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Improving Urine Culture Results

Urine cultures are the most frequently ordered microbiology tests, reflecting the fact that urinary tract infections (UTIs) are very common. Urine cultures are essential for accurate identification of UTI pathogens because:

  • Although more than 90% of uncomplicated UTIs are caused by E. coli, a wide variety of other pathogens can also cause UTIs, including Klebsiella, Proteus, Staphylococcus, Enterococcus, etc.
  • The various pathogens associated with UTIs respond to different antibiotics and have different clinical implications.
  • In addition, urinary pathogens are rapidly developing resistance to antibiotics previously effective for UTI, and antimicrobial susceptibility testing is essential for most urinary pathogens to guide selection of effective therapy.

An old adage in clinical microbiology is that a culture is only as good as the specimen it is performed on, and this is especially true for urine cultures. Because most urine specimens pass through the urethra with its resident normal flora, specimens can become contaminated and produce useless culture results. If specimens are not collected and transported to the laboratory properly, initially small numbers of normal flora bacteria introduced into the specimen during collection may grow to large numbers. These normal flora organisms may overwhelm the pathogen and mask its presence, or they may grow along with the pathogen making interpretation of the culture result difficult.

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