Antimicrobial resistance in invasive and colonising Streptococcus pneumoniae in North India

The present study was done to detect the antibiotic resistance in S. pneumoniae. One hundred twenty S. pneumoniae isolates from clinical specimens and 50 from nasopharyngeal sites were subjected to antimicrobial susceptibility testing by Kirby Bauer disk diffusion method and minimum inhibitory concentration (MIC) determination for penicillin and cefotaxime non-susceptible isolates. A total of 22 isolates (18.3%) from clinical sites and eight (16%) from nasopharyngeal sites showed decreased susceptibility to penicillin by oxacillin disk diffusion test. MICs of 26 of these resistant strains ranged from 0.12-1 microg/mL (intermediate resistance) by broth dilution and E test. Only four isolates, two from sputum and two from nasopharyngeal swabs, showed MIC of 2 microg/mL (complete resistance). However, MIC of two cefotaxime resistant isolates (by disk diffusion) was in the susceptible range (0.5 microg/mL). Highest antimicrobial resistance was seen to cotrimoxazole (55.2%) and tetracycline (61.2%). Antimicrobial resistance to cotrimoxazole and tetracycline was much more in clinical isolates than colonizing isolates. Multi-drug resistant phenotype was detected in 76.9% (20 of 26) of isolates that were intermediately sensitive to penicillin and 50% (2 of 4) of penicillin resistant isolates (co-resistant to tetracycline and cotrimoxazole). Routine screening for antibiotic susceptibility is recommended for clinical isolates of pneumococci. Strains with reduced susceptibility to penicillin should be subjected to MIC determination to detect relative resistance or true resistance as such strains are associated with increased virulence. The choice of antibiotics should be guided by the prevalence of local resistance patterns of pneumococci.