are facultative intracellular pathogens and reside in the host within acidified phagosomes, and this environment is important for the expression of virulence genes, such as virB, and thus could be expected to demonstrate tolerance to low pH conditions. It must also be recognized that Brucella spp. There is evidence that this is not under the control of the rpoS gene, a major regulator of stationary phase growth and a stress response inducer in bacteria. Brucella suis also demonstrated an acid tolerance response with a 30-min exposure to pH 5.8, compared with a control (at optimum growth pH of 7.2), inducing a twofold increase in resistance to a pH value of 3.2. The same species showed 90% survival after 3 h exposure to pH 3.8 and this dropped to only 60% survival after 24 h. Rowe, in Encyclopedia of Food Microbiology (Second Edition), 2014 pH Valueīrucella abortus survived in a model system using sterilized milk and lactic acid for 34 days at a pH range of 5.0–5.8, but when the pH dropped to 3.9, the survival period decreased to only 2 days.
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