From the Guidelines
A urine culture showing mixed flora typically indicates contamination of the sample rather than a true urinary tract infection (UTI). This result means multiple bacterial species were detected, which usually happens when skin or genital bacteria enter the sample during collection 1. No antibiotic treatment is recommended based solely on this result. Instead, proper collection technique should be used for a repeat urine sample. For accurate collection, thoroughly clean the genital area with antiseptic wipes, collect a midstream sample (urinate briefly into the toilet first, then collect the middle portion of urine in the sterile container), and avoid touching the inside of the container.
Key Considerations
- If you have UTI symptoms like burning with urination, frequency, urgency, or lower abdominal pain, inform your healthcare provider as they may consider empiric antibiotic treatment while awaiting new culture results 1.
- Mixed flora results are common and don't necessarily indicate infection, as normal urine should be sterile.
- Proper sample collection is crucial for accurate diagnosis and appropriate treatment of urinary tract conditions.
Collection Methods
- Midstream clean-catch collection is preferred for most patients, but other methods like catheterization may be necessary in certain cases 1.
- Contamination rates vary by collection method, with midstream clean-catch having lower contamination rates compared to other methods 1.
Clinical Guidelines
- The American Urological Association (AUA) and other organizations provide guidelines for the diagnosis and treatment of urinary tract infections, including recommendations for urine culture collection and interpretation 1. In summary, a mixed flora result on a urine culture should be interpreted with caution, and a repeat sample should be collected using proper technique to ensure accurate diagnosis and treatment.
From the Research
Urine Culture Mixed Flora
- Urine cultures that contain more than one organism are usually considered contaminated, but the frequency with which such growth truly represents mixed infection is unknown 2
- The clinical significance of polymicrobial growth from urine can be demonstrated by recovering the same combination of microorganisms from blood and urine, or by the reproducibility of the same mixture of bacteria from sequential urine cultures 2
- In certain clinical settings, polymicrobial bacteriuria is not only frequently significant but its overall clinical impact seems to be substantial, particularly in cases of long-term catheterization 2
Clinical Significance and Treatment
- Bacteriuria associated with long-term catheterization is predominantly polymicrobial, and symptomatic urinary tract infection is a common outcome of such bacteriuria, which has been associated with increased risk for bloodstream infections and excess mortality 2
- Early species identification and antimicrobial susceptibility testing of each urinary isolate may be of paramount benefit to the care of these patients 2
- Amoxicillin-clavulanate may be a useful alternative therapy for the treatment of ceftriaxone non-susceptible Enterobacterales UTIs 3
- Prior antibiotic exposure, particularly to amoxicillin-clavulanate or fluoroquinolones, is a significant risk factor for the development of amoxicillin-clavulanate resistance in E. coli and K. pneumoniae urinary isolates 4
Diagnosis and Prediction
- The predictive value of a prior culture in guiding empirical prescribing for recurrent urinary tract infections can be quantified using test metrics such as sensitivity, specificity, and Bayes' positive and negative predictive values 5
- Prior cultures can have good predictive value for detecting future susceptibility to first-line agents, and excellent predictive values for certain antibiotics 5
- Urinary concentrations and bactericidal activity of amoxicillin-clavulanate against amoxicillin-nonsusceptible strains of E. coli can be determined in healthy volunteers, and may inform treatment decisions 6