Bartonella and Brucella--weapons and strategies for stealth attack

Abstract

Bartonella spp. and Brucella spp. are closely related α-proteobacterial pathogens that by distinct stealth-attack strategies cause chronic infections in mammals including humans. Human infections manifest by a broad spectrum of clinical symptoms, ranging from mild to fatal disease. Both pathogens establish intracellular replication niches and subvert diverse pathways of the host's immune system. Several virulence factors allow them to adhere to, invade, proliferate, and persist within various host-cell types. In particular, type IV secretion systems (T4SS) represent essential virulence factors that transfer effector proteins tailored to recruit host components and modulate cellular processes to the benefit of the bacterial intruders. This article puts the remarkable features of these two pathogens into perspective, highlighting the mechanisms they use to hijack signaling and trafficking pathways of the host as the basis for their stealthy infection strategies.

Figure 1.

Phylogeny, T4SS, and epidemiology of Bartonella and Brucella. At least one type IV secretion system (T4SS; VirB, Vbh, and Trw) is present in all Bartonella species except for Bartonella bacilliformis. A related VirB T4SS is also present in Brucella.

Figure 2.

Intracellular life of Bartonella and Brucella. Bartonella and Brucella invade cells in vacuolar structures (BCV) or, in the case of B. henselae, as an aggregate in invasomes. Once internalized, these structures interact with specific host components and compartments subverting their function. AIM, Autophagy initiation markers; COPII, coatomer protein II; ER, endoplasmic reticulum; ERGIC, ER–Golgi intermediate compartment; ERES, ER exit sites; MVB, multivesicular bodies; T4SS, type IV secretion system.