[Antibiotic resistance of Streptococcus pneumoniae and Streptococcus pyogenes in 1996-2009].

STUDY OBJECTIVES

To analyze trends in the resistance of Streptococcus pneumoniae to penicillin and macrolides and of S. pyogenes to macrolides over a 14-year period and to determine serotypes and molecular characteristics in a selected group of S. pneumoniae strains resistant to these antibiotics.

MATERIAL AND METHODS

Susceptibility to antibiotics was tested by the participating laboratories by the disk diffusion method in isolates of both bacterial species from the lower and upper respiratory tract from 1996-2009. The National Reference Laboratory for Antibiotics (NRL/ATB) determined the minimal inhibitory concentrations of penicillin and erythromycin for invasive pneumococcal isolates from 2000-2009 and performed multilocus sequence analysis of selected resistant strains.

RESULTS

Over the 14-year period monitored, penicillin resistance of S. pneumoniae isolates from the upper and lower respiratory tract showed a slightly downward trend similarly to blood isolates monitored since 2000. Resistance to macrolides in S. pneumoniae isolates was lower than penicillin resistance, regardless of the sample origin until 2005, but became higher than penicillin resistance in 2006 to follow a continuously upward trend since then. In 2009, the penicillin resistance rates of S. pneumoniae isolates from the upper respiratory tract, lower respiratory tract and blood were 3.5%, 5.1% and 4.7%, respectively, while the respective erythromycin resistance rates reached 8.4%, 12.2% and 5.5%. When using the new clinical breakpoints for pneumococci from pneumonia cases depending on penicillin dose and administration interval, only two (0.1%) of 1528 strains from the blood were confirmed as penicillin resistant (MIC 4 mg/l). Resistance of S. pyogenes to macrolides, reported in 16.5% of strains in 2001, sharply decreased to 9% in 2003 as a result of an intervention to promote the use of penicillin for the treatment of tonsillopharyngitis, and reached 11.1% in 2009. Among penicillin resistant strains of S. pneumoniae, the spread of clone Spain9V-3 (ST156) was confirmed, and among S. pneumoniae strains resistant to erythromycin alone, the spread of clones Poland6B-20 (ST315) and England9V-14 (ST9) was found.

CONCLUSIONS

The favourable low prevalence of penicillin resistance among S. pneumoniae strains, which in addition is negligible in the light of the new clinical breakpoints for penicillin resistance in strains from patients with pneumonia, contrasts with the ever increasing resistance of this species to macrolides. The highest rates of resistance to macrolides found in the strains isolated mainly from the sputum of adult patients confirm the preference for macrolides over the drugs of choice amoxicillin or penicillin G in the treatment of adults with pneumococcal pneumonia. Further spread of successful multiresistant clones of S. pneumoniae, the presence of which has been revealed in the Czech Republic, can only be prevented by a radical reduction in overuse or misuse of antibiotics.