Elimination of plasmids by new 4-quinolones.

Nalidixic acid and six of the new 4-quinolones eliminated F'lac and various native R plasmids from Escherichia coli at one half or one quarter the MIC. Four of eight plasmids tested were cured by all derivatives, with frequencies from 10 to 98%. Quinolones did not eliminate all plasmids that were cured by novobiocin, and vice versa.     

Elimination of plasmids from Enterobacteriaceae by 4-quinolone derivatives

Twelve 4-quinolones (cinoxacin, ciprofloxacin, enoxacin, flumequin, nalidixic acid, norfloxacin, oxolinic acid, pefloxacin, pipemidic acid, rosoxacin, and piromidic and beta-hydroxypiromidic acids) and novobiocin, were used at subinhibitory concentrations to eliminate from Escherichia coli 11 antibiotic resistance plasmids belonging to different incompatibility groups. The 12 4-quinolones were also tested for their ability to cure virulence plasmids from five species of Enterobacteriaceae. All quinolones eliminated three antibiotic resistance plasmids (R446b, R386, S-a) and one virulence plasmid (pWR105), but at a low rate. Optimal curing of antibiotic resistance plasmids was obtained in human urine. Two virulence plasmids (pWR24 and pWR110) were eliminated only by flumequin and pefloxacin. Novobiocin eliminated three antibiotic resistance plasmids (R446b, R386, pIP24). The variable and low level of plasmid loss may be explained by the induction of the recA system. In addition, the inability to eliminate certain plasmids could be due to their presence in high numbers per cell.     

Elimination of plasmids by enoxacin and ofloxacin at near inhibitory concentrations

The abilities of the 4-quinolones enoxacin and ofloxacin, inhibitors of DNA gyrase subunit A, to eliminate plasmids from Escherichia coli have been studied in a narrow concentration range just below the MIC. These compounds cured most efficiently at the highest concentration which still allows cell growth and produced 20% to 100% plasmid-free cells, depending upon the plasmid tested. Higher concentrations were required to eliminate plasmids from a gyrANalr strain, consistent with their higher MICs, but maximal curing frequencies were similar to those obtained with the Nals strain. Kinetics of plasmid elimination indicated that plasmid loss occurred by inhibition of plasmid replication, which seems to be somewhat more sensitive to the action of 4-quinolones than chromosome replication. Low or high curing frequencies with a given curing agent seem to be a property of the plasmid tested.     

New classification and update on the quinolone antibiotics

The newer fluoroquinolones have broad-spectrum bactericidal activity, excellent oral bioavailability, good tissue penetration and favorable safety and tolerability profiles. A new four-generation classification of the quinolone drugs takes into account the expanded antimicrobial spectrum of the more recently introduced fluoroquinolones and their clinical indications. First-generation drugs (e.g., nalidixic acid) achieve minimal serum levels. Second-generation quinolones (e.g., ciprofloxacin) have increased gram-negative and systemic activity. Third-generation drugs (e.g., levofloxacin) have expanded activity against gram-positive bacteria and atypical pathogens. Fourth-generation quinolone drugs (currently only trovafloxacin) add significant activity against anaerobes. The quinolones can be differentiated within classes based on their pharmacokinetic properties. The new classification can help family physicians prescribe these drugs appropriately.     

Elimination of quinolone antibiotic carryover through use of antibiotic-removal beads.

To prove the utility of antibiotic-removal beads in separating antibiotics from bacterial samples, Escherichia coli ATCC 25922 was exposed to five separate quinolones before and after each was exposed to antibiotic-removal beads. Plates treated with antibiotic solutions that were exposed to beads demonstrated antibiotic removal, and plates treated with antibiotic solutions that were not exposed to beads demonstrated antibiotic carryover. After exposure to beads, fluoroquinolone concentrations decreased from 5 micrograms/ml to 0.14 micrograms/ml (ciprofloxacin), 0.04 micrograms/ml (temafloxacin), < 0.01 microgram/ml (ofloxacin), < 0.01 microgram/ml (sparfloxacin), and 0.02 micrograms/ml (clinafloxacin). These data indicate that antibiotic carryover can be successfully circumvented through the use of antibiotic-removal beads.     

