Tetracycline and macrolide co-resistance in Streptococcus pyogenes: co-selection as a reason for increase in macrolide-resistant S. pyogenes?

In Denmark, tetracycline resistance in Streptococcus pyogenes is frequent (>30%) whereas macrolide resistance is low (<5%). The aim of this study was to investigate the genetic background of tetracycline- and macrolide resistance in macrolide-resistant S. pyogenes (MRSP) and to investigate the correlation between the use of macrolide and tetracycline and macrolide resistance using international data. A total of 133 MRSP isolates were received at Statens Serum Institut from nine Danish clinical microbiology laboratories between. November 2000, and November 2002. The macrolide-resistance genes, erm(B), erm(A), and mef(A) were detected in 46%, 18%, and 32% of the tested MRSP isolates, respectively. In 4% of MRSP isolates, none of the MR genes were detected. Tetracycline resistance was found in 52% of MRSP. Tetracycline resistance was encoded by either tet(M) or tet(O). erm(B) and mef(A) were associated with tet(M). Sixteen different T types were detected among the 133 MRSP. Analysis of the importance of antibiotic use for development of macrolide resistance in S. pyogenes showed no correlation with macrolide use alone (p = 0.15) but a significant correlation (p = 0.03) for the combination of macrolide and tetracycline use. The frequency of macrolide resistance in Danish S. pyogenes was low and mainly due to erm genes. A high frequency of macrolide-tetracycline coresistance in S. pyogenes is found in many countries including Denmark, hence tetracycline use must be considered as a co-factor in selection of MRSP.

Nasopharyngeal pathogens in children with acute otitis media in a low-antibiotic use country.

OBJECTIVE: Acute otitis media (AOM) is one of the most common diseases of childhood. Knowledge, of which bacteria are the most common pathogens in AOM and their susceptibilities towards antibiotics, is essential for the reasonable empiric treatment. With rapidly increasing frequencies of antibiotic resistance surveillance of the common etiologic pathogens has become pertinent. The purpose of this paper is to present the bacteriological findings and antibiotic susceptibilities, in cultures from nasopharyngeal swabs, in Danish children with AOM. METHODS: Children aged up to 10 years who had AOM diagnosed in general practice in Denmark were swabbed in nasopharynx, cultures were incubated and susceptibility testing was performed as tablet diffusion and minimal inhibitory concentrations (MICs) were determined by E-test. RESULTS: We included 331 patients, in 257 bacteria were found, which could be classified as commonly ear pathogenic. The most frequent bacteria found was Streptococcus pneumoniae followed by Haemophilus influenzae and Moraxella catarrhalis. Ninety-six percent of the tested S. pneumoniae were susceptible towards penicillin and 99% towards erythromycin. Eighty-nine percent of the H. influenzae were susceptible to ampicillin and all tested M. catarrhalis were susceptible towards erythromycin. In more than 30% of H. influenzae MIC of phenoxymethylpenicillin were above the level that could be achieved in middle ear fluid. CONCLUSION: Antimicrobial resistance is still infrequent in pathogens that might cause AOM in children in Denmark; this is probably due to minimal use of antibiotics as well as the use of phenoxymethylpenicillin as primary drug for treatment of AOM. Phenoxymethylpenicillin and azithromycin are not efficient for treating the majority of infections due to H. influenzae.