Survival of Brucella abortus in milk fermented with a yoghurt starter culture

Abstract

In countries such as Mexico, brucellosis is still an important public health problem due to the consumption of non-pasteurized milk and dairy products, contaminated with Brucella spp. The aim of this study was to look into the survival of Brucella abortus during fermentation of milk with a yoghurt starter culture and storage at refrigeration temperature. Sterile skim milk was inoculated with B. abortus at two concentrations, 105 and 108 CFU/ml simultaneously with a yoghurt starter culture of lactic acid bacteria (Streptococcus thermophilus and Lactobacillus delbrueckii subsp bulgaricus). Inoculated flasks were incubated at 42ºC, followed by refrigeration at 4ºC. Samples were taken during fermentation and during storage and a viable count of B. abortus and lactic acid bacteria and pH were determined. Results showed that after 10 days of storage at 4°C, B. abortus was recovered in fermented milk at a level of 105 CFU/ml, despite the low pH below 4.0. Therefore B. abortus is able to survive in fermented milk. This finding may imply that non-pasteurized fermented milk contaminated with Brucella abortus could be a means of transmission of these bacteria.