Contribution of different mechanisms to the resistance to fluoroquinolones in clinical isolates of Salmonella enterica

ObjectivesTo study the potential factors include gene mutation, efflux pump and alteration of permeability associated with quinolone-resistance of Salmonella enterica strains isolated from patients with acute gastroenteritis and to evaluate the degree of synergistic activity of efflux pump inhibitors when combined with ciprofloxacin against resistant isolates.MethodsAntimicrobial resistance patterns of fifty-eight Salmonella isolates were tested. Five isolates were selected to study the mechanism of resistance associated with quinolone group, including mutation in topoisomerase-encoding gene, altered cell permeability, and expression of an active efflux system. In addition, the combination between antibiotics and efflux pump inhibitors to overcome the microbial resistance was evaluated.ResultsFive Salmonella isolates totally resistant to all quinolones were studied. All isolates showed alterations in outer membrane proteins including disappearance of some or all of these proteins (Omp-A, Omp-C, Omp-D and Omp-F). Minimum inhibitory concentration values of ciprofloxacin were determined in the presence/absence of the efflux pump inhibitors: carbonyl cyanide m-chlorophenylhydrazone, norepinephrin and trimethoprim. Minimum inhibitory concentration values for two of the isolates were 2–4 fold lower with the addition of efflux pump inhibitors. All five Salmonella isolates were amplified for gyrA and parC genes and only two isolates were sequenced. S. Enteritidis 22 had double mutations at codon 83 and 87 in addition to three mutations at parC at codons 67, 76 and 80 whereas S. Typhimurium 57 had three mutations at codons 83, 87 and 119, but no mutations at parC.ConclusionsEfflux pump inhibitors may inhibit the major AcrAB-TolC in Salmonella efflux systems which are the major efflux pumps responsible for multidrug resistance in Gram-negative clinical isolates.     

Ofloxacin resistance mechanism in PA150 and PA300-clinical isolates ofPseudomonas aeruginosa in Korea

Five hundred and seventy clinical strains ofPseudomonas aeruginosa were isolated from August 1993 to August 1994 in Korea and screened for their resistance to ciprofloxacin, norfloxacin, and ofloxacin. Among these, twoP. aeruginosa strains (PA150 and PA300) were selected based on their strong resistance (MICs>50 μg/ml) to all three quinolones. The susceptible strain as well as two resistant strains had proton gradient-dependent efflux system. Efflux system in PA300 showed different specificities to ofloxacin and ciprofloxacin while PA 150 had less permeability for ofloxacin. Ofloxacin had a less inhibitory action on DNA synthesis in permeabilized cells of PA150 and PA300 than 1771M. When quinolone resistance determining region (QRDR) ingyrA was sequenced, PA300 had one missense mutation, Asn 116Tyr, which was newly reported in this work. The results showed that PA150 became ofloxacin resistant by reduced ofloxacin accumulation due to the existence of efflux system and low permeability, while resistance of PA300 was due to the efflux system and a mutation in QRDR ofgyrA-the target site of quinolone.     

Synthesis of 6-fluoro-1,4-dihydro-4-oxo-quinoline-3-carboxylic acid derivatives as potential antimicrobial agents

In the present study, a series of 1-ethyl/benzyl-6-fluoro-7-(substituted piperazin-1-yl)1,4-dihydro-4-oxo-quinoline-3-carboxylic acid were synthesized and characterized by IR, 1H-NMR, mass spectral and elemental analysis. The in vitro antibacterial and antifungal activities of the compounds were evaluated by paper disc diffusion method. The minimum inhibitory concentrations (MIC) of the compounds were also determined by agar streak dilution method. The in vivo antibacterial activity of the compounds against Escherichia coli was also evaluated by mouse protection test. All the compounds exhibited significant antibacterial and weak antifungal activities. The in vivo antibacterial activity (ED50) against E. coli was 50-160 mg kg(-1) in the order of 7<9<8<10. 1-ethyl-6-fluoro-7-(2,5-dioxo-piperazin-1-yl)1,4-dihydro-4-oxo-quinoline-3-carboxylic acid (7) was found to exhibit the most potent in vitro antimicrobial activity with MIC of 4.1, 3.1, 3.1, 2.4, 1, 1, 25 and >100 microg mL(-1) against Staphylococcus aureus, Staphylococcus epidermidis, Micrococcus luteus, Bacillus cereus, E. coli, Klebsiella pneumoniae, Candida albicans and Aspergillus niger.     

