Impact Of Fluoroquinolone Resistance Research Articles

Target-Mediated Fluoroquinolone Resistance in Neisseria gonorrhoeae: Actions of Ciprofloxacin against Gyrase and Topoisomerase IV.

Fluoroquinolones make up a critically important class of antibacterials administered worldwide to treat human infections. However, their clinical utility has been curtailed by target-mediated resistance, which is caused by mutations in the fluoroquinolone targets, gyrase and topoisomerase IV. An important pathogen that has been affected by this resistance is Neisseria gonorrhoeae, the causative agent of gonorrhea. Over 82 million new cases of this sexually transmitted infection were reported globally in 2020. Despite the impact of fluoroquinolone resistance on gonorrhea treatment, little is known about the interactions of this drug class with its targets in this bacterium. Therefore, we investigated the effects of the fluoroquinolone ciprofloxacin on the catalytic and DNA cleavage activities of wild-type gyrase and topoisomerase IV and the corresponding enzymes that harbor mutations associated with cellular and clinical resistance to fluoroquinolones. Results indicate that ciprofloxacin interacts with both gyrase (its primary target) and topoisomerase IV (its secondary target) through a water-metal ion bridge that has been described in other species. Moreover, mutations in amino acid residues that anchor this bridge diminish the susceptibility of the enzymes for the drug, leading to fluoroquinolone resistance. Results further suggest that ciprofloxacin primarily induces its cytotoxic effects by enhancing gyrase-mediated DNA cleavage as opposed to inhibiting the DNA supercoiling activity of the enzyme. In conclusion, this work links the effects of ciprofloxacin on wild-type and resistant gyrase to results reported for cellular and clinical studies and provides a mechanistic explanation for the targeting and resistance of fluoroquinolones in N. gonorrhoeae.

Impact of fluoroquinolone resistance in Gram-negative bloodstream infections on healthcare utilization

There has been a concerning increase in fluoroquinolone resistance among Gram-negative bloodstream isolates. This retrospective cohort study examines the implications of fluoroquinolone resistance on use of healthcare resources in patients with Gram-negative bloodstream infections (BSI). Hospitalized adults with first episodes of community-onset Gram-negative BSI from 2010 to 2012 at Palmetto Health Hospitals in Columbia, SC, USA were identified. Multivariate linear regression was used to examine risk factors for prolonged hospital length of stay (HLOS) in survivors of Gram-negative BSI. Among 474 unique patients, 384 (81%) and 90 (19%) had BSI due to fluoroquinolone-susceptible (FQ-S) and fluoroquinolone non-susceptible (FQ-NS) Gram-negative bacilli, respectively. The FQ-NS bloodstream isolates, particularly Escherichia coli, were more likely than FQ-S isolates to be multi-drug resistant (56% versus 6%, p < 0.001). Compared with patients with BSI due to FQ-S bloodstream isolates, those with FQ-NS isolates were more likely to receive inappropriate empirical antimicrobial therapy (26% versus 3%, p < 0.001), have longer mean HLOS (11.6 versus 9.3 days, p 0.03) and treatment duration with intravenous antibiotics during hospitalization (9.1 versus 7.1 days, p 0.001), and use outpatient intravenous antibiotics at hospital discharge (15% versus 8%, p 0.05). After adjustments in the multivariate model, inappropriate empirical antimicrobial therapy was an independent risk factor for prolonged HLOS in survivors of Gram-negative BSI (parameter estimate 3.65 days, 95% CI 0.43–6.86). Multi-drug resistance among FQ-NS bloodstream isolates limits both empirical and definitive antimicrobial treatment options and poses excessive burdens on the healthcare system.

Activity of ceftazidime-avibactam against fluoroquinolone-resistant Enterobacteriaceae and Pseudomonas aeruginosa.

