A urine culture is a common laboratory test used to identify the specific type of bacteria causing a urinary tract infection (UTI). When this test returns a result of “mixed urogenital flora,” it often causes confusion for the patient, as it does not clearly confirm or rule out an infection. This specific finding suggests that multiple types of microorganisms are present in the collected sample. Understanding this result requires a look at the components of the phrase and the common cause behind it.
Decoding the Terminology
“Urogenital flora” refers to the diverse community of microorganisms, primarily bacteria, that naturally live on the skin and mucosal surfaces near the urethra and genital area. These organisms are normal residents and do not typically cause infection in the urinary tract itself. This flora includes species like Lactobacillus and certain types of Staphylococcus and Corynebacterium that help maintain a healthy microbial balance.
A urine “culture” is a laboratory process where a sample is placed onto a growth medium to identify bacteria. This test is designed to isolate a single, dominant type of bacteria at a high concentration, which indicates a true UTI. The term “mixed” means that multiple different types of bacteria, usually three or more, are growing, and none is clearly dominant.
The lab report indicates a blend of bacteria instead of isolating a single pathogen. When no single organism is present at high levels, such as 100,000 colony-forming units per milliliter (CFU/mL), the result is less likely to represent a straightforward infection.
The Role of Sample Contamination
The most frequent reason a urine culture is reported as “mixed urogenital flora” is contamination of the specimen during the collection process. When urine is voided, it passes by the skin and mucosal surfaces surrounding the urethra, where the normal urogenital flora resides. If the area is not properly cleansed before collection, these harmless surface bacteria can be inadvertently washed into the collection cup.
Contamination invalidates the test by introducing multiple, non-pathogenic organisms into the sample. The presence of multiple organisms at a low concentration, often less than 10,000 CFU/mL, is a strong indicator of an improperly collected sample. The lab cannot distinguish a low concentration of a true pathogen from the high presence of multiple, non-infectious organisms picked up from the skin. The presence of epithelial cells, which are shed from the skin, often supports the conclusion that the specimen was contaminated.
This result means the test failed to capture a clean sample of urine directly from the bladder, preventing the isolation of a single, high-concentration organism that would confirm a true UTI. While a true polymicrobial infection can occur, contamination is far more common in the general population. Such infections are usually limited to patients with long-term catheters or other complex urological issues, meaning the mixed flora result typically points to a collection error.
Clinical Interpretation and Follow-Up
The clinical significance of a “mixed flora” result is dependent on whether the patient is experiencing symptoms of a UTI. If a patient is asymptomatic (no burning sensation, increased frequency, or pain), the mixed flora result is generally disregarded. No treatment is necessary, and the finding is acknowledged as a contaminated sample. Treating an asymptomatic, contaminated sample with antibiotics is discouraged by medical guidelines to avoid unnecessary medication use and antibiotic resistance.
If the patient is symptomatic, exhibiting classic signs of a UTI, the doctor cannot rely on the contaminated culture to guide treatment. The presence of symptoms suggests a possible infection that the sample failed to capture accurately. The typical follow-up is to request a repeat urine sample collected using the proper “clean catch” technique to minimize external contamination.
In cases where symptoms are severe or the patient is at risk for complications, a physician may start empirical treatment before repeat culture results are available. The goal is to differentiate common contamination from a rare, true polymicrobial infection. A true infection is usually confirmed by finding a high concentration of a single organism, or consistently finding the same mix of organisms in multiple, properly collected samples.
How to Obtain a Clean Catch Sample
To prevent contamination and ensure an accurate urine culture result, a proper “midstream clean catch” technique must be followed. This method is specifically designed to minimize the introduction of external urogenital flora into the sample cup. The process begins with thoroughly washing the hands with soap and water to remove surface bacteria.
The following steps should be taken to obtain a clean catch sample:
- Clean the genital area with the provided towelettes to reduce normal flora surrounding the urethra. For females, separate the skin folds and wipe from front to back, using a fresh wipe for each pass. For males, wipe the tip of the penis and retract the foreskin if uncircumcised.
- Begin urinating a small amount into the toilet first; this flushes out residual bacteria from the end of the urethra.
- While the stream is flowing, place the cup into the path to collect the “midstream” sample, filling it about halfway.
- Void the remaining urine into the toilet, and secure the lid onto the cup without touching the inside of the container.