Potassium current antagonist properties and proarrhythmic consequences of quinolone antibiotics

Quinolones are clinically important antibiotic drugs. One quinolone antibiotic, sparfloxacin (SPX), has been recently reported to increase the QT interval, and another quinolone, grepafloxacin (GRX), was withdrawn because it induced torsade de pointes (TdP), a polymorphic ventricular tachycardia (VT) linked to excessive QT interval prolongation. To determine whether SPX, GRX, and other recently developed quinolones, gatifloxacin (GAT) and moxifloxacin (MOX), have similar, potentially deleterious, properties we compared these agents in two ways. First, we measured their relative antagonist potency against the rapid component of the delayed rectifier K(+) current (I(Kr)), and second we determined the QT interval prolongation and inducibility of VT and TdP using a well established in vivo rabbit arrhythmia model. All of these agents are I(Kr) antagonists with the following IC(50) values (mean +/- S.E.) for I(Kr) block: SPX, 0.23 +/- 0.07 microM; MOX, 0.75 +/- 0.31 microM; GAT, 26.5 +/- 13.4 microM; and GRX, 27.2 +/- 11.6 microM. All agents also increased the maximum QT interval (mean +/- S.E.) from baseline (241 +/- 10 ms): SPX, 370 +/- 30 ms; MOX, 270 +/- 30 ms; GRX, 280 +/- 25 ms; and GAT, 255 +/- 23 ms. No agents caused TdP during a standard 30-min observation period, but SPX-treated animals developed nonsustained VT (three of six) and TdP (one of six) during an extended 60-min observation period. These findings show that I(Kr) block may be a common feature of many quinolone antibiotics, and that the proarrhythmic consequences vary according to I(Kr) antagonist potency, but are also influenced by additional, unidentified factors.     

Compatibility and stability of linezolid injection admixed with three quinolone antibiotics

OBJECTIVE: To evaluate the physical compatibility and chemical stability of linezolid 200 mg/100 mL admixed with ciprofloxacin 400 mg, ofloxacin 400 mg, and levofloxacin 500 mg for seven days at 4 and 23 degrees C. METHODS: The test samples were prepared by adding the required amount of the quinolone antibiotic to bags of linezolid injection. Evaluations for physical and chemical stability were performed initially and after one, three, five, and seven days of storage at temperatures of 4 and 23 degrees C. Physical stability was assessed using visual observation in normal light and using a high-intensity monodirectional light beam. In addition, turbidity and particle content were measured electronically. Chemical stability of the drugs was evaluated by using stability-indicating HPLC analytical techniques. RESULTS: The linezolid admixtures with levofloxacin and ofloxacin were clear and pale yellow when viewed in normal fluorescent room light, and slightly hazy with a green cast when viewed using a Tyndall beam. Measured turbidity and particulate content were low and exhibited little change. HPLC analysis found no loss of the drugs in any sample stored at either temperature throughout the study. The linezolid admixtures with ciprofloxacin stored at room temperature (23 degrees C) were clear and nearly colorless in normal room light and when viewed using a Tyndall beam. They exhibited little or no change in measured turbidity or particulate content during the study period. HPLC analysis found no loss of either drug in seven days. However, the refrigerated samples were only compatible for 24 hours and developed a gross white precipitate thereafter. CONCLUSIONS: Admixtures of linezolid 200 mg/100 mL with levofloxacin 500 mg and with ofloxacin 400 mg were physically compatible and chemically stable for at least seven days stored at 4 and 23 degrees C. Admixtures of linezolid with ciprofloxacin 400 mg were compatible and stable for seven days at 23 degrees C, but ciprofloxacin precipitation occurred after 24 hours stored under refrigeration. Linezolid/ciprofloxacin admixtures should not be stored under refrigeration.     