Efficacy of pazufloxacin mesilate in Legionnaires’ disease: a case report and in vitro study of the isolate

We report here a case of culture-proven Legionnaires’ disease successfully treated with intravenous injection of pazufloxacin mesilate (PZFX), a fluoroquinolone newly approved in Japan. The patient was a 51-year-old man hospitalized after a diagnosis of community-acquired pneumonia. Legionella pneumophila SG1 was isolated from the patient’s bronchoalveolar lavage (BAL) fluid, and the soluble antigen of the bacterium was detected in the fluid as well. Subsequently, intravenous PZFX was administered for a week and proved markedly effective. An in vitro study confirmed that PZFX had excellent extracellular and intracellular activity against the isolate from the patient. This case suggests that PZFX is an option for treating Legionnaires’ disease.     

De-Escalation and Discontinuation of Empirical Antibiotic Treatment in a Cohort of Allogeneic Hematopoietic Stem Cell Transplantation Recipients during the Pre-Engraftment Period

To investigate rates and outcomes of antibiotic de-escalation during pre-engraftment neutropenia in allogeneic hematopoietic stem cell transplantation (HSCT) recipients. 110 consecutive HSCTs performed between January 2013 and March 2014 were analyzed. De-escalation was defined as narrowing the spectrum of antibiotic treatment either within (early) or after 96 hours (late) from starting antibiotics. Discontinuation, considered a form of de-escalation, was defined as stopping antibiotics before engraftment. De-escalation failure was defined as restarting/escalating antibiotics within 96 hours after de-escalation. Predictors of de-escalation were analyzed. Among 102 patients who started antibiotics and were included, 68 (67%) received monotherapy (mainly piperacillin-tazobactam, n?=?58), whereas 34 (33%) received combination therapy (mainly meropenem plus glycopeptide, n?=?24). Median duration of neutropenia was 17 days. Bloodstream infections (BSIs) were diagnosed in 28 patients (20%). Early de-escalation rate was 25.5% (n?=?26) and mostly consisted of reducing the spectrum of β-lactams (n?=?11, 42%). In comparison with theoretical scenario of continuing therapy until engraftment, the median savings in terms of antibiotic days were 10 for meropenem, 8 for piperacillin-tazobactam, and 7 for vancomycin. Failure rate of early de-escalation was 15% (4/26). Late de-escalation rate was 30.4% (n?=?31) and failure rate 19% (6/31). The rate of de-escalation any time before engraftment was 55.9% (n?=?57), including discontinuation in 33 patients (32%). Death at day 60 after HSCT occurred in 3 patients who never underwent de-escalation. Acute myeloid disease and BSIs were independent predictors of early de-escalation. De-escalation, including discontinuation, is feasible and safe in pre-engraftment neutropenia after allogeneic HSCT.     

Synthesis and in-vitro antibacterial activity of 7-(3-aminopyrrolo[3,4-c]pyrazol-5(2H,4H,6H)-yl)-6-fluoro-4-oxo-1,4-dihydroquinoline-3-carboxylic acid derivatives

