In vitro activity of telithromycin against erythromycin-susceptible and resistant pneumococci

Abstract number: 1134_02_422

Poulakou G., Katsarolis I., Matthaiopoulou I., Panagopoulos P., Avlamis A., Antachopoulos C., Sofianou D., Skevaki C., Kazantzi M., Ftika L., Papatolis V., Kastrisiou E., Pangalis A., Konstantopoulos K., Koubaniou C.,  H.

Objectives:

To assess the in vitro activity of telithromycin (TEL) against erythromycin-sensitive (Ery S) and resistant (Ery R) isolates of Streptococcus pneumoniae isolated from the nasopharynx of healthy children in Greece 2004.

Methods:

The strains studied were isolated by nasopharyngeal sampling in healthy children, aged 2–6 y, attending day-care centres and were collected during a nation-wide surveillance study for the susceptibility of pneumococci. Ery MICs were determined by E-test according to NCCLS methodology. TEL MICs were determined by agar dilution. NCCLS breakpoints (Jan 2004) were applied for Ery and TEL: for susceptibility (0.5 and 1 mg/L, respectively; >=1 and 4 mg/L for resistance. For macrolide resistance phenotype, the double disk diffusion test was used and 3 phenotypes identified: M, constitutive and inducible MLSB (cMLSB and iMLSB, respectively).

Results:

Of the 275 strains studied, 76 were Ery S and 159 were Ery R. All strains but two (MIC 4 and 8 mg/L) were susceptible to TEL. In particular, results for telithromycin for the Ery S strains, showed an MIC range for TEL between 0.008–0.5, with MIC50 of 0.015 and MIC90 of 0.06. For Ery R in total, MIC50 and MIC90 were 0.125 and 0.5 (range 0.008–8). With respect to macrolide resistance phenotype, the distribution per type was: M 54.5% (Ery MIC range 1–32), and cMLSB and iMLSB (Ery MIC range 4 to (256) 39% and 6.5% respectively. The two strains resistant to TEL displayed the cMLSB phenotype (Ery MIC ( 256). For each different macrolide resistance phenotype, MIC50/MIC90 of TEL had the following values: M phenotype 0.25/0.5 – cMLSB 0.06/1 – iMLSB 0.03/0.06.

Conclusions:

TEL is active against both Ery S and R strains, irrespective of macrolide resistance mechanisms, although MICs for resistant strains are higher. This finding along with the very low-level of pneumococci resistance to TEL (<1%), in accordance to other European and global surveillance data, render TEL an alternative potent agent for the treatment of respiratory tract infections caused by pneumococci, especially in the setting of macrolide resistance.