Streptococcus pneumoniae (pneumococcus), Gram stain morphology
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The pneumococcus is a Gram positive diplococcus. Like all streptococci, it will occasionally form head-to-tail chains of organisms. Around some organisms in this field, you may be able to discern a halo. This is indicative of capsule formation. The capsule provides a survival advantage to the pneumococcus, and is perhaps why it survives in the lung and causes lobar pneumonia following aspiration, whereas other mouth flora apparently do not.