Urine Culture, Prenatal, With Group B Streptococcus Susceptibility Reflex

A single culture is about 80% accurate in the female; two containing the same organism with count of 10⁵ or more represents 95% chance of true bacteriuria; three such specimens mean virtual certainty of true bacteriuria.² If the patient is receiving antimicrobial therapy at the time the specimen is collected, any level of bacteriuria may be significant. When more than two organisms are recovered, the likelihood of contamination is high; thus, the significance of definitive identification of the organisms and susceptibility testing in this situation is severely limited. A repeat culture with proper specimen collection, including patient preparation, is often indicated. Cultures of specimens from Foley catheters yielding multiple organisms with high colony counts usually represents colonization of the catheter and not true significant bacteriuria. Most laboratories limit to two the number of organisms that will be identified when recovered from urine. Similarly, most do not routinely perform susceptibility tests on isolates from presumably contaminated specimens. Failure to recover aerobic organisms from patients with pyuria or positive Gram stains of urinary sediment may indicate the presence of mycobacteria or anaerobes.