采用噬菌体联合抗生素治疗多种耐药菌所致的骨感染

一例外伤所致左下肢胫骨感染,致病菌为广泛耐药鲍曼不动杆菌和多重耐药肺炎克雷伯菌。经噬菌体联合黏菌素及美罗培南治疗后,感染部位培养转阴,局部组织迅速愈合。患者得以避免截肢,目前正进行康复治疗中。     

Effectiveness of quinolone antibiotics in modulating the effects of antifungal drugs.

Quinolone antibacterial drugs inhibit DNA gyrase, a type 2 topoisomerase. Since topoisomerases are present in eukaryotic cells, it was of interest to evaluate the antifungal activities of two clinically available quinolones, ciprofloxacin and trovafloxacin, alone and in combination with amphotericin B or fluconazole, in vitro against Candida albicans and in a murine model of invasive candidiasis. The in vitro activity of trovafloxacin was also tested against other yeasts and molds. In vitro, trovafloxacin exhibited no antifungal activity against any of the fungi (MIC, >250 microg/ml). There was also no effect of the quinolone on the in vitro activity of either antifungal drug. Marked antifungal effects were seen, however, in the murine model of candidiasis. In all experiments, control mice infected intravenously with C. albicans were dead by day 24. While either quinolone had minimal effects on survival of mice when used alone in oral doses of up to 40 mg/kg twice daily, the combination of the quinolone with fluconazole (40 or 80 mg/kg given twice daily by oral gavage) was more effective in prolonging survival than was fluconazole alone. Colony counts of kidneys on days 12 and 30 showed similar reductions in C. albicans recovered from mice treated with fluconazole with or without trovafloxacin or amphotericin B with or without trovafloxacin. Survival of mice treated with a suboptimal dose of amphotericin B (0.2 mg/kg/day) was also improved when trovafloxacin (40 mg/kg) given twice daily was included (0 versus 27%, respectively; P < 0.05). While the mechanisms of action of the combination of trovafloxacin and amphotericin B or fluconazole are unclear, further work focused on fungal topoisomerase inhibition and the mechanism of the antifungal effect of quinolone antibacterial drugs is warranted.     

Activities of various quinolone antibiotics against Mycobacterium leprae in infected mice.

Previously, pefloxacin and ofloxacin were found to be active against Mycobacterium leprae in vitro, in experimental animals, and in clinical trials of lepromatous leprosy patients. In this study, we compared certain more recently developed fluoroquinolones (lomefloxacin, PD 124816, WIN 57273, temafloxacin, and sparfloxacin) with pefloxacin and ofloxacin in M. leprae-infected mice at doses of 50, 150, and 300 mg/kg given five times weekly. All seven of the fluoroquinolones studies were active against M. leprae; temafloxacin and sparfloxacin were the most active, being fully bactericidal at all three dosage schedules. Additionally, sparfloxacin was found to be fully bactericidal at 15 and 30 mg/kg given five times weekly.     

In vitro susceptibility of recent antibiotic-resistant urinary pathogens to ertapenem and 12 other antibiotics

Background: The treatment of complicated urinary tract infections may require the use of a parenteral antibiotic with potent activity against the most common urinary pathogens. Ertapenem is a broad-spectrum 1beta-methyl carbapenem with a long plasma half-life that allows administration of a single daily dose. METHODS: The purpose of this work was to test the in vitro susceptibility to ertapenem, ampicillin, cefazolin, cefuroxime, cefotaxime, co-amoxiclav, piperacillin/tazobactam, imipenem, gentamicin, amikacin, fosfomycin, ciprofloxacin and co-trimoxazole of 482 strains of urinary pathogens of the family Enterobacteriaceae isolated from patients in the community of Madrid (40% from males). The distribution was as follows: Escherichia coli (n = 315), Proteus mirabilis (n = 42), Klebsiella spp. (n = 14) and AmpC-producing Enterobacteriaceae (n = 111). The strains studied were selected based on their resistance to quinolones and aminoglycosides, and their production of extended-spectrum beta-lactamases (ESBLs) or AmpC-type beta-lactamases. RESULTS: All the strains were susceptible to ertapenem, imipenem and amikacin. The MIC(90) of ertapenem ranged from a minimum of 0.03 mg/L for Proteus vulgaris and a maximum of 1 mg/L for Enterobacter spp. Ertapenem was the most active of all drugs tested in all cases. On comparing antibiotic resistance among ESBL-producing strains of E. coli (n = 35) and E. coli strains not producing ESBLs (n = 280), statistically significant differences were obtained for ciprofloxacin (P = 0.002) and gentamicin (P = 0.011). Regarding ertapenem, only a slight increase in MIC(50) was seen, the value being 0.015 mg/L for strains not producing ESBLs versus 0.03 mg/L for ESBL-producing strains. CONCLUSIONS: In view of its significant antibiotic potency against antibiotic-resistant Enterobacteriaceae, ertapenem may constitute a good therapeutic alternative in urinary infections caused by these pathogens.     

