Laboratoire de Bactériologie, Université Victor Segalen Bordeaux 2, 146 rue Léo Saignat, 33076, Bordeaux Cedex, France
Sir,
Macrolides are a class of antibiotics commonly used for the treatment of mycoplasmal1 and chlamydial infections. They have been regarded as the drug of choice for the treatment of respiratory tract infections caused by the atypical microorganisms Mycoplasma pneumoniae and Chlamydia pneumoniae. Among this class, different molecules show various activities. Midecamycin diacetate is a natural 16-membered macrolide, and we have investigated the in vitro activity of midecamycin diacetate (Menarini, Rungis, France) against 26 strains of M. pneumoniae (25 clinical isolates and one reference strain, FH) and one reference strain of C. pneumoniae (CM-1 ATCC VR-1360) in comparison with that of other macrolides. The comparator drugs were erythromycin and roxithromycin (Hoechst-Marion-Roussel, Romainville, France), clarithromycin (Abbott, Rungis, France), azithromycin (Pfizer, Orsay, France) and josamycin (Rhône-Poulenc Rorer, Vitry-sur-Seine, France).
Susceptibility testing of M. pneumoniae was performed as described previously by an agar dilution method on Hayflick modified medium with an inoculum of 104105 colour changing units per mL.2 The drug concentrations tested ranged from 0.015 to 32 mg/L. The MIC was read as the lowest concentration of each drug completely inhibiting growth, when visible growth could be seen on the control plate without antibiotics. Susceptibility testing of C. pneumoniae was determined by the standard method. Briefly, HL (human lung) cell monolayers were inoculated with 105 inclusion forming units per mL, centrifuged at 1200 g for 1 h and incubated at 37°C in 5% CO2 for 2 h. Then, the medium was removed and replaced by medium containing 1.5 mg/L of cycloheximide and serial two-fold dilutions of the test drug. After incubation at 37°C for 72 h, cells were fixed and stained for inclusions with fluorescein isothiocyanate-conjugated monoclonal antibody (C. pneumoniae FITC Research Reagent K6601, Dako diagnostics, Cambridge, UK). The MIC was defined as the lowest antibiotic concentration at which no chlamydial inclusions were seen.
Midecamycin diacetate showed activity against M. pneumoniae strains with MIC50 and MIC90 (MIC at which 50% and 90% of strains were inhibited) 0.015 mg/L. Midecamycin diacetate was as active as other macrolides tested [for which MICs were found to be identical to that of midecamycin diacetate, except for josamycin (MIC90 0.03 mg/L)]. This study confirms the results described previously3 on the activity of the 14-, 15- and 16-membered macrolides against M. pneumoniae. Moreover, midecamycin diacetate appeared to be as active as telithromycin,3,4 which belongs to the ketolides, a new class of macrolide-related antibiotics.
C. pneumoniae was susceptible in vitro to midecamycin diacetate with an MIC of 0.5 mg/L. This activity was similar to that of josamycin (MIC 0.25 mg/L), another 16-membered macrolide, but lower than those of the 15- and 14-membered macrolides, azithromycin (MIC 0.125 mg/L), erythromycin (MIC 0.05 mg/L), roxithromycin (MIC 0.03 mg/L) and clarithromycin (MIC 0.012 mg/L), as described previously.5 Midecamycin diacetate seemed to be less potent than telithromycin against C. pneumoniae for which a MIC90 of 0.06 mg/L has been obtained.6 However, the midecamycin diacetate MIC for C. pneumoniae of 0.5 mg/L, is below the breakpoint (1 mg/L).
To summarize, midecamycin diacetate possesses in vitro activity against both M. pneumoniae and C. pneumoniae. As these microorganisms are both responsible for many community-acquired respiratory tract infections in adults and children worldwide, midecamycin diacetate could be an interesting choice for the treatment of these infections.
Notes
J Antimicrob Chemother 2001; 47: 240241
* Corresponding author. Tel: +33-5-57-57-16-25; Fax: +33-5-56-93-29-40; E-mail: cecile.bebear{at}u-bordeaux2.fr
References
1 . Taylor-Robinson, D. & Bébéar, C. (1997). Antibiotic susceptibilities of mycoplasmas and treatment of mycoplasmal infections. Journal of Antimicrobial Chemotherapy 40, 62230.[Abstract]
2 . Bébéar, C. & Robertson, J. (1996). Determination of minimal inhibitory concentration. In Molecular and Diagnostic Procedures in Mycoplasmology, Volume II, Diagnostic Procedures, (Tully, J. G. & Razin, S., Eds), pp. 18999. Academic Press, Inc., San Diego, CA.
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Yamaguchi, T., Hirakata, Y., Izumikawa, K., Miyazaki, Y., Maesaki, S., Tomono, K. et al. (2000). In vitro activity of telithromycin (HMR 3647), a new ketolide against clinical isolates of Mycoplasma pneumoniae in Japan. Antimicrobial Agents and Chemotherapy 44, 13812.
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Bébéar, C. M., Renaudin, H., Bryskier, A. & Bébéar, C. (2000). Comparative activities of telithromycin (HMR 3647), levofloxacin, and other antimicrobial agents against human mycoplasmas. Antimicrobial Agents and Chemotherapy 44, 19802.
5 . Ridgway, G. L., Mumtaz, G. & Fenelon, L. (1991). The in-vitro activity of clarithromycin and other macrolides against the type of Chlamydia pneumoniae (TWAR). Journal of Antimicrobial Chemotherapy 27, Suppl. A, 435.[ISI][Medline]
6 . Strigl, S., Roblin, P. M., Reznik, T. & Hammerschlag, M. R. (2000). In vitro activity of ABT 773, a new ketolide antibiotic, against Chlamydia pneumoniae. Antimicrobial Agents and Chemotherapy 44, 11123.