A series of novel 7-(3-aminopyrrolo[3,4-c]pyrazol-5(2H,4H,6H)-yl)-6-fluoro-4-oxo-1,4-dihydroquinoline-3-carboxylic acid derivatives was designed, synthesized and characterized by (1)H-NMR, MS and HRMS. These fluoroquinolones were evaluated for their in-vitro antibacterial activity against representative Gram-positive and Gram-negative strains. Generally, all of the target compounds display rather weak potency against the tested Gram-negative strains, but most of them exhibit good potency in inhibiting the growth of S. aureus including methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus epidermidis including methicillin-resistant S. epidermidis (MRSE) (MIC: 0.125-8 μg/mL). In particular, the compound 9g is 2 to 32 fold more potent than gemifloxacin (GM), moxifloxacin (MX), gatifloxacin (GT), and levofloxacin (LV) against S. pneumoniae 08-3, K. pneumoniae 09-23, and P. aeruginosa ATCC27853, 4 to 32 fold more potent than MX, GM, and LV against K. pneumoniae 09-21, and more active than or comparable to the four reference drugs against P. aeruginosa 09-32.     

Prevalence of efflux-mediated ciprofloxacin and levofloxacin resistance in recent clinical isolates of Pseudomonas aeruginosa and its reversal by the efflux pump inhibitors 1-(1-naphthylmethyl)-piperazine and phenylalanine-arginine-β-naphthylamide

To assess the prevalence of efflux-driven fluoroquinolone (FQ) resistance in recent clinical isolates of Pseudomonas aeruginosa, a worrisome and often hospital-acquired pathogen, 115 unique strains were collected over a 5-month period, of which 27 and 33 had decreased susceptibility to ciprofloxacin (CIP) and levofloxacin (LVX), respectively. The MIC₅₀ (minimum inhibitory concentration for 50% of the organisms) was 16 μg/mL for both FQs. The efflux pump inhibitors (EPIs) phenylalanine-arginine-β-naphthylamide (PAβN) and 1-(1-naphthylmethyl)-piperazine (NMP) were then used to evaluate their efficacy in reducing CIP and LVX MICs. NMP did not significantly modify CIP MICs, whilst PAβN resulted in MIC₅₀ values of 2 μg/mL and 0.125 μg/mL for CIP and LVX, respectively. With the addition of PAβN, susceptibility to CIP and LVX was recovered in 6 (22.2%) and 31 (93.9%) strains, respectively. The best combination to reverse FQ resistance in this set of strains was LVX with PAβN. The results of this study show that the effect of an EPI is not only dependent on the species on which it is used but also on the molecule associated with it. Therefore, the design of an EPI equally efficient on all resistance-nodulation-cell division (RND) efflux pumps appears to be difficult and, from a practical point of view, if an EPI is developed for clinical use, the efficiency of its combination with a definite molecule should be assessed carefully against a wide range of clinical isolates to evaluate the real benefit of this combination.     

Safety profile of Tysabri: international risk management plan

An 83-year-old man was admitted for right lower lobe pneumonia which did not improve after a 5-day outpatient treatment with amoxicillin/clavulinate and clarithromycin. An empiric treatment with levofloxacin was started with a significant improvement after 24 h of this treatment. On the third day of hospitalization, delirium developed, while the patient was afebrile and with normal blood oxygenation. Treatment with levofloxacin was stopped, and a complete resolution of the patient’s delirium was observed 2 days later. To the best of our knowledge, this is the third case of levofloxacin-induced delirium described in the medical literature.     

Fluorinated 1,2,4‐Triazolo[1,5‐a]pyrimidine‐6‐carboxylic Acid Derivatives as Antimycobacterial Agents

A series of fluorinated 1,2,4‐triazolo[1,5‐a]pyrimidine‐6‐carboxylic acid derivatives was designed and synthesized as fluoroquinolone analogues. The synthesized compounds were screened against Mycobacterium tuberculosis H₃₇R_v strain at 6.25 μg/mL concentration. Compound 4 , the 7‐oxo‐2‐(trifluoromethyl)‐4,7‐dihydro‐1,2,4‐triazolo[5,1‐a]pyrimidine‐6‐carboxylic acid was found to be a very potent inhibitor, being able to inhibit 92% growth of M. tuberculosis H₃₇R_v at 6.25 μg/mL concentration. At the same time, it proofed to be nontoxic to mammalian cells (IC₅₀ > 62.5 μg/mL in VERO cells).