Changing trend in susceptibility pattern of Streptococcus pneumoniae to penicillin in India

Prior to 1995 all strains of Streptococcus pneumoniae isolated at a tertiary care hospital in south India were uniformly susceptible to penicillin. However, since late 1995 strains of S. pneumoniae with intermediate resistance to penicillin have been observed. Altogether there were 25 such isolates, 9 from invasive (5 from CSF as well as blood, 1 from pleural fluid and 3 from CSF alone) and 16 from noninvasive sites (6 from throat, 6 from sputum, 3 from eye and 1 from ear) respectively, thus 4.6 per cent of S. pneumoniae showed intermediate resistance of a total of 535 strains studied so far. The minimum inhibitory concentration (MIC) values of penicillin, erythromycin, chloramphenicol and cefotaxime were determined by agar dilution method and for confirmation, E test was carried out for penicillin alone. The MIC range obtained for penicillin was between 0.125-1.0 μg/ml. Kirby-Bauer disc diffusion method was adopted for testing of erythromycin, chloramphenicol, co-trimoxazole, cefotaxime, tetracycline and vancomycin. We observed that none of the strains with intermediate resistance to penicillin were multidrug resistant. These strains belonged predominantly to serotype 14 (n=10), 7B (n=9), 19A (n=3), 7F (n=2) and 23F (n=1). Clonality was not observed in the 5 representative strains subjected to Box A finger printing method.