Bacteria can be categorized into two main groups, Gram (+) and Gram (-) bacteria, by Gram staining methods, based on the different components of the cell wall of the bacteria. Depending on the nature of the Gram stain of the bacteria, the identification of the bacteria can be narrowed down, which is conducive to the further isolation and identification of the bacterial category, and to make a diagnosis of the disease. Gram (+) bacteria and Gram (-) bacteria, also show different sensitivity to antibiotics. Generally Gram (+) bacteria are highly sensitive to penicillins, 1st generation cephalosporins, 2nd generation cephalosporins, vancomycin, clindamycin, etc.; Gram (-) bacteria are mainly sensitive to 3rd generation cephalosporins, aminoglycosides, carbapenems. The pathogenicity of Gram (+) bacteria and Gram (-) bacteria is also different, Gram (+) bacteria mainly produce exotoxin, Gram (-) bacteria produce endotoxin.