Pneumonia. Coloured frontal chest X-ray of the lungs (green) of a patient with pneumonia. One of the upper lobes (yellow/brown, upper left) of the right lung has solidified. This disease was caused by the bacterium Streptococcus pneumoniae. The alveoli (the air sacs of the lungs, too small to be seen) become blocked with pus and solidify. Symptoms are coughing and chest pain. Treatment is with antibiotic drugs.