In vitro susceptibility of Clostridium difficile to new beta-lactam and quinolone antibiotics.

The in vitro susceptibilities of 34 to 73 clinical isolates of Clostridium difficile to 24 antimicrobial agents, including 18 beta-lactams, 4 fluoroquinolones, clindamycin, and metronidazole were examined. Metronidazole was the most active (MIC for 90% of the isolates [MIC90], 0.5 microgram/ml), followed by the carbapenems (Sch 34343, 4 micrograms/ml; imipenem, 8 micrograms/ml) and the antipseudomonas penicillins (piperacillin, 8 micrograms/ml; ticarcillin, 32 micrograms/ml; carbenicillin, 32 micrograms/ml). A monobactam (aztreonam) and most cephalosporins were either highly inactive (cefoxitin, cefuroxime, cefotiam, cefsulodin, ceftizoxime, cefbuperazone, and cefotaxime), with an MIC90 of greater than or equal to 128 micrograms/ml, or moderately inactive (ceftriaxone, cefmenoxime, cefoperazone, ceftazidime, and moxalactam), with an MIC90 of greater than or equal to 32 micrograms/ml. Clindamycin (MIC90, 32 micrograms/ml) and the fluoroquinolones (ciprofloxacin, 8 micrograms/ml; A-56619, 8 micrograms/ml; A-56620, 8 micrograms/ml; norfloxacin, 32 micrograms/ml) were only variably active. These in vitro data per se may not necessarily predict the relative risks for C. difficile-associated diarrhea or colitis during therapy with these agents. However, these data, in concert with knowledge of drug bioavailability in feces and the broad-spectrum antimicrobial activity on the resident bowel flora, may provide additional insight into the mechanisms and predictability of this complication with these agents. Careful monitoring for the emergence of C. difficile and fecal cytotoxin and for diarrhea during therapy with these agents is clearly indicated.     

全面QT/QTc研究方法在喹诺酮类抗菌药物中研究的进展

近年来新药的研发费用越来越高,风险越来越大。因此如何及早发现新药研发过程中的不利因素,合理评估药物的研发前景对药物研发十分重要。其中药物引发的心电图QT间期延长,虽然发生率不高,但潜在危险性大,心电复极化延长可潜在增加室性心律失常的风险,严重时甚至可引起尖端扭转型室性心动过速（torsades de pointes ventricular heartbeat tachycardia,TdP）。TdP是介于室性心动过速与心室颤动之间的一种特殊类型的恶性心律失常,易致猝死[1]。国内外对此问题已达成基本共识,因此新药研发过程中的及时发现和综合评估对加强致QT间期延长药物的认识和管理就显得尤为重要。美国食品药品监督管理局（Foodand Drug Adminis—tration,FDA）为此于2002年11月发布了非抗心律失常药潜在致QT／Qrrc间期延长和致心律失常的临床前评价和临床评价两个指导原则的讨论稿。     

