The sputum specimen of a 70 year old male was cultured on a 5% sheep blood agar. The culture showed the presence of a-haemolytic colonies next day. The fuher processing of this organism is most likely to yield -

Ans. is 'b' i.e., Gram positive cocci in pair, catalase negative and bile soluble Streptococci have been categorised into three varieties based on their growth in 5% blood agar pour plate cultures:- . In the question isolated organism is showing alpha hemolysis. Streptococci causing oc-hemolysis are ? Str. pneumoniae Viridans streptococci --> str. mutans, str. sanguis, str. salivarius, str. mitis Some strains of enterococci . Viridans streptococci and enterococci usually do not cause respiratory tract infection. . Now we are left with pneumococci only. . The fact that pneumococcus infection is predisposed by old age also ours pneumococci as causative organism in this question. So, most likely the infective organism in this question is pneumococcus which is catalase positive, bile soluble and occurs in pairs (diplococci) with broad ends in opposition presenting aflame shaped or lanceolate appearance.