Department of Medical Microbiology, City Hospital NHS Trust, Dudley Road, Birmingham B18 7QH, UK
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Abstract |
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Introduction |
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BMS-284756 (previously known as T-3811ME) is a des-fluoro(6) quinolone and, as such, lacks the fluorine at position 6, a characteristic differentiating it from existing agents in this group. It was initially thought that the 6-fluoro group was responsible for enhanced bacterial penetration and killing via gyrase inhibition.3 Recently it has been discovered that compounds without this component can also have broad antimicrobial activity.
In vitro studies of BMS-284756 have demonstrated that its activity against Gram-positive cocci is similar to or greater than that of other quinolones. In particular it is active against penicillin-resistant and ciprofloxacin-resistant S. pneumoniae.4,5 BMS-284756 also has good activity against methicillin-susceptible Staphylococcus aureus (MSSA) and potentially against methicillin-resistant S. aureus (MRSA).4,6 In addition, its spectrum includes the Enterobacteriaceae, anaerobes, fastidious organisms, Legionella spp. and cell wall-deficient bacteria.4,6 BMS-284756 is less active than other quinolones against P. aeruginosa and less active than moxifloxacin against Mycobacterium spp.4,6
In these investigations we compared the in vitro activity of BMS-284756 with four fluoroquinolones and two ß-lactams. The study included an investigation of the effects of increasing the inoculum and the presence of human serum.
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Materials and methods |
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Antimicrobials investigated were BMS-284756 (Bristol-Myers Squibb, Wallingford, CT, USA), ciprofloxacin and moxifloxacin (Bayer AG, Wuppertal, Germany), amoxicillin, clavulanic acid, ceftazidime and gemifloxacin (GlaxoSmithKline, Worthing, UK) and levofloxacin (Aventis Ltd, Uxbridge, UK). All agents were prepared and stored following the manufacturer's instructions.
Isolates
A total of 926 clinical isolates, collected over the previous 3 years from many different centres in the UK, were used in the study. The collection contained 296 Gram-positive bacteria (including 36 penicillin-resistant and 14 ciprofloxacin-resistant S. pneumoniae), 537 Gram-negative bacteria (including nine ciprofloxacin-resistant E. coli), 86 anaerobic bacteria, three Chlamydia spp. and four Mycobacterium spp. A further 25 selected Gram-negative isolates known to produce different types of ß-lactamase were also tested.
Susceptibility testing
The MIC of each isolate was determined following the standard agar plate dilution method recommended by the BSAC.7 The incubation conditions used are shown in Table 1. A final inoculum of 104 cfu/spot was employed for all bacteria using a multipoint inoculator (Mast, Bootle, UK). A selection of organisms was also tested with a final concentration of 106 cfu/spot. The MIC was defined as the lowest concentration of antimicrobial to inhibit bacterial growth, one or two colonies being ignored.
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Two isolates of Chlamydia trachomatis and one of Chlamydia pneumoniae were tested against BMS-284756, ciprofloxacin and erythromycin, using the technique of Webberley et al.8 McCoy cell coverslip cultures were infected with c. 1000 inclusion forming units of chlamydiae, then exposed to doubling dilutions of the three antimicrobials. Following incubation at 3537°C in 46% CO2 for 48 h, the coverslips were stained using a fluorescein-labelled immunoantibody kit (Imagen Chlamydia; Organon Technika Ltd, Cambridge, UK). The MIC was defined as the lowest concentration of antimicrobial to inhibit the development of inclusions. The minimal lethal concentration (MLC) was taken as the lowest concentration of antimicrobial to inhibit additional inclusion development after incubation in antimicrobial-free media for a further 48 h.