Carriage of antibiotic-resistant bacteria by healthy children

The frequency of carriage of antibiotic-resistant bacteria in healthy 7- and 8-year-old children in Bristol was studied. Children born in Avon between 1 April 1991 and 31 December 1992, attending the Avon Longitudinal Study of Pregnancy and Childhood (ALSPAC) 7 year follow-up clinic, formed the study population. Carriage was estimated using mouth and stool samples. None of 105 children on whom information was available had received tetracycline, chloramphenicol, ciprofloxacin or an extended-spectrum cephalosporin in the previous year. Staphylococcus aureus was isolated from mouthwashes from 200 (37.1%) of 539 children sampled. Six (3%) of the isolates were resistant to chloramphenicol or tetracycline and four (2%) were methicillin resistant. Haemophilus spp. were isolated from 369 (72%) of 513 samples and 63 (17%) were ampicillin resistant, 49 (13.3%) were erythromycin resistant and seven (1.9%) were tetracycline resistant. Branhamella catarrhalis was isolated from 333 (74%) of 450 samples. Twenty-eight (8.4%) were erythromycin resistant and 14 (4.2%) strains were tetracycline resistant. Group A beta-haemolytic streptococci were isolated from 17 of 507 children sampled. One (5.9%) was tetracycline resistant. Stool samples were returned from 335 (62%) of 539 children from whom they were requested. Eleven per cent of samples yielded Gram-negative bacilli with high-level resistance to chloramphenicol, which was frequently linked to resistance to ampicillin, spectinomycin and streptomycin. Isolates demonstrating resistance to the third-generation cephalosporin ceftazidime were recovered from 17 subjects (3.2%). Six (35%) of 17 isolates possessed extended-spectrum beta-lactamases. Healthy children carry bacteria resistant to antibiotics to which children are not usually exposed. Resistance to ceftazidime, chloramphenicol and tetracycline may be co-selected by exposure to other antibiotics used in children or may be acquired from family members, pets, other children or food. These results suggest that antibiotic-resistant bacteria are widely disseminated and may be acquired by children before exposure to specific selection pressure.     

Comparison of in vitro activity of quinolone antibiotics and vancomycin against gentamicin- and methicillin-resistant Staphylococcus aureus by time-kill kinetic studies.

Quinolone antibiotics have been proposed as possible alternatives to vancomycin for methicillin-resistant Staphylococcus aureus infections. We investigated the activities of amifloxacin, ciprofloxacin, norfloxacin, and vancomycin by time-kill kinetic studies. Antibiotic concentrations of 0, 1.0, and 4.0 times the MIC were used against four strains of gentamicin- and methicillin-resistant S. aureus. Staphylococci were plated onto ciprofloxacin-containing agar at all time points, in repeat time-kill kinetic studies. Macrobroth dilution MICs and MBCs were determined. Ciprofloxacin levels were measured by bioassay. Replica plating was performed from the original susceptible inoculum (MIC, 0.125 micrograms/ml) onto ciprofloxacin-supplemented agar. At 4.0 times the MIC, only with ciprofloxacin was there regrowth at 24 and 48 h. All four strains of staphylococci grew on agar supplemented with 1 microgram of ciprofloxacin per ml; three of four grew on agar supplemented with 2 micrograms of ciprofloxacin per ml. MICs and MBCs for these resistant clones ranged from 8 to 32 micrograms/ml. No degradation in activity or amount of ciprofloxacin could be detected in the bioassay. Replica-plated staphylococci grew on agar containing 1 microgram/ml but not higher concentrations of ciprofloxacin at 48 h. Amifloxacin and norfloxacin sustained bactericidal activity comparable to that of vancomycin. We conclude that heteroresistant subpopulations of gentamicin- and methicillin-resistant S. aureus can emerge under antibiotic selection pressure. Such resistant clones may then mutate in the presence of subinhibitory concentrations of antibiotic to higher levels of ciprofloxacin resistance.     

Variability of IncHI1 plasmids from Salmonella typhi with special reference to Peruvian plasmids encoding resistance to trimethoprim and other antibiotics.

In spite of extensive DNA homology among IncHI1 plasmids, ApaI and XbaI restriction digests of plasmids from Peruvian Salmonella typhi varied considerably from other IncHI1 plasmids isolated previously. IncHI1 plasmids appear to be undergoing a process of modular evolution, probably by sequential acquisition of resistance determinants.