RESULTS

The frequencies of CYP3A5 polymorphisms were: 90.6% (G/G), 9.4% (G/A) and 0% (A/C) in donors and 88.7% (G/G), 11.3% (G/A), and 0% (A/A) in recipients. For the MDR1 gene, they were: 26.4% (C/C), 50.9% (C/T), and 22.6% (T/T) in donors and 17.0% (C/C), 71.7% (C/T), and 11.3% (T/T) in recipients. In the early days after transplant, G/A recipients from G/A donors did not reach the minimum drug levels. Between days 30 and 60, G/G recipients from G/A donors required higher tacrolimus doses. G/G recipients (CYP3A5) from C/T donors (MDR1) had a lower frequency of renal dysfunction, the same rejection rate, and a higher rate of diabetes than the other groups.

CONCLUSIONS

For CYP3A5, the presence of the A allele appeared to be related to greater requirements for tacrolimus in the early days after transplantation. Pharmacogenetics combined with pharmacodynamics may be a useful tool to adjust the concentration of tacrolimus depending on the absorption by the individual patient.