What organisms commonly cause lower UTIs?
June 19th, 2011 | 
Author: Escherichia coli causes most (up to 80%) of the community-acquired uncomplicated UTIs, with Klebsiella, Enterobacter, and Proteus organisms more likely to cause complicated or hospital-acquired UTIs. These are all gram-negative organisms that usually originate from the patient’s own gastrointestinal flora. There are, however, several gram-positive organisms that occur as urinary pathogens. Staphylococcus saprophyticus, a coagulase-negative Staphylococcus organism, causes 20% or more of the UTIs in women 16 to 35 years of age. Streptococcus faecalis causes 2% to 3% of the UTIs in otherwise healthy young women. When Staphylococcus aureus is found in the urine, a bacteremic infection of the kidney should be suspected.
Chlamydia, Ureaplasma, Mycoplasma, and Neisseria gonorrhoeae are sexually transmitted pathogens that usually cause vaginal or cervical infections; however, they may be implicated in cases of acute urethral syndrome in which Gram’s-stained urine samples exhibit pyuria without bacteriuria.
Pseudomonas and Serratia are more commonly nosocomial gram-negative pathogens that are not usually seen in community-acquired, uncomplicated UTIs.