Bacteria That Cause Urinary Tract Infections

iComstock/Stockbyte/Getty Images

According to Maxwell Meng, M.D., Associate Professor at the University of California in “Current Medical Diagnosis & Treatment,” it is quite common for physicians to see urinary tract infections. Thus, medical students have found an easy way to remember the main bacteria that cause them. They do so by memorizing the phrase “SEEKS PP.” Each letter stands for the name of a bacterium.

Staphylococcus Saprophyticus

Microbiologists can classify bacteria by using a staining process called a gram stain. S. saprophyticus is called gram positive, because it keeps the first stain used during this staining process. It is also cocci or has a round shape. In “Review of Medical Microbiology and Immunology,” Warren Levinson, M.D., Ph.D., Professor of Microbiology at the University of California writes that this bacterium remains the second most common cause of urinary tract infections (UTIs) in young women.

Escherichia Coli

E. coli is a gram negative rod because it does not keep the first stain in the staining process. It has a rod shape. This bacterium proves the most common cause of UTIs. It lives in the large intestines, but since the urethra is close to the anus, it can reach the urethra. From there, it will ascend to the bladder, cause an infection there and continue migrating upward. Women prove more susceptible than men because their urethra is much shorter. The female urethra is 1 to 2 inches long. A male urethra is 7 to 8 inches. Thus, E. coli has a shorter distance to travel in the female urethra.


Also listed gram negative rods, several species of Enterobacter exist, but E. aerogenes and E. cloacae cause most of the infections. Thomas Russo, M.D., Professor of Medicine and Microbiology at the State University of New York writes in “Harrison’s Principles of Internal Medicine,” that most UTIs caused by Enterobacter come from contaminated catheters.


According to Burke Cunha, M.D., Professor of Medicine at the State University of New York School of Medicine in “The Merck Manual for Healthcare Professionals,” Klebsiella shares similarities with Enterobacter. This gram negative rod and most of the UTIs that it causes, also result from contaminated catheters.


Dr. Levinson writes in “Review of Medical Microbiology and Immunology,” that this gram negative rod bacterium exists in water, soil and the large intestines. The UTIs that occur because of Serratia infections usually result from urinary tract procedures performed in the hospital.


Proteus is a gram negative rod bacterium found in the water, soil and the large intestines. In “Review of Medical Microbiology and Immunology,” Dr. Levinson explains that Proteus causes UTIs in the same way that E. coli does. But Proteus also proves a very mobile bacterium, which helps it to ascend the urinary tract. In addition, it has an enzyme called urease. The enzyme makes the urine less acidic. That type of environment proves more favorable to Proteus and also leads to the formation of kidney stones.


This gram negative rod can cause infections in people who have an impaired immune system. One of the infections that it causes occurs because of a UTI by contaminating a catheter. But once it causes the infection, it will enter the bloodstream and spread to the skin.