SUMMARY Eradication of persistent intracellular bacterial pathogens with antibiotic therapy is often slow or incomplete. However, strategies to augment antibiotics are hampered by our poor understanding of the nutritional environment that sustains chronic infection. Here we show that the intracellular pathogen Brucella abortus survives and replicates preferentially in alternatively activated macrophages (AAM), which are more abundant during chronic infection. A metabolic shift induced by peroxisome proliferator activated receptor γ (PPARγ), which increases intracellular glucose availability, is identified as a causal mechanism promoting enhanced bacterial survival in AAM. Glucose uptake was crucial for increased replication of B. abortus in AAM, and chronic infection, as inactivation of the bacterial glucose transporter gluP reduced both intracellular survival in AAM and persistence in mice. Thus, a shift in intracellular nutrient availability induced by PPARγ promotes chronic persistence of B. abortus within AAM and targeting this pathway may aid in eradicating chronic infection.

No abstract

Brucellosis is a chronic infectious disease caused by Brucella spp., a Gram-negative facultative intracellular pathogen that affects humans and animals, leading to significant impact on public health and animal industry. Human brucellosis is considered the most prevalent bacterial zoonosis in the world and is characterized by fever, weight loss, depression, hepato/splenomegaly, osteoarticular, and genital infections. Relevant aspects of Brucella pathogenesis have been intensively investigated in culture cells and animal models. The mouse is the animal model more commonly used to study chronic infection caused by Brucella. This model is most frequently used to investigate specific pathogenic factors of Brucella spp., to characterize the host immune response, and to evaluate therapeutics and vaccines. Other animal species have been used as models for brucellosis including rats, guinea pigs, and monkeys. This paper discusses the murine and other laboratory animal models for human and animal brucellosis.

Brucella ovis is a major cause of reproductive failure in sheep, which is associated with epididymitis and infertility in rams. Importantly, B. ovis is one of the few Brucella species that is not zoonotic. Due to the scarcity of studies on B. ovis infection, a murine model of infection was developed. The roles of B. ovis genes encoding a putative hemagglutinin and an ABC transporter were investigated in the mouse model. The kinetics of B. ovis infection were similar in BALB/c and C57BL/6 mice, and both strains of mice developed multifocal microgranulomas in the liver and spleen, but only minimal colonization and histopathological changes were observed in the genital tract. Therefore, the mouse was considered a suitable infection model for B. ovis but not for B. ovis-induced genital disease. Two mutant strains were generated in this study (the ⌬abcAB and ⌬hmg strains). The B. ovis ⌬abcAB strain was attenuated in the spleens and livers of BALB/c mice compared to the wild-type (WT) strain (P < 0.001). Conversely, the ⌬hmg strain infected mice at the same level as WT B. ovis, suggesting that a putative hemagglutinin is not required for B. ovis pathogenesis. Additionally, the ⌬abcAB strain did not survive in peritoneal macrophages, extracellularly in the peritoneal cavity, or in RAW 264.7 macrophages. Moreover, infection with the ⌬abcAB strain was not lethal for male regulatory factor 1-knockout mice, whereas infection with the B. ovis WT strain was 