| Infections caused by gram-negative bacteria Overview of Gram-Negative Bacteria Bacteria are classified by how they appear under the microscope and by other features. Gram-negative bacteria are classified by the color they turn after a chemical process called Gram staining... read more , such as Pseudomonas aeruginosa Pseudomonas Infections Any of several types of the gram-negative bacteria Pseudomonas, especially Pseudomonas aeruginosa, can infect different parts of the body, particularly in people who have serious... read more , Escherichia coli Escherichia coli Infections Escherichia coli (E. coli) are a group of gram-negative bacteria that normally reside in the intestine of healthy people, but some strains can cause infection in the digestive... read more , and Klebsiella species Klebsiella, Enterobacter, and Serratia Infections Klebsiella, Enterobacter, and Serratia are closely related gram-negative bacteria that occasionally infect the urinary tract or respiratory tract of people in hospitals... read more | |