A urine culture is a common diagnostic test performed to identify bacteria in a urine sample, often when a healthcare provider suspects a urinary tract infection (UTI). This test helps pinpoint the specific type of bacteria causing an infection, guiding appropriate treatment. However, results can sometimes be unclear, and “mixed flora” is one such finding that can cause confusion. Understanding this term is important for patients reviewing their results.
Understanding Mixed Flora
“Mixed flora” in a urine culture indicates the presence of multiple different types of bacteria growing in the collected urine sample. This finding most commonly occurs due to contamination of the sample during collection. Bacteria that naturally reside on the skin, around the genitals, or near the rectum can accidentally enter the urine sample as it is being collected.
The human bladder and urine are typically sterile. However, external areas, particularly around the urinary opening, are home to diverse microorganisms. When a urine sample is collected, especially through the standard “clean-catch” method, these external bacteria can inadvertently mix with the urine, leading to a “mixed flora” result.
Interpreting Your Result
Interpreting a “mixed flora” result primarily distinguishes between contamination and a true urinary tract infection. Mixed flora often suggests sample contamination, especially if the patient is not experiencing common UTI symptoms. Common UTI symptoms include painful urination, frequent urges to urinate, a feeling of urgency, lower abdominal discomfort, or even fever.
If a urine culture shows significant growth of a single type of bacteria, this is more indicative of a true infection. For example, a colony count exceeding 100,000 colony-forming units per milliliter (CFU/mL) of a single organism typically suggests a significant UTI. While some mixed bacteria might be present in lower numbers, a dominant single organism strongly points to an infection. Conversely, if multiple organisms are present at lower counts, such as 10,000 to 25,000 CFU/mL, it often indicates contamination unless specific symptoms are present. Healthcare providers evaluate these results in conjunction with a patient’s symptoms and the specific types and quantities of bacteria identified.
What Happens Next
After receiving a “mixed flora” result, your healthcare provider will assess it considering your overall health and symptoms. If you have no UTI symptoms and contamination is suspected, the provider might recommend no immediate treatment. In such cases, a re-test with careful attention to collection instructions is advised to obtain a cleaner sample.
However, if you are experiencing UTI symptoms, or if a true infection is suspected despite the “mixed flora” label, further action may be necessary. This might involve ordering a repeat urine culture, considering empiric antibiotic treatment, or conducting additional investigations. To minimize contamination in future tests, proper urine sample collection techniques, such as the midstream clean-catch method, are important. This method involves cleaning the genital area and collecting the middle portion of the urine stream in a sterile container, helping to ensure the sample accurately reflects the bacteria within the bladder.