European Society of Mycobacteriology - Instituto Nacional de Saúde ...

PP-99
VARIOUS STRATEGIES TO DECONTAMINATE ACID FAST BACILLI
POSITIVE LIQUID CULTURES FROM BACTEC MGIT 960
Balmoi, Faith
Joint Clinical Research Centre, Kampala, Uganda
Introduction
Though liquid culture is enriched and more sensitive in the recovery of MTB, it yields a greater percentage
of contaminants as well. It is essential that MTB cultures be isolated pure to permit drug susceptibility
testing which is vital for prognosis of patients besides determining the presence of MDR-TB and XDR-TB.
In this study we evaluated various approaches to reduce or eliminate contamination in Bactec MGIT 960 cultures.
Method
Contaminated AFB PCR positive MGIT cultures were subjected to decontamination methods of:
i) Double PANTA Polymyxin B (750µg/ml); Amphotericin (75µg/ml); Nalidixixic (300µg/ml); Trimethoprim (75µg/ml) and
Azlocillin (75µg/ml)
ii) VAN vancomycin (30.5µg/ml), Amphotericin (106µg/ml) and Nalidixic acid (226.7µg/ml)
iii) 2% NaOH each contaminated culture was divided and subjected to all three decontaminating
procedures. The decontaminated cultures were then inoculated in MGIT tubes and 7H10 selective
whole plates and incubated in Bactec MGIT 960 and a 5%-10% CO2 at 37°C respectively.
The plates were read weekly until a sufficient colonial growth was achieved. The positive MGIT was subjected to Ziehl-
Neelsen (ZN) smear and blood agar culture for purity check.
Results
A total of 50 specimens had analyzable results for each method. Double PANTA was able to recover 62.0%, VAN 60.0%
and 2% NaOH 24.4% while 16.0%, 14.0% and 6.7% respectively remained contaminated. However, 22.0%, 26.0% and
68.9% were non-viable after decontamination with double PANTA, VAN and 2% NaOH respectively. Further testing is
being done so as to generate more reliable results.
Conclusion
• VAN and double PANTA were comparable as far as giving more specimens (p value = 0.614). With pure cultures
when they are used for decontamination.
• More specimens were unrecoverable when 2% NaOH was used than the other two methods.
• The cost of decontaminating a sample using VAN was ~$1 while double PANTA was ~$5.70
European Society of Mycobacteriology | 30 th Annual Congress | July 2009 | Porto - Portugal
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