Regional trends in telithromycin and azithromycin resistance among Streptococcus pneumoniae isolates

Abstract number: P606

Allizond V., Banche G., Roana J., Li Vigni N., Mandras N., Scalas D., Tullio V., Carlone N., Savoia D., Barbui A., Cuffini A.

Objectives: This study compared the in vitro activity of telithromycin, the first ketolide developed for clinical use, with that of azithromycin, one of the most commonly used macrolide for treatment of respiratory tract infections, against 198 Streptococcus pneumoniae isolates at some North West Italy's hospitals between 2005–2007. Erythromycin-resistance phenotypes were determined to correlate the different bacterial resistant pattern to antimicrobial susceptibility.

Methods: The determination of minimal inhibition concentration (MIC) was carried out using the microdilution broth method according to Clinical and Laboratory Standards Institute (CLSI) with an inoculum of 105 cfu/ml and antimicrobial concentrations ranged from 0.03 to 64 mg/L. Minimal bactericidal concentration (MBC) was determined by plating 0.1 ml from the wells showing no visible growth on agar plates and incubating for 18 h. The erythromycin-resistance phenotype was determined by the triple-disk test described by Giovanetti et al. Commercial disks of erythromycin, clindamycin and josamycin were used.

Table. In vitro antimicrobial activity of telithromycin and azithromycin against erythromycin-susceptible and erythromycin-resistant S. pneumoniae isolates

Results: 69.2% of the S. pneumoniae isolates were erythromycin-susceptible (Ery-S). Among the 30.8% erythromycin-resistant (Ery-R) pneumococci, 42.6% expressed the constitutive MLSB phenotype, 42.6% the M phenotype and 14.8% the inducible MLSB phenotype. Azithromycin showed a high activity against S. pneumoniae Ery-S strains, with MIC values ranging from leqslant R: less-than-or-eq, slant 0.03 to 0.5 mg/L. The Ery-R isolates were all resistant to azithromycin (MICs geqslant R: gt-or-equal, slanted 8 mg/L). On the contrary, both Ery-S and Ery-R streptococci isolates were homogeneously susceptible to telithromycin, with MIC values leqslant R: less-than-or-eq, slant 1 mg/L, according to CLSI. Telithromycin and azithromycin MBC values were generally higher than the corresponding MICs, reflecting the same trend observed for MIC values for all the strains.

Conclusion: The uniform activity of telithromycin against S. pneumoniae, including Ery-R isolates, suggests that this ketolide may offer a valuable alternative for treatment of streptococcal infections. Furthermore, in addition to several other reports, even the findings from this regional study, emphasize that an active surveillance of phenotype distribution and antibacterial resistance in pneumococci is essential to guide the effective use of empirical treatment option for streptococcal infections.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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