Ceftazidime-avibactam and comparator antibiotics were tested by the broth microdilution method against 200 Enterobacteriaceae and 25 Pseudomonas aeruginosa strains resistant to fluoroquinolones (including strains with the extended-spectrum β-lactamase [ESBL] phenotype and ceftazidime-resistant strains) collected from our institution. The MICs and mechanisms of resistance to fluoroquinolone were also studied. Ninety-nine percent of fluoroquinolone-resistant Enterobacteriaceae strains were inhibited at a ceftazidime-avibactam MIC of ≤4 mg/liter (using the susceptible CLSI breakpoint for ceftazidime alone as a reference). Ceftazidime-avibactam was very active against ESBL Escherichia coli (MIC90 of 0.25 mg/liter), ESBL Klebsiella pneumoniae (MIC90 of 0.5 mg/liter), ceftazidime-resistant AmpC-producing species (MIC90 of 1 mg/liter), non-ESBL E. coli (MIC90 of ≤0.125 mg/liter), non-ESBL K. pneumoniae (MIC90 of 0.25 mg/liter), and ceftazidime-nonresistant AmpC-producing species (MIC90 of ≤0.5 mg/liter). Ninety-six percent of fluoroquinolone-resistant P. aeruginosa strains were inhibited at a ceftazidime-avibactam MIC of ≤8 mg/liter (using the susceptible CLSI breakpoint for ceftazidime alone as a reference), with a MIC90 of 8 mg/liter. Additionally, fluoroquinolone-resistant mutants from each species tested were obtained in vitro from two strains, one susceptible to ceftazidime and the other a β-lactamase producer with a high MIC against ceftazidime but susceptible to ceftazidime-avibactam. Thereby, the impact of fluoroquinolone resistance on the activity of ceftazidime-avibactam could be assessed. The MIC90 values of ceftazidime-avibactam for the fluoroquinolone-resistant mutant strains of Enterobacteriaceae and P. aeruginosa were ≤4 mg/liter and ≤8 mg/liter, respectively. We conclude that the presence of fluoroquinolone resistance does not affect Enterobacteriaceae and P. aeruginosa susceptibility to ceftazidime-avibactam; that is, there is no cross-resistance.

Interplay in the Selection of Fluoroquinolone Resistance and Bacterial Fitness

Fluoroquinolones are antibacterial drugs that inhibit DNA Gyrase and Topoisomerase IV. These essential enzymes facilitate chromosome replication and RNA transcription by regulating chromosome supercoiling. High-level resistance to fluoroquinolones in E. coli requires the accumulation of multiple mutations, including those that alter target genes and genes regulating drug efflux. Previous studies have shown some drug-resistance mutations reduce bacterial fitness, leading to the selection of fitness-compensatory mutations. The impact of fluoroquinolone-resistance on bacterial fitness was analyzed in constructed isogenic strains carrying up to 5 resistance mutations. Some mutations significantly decreased bacterial fitness both in vitro and in vivo. We identified low-fitness triple-mutants where the acquisition of a fourth resistance mutation significantly increased fitness in vitro and in vivo while at the same time dramatically decreasing drug susceptibility. The largest effect occurred with the addition of a parC mutation (Topoisomerase IV) to a low-fitness strain carrying resistance mutations in gyrA (DNA Gyrase) and marR (drug efflux regulation). Increased fitness was accompanied by a significant change in the level of gyrA promoter activity as measured in an assay of DNA supercoiling. In selection and competition experiments made in the absence of drug, parC mutants that improved fitness and reduced susceptibility were selected. These data suggest that natural selection for improved growth in bacteria with low-level resistance to fluoroquinolones could in some cases select for further reductions in drug susceptibility. Thus, increased resistance to fluoroquinolones could be selected even in the absence of further exposure to the drug.

Association between Fluoroquinolone Resistance and Mortality in Escherichia coli and Klebsiella pneumoniae Infections: The Role of Inadequate Empirical Antimicrobial Therapy

The prevalence of fluoroquinolone (FQ) resistance among Escherichia coli and Klebsiella pneumoniae has increased markedly in recent years. However, the impact of FQ resistance on mortality remains unknown. To identify the association between FQ resistance and mortality, we conducted a retrospective cohort study of hospitalized patients with infections due to FQ-resistant strains and FQ-susceptible strains of E. coli and K. pneumoniae between 1 January 1998 and 30 June 1999. Of 123 patients with FQ-resistant infection, 16 (13.0%) died, compared with 4 (5.7%) of 70 patients with FQ-susceptible infection (odds ratio [OR], 2.47; 95% confidence interval [CI], 0.75-10.53). After adjustment for other significant risk factors and confounders, there remained an independent association between FQ-resistant infection and mortality (adjusted OR, 4.41; 95% CI, 1.03-18.81). Patients with FQ-resistant infection were significantly less likely to have received antimicrobial therapy with activity against the infecting pathogen within the first 24 h and 48 h of infection (P=.002 and P<.001, respectively). The association between FQ resistance and mortality was no longer significant, after adjusting for inadequate empirical therapy. FQ resistance is an independent risk factor for mortality in patients with health care-acquired E. coli and K. pneumoniae infections. This may be explained, at least in part, by a delay in the initiation of appropriate antimicrobial therapy in patients with FQ-resistant infection. These results highlight the grave clinical consequences of FQ resistance and emphasize the importance of efforts designed to curb the increase in the prevalence of resistance to these agents.