A 71 year old female presents with fever, chills, difficulty in breathing and productive cough. She also complaints of left sided chest pain. Physical examination shows, increased VF, dullness to percussion, decreased bronchial sounds. Chest X-ray shows left lower lobe consolidation. Culture grows organisms that are catalase negative and shows positive Quellung reaction. Gram staining of organism is

Answer: a) Gram positive diplococcus (PANIKER 9th EDITION P-223)> History, Physical examination and Chest X-ray suggest pneumonia> Catalase negative organism showing positive Quellung reaction indicates Streptococcus pneumoniae Gram positive cocci Catalase positive-StaphylococciCatalase negativeCoagulase positiveCoagulase negative(CoNS)Streptococci* Staph, aureusNovobiocin susceptible* Staph.epidermidis* Staph, haemolyticus* Staph.hominisNovobiocin resistant* Staph. saprophyticus* Staph.xylosusPneumococciSTREPTOCOCCUS PNEUMONIAE (PNEUMOCOCCI)* Capsulated, flame shaped or lanceolate diplococci* MCC of lobar pneumonia, sinusitis, otitis media* MCC of bacterial meningitis in adults* Culture - Draughtsman or carom coin appearance* Ferments inulin - tested on Hiss's serum sugars* Quellung reaction - capsular swelling when mixed with type specific antisera and methylene blue* Virulence factors - capsular polysaccharide or specific soluble substance(SSS), pneumolysin* Type 3 pneumococci is most virulent as it contains abundant capsular material* Oxygen labile hemolysin and leucocidin make no contributions to virulence* Biomarkers- CRP, Procalcitonin (both elevated in invasive pneumococcal disease)* Splenectomy and sickle cell disease are important predisposing conditions for infection