In vitro activity of macrolides against Streptococcus pneumoniae and Streptococcus pyogenes in the Russian Federation: “Status praesens”

Objective.

To evaluate in vitro activity of various macrolide antibiotics against a current collection of clinical isolates of Streptococcus pneumoniae and Streptococcus pyogenes isolated from patients with community-acquired infections in different regions of the Russian Federation.

Materials and Methods.

A total of 350 clinical isolates from patients with community-acquired infections, including 200 S. pneumoniae and 150 S. pyogenes, were included in the study. To further evaluate the in vitro activity of 16-member macrolides against erythromycin-resistant isolates (MIC ≥ 0.5 mg/L), a retrospective collection of 253 erythromycin-resistant S. pneumoniae and 112 S. pyogenes isolates was tested. Susceptibility to antimicrobials was determined by broth microdilution method in accordance with the recommendations of the European Committee on Antimicrobial Susceptibility Testing (EUCAST, v.14.0).

Results.

Resistant to 14- and 15-member macrolides erythromycin, clarithromycin, and azithromycin were 41.5%, 42% and 40.5% of S. pneumoniae isolates (MIC50/MIC90 values were 0.06/128, 0.03/128, and 0.¹²⁵⁄₁₂₈ mg/L, respectively). MIC50/MIC90 values for spiramycin and josamycin were 0.06/128 mg/L and ²⁵⁄₃₂ mg/L, respectively. When the previously used 1996 French Society for Microbiology (SFM) criteria (Ch, ≤ 1 mg/L; P, > 4 mg/L) were applied, 70.5% of S. pneumoniae isolates could be considered as susceptible to spiramycin. MIC value ≥0.5 mg/L accounted for 31.5% of isolates for spiramycin and 48% for josamycin. Among the retrospective collection of erythromycin-resistant S. pneumoniae isolates, 64.0% of isolates could be considered as resistant to spiramycin using the old SFM interpretative criteria; 74.9% of isolates had spiramycin MIC ≥ 0.5 mg/L. Among the S. pyogenes isolates, 19.3%, 22%, and 26.7% were resistant to the 14- and 15-member macrolides erythromycin, clarithromycin, and azithromycin (MIC50/MIC90 0.03/1, 0.03/2, and 0.06/8 mg/L, respectively). MIC50/MIC90 values for the 16-member macrolides spiramycin and josamycin were 0.²⁵⁄₀.5 mg/L and 0.¹²⁵⁄₀.5 mg/L, respectively. When the 1996 SFM criteria (S – ≤ 1 mg/L; R – > 4 mg/L) were applied, 94.7% of S. pyogenes isolates could be considered as susceptible to spiramycin; MIC values ≥ 0.5 mg/L had 15.3% of isolates for spiramycin and 16.5% for josamycin.

Conclusions.

The 16-member macrolide spiramycin can retain in vitro activity against a significant proportion of S. pneumoniae and S. pyogenes isolates resistant to 14- and 15-member macrolides, which should be taken into account when choosing therapy for infections caused by these microorganisms.