Effect of sample volume, storage temperature, and culture medium on Brucella melitensis isolation from goat milk

Background: The effect of sample volume, storage temperature, and culture media on the isolation of Brucella melitensis from goat milk is unknown. The diagnosis of infected goat herds through milk culture may help prevent human and animal disease but is difficult to achieve in resource-poor settings, given the challenges of sample collection, storage, and transport. In this study, we evaluate the effects of these variables on culture yield under simulated field conditions.

Methods: Pooled milk samples were collected from disease-free goats in Lima, Peru. 1 x 104 CFUs of B. melitensis strain 16M were inoculated into 2ml and 5ml aliquots of milk and stored with ice packs (~4-7„aC) or liquid nitrogen (-70„aC) for 7 days (n=400). Half of the aliquots were instilled into tryptone soya broth with vancomycin, colistin, nystatin, trimethoprim, and polymyxin B for three days, followed by subculture onto modified Farrell's medium with Brucella selective supplement. Remaining aliquots were instilled into Eugon broth followed by Eugon agar with BACTO supplement B. The primary endpoint was the rate of culture positivity, compared using chi-square tests. The effects of volume, temperature, and medium were modeled using logistic regression.

Results: Study results will be discussed. Preliminary data shows 60% positive cultures for Farrell's medium at 4„aC after 7 days. Conclusions: Brucellosis remains a significant public health issue in resource-poor regions. Improved ability to detect disease through milk culture, as demonstrated by this study, will aid authorities in the development of disease prevention and eradication programs and in reduction of disease incidence.