Defining the atypical quorum sensing system of Brucella spp.

Project Summary
Brucella spp. are bacteria that naturally infect a variety of domesticated and wild animals leading to
abortions and sterility, and these bacteria are also capable of causing debilitating human infections, which
often result from human exposure to infected animals and animal products. Brucella spp. are considered
threats as potential biological weapons. Importantly, antibiotic treatment against brucellosis is prone to disease
relapse, and there is currently no safe and effective vaccine to protect humans against infection with Brucella.
The brucellae are intracellular pathogens that reside within immune cells called macrophages where they
replicate in a specialized compartment, and the capacity of Brucella to survive and replicate within
macrophages is essential to their ability to cause disease. Interestingly, quorum sensing is an important
component of Brucella virulence, but traditionally, quorum sensing is an activity performed by large populations
of bacteria, while the brucellae exists primarily in intracellular vacuoles in small numbers. Thus, the Brucella
quorum sensing system is atypical to the paradigm of Gram-negative quorum sensing systems, and this
application seeks to define novels elements of this pathway.
Preliminary work in our group led to the development of a B. abortus strain that is unable to sense the
quorum sensing molecule, acyl homoserine lactone (AHL). Deletion of the two genes encoding transcriptional
regulators of the LuxR family yielded a quorum sensing “deaf” strain, and this strain will be used to define the
Brucella quorum sensing transcriptome in order to identify genetic elements critical to virulence. Additionally,
we will test the hypothesis that the quorum sensing “deaf” strain will be highly attenuated in both cellular and
animal models of Brucella infection. Finally, it is known that Brucella strains produce a 12 carbon AHL, but no
genes are present that encode known AHL synthases. As such, we have developed an unbiased screening
strategy to identify the Brucella AHL synthase. In the end, the information gleaned from these studies may be
used to develop new therapeutic and vaccine strategies against human Brucella infection.

Grant Number: 5R21AI180524-02
NIH Institute/Center: NIH
Principal Investigator: Clayton Caswell