Department of Microbiological and Gynaecological SciencesSection of Microbiology, University of Catania, Via Androne 81, 95124 Catania, Italy
Received 3 September 2002; returned 24 September 2002; revised 10 December 2002; accepted 13 December 2002
![]() |
Abstract |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
Keywords: faropenem, anaerobic pathogens, antibacterial activity
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
Faropenem is a unique antimicrobial penem being developed for oral administration as the pro-drug ester, faropenem-daloxate. Penems share structural similarities with both penicillins and cephalosporins, and are characterized by a broad antibacterial spectrum, a potent penicillin-binding protein affinity and good ß-lactamase stability.57
The aim of this study was to evaluate the antibacterial activity of faropenem in comparison with that of other antibiotics against anaerobic pathogens involved in systemic infections, and to evaluate the in vitro pharmacodynamic properties of faropenem by studies of timekill kinetics and post-antibiotic effect (PAE).
![]() |
Materials and methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
We tested 106 recent isolates collected from periodontal infections: Porphyromonas gingivalis (29), Prevotella spp. (eight), Prevotella melaninogenica (seven), Prevotella intermedia (five), Actinomyces spp. (25), Fusobacterium nucleatum (14), Peptostreptococcus spp. (11), Bacteroides ureolyticus (five) and Bacteroides forsythus (two). The identification of bacteria was made by colony and cellular morphology, staining characteristics, motility test and biochemical tests.8,9 Further bacterial identifications were carried out using API 20A, API-ZYM and rapid ID32A (bioMérieux).
All isolates with penicillin MICs 0.25 mg/L were tested for production of ß-lactamase by spreading fresh (2448 h) cultures on filter paper moistened with 500 mg/L nitrocefin.
Antibiotics
The antibacterial activity of faropenem was studied in comparison with that of penicillin G (Pharmacia), co-amoxiclav (SmithKline Beecham), cefoxitin (Merck, Sharp & Dôhme), erythromycin (Abbott), clindamycin (Upjohn) and metronidazole (Bristol-Myers Squibb). The agents tested, as powders of known potency, were gifts from their respective manufacturers.
Determination of MICs and MBCs
MICs of faropenem and of the other antimicrobials in the comparison were determined by the microdilution method using Brucella broth supplied with haemin (0.005 mg/L) and vitamin K1 (0.0004 ml/L) with an inoculum of 105 cfu/mL, in accordance with the guidelines of the NCCLS.10 Bacteroides fragilis ATCC 25285 was used as a control strain. The MIC was defined as the lowest concentration at which there was no visible growth after incubation at 3537°C for 48 h.
The susceptibility breakpoints recommended by the NCCLS for anaerobic bacteria were: penicillin 0.5 mg/L, co-amoxiclav
4/2 mg/L, cefoxitin
16 mg/L, clindamycin
2 mg/L and metronidazole
8 mg/L. For erythromycin, the value of
0.5 mg/L was used according to the recommendations for aerobic bacteria.11 NCCLS breakpoints for faropenem are not yet available.
After the determination of faropenem MICs, subcultures onto supplemented Brucella agar were obtained from the wells devoid of growth by means of a 6 mm loop. Incubation was carried out at 3537°C in anaerobic jars for 48 h. The MBC was defined as the lowest antibiotic concentration resulting in no visible colony growth.
Timekill kinetics
The killing curves of faropenem and co-amoxiclav were carried out in accordance with the method of Rosenblatt,12 against two isolates each of P. gingivalis, B. ureolyticus and Actinomyces spp. and one isolate of Prevotella sp. and F. nucleatum. In a closed system the bacteria were incubated with faropenem at concentrations equivalent to the MIC, 4 x and 10 x MIC, and with co-amoxiclav at MIC and 4 x MIC. Bactericidal activity was defined as a 3 log10 decrease (99.9% kill) in cfu/mL.
PAE
The PAE of faropenem was determined by the viable plate count method of Craig & Gudmundsson13 against eight isolates of periodontal bacteria: two isolates each of P. gingivalis (CT 12 ß-lac+, MIC 0.125 mg/L and CT 23 ß-lac, MIC 0.25 mg/L), B. ureolyticus (CT 21 ß-lac, MIC 0.06 mg/L and CT 42 ß-lac+, MIC 0.06 mg/L), Actinomyces sp. (CT 10 ß-lac, MIC 0.06 mg/L and CT 25 ß-lac, MIC 0.125 mg/L), Prevotella sp. (CT 7 ß-lac, MIC 0.06 mg/L) and F. nucleatum (CT 2 ß-lac, MIC 0.125 mg/L).
The PAE was determined in duplicate on supplemented Brucella agar at faropenem concentrations of 4 x and 10 x MIC. A significant PAE was defined as an effect of >0.5 h.