Effect of human serum
The effects of human serum on the MIC and MBC of BMS-284756 were determined using two isolates each of group A ß-haemolytic streptococci, Moraxella catarrhalis, MSSA, S. pneumoniae and E. coli. A microdilution technique, as described previously,9 was employed using IsoSensitest broth (Oxoid, Basingstoke, UK) plus 0, 20 or 70% human serum (TCS, Bodolph Clayton, UK) and supplemented with 5% laked horse blood (Oxoid) for fastidious bacteria. Doubling dilutions of BMS-284756 were inoculated with 105 cfu/mL of the test organism and incubated as previously. The MIC was defined as above, the minimal bactericidal concentration (MBC) as the lowest concentration of antimicrobial to prevent growth on subculture of the broth for 1824 h in appropriate conditions.
Mycobacteria susceptibilities
Three isolates of Mycobacterium tuberculosis (two clinical isolates and control strain NCTC 7416) and one of Mycobacterium avium were tested against BMS-284756 and ciprofloxacin using an agar incorporation method.10 Briefly, a concentration range of antibiotic was incorporated into Middlebrook 7H10 medium (Becton Dickinson Microbiology Systems, Oxford, UK) containing 10% Middlebrook oleic acidalbumin dextrose catalase (Becton Dickinson) enrichment as a supplement. Plates were incubated at 3537°C in Genboxes (bioMérieux, Hampshire, UK) with 510% CO2 for 21 days. The MIC was the lowest concentration of antibiotic that inhibited >99% of the bacterial population.
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Results |
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BMS-284756 was the most active agent for all species of staphylococci. However, the MIC90 for the MRSA isolates was 32-fold greater than that for the MSSA isolates. BMS-284756 and gemifloxacin displayed very high activity against streptococci, including the penicillin-resistant and ciprofloxacin-resistant S. pneumoniae. In particular, BMS-284756 was 32-fold more active than levofloxacin. BMS-284756 and co-amoxiclav had the greatest activity against Enterococcus faecalis, the former being four-fold more active than moxifloxacin. Similarly BMS-284756 showed enhanced activity in comparison with the other agents tested against Enterococcus faecium.
Isolates of Neisseria meningitidis, Neisseria gonorrhoeae, Haemophilus influenzae and M. catarrhalis were all highly susceptible to the quinolones, BMS-284756 being amongst the most active. BMS-284756 was also the most active antibiotic against the anaerobes tested, including Clostridium difficile.
An increase in the inoculum from 104 to 106 cfu/mL did not raise the MIC by more than four-fold for any isolates. Addition of human serum at either 20% or 70% raised the MIC or MBC by more than four-fold for five [Streptococcus group A, S. pneumoniae (2), M. catarrhalis and E. coli] of the 10 isolates examined.
For three isolates of M. tuberculosis the MIC of BMS-284756 was 24 mg/L and within one dilution of that obtained with ciprofloxacin (MIC 12 mg/L). For one isolate of M. avium the MIC was 16 mg/L of both BMS-284756 and ciprofloxacin. BMS-284756 was highly active against two isolates of C. trachomatis (MIC 0.015 and 0.03 mg/L, MLC 0.06 mg/L) and one isolate of C. pneumoniae (MIC and MLC 0.015 mg/L). The MIC and MLC of ciprofloxacin for the three isolates was 24 mg/L; the MIC of erythromycin was 0.250.5 mg/L and the MLC was 0.52 mg/L.
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Discussion |
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BMS-284756 was the most active agent tested against all species of staphylococci. All isolates of MSSA were found to have an MIC < 0.03 mg/L, and 18 of 20 MRSA isolates had an MIC < 2 mg/L, despite consistent resistance (MIC > 2 mg/L) to ciprofloxacin. With the paucity of antibiotics available for treating invasive MRSA infection, this feature of BMS-284756 may prove to be very useful in clinical practice.
The relative increase in the activity of BMS-284756 against Gram-positive pathogens compared with other quinolones has been accompanied by a relative decrease in activity against Gram-negative bacilli. The MIC50 and MIC90 of ciprofloxacin were one or two dilutions lower than those of BMS-284756 for the Enterobacteriaceae and P. aeruginosa. On the other hand, for Acinetobacter spp. the MIC50 and MIC90 of BMS-284756 and the other new quinolones were three- to four-fold lower than that of ciprofloxacin.
