Comparison of the bactericidal activities and post-antibiotic effects of the Des-F(6)-quinolone BMS-284756, levofloxacin, and ciprofloxacin against methicillin-susceptible and methicillin-resistant Staphylococcus aureus.

The bactericidal activities and post-antibiotic effects of BMS-284756 (T-3811ME), levofloxacin, and ciprofloxacin were evaluated against a methicillin-susceptible and a methicillin-resistant Staphylococcus aureus strain. Minimum inhibitory concentrations (MICs), minimum bactericidal concentrations, post-antibiotic effects, and post-antibiotic sub-MIC effects were determined and time-kill studies were performed for BMS-284756, levofloxacin, and ciprofloxacin. At 4-times and 10-times the MIC, time-kill kinetics over 3 h and over 24 h were similar for all three quinolones when effects were considered as multiples of the MIC. All three quinolones achieved a 3 log10 reduction in cfu/ml within 2 h. At 10-times the MIC, the post-antibiotic effects of BMS-284756, levofloxacin, and ciprofloxacin were 1.6-2.6 h for the methicillin-susceptible Staphylococcus aureus strain and 1.5-1.9 h for the methicillin-resistant Staphylococcus aureus strain. When actual concentrations were considered, BMS-284756 achieved results comparable to levofloxacin and ciprofloxacin at concentrations nearly 10-fold less. When relating the pharmacokinetic properties of the three quinolones to their in vitro activities, the resulting Cmax/MIC and AUC/MIC ratios were. respectively, 120-240.7 and 1,321.7-2,643 for BMS-284756, 22.8 and 190 for levofloxacin, and 5.9-11.9 and 54.8-109.6 for ciprofloxacin. The greater in vitro activity and favorable human pharmacokinetics of BMS-284756 may translate to improved clinical effectiveness of this agent compared to currently marketed quinolones.

Mechanism of action of the des-F(6) quinolone BMS-284756 measured by supercoiling inhibition and cleavable complex assays.

BMS-284756 (T-3811ME), a novel des-F(6) quinolone, was tested in the supercoiling inhibition and cleavable complex assays against Escherichia coli DNA gyrase, a target of quinolones. The results suggest that BMS-284756 has the same mechanism of action against DNA gyrase as other quinolones and a similar level of potency.

Staphylococcus aureus mutants selected by BMS-284756.

BMS-284756, a novel des-fluoro(6)-quinolone, was used to select for in vitro mutants of Staphylococcus aureus ISP794. Step mutants were obtained, and the quinolone resistance-determining regions of four target genes, gyrA, gyrB, grlA, and grlB, were sequenced. The data suggest that DNA gyrase is the primary target for BMS-284756 in S. aureus.

ABT-773 (Abbott Laboratories).

ABT-773 is a macrolide antibacterial agent under development by Abbott Laboratories and Taisho Pharmaceutical Co Ltd for the potential treatment of bacterial infection [266579]. As of February 2001, ABT-773 had entered phase III trials in the US [398274]. Japanese phase II trials were expected to commence in June 2000 and a phase II trial is being designed for respiratory infections, with Abbott expecting filing in March 2002 [360455]. The bioavailability of ABT-773 in humans is unaffected by food [383228] and in a phase I, randomized, double-blind trial in healthy males only mild adverse effects, usually affecting the gastrointestinal system, were observed [383208]. Under an agreement, Abbott and Taisho are conducting joint research to discover new compounds; Abbott will have worldwide marketing, manufacturing and supply rights (except in Japan), and Taisho will receive royalties on Abbott's sales in consideration of granted rights. In Japan, the companies will co-market any resulting compounds [266579]. ABT-773 demonstrated good activity in vitro and in vivo against Streptococcus pneumoniae and Staphylococcus aureus [383229], [383231], and was highly potent even against macrolide-resistant [382149], [382150] and invasive [383782] S pneumoniae.

Selection and genetic characterization of Streptococcus pneumoniae mutants resistant to the des-F(6) quinolone BMS-284756.

