Selection of resistance of telithromycin against Haemophilus influenzae, Moraxella catarrhalis and streptococci in comparison with macrolides.
OBJECTIVE
The in vitro abilities of telithromycin, azithromycin and clarithromycin to select for resistance were compared by testing isolates of Haemophilus influenzae, Moraxella catarrhalis, Streptococcus pneumoniae and beta-haemolytic streptococci.


METHODS
Five strains each of beta-lactamase-positive and beta-lactamase-negative H. influenzae, beta-lactamase-positive and beta-lactamase-negative M. catarrhalis, S. pneumoniae, beta-haemolytic group A, group C and group G streptococci and three strains of beta-lactamase-negative ampicillin-resistant H. influenzae were evaluated. Development of resistance was determined by multi-step and single-step methodologies. For multi-step studies, MIC values were determined after five serial passages on antibiotic-gradient plates and after 10 serial passages on antibiotic-free plates. Acquisition of resistance was defined as an increase of >/=4-fold from the starting MIC. In single-step studies, the rate of spontaneous mutations was calculated after a passage on plates containing antibiotics at concentrations equal to the highest NCCLS breakpoints.


RESULTS
Azithromycin, clarithromycin and telithromycin gave a >/=4-fold increase in 20, 20 and 10 streptococcus strains, in 4, 5 and 0 H. influenzae strains and in 2, 7 and 4 M. catarrhalis strains, respectively. After 10 passages on antibiotic-free plates, 21/26 strains for azithromycin, 22/32 for clarithromycin and 1/14 for telithromycin maintained high MIC values. In single-step studies, the frequency of mutations was <10(-10) for H. influenzae and M. catarrhalis for telithromycin, azithromycin and clarithromycin. Telithromycin induced mutations at a lower rate than azithromycin and clarithromycin in streptococcal strains.


CONCLUSIONS
Telithromycin showed a very limited ability to select for resistance in respiratory pathogens compared with azithromycin and clarithromycin.
Drago
Lorenzo
L
Laboratory of Clinical Microbiology, Department of Clinical Sciences L. Sacco Teaching Hospital, University of Milan, Via GB Grassi 74, 20157 Milan, Italy. microbio@unimi.it
De Vecchi
Elena
E
Nicola
Lucia
L
Colombo
Alberto
A
Gismondo
Maria Rita
MR
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D017963:Azithromycin / Q000494:pharmacology; D017291:Clarithromycin / Q000494:pharmacology; D024881:Drug Resistance, Bacterial; D005787:Gene Frequency; D006193:Haemophilus influenzae / Q000187:drug effects*; D006801:Humans; D048628:Ketolides; D018942:Macrolides / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D001936:Moraxella catarrhalis / Q000187:drug effects*; D009154:Mutation / Q000235:genetics; D012141:Respiratory Tract Infections / Q000382:microbiology; D013291:Streptococcus / Q000187:drug effects*; D013296:Streptococcus pneumoniae / Q000187:drug effects
D000900:Anti-Bacterial Agents; D048628:Ketolides; D018942:Macrolides; D017963:Azithromycin; D017291:Clarithromycin; C106791:telithromycin