The microbiological flora of the lower female genital tract and perineum provides a dynamic, complex example of microbial colonization, the regulation of which is not fully understood. When an exogenous bacterial species, with its array of virulence factors, is introduced into the host, disease does not always occur. Conversely, under selected conditions, commensal endogenous bacteria—for example, Gardnerella vaginalis and group B streptococci—can participate in disease processes. Disease caused by both exogenous and endogenous bacteria correlates positively with a markedly increased level of bacterial replication. The key question is what determines the quantity of a given bacterium at any given time. For disease to occur, exogenous or endogenous bacteria that possess pathogenic prerequisites must attain replicative dominance. Their ability to do so is potentially governed by inhibitory or synergistic interrelationships with other microbes.
Often these microbes contamine urine samples in a culture and leads to wrong diagnosis. A urine culture may be ordered when symptoms indicate the possibility of a urinary tract infection, such as pain and burning when urinating and frequent urge to urinate. Antibiotic therapy may be prescribed without requiring a urine culture for symptomatic young women who have an uncomplicated lower urinary tract infection. If there is suspicion of a complicated infection or symptoms do not respond to initial therapy, then a culture of the urine is recommended. A urine culture may be ordered with a urinalysis or as follow up to abnormal results on a urinalysis.
Results of a urine culture are often interpreted in conjunction with the results of a urinalysis and with regard to how the sample was collected and whether symptoms are present. Since some urine samples have the potential to be contaminated with normal flora from the skin, care must be taken with interpreting some culture results.
Typically, the presence of a single type of bacteria growing at high colony counts is considered a positive urine culture. For clean catch samples that have been properly collected, cultures with greater than 100,000 colony forming units (CFU)/mL of one type of bacteria usually indicate infection. In some cases, however, there may not be a significantly high number of bacteria even though an infection is present. Sometimes lower numbers (1,000 up to 100,000 CFU/mL) may indicate infection, especially if symptoms are present. Likewise, for samples collected using a technique that minimizes contamination, such as a sample collected with a catheter, results of 1,000 to 100,000 CFU/mL may be considered significant.
The culture media used and the method of collection are two key factor that keep contaminants away. Please get in touch with your doctor for further details.
These Q&A’s are for educational purposes and should not be relied upon as a substitute for medical advice you may receive from your physician. If you have a medical emergency, please call 911. These answers do not constitute or initiate a patient/doctor relationship.