All Neisseria isolates were highly susceptible to all the antibiotics examined. BMS-284756 has already been shown to be effective against pneumococci in a rabbit meningitis model.5 It therefore has potential in the treatment of meningitis of unknown cause if it is shown to pass the blood brain barrier in humans. Its activity against anaerobes, demonstrated previously4,6 and confirmed in this study, also indicates that BMS-284756 could be used as a single agent in the treatment of intra-abdominal sepsis.11
Human serum raised the MIC or MBC by more than four-fold for five of the 10 isolates examined. This difference is possibly explained by the protein binding of BMS-284756 being c. 75% (Bristol-Myers Squibb, unpublished data). Although it is possible that penetration into some tissues will be slower than for less highly bound quinolones, it is unlikely that activity in vivo will be adversely affected. Thus the breakpoint need not be raised to take this into account. Size of inoculum had little effect on the MIC for any organism tested. This is to be expected for a rapidly bactericidal drug such as BMS-284756.
In summary, BMS-284756 is a des-fluoro(6) quinolone with activity against a wide variety of organisms, including penicillin-resistant S. pneumoniae, MRSA, Enterobacteriaceae, fastidious organisms and Chlamydia spp. It has potential as an agent for the treatment of community-acquired respiratory tract infections and other common bacterial diseases caused by susceptible pathogens.
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Acknowledgements |
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Notes |
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References |
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2
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Fung-Tomc, J., Minassian, B., Kolek, B., Huczko, E., Aleksunes, L., Stickle, T. et al. (2000). Antibacterial spectrum of a novel des-fluoro(6) quinolone, BMS-284756. Antimicrobial Agents and Chemotherapy 44, 33516.
5 . Cottagnoud, P., Acosta, F., Cottagnoud, M., Neftel, K. A. & Tauber, M. G. (2000). Efficacy of BMS 284756 (BMS) against penicillin-sensitive, penicillin and quinolone-resistant pneumococci in the experimental meningitis model. In Program and Abstracts of the Fortieth Interscience Conference on Antimicrobial Agents and Chemotherapy, Toronto, Canada, 2000. Abstract 871, p. 51. American Society for Microbiology, Washington, DC.
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8 . Webberly, J. M., Matthews, R. S., Andrews, J. M. & Wise, R. (1987). Commercially available fluorescein-conjugated monoclonal antibody for determining the in vitro activity of antimicrobial agents against Chlamydia trachomatis. European Journal of Microbiology and Infectious Diseases 6, 5879.
9 . Woodcock, J. M., Andrews, J. M., Boswell, F. J., Brenwald, N. P. & Wise, R. (1997). In vitro activity of BAY 12-8039, a new fluoroquinolone. Antimicrobial Agents and Chemotherapy 41, 1016. [Abstract]
10 . Perronne, C., Gikas, A., Tuffot-Pernot, C., Grosset, J., Pocidalo, J. J. & Vilde, J. L. (1990). Activities of clarithromycin, sulfisoxazole, and rifambutin against Mycobacterium avium complex multiplication within human macrophages. Antimicrobial Agents and Chemotherapy 34, 150811. [ISI][Medline]
11 . Cisneros, R. L., Panzo, R. J. & Onderdonk, A. B. (2000). Therapeutic efficacy of BMS-284756 for the treatment of intraabdominal sepsis (IAS). In Program and Abstracts of the Fortieth Interscience Conference on Antimicrobial Agents and Chemotherapy, Toronto, Canada, 2000. Abstract 996, p. 55. American Society for Microbiology, Washington, DC.
Received 21 June 2001; returned 30 August 2001; revised 20 September 2001; accepted 3 October 2001