Are Pneumococci Resistant to Macrolides ?

Abstract

Background: Streptococcus pneumoniae is the most common cause of acute community-­acquired pneumonia and accounts for 30‑40% of lower respiratory tract infections. It accounts also for about 50% of hospital-acquired pneumonia. Macrolides remain the primary antibiotic of choice for physicians treating such infections. Macrolide resistance in Strept. pneumoniae is primarily due to two mechanisms; target site modification (encoded by the erm (B) gene) and efflux pump expulsion (encoded by the mef gene). Objectives: The aim of this study was to identify the incidence of Strept. pneumoniae among acute and chronic otitis media cases; to perform the antimicrobial sensitivity tests for such isolates, to determine the percentage of Strept. pneumoniae resistant to erythromycin, clarithromycin and azithromycin, to assess the antibiotic susceptibility profile of macrolide-resistant Strept. pneumoniae and lastly to detect the frequency of common macrolide resistant genes (The mefE and ermB genes) among erythromycin resistant Strept. pneumoniae by PCR technique. Methodology: 317 patients suffering from acute or chronic otitis media, attended to pediatric and ENT- Outpatient Clinics at Al- Azhar University Hospital of Assiut, were isolated and tested for Strept. pneumoniae and for antibiotics sensitivity pattern. Resistant strains for erythromycin, clarithromycin and azithromycin were assayed for MIC using E test. PCR for erm(B) and mef(E) resistant determinant genes by multiplex PCR was applied. Results: 78 (24.6%) isolates of Strept. pneumoniae were isolated. Of them 66 and 12 isolates from acute and chronic otitis media respectively. Cefoperazone was the most sensitive drug, followed by Cefotaxime, Azithromycin and Amoxacillin-clavulanate. Tetracyclin was the most resistant drug followed by Clindamycin and Apramycin. The E- test confirmed the results of disc diffusion test. By PCR, 10 (41.7%) isolates have both erm B and mef E genes, while 8 (33.3%) isolates have mef E gene only and 2 (8.3%) isolates showed erm B gene only. Conclusion: There is a high prevalence of erythromycin resistant Strept. pneumoniae. So macrolides cannot be recommended for the treatment of pneumococcal infections without susceptibility testing. Results point to the importance of detection of erm B and mef E genes for epidemiological aspects and to track possible presence of macrolide resistance.