Antimicrobial susceptibility of select respiratory tract pathogens in Dakar, Senegal

Background : Haemophilus influenzae, Moraxella catarrhalis, Streptococcus pyogenes, and Streptococcus pneumoniae are the most common causative agents of respiratory tract infections (RTIs).  The increase in resistance to current antibacterial agents highlights the need to monitor the resistance pattern of these bacterial pathogens. Methodology: In this study, we assessed the antibacterial susceptibility of these pathogens causing respiratory tract infections in Dakar, Senegal, during 2007-2008.  A total of 290 bacterial isolates (75 H. influenzae, 10 M. catarrhalis, 105 S. pneumoniae, and 100 S. pyogenes) were collected.  Results and Conclusions: All H. influenzae isolates were susceptible to amoxicillin/clavulanic acid, ofloxacin, clarithromycin, cephalosporins, and macrolides.  Overall, 26.7% of H. influenzae isolates were completely resistant to ampicillin.  Among the M. catarrhalis isolates, 30% were resistant to ampicillin.  All the isolates of H. influenzae and M. catarrhalis that were resistant to ampicillin were beta-lactamase producing strains.  Among the S. pneumoniae isolates, 33.3% isolates exhibited intermediate susceptibility to penicillin G, and one isolate was completely resistant.  All five isolates that were resistant to erythromycin expressed the M phenotype.  S. pyogenes exhibited high susceptibility to all other antibiotics, except tetracycline.  Our study suggests that except for M. catarrhalis, all other bacterial isolates are susceptible to cephalosporins, macrolides, and fluroquinolones.