From the Research
For genitourinary tuberculosis (TB) diagnosis, Middlebrook 7H11 agar medium is the most reliable culture medium, as it has been shown to have lower contamination rates and higher reliability in determining the presence or absence of M. tuberculosis compared to Löwenstein-Jensen medium 1.
Key Points for Genitourinary TB Culture
- Specimens should be collected as first-void morning urine samples on three consecutive days, decontaminated with N-acetyl-L-cysteine-sodium hydroxide, concentrated by centrifugation, and then inoculated onto the medium.
- Cultures typically require 3-8 weeks of incubation at 37°C for visible growth on solid media, while liquid culture systems like BACTEC MGIT can provide faster results (10-14 days) 2.
- Liquid media contain modified Middlebrook 7H9 broth with growth supplements and are more sensitive than solid media.
- For optimal diagnosis, both solid and liquid media should be used concurrently, as M. tuberculosis from genitourinary sites often grows slowly and may be present in low numbers.
- Drug susceptibility testing should follow positive cultures to guide appropriate treatment.
Comparison of Culture Media
- Middlebrook 7H11 agar medium has been shown to be more reliable than Löwenstein-Jensen medium in determining the presence or absence of M. tuberculosis, with lower contamination rates 1.
- MB BACT has been shown to be a better medium than Löwenstein-Jensen and Middlebrook 7H10 in terms of the number of isolates and isolation rate, with an average isolation time of 18.70 days compared to 30.81 days for Löwenstein-Jensen and 31.06 days for Middlebrook 7H10 3.
- BACTEC 460TB liquid medium has been shown to give a higher yield than Löwenstein-Jensen medium in abdominal tuberculosis, with a 64% increment in yield 2.