<prompt> In a patient of orbital cellulitis, micro organism on culture show greenish colonies and optochin sensitivity. The most likely organism is :Strep. viridansStaphylococcusPseudomonasPneumococcus  <response>: Pneumococci is optochin sensitive and forms green colonies on blood agar due to Α hemolysis.Characteristic features of Pneumococci :Bile soluble, optochin sensitiveInulin fermenterCapsulated, shows quellung reactionColonies show central umbonation, appear as draughtsmann or carrom coinMC causative agent of lobar Pneumonia, Adult meningitis, otitis media, sinusitis orbital cellulitis is complication of sinusitis. 