Establishment of Systemic Brucella melitensis Infection through the Digestive Tract Requires Urease, the Type IV Secretion System, and Lipopolysaccharide O Antigen

Abstract

Human brucellosis is caused mainly by Brucella melitensis, which is often acquired by ingesting contaminated goat or sheep milk and cheese. Bacterial factors required for food-borne infection of humans by B. melitensis are poorly understood. In this study, a mouse model of oral infection was characterized to assess the roles of urease, the VirB type IV secretion system, and lipopolysaccharide for establishing infection through the digestive tract. B. melitensis strain 16M was consistently recovered from the mesenteric lymph node (MLN), spleen, and liver beginning at 3 or 7 day postinfection (dpi). In the gut, persistence of the inoculum was observed up to 21 dpi. No inflammatory lesions were observed in the ileum or colon during infection. Mutant strains lacking the ureABC genes of the ure1 operon, virB2, or pmm encoding phosphomannomutase were constructed and compared to the wild-type strain for infectivity through the digestive tract. Mutants lacking the virB2 and pmm genes were attenuated in the spleen (P < 0.05) and MLN (P < 0.001), respectively. The wild-type and mutant strains had similar levels of resistance to low pH and 5 or 10% bile, suggesting that the reduced colonization of mutants was not the result of reduced resistance to acid pH or bile salts. In an in vitro lymphoepithelial cell (M-cell) model, B. melitensis transited rapidly through polarized enterocyte monolayers containing M-like cells; however, transit through monolayers containing only enterocytes was reduced or absent. These results indicate that B. melitensis is able to spread systemically from the digestive tract after infection, most likely through M cells of the mucosa-associated lymphoid tissue.Brucella spp. are facultative intracellular gram-negative bacteria that cause chronic infections in mammalian hosts. Brucella melitensis infects mainly goats and sheep, causing abortion, placentitis, and infertility, and it is considered the most pathogenic species of Brucella to humans (15). Human brucellosis is an important worldwide zoonosis that causes social and economic impacts on public health and animal production. The disease is prevalent mostly in the Middle East, Mediterranean, Central Asia, Latin America, and North Africa, with over 500,000 new cases of human brucellosis registered annually (41).Human brucellosis usually does not present with specific clinical symptoms. It is frequently associated with intermittent fever, anorexia, weakness, soreness, and inflammation affecting several organs. Spondylitis, arthritis, osteomyelitis, and epididymo-orchitis are common manifestations of the infection. However, infection of the heart and brain may also occur and can result in death (34). Human brucellosis caused by B. melitensis results mostly from ingestion of unpasteurized milk and dairy products from infected goats, sheep, camels, and cattle. The importance of food-borne infection is underlined by a recent study in Mexico, which reported that in 98% of cases, the major risk factor for brucellosis was ingestion of contaminated dairy p...

Putative ATP-Binding Cassette Transporter Is Essential for Brucella ovis Pathogenesis in Mice

“…Previous studies have described hepatic and splenic microgranulomas during systemic infections with pathogenic Brucella spp. in the mouse (13,25,34). In this study, these same histopathological changes were observed mainly at 7 and 30 dpi, i.e., in chronic stages of B. ovis infection.…”

“…In addition, the mouse has frequently been used as an infection model to study chronic infections with Brucella spp. (2,13,21,34,43). In this study, we developed and characterized a murine model for B. ovis infection for up to 90 dpi in male BALB/c and C57BL/6 mice.…”

CLINICAL AND REPRODUCTIVE PATHOLOGICAL CHANGES ASSOCIATED WITH <i>BRUCELLA MELITENSIS</i> AND ITS LIPOPOLYSACCHARIDES IN FEMALE MICE VIA ORAL INOCULATION

“…The onset of clinical signs observed in this study was longer compared to intraperitoneal inoculation of Brucella immunogens (Abdullah et al, 2013). These findings could be explained by a study conducted by Grillo et al (2012) that stated that only low proportion of bacteria (1 to 2%) will translocate through the gut cells as the digestive tract holds many defenses towards colonization and multiplication of pathogenic microorganisms (Paixao et al, 2009).…”

“…The pathogens are then shed to the environment in large numbers through the placenta, vaginal fluids and milk (Megid et al, 2010). This facultative intracellular bacterium is able to invade into and survive within macrophages and non-professional phagocytes which results in its ability to cause chronic infection in the host (Paixao et al, 2009;Sa et al, 2012). Brucella does not evade phagocytosis by macrophages or neutrophils but inhibits the degranulation of both primary and secondary neutrophil granules and the myeloperoxidase-hydrogen peroxide-halide system.…”

Structure-Guided Investigation of Lipopolysaccharide O-Antigen Chain Length Regulators Reveals Regions Critical for Modal Length Control

“…While lipid A and core OS structures are relatively conserved, the OAg is highly diverse, giving rise to thousands of O-specific serotypes among Gram-negative bacteria. In certain bacteria, the OAg plays a role in pathogenesis by influencing macrophage recognition and resistance to the lytic action of the complement system (3,25,26,32), epithelial cell invasion (7,38), and intracellular survival (27).…”