Existing quinolones are known to target the type II topoisomerases in bacteria. In order to determine which of these targets are of key importance in Streptococcus pneumoniae treated with BMS-284756 (T-3811ME), a novel des-F(6) quinolone, resistant mutants were selected in several steps of increasing resistance by plating pneumococci on a series of blood agar plates containing serial twofold-increasing concentrations of drug. After incubation, colonies that arose were selected and passaged twice on antibiotic-containing media at the selection level. Mutants generally showed increases in resistance of four- to eightfold over the prior level of susceptibility. Mutants in the next-higher level of resistance were selected from the previous round of resistant mutants. Subsequently, chromosomal DNA was prepared from parental (R6) pneumococci and from at least three clones from each of four levels of increasing antibiotic resistance. Using PCR primers, 500- to 700-bp amplicons surrounding the quinolone resistance determining regions (QRDR) of gyrA, gyrB, parC, and parE genes were prepared from each strain. Internal primers were used to sequence both DNA strands in the regions of approximately 400 bp centered on the QRDR. Mutations identified with increasing levels of resistance included changes in GyrA at Ser-81 and Glu-85 and changes in ParC at Ser-79 and Asp-83. Changes in GyrB and ParE were not observed at the levels of resistance obtained in this selection. The resistance to comparator quinolones (levofloxacin, ciprofloxacin, and moxifloxacin) also increased in four- to eightfold steps with these mutations. The intrinsically greater level of antibacterial activity and thus lower MICs of BMS-284756 observed at all resistance levels in this study may translate to coverage of these resistant pneumococcal strains in the clinic.

The inhibition and selectivity of bacterial topoisomerases by BMS-284756 and its analogues.

Analogues of BMS-284756, a novel des-F(6)-quinolone, were synthesized and evaluated in order to determine the effects of modification of substituents on in vitro target inhibition. BMS-340281 (stereoisomer of BMS-284756), BMS-340280 (C-6 fluorinated analogue of BMS-284756), BMS-340278 (C-8-H derivative), BMS-433366 (C-8 methoxy analogue) and fluoroquinolone comparators were evaluated for antibacterial activity. The MICs of BMS-284756 were generally found to be within two-fold of the MICs of BMS-284756 analogues against a panel of Gram-positive and -negative organisms. BMS-284756 had MICs of 0.03-0.125 mg/L against Streptococcus pneumoniae strains with GyrA and ParC mutations, and was the most active quinolone. BMS-284756 and its analogues had similar activity compared with ciprofloxacin and moxifloxacin against topoisomerase IV decatenation, but were three times more active than levofloxacin. The IC(50) of BMS-284756 for human topoisomerase II (hTopo II) was 3000 times higher than its IC(50) for DNA gyrase, and no whole-cell cytotoxicity was noted. Two analogues, BMS-340280 and BMS-340278, demonstrated moderate inhibition against hTopo II and cytotoxicity in the cellular assay. BMS-284756 demonstrated greater Gram-positive antibacterial activity and similar inhibition of targets compared with other fluoroquinolones, and more favourable selectivity compared with the other BMS-284756 analogues.

39th Interscience Conference on Antimicrobial Agents and Chemotherapy of the American Society for Microbiology.

The 39th ASM ICAAC Meeting, attended by over 16,000 delegates, highlighted numerous late-stage development antibacterials. The presentation of over 600 reports (posters, symposia and oral presentations) regarding resistance emergence underscores the evolving landscape of antibiotic susceptibility worldwide. Although bacterial genomic efforts are slowly expanding the potential sources of novel targets, the established antibacterial classes, including quinolones, beta-lactams, protein synthesis inhibitors and carbapenems, were most prevalent among the presentations. Quinolones dominated this conference, with many presentations of moxifloxacin (> 72 presentations), gatifloxacin (> 66 presentations) and gemifloxacin (> 59 presentations). The new class of antibacterials, the oxazolidinones, represented by Linezolid, was also highlighted.

Antibacterial agents that inhibit two-component signal transduction systems.

