![]() The time between collection and plating can be extended to 24 hours if the sample is kept refrigerated or is transported in a container with boric acid as a preservative. If the urine sample is kept at room temperature, it should be plated within 2 hours of collection. Because bacterial quantity is an important factor in assessing the potential clinical significance of any organisms present in the sample, it is important to limit bacterial growth between the time of sample collection and plating for culture. Once a urine sample has been collected, it must be transported to the laboratory. As we will see, the relative likelihood of contamination with different specimen collection methods becomes important in the clinical interpretation of urine culture results. (By contrast, the much-reviled “bagged urine” collection method sometimes used in infants, in which urine is collected in a plastic bag taped to the perineal region, may not be as prone to clinically significant contamination as is generally assumed). However, there is no way to entirely prevent the possibility of contamination, and recent evidence suggests that cleaning and using a mid-stream specimen may not actually reduce contamination at all. The midstream clean-catch approach is recommended for voided urine specimens in order to decrease the likelihood of contamination. Older children and adults who are able to do so can simply provide a “voided” urine specimen: that is, they pee in a cup. For infants, young children and others who are not able to urinate directly into a specimen container (for example, people who have a neurogenic bladder), urine can be collected using a Foley catheter, which is inserted through the urethra into the bladder this method also limits contamination. A suprapubic aspirate, in which a needle is inserted directly through thoroughly cleansed skin into the bladder, is the most effective way to avoid the risk of urogenital contamination, but this method is relatively invasive and rarely used. The bladder itself is generally considered a sterile environment (although, as we will discuss later, that isn’t always the case), but the external genitalia are colonized by commensal bacteria that can contaminate urine samples and ultimately grow in culture. One of the most important variables in the process of culturing urine is the method of collection. ![]() But what exactly happens to that urine, and the organisms that may grow from it, between the time it leaves the bladder and the time the report appears in the medical record? From the Bladder To the Cup To the Bench If you’re a clinician, you’re probably familiar with the process of requesting urine samples in patients with UTI symptoms, and equally familiar with receiving and acting on the results. (-) = non-lactose fermenters, colorless (or very faint pink) growth.Urinary tract infections (UTIs) include infections restricted to the bladder (cystitis), which are extremely common in women and may cause pain with urination, as well as more serious infections that also involve the kidneys (pyelonephritis). Green sheen = vigorous fermentation of lactose Weak fermenters will have pink mucoid growth. ![]() (+) = Lactose fermentation, dark purple colonies with dark center. K.C.Burke CC BY-NC SAĭirections: Streak agar in a straight line and incubate for 24 – 48 hours. \): Two lactose fermenters growing on EMB.
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