Bacterial croup includes laryngeal diphtheria, bacterial tracheitis, laryngotracheobronchitis, and laryngotracheobronchopneumonitis. "Corynebacterium diphtheriae" causes laryngeal diphtheria; bacterial tracheitis, laryngotracheobronchitis, and laryngotracheobronchopneumonitis come from a virus infection, followed by a bacteria infection. The most common bacteria that cause croup are"Staphylococcus aureus", "Streptococcus pneumoniae", "Hemophilus influenzae", and "Moraxella catarrhalis".