It is possible for a gram negative bacteria infection to be not only serious but life-threatening, according to the Centers for Disease Control and Prevention. One type of gram negative bacteria is Yersinia pestis, which caused the plague that wiped out much of Europe in the 14th century.
Another gram negative bacteria is the Brucella bacteria, notes HighVeld. This bacteria causes brucellosis in both humans and cattle, explains the CDC. The initial symptoms of the disease are fever, sweats, loss of appetite and a general feeling of malaise. Some symptoms recur or never resolve. These are endocarditis, arthritis, swelling of the scrotum and fevers. Patients also suffer recurrent depressions, fatigue, and swelling of the spleen, liver or both.
Other potentially dangerous gram negative bacteria are Escherichia coli, which causes urinary tract infections, and Pseudomonas aeruginosa, which infects the blood of hospital patients and is a leading cause of pneumonia in cystic fibrosis sufferers, reports the National Institute of Allergy and Infectious Diseases. Neisseria gonorrhoeae causes gonorrhea, and Vibrio cholerae causes cholera.
Gram negative bacteria are dangerous because they are difficult to combat, notes the National Institute of Allergy and Infectious Diseases. Their cell walls resist antibiotics, and they develop resistance to new antibiotics fairly quickly. Medical personnel sometimes resort to treating patients with older types of antibiotics, which can have serious side effects.