A class of antibacterials has been discovered that inhibits the growth of Gram-positive pathogenic bacteria. RWJ-49815, a representative of a family of hydrophobic tyramines, in addition to being a potent bactericidal Gram-positive antibacterial, inhibits the autophosphorylation of kinase A of the KinA::Spo0F two-component signal transduction system in vitro. Analogs of RWJ-49815 vary greatly in their ability to inhibit growth of bacteria and this ability correlates directly with their activity as kinase A inhibitors. Compared with the potent quinolone, ciprofloxacin, RWJ-49815 exhibits reduced resistance emergence in a laboratory passage experiment. Inhibition of the histidine protein kinase::response regulator two-component signal transduction pathways may present an opportunity to depress chromosomal resistance emergence by targeting multiple proteins with a single inhibitor in a single bacterium. Such inhibitors may represent a class of antibacterials that potentially may represent a breakthrough in antibacterial therapy.

38th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC), September 24-27, 1998, San Diego, CA, USA.

This year's ICAAC meeting was dominated by exciting late-stage development antibiotics that represent breakthroughs in covering pathogens of unmet medical need, including drug-resistant pathogens. There are several exciting antibiotics in late-stage development, among them, linezolid, gatifloxacin, moxifloxacin, SB-265805, HMR 3647, SCH27899 and the resurrected daptomycin. The development of new technology for screening and the cross-application into genomics have led to numerous breakthroughs in techniques and strategies for the identification of novel prokaryotic targets.

Efflux pumps in bacteria: overview, clinical relevance, and potential pharmaceutical target.

Trends in microbial resistance suggest a dramatic increase in the frequency of reports of multi-drug efflux pumps in bacteria and fungi. Although it is difficult to determine whether this increase is due to the increased attention given to this resistance mechanism, or an increase in frequency, efflux pumps are becoming an important consideration in resistance emergence. These efflux pumps comprise at least four different classes in Gram-positive and Gram-negative bacteria, as well as in Streptomyces and fungi. As more efflux pumps are characterised and studied, both biochemically and structurally, the opportunity for intervention may arise.

The 97th Annual Meeting of the American Society for Microbiology.

The Annual Meeting of the American Society for Microbiology took place in Miami Beach, Florida, from May 4-8, 1997. Over 9000 scientists attended this meeting, which covers all major aspects of prokaryotic research (basic, applied, medical, and diagnostic). Genomics discussions were a major part of the meeting agenda, with scientists detailing both basic and applied research effort using genomics and bioinformatics. New ideas for potential novel antimicrobials have also surfaced as the tools to pursue Drug Discovery have fallen into place and pharmaceutical companies have ;rediscovered' anti-infectives.

Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC).

Over 10,000 research scientists attended the ICAAC meeting in Toronto, Canada. The continued increase in the rate of resistance in bacteria and fungi and the underlying mechanisms of resistance were the focus of many presentations this year. So, too, were the attempts to combat this emerging resistance crisis. Many papers described new modifications to older antimicrobials, novel classes of antimicrobials and the potential use of new antibacterial and antifungal targets.

The effects of certain student and institutional characteristics on minority medical student specialty choice.

This article investigates the possible effects of minority status, presence of a Minority Affairs Office or Student National Medical Association (SNMA) Chapter, level of indebtedness, and number of years (4 to 5) to complete medical school on specialty choice of minority medical students. The 5-year experiences of 20 medical schools in the southern region (including three in Puerto Rico) were examined via a questionnaire. Information was sought for African Americans, Afro-Caribbean, Mexican American, other minority, and nonminority students. Minority graduates entered the specialities of internal medicine, pediatrics, and family medicine in far greater numbers than any other speciality. Also, the percentage of minorities who entered these fields was greater than the percentage of non-minorities. Conversely, minorities were significantly underrepresented in the surgical subspecialties and radiology. Additional study is needed to further examine the medical school experience for indications of why the clustering in primary care specialities occurs. Moreover, while most schools had some kind of minority affairs organization, few were active in the writing of the Dean's letter. Other suggestions to assure adequate minority representation across specialties include early exposure to the different specialties and subspecialties for minority students, a mentorship program with practicing physicians, and stronger recruitment of minorities into underrepresented specialties.