Streptococcus pseudopneumoniae: an emerging respiratory tract pathogen

BACKGROUND & OBJECTIVES Streptococcus pseudopneumoniae a member of the Viridans Streptococci, is known to be associated with chronic obstructive pulmonary disease and respiratory tract infections (RTI). Very scanty information is available on the isolation of S. pseudopneumoniae from India. Hence, the present study was an attempt to isolate S. pseudopneumoniae from clinical samples and to study their drug resistance pattern. METHODS Sputum samples (n=150) submitted to the microbiology laboratory for routine culture from patients clinically suspected to have lower respiratory tract infection were inoculated onto sheep blood agar and chocolate agar plates. Alpha haemolytic colonies were identified as S. pseudopneumoniae based on absence of capsule, bile solubility and optochin susceptibility in 5 per cent CO₂ and ambient air. Disk diffusion method was used for antibiotic susceptibilily testing. RESULTS Among the samples screened, 4 per cent showed the growth of only S. pseudopneumoniae. Other pathogens isolated were Streptococcus pneumoniae, Moraxella catarrhalis, Klebsiella spp., Enterococcus spp., Pseudomonas spp., Haemophilus influenzae, Staphylococcus aureus, Candida albicans. All the S. pseudopneumoniae isolates were resistant to erythromycin. INTERPRETATION & CONCLUSIONS Our preliminary results showed presence of S. pseudopneumoniae in this part of the country and these were associated with RTI. Currently, most clinical laboratories report optochin susceptible isolates in 5 per cent CO₂ as S. pneumoniae and the resistant ones are not further tested for susceptibility in ambient air. As a result, S. pseudopneumoniae may be missed out. Hence, performance of at least two tests, viz. optochin susceptibility with incubation in 5 per cent CO₂ and ambient air along with bile solubility is necessary to differentiate S. pneumoniae from S. pseudopneumoniae.