From the Guidelines
A moderate mixed growth on urine culture is typically considered contaminated and not indicative of a true urinary tract infection (UTI), unless the patient is symptomatic, in which case a repeat clean-catch midstream urine sample should be collected and empiric treatment may be considered. This finding often represents contamination from the skin or genital area during sample collection, with multiple bacterial species present in moderate quantities, typically between 10,000 to 100,000 colony-forming units per milliliter (CFU/mL) 1. According to the European Association of Urology guidelines, a urine culture is recommended in situations where the diagnosis is unclear, or in patients with suspected acute pyelonephritis, symptoms that do not resolve or recur after treatment, or atypical symptoms 1.
Key Considerations
- The presence of multiple bacterial species in moderate quantities may indicate contamination rather than a true UTI 1.
- A repeat clean-catch midstream urine sample should be collected after proper cleansing of the genital area if symptoms of UTI are present 1.
- Empiric treatment with nitrofurantoin or trimethoprim-sulfamethoxazole may be considered for symptomatic patients awaiting new results 1.
- Proper collection technique involves thorough cleaning of the genital area, starting urination in the toilet, then collecting the midstream portion in a sterile container without touching the inside of the container 1.
Treatment Approach
- For symptomatic patients, empiric treatment with nitrofurantoin 100mg twice daily for 5 days (for uncomplicated cases) or trimethoprim-sulfamethoxazole twice daily for 3 days may be considered 1.
- The choice of antimicrobial therapy should be guided by the spectrum and susceptibility patterns of the aetiological pathogens, efficacy, tolerability, and adverse reactions 1.
- Routine post-treatment urinalysis or urine cultures are not indicated for asymptomatic patients 1.
From the Research
Definition of Moderate Mixed Growth on Urine
- Moderate mixed growth on urine refers to the presence of more than one type of bacteria in a urine culture, with no single organism dominating the culture 2.
- This type of growth can be significant in certain clinical settings, such as in patients with long-term catheterization, where polymicrobial bacteriuria is common 2.
Clinical Significance of Mixed Growth Urine Cultures
- Mixed growth urine cultures can represent true mixed infections, and early species identification and antimicrobial susceptibility testing of each urinary isolate may be beneficial for patient care 2.
- A study found that 12.4% of urine specimens processed to detect bacterial pathogens were reported as mixed growth urine cultures, with Enterococcus species and Escherichia coli being the most frequently isolated organisms 3.
- Clinicians believe that mixed growth urine culture reports represent the detection of many commensal bacteria, but they are more likely to diagnose and treat a UTI when provided with detailed microbial analysis of mixed growth urine cultures, including identity and antibiotic sensitivity of organisms 3.
Treatment of Urinary Tract Infections with Mixed Growth
- The treatment of urinary tract infections (UTIs) with mixed growth may involve the use of broad-spectrum antibiotics, such as fluoroquinolones or cephalosporins, which are effective against a wide range of bacteria 4, 5.
- In some cases, the treatment of UTIs with mixed growth may require the use of multiple antibiotics, or the use of antibiotics that are effective against specific types of bacteria, such as ESBL-producing Enterobacteriales or carbapenem-resistant Enterobacteriales 4.