Increasing antimicrobial resistance in clinical isolates of Streptococcus pneumoniae.

The presence of antibiotic-resistant Streptococcus pneumoniae has become a major clinical problem in several parts of the world. However, there is a lack of data from Southeast Asia. We therefore initiated a study to determine the serogroups/serotypes and antimicrobial susceptibilities of clinical strains of S. pneumoniae isolated in our laboratory. In 1995, we isolated 144 strains of S. pneumoniae. Thirty-six (25.0%) strains were resistant to penicillin of which 19 (13.2%) were highly resistant (minimal inhibitory concentration > 1.0 microgram/ml). Thirty-eight (26.4%) strains were resistant to erythromycin, 75 (52.1%) were resistant to tetracycline, 48 (33.3%) were resistant to sulfamethoxazole-trimethoprim and 29 (20.1%) were resistant to chloramphenicol. Twenty of the penicillin-resistant strains also had diminished susceptibility to ceftriaxone. Strains resistant to penicillin belonged to serogroups/serotypes 6 (n = 1), 9 (n = 1), 23 (n = 4), 14 (n = 6) and 19 (n = 20). Children under 5 years of age were more likely than older children and adults to have isolates resistant to penicillin (52.9% versus 16.2%, P = 0.00002). Penicillin-resistant strains were more likely than penicillin-susceptible strains to be multidrug-resistant (86.1% versus 7.4%, P < 0.000005). We concluded that there is a high prevalence of penicillin-resistant pneumococci in our isolates especially among very young children. Most penicillin-resistant strains belong to serogroup 19 and are also resistant to multiple drugs.