Distinguish between bacterial pneumonia and diphtheria?

Different organisms. Cornynebacterium diphtheria produces illness via toxin that causes inflammation whereas bacterial pneumonia such as strep pneumonia or mycoplasma cause infection by multplying and causing inflmation. This is not to say that diptheria do not multiply, quit the contrary but to stabelize this infection you need antitoxin whereas with bacterial pneumonia, you attack this will antibiotics.