![]() |
Results and discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
Since breakpoint interpretative criteria for faropenem have not been established for anaerobic bacteria, our study does not report percentage susceptibility. The overall percentage of isolates susceptible to penicillin was 91%. Except for Peptostreptococcus spp. (91%), all the species tested were susceptible to co-amoxiclav and cefoxitin (100%). The percentage of susceptibility to clindamycin of all isolates tested was 95%, whereas the susceptibility to metronidazole was 100%, except for Actinomyces spp. (34%). Using the value of 0.5 mg/L, according to the recommendations for aerobic bacteria,12 the overall susceptibility percentage to erythromycin was 77%; however, the activity of erythromycin can be affected by anaerobic conditions, mainly when fusobacteria are tested.
MBCs of faropenem were equal to or 24 x higher than MICs.
Against the isolates of P. gingivalis and Actinomyces spp. (Figure 1ad), faropenem exhibited a bactericidal activity at 10 x MIC at 12 h, whereas against B. ureolyticus and F. nucleatum (Figure 1eg) a bactericidal effect was observed at 24 h.
|
For P. gingivalis and Actinomyces spp. isolates, co-amoxiclav at 10 x MIC was bactericidal at 12 h (Figure 1ad). At 4 x MIC, co-amoxiclav exerted a bactericidal effect at 8 h against Actinomyces spp. (Figure 1c and d) and at 12 h against B. ureolyticus CT 42 (Figure 1e).
Unlike most ß-lactams, faropenem exhibited an in vitro PAE on some clinically relevant anaerobic bacteria, and this effect was not influenced by ß-lactamase production.13 Generally, increasing concentrations of faropenem were associated with increases in the PAE. The PAE was marked for P. gingivalis both at 4 x and 10 x MIC. However, in all cases the greatest effect was observed at 10 x MIC. The shortest PAE was observed for Actinomyces spp. at both 4 x and 10 x MIC (Table 2). The differences in PAE duration at 4 x and 10 x MIC of faropenem were not significant, except for Actinomyces spp., against which 10 x MIC produced a PAE two to three times longer than that obtained at 4 x MIC.
|
![]() |
Acknowledgements |
---|
![]() |
Footnotes |
---|
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
2 . Brook, I. (1995). Prevotella and Porphyromonas infections in children. Journal of Medical Microbiology 42, 3407.[Abstract]
3 . King, A., Downes, J., Nord, C. E. & Phillips, I. (1999). Antimicrobial susceptibility of non-Bacteroides fragilis group anaerobic Gram-negative bacilli in Europe. Clinical Microbiological Infections 5, 40416.[Medline]
4 . Lo Bue, A. M., Blandino, G., Milazzo, I., Pasquantonio, G., Speciale, A. & Nicoletti, G. (2001). Antibacterial activity and post-antibiotic effect of flurithromycin compared with other macrolides and penicillins against periodontal pathogens. Journal of Chemotherapy 13, 30812.
5
.
Goldstein, E. J., Citron, D. M., Merriam, C. V., Warren, Y. A., Tyrrell, K. L. & Fernandez, H. T. (2002). Comparative in vitro activity of faropenem and 11 other antimicrobial agents against 405 aerobic and anaerobic pathogens isolated from skin and soft tissue infections from animal and human bites. Journal of Antimicrobial Chemotherapy 50, 41120.
6
.
Woodcock, J. M., Andrews, J. M., Brenwald, N. P., Ashby, J. P. & Wise, R. (1997). The in-vitro activity of faropenem, a novel oral penem. Journal of Antimicrobial Chemotherapy 39, 3543.
7 . Boswell, F. J., Andrews, J. M. & Wise, R. (1997). Pharmacodynamic properties of faropenem demonstrated by studies of timekill kinetics and post-antibiotic effect. Journal of Antimicrobial Chemotherapy 39, 4158.[Abstract]
8 . Summanenn, P., Baron, E. J., Citron, D. M., Strong, C. A., Wexler, H. M. & Finegold, S. M. (1993). Wadsworth Anaerobic Bacteriology Manual, 5th edn. Star Publishing, Belmont, CA, USA.
9 . Koneman, E. W., Allen, S. D., Janda, W. M., Schreckenberger, P. C. & Winn, W. C. (1999). Color Atlas and Textbook of Diagnostic Microbiology. Lippincott, Philadelphia, PA, USA.
10 . National Committee for Clinical Laboratory Standards. (1997). Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow AnaerobicallyFourth Edition: Approved Standard M7-A4. NCCLS, Villanova, PA, USA.
11 . National Committee for Clinical Laboratory Standards. (2001). Performance Standards for Antimicrobial Susceptibility Testing, Eleventh Informational Supplement: M100-S11. NCCLS, Villanova, PA, USA.
12 . Rosenblatt, J. E. (1991). Antimicrobial susceptibility testing of anaerobic bacteria. In Antibiotics in Laboratory Medicine, 3rd edn (Lorian, V., Ed.), pp. 12930. Williams and Wilkins, Baltimore, MD, USA.
13 . Craig, W. A. & Gudmundsson, S. (1991). The post-antibiotic effect. In Antibiotics in Laboratory Medicine, 3rd edn (Lorian, V., Ed.), pp. 40331. Williams and Wilkins, Baltimore, MD, USA.
|