[Antimicrobial susceptibility and serotype distribution of streptococcus pneumoniae isolates in children in Tunis]

Streptococcus pneumoniae is a major causative agent of severe infectious diseases. More than 90 pneumococcal serotypes are known, although most invasive and noninvasive diseases are associated with a much smaller number of serotypes. The aim of this study was to determine the antimicrobial susceptibility of S. pneumoniae isolates in children, the distribution of serogroups and serotypes, and the coverage by the serotypes included in the seven-valent pneumococcal conjugate vaccine toward pneumococcal disease. This study investigated 210 nonrepetitive isolates of S. pneumoniae isolated between 1998 and 2004. Antimicrobial susceptibility was tested using the disk diffusion method as determined by the CA-SFM guidelines. Penicillin susceptibility was determined using the oxacillin 5-microg disk screening test. The MICs of penicillin G, amoxicillin, and cefotaxime were determined using the E-test (ABBIODISK). Serotype was determined using rapid latex agglutination (Pneumotest Latex) and the capsular reaction test used antisera from the Staten Serum Institute. The evaluation of susceptibility to ss-lactamins showed that 52.8% of the strains were penicillin non susceptible strains (PNSs), 16.6% had decreased susceptibility to amoxicillin, and 8.5% to cefotaxime. Among noninvasive isolates, 55.2% were PNSs and 50.4% were invasive PNSs. The PNS strains were more frequently resistant to other antibiotics, with 68.4% resistance to erythromycin, 44.1% to trimethoprim-sulfamethoxazole, and 9.9% to chloramphenicol versus 32.3, 11.1, and 1%, respectively, in penicillin-susceptible strains. The predominant serogroups/serotypes of our study were 14 (22%), 23 (14.3%), 19 (11.9%), and 4 (8.5%). The study of the vaccine serotype distribution showed that the theoretical vaccinal coverage of the seven valent vaccines was 62.8% for all the isolates, 55.2% for the invasive isolates, and 67.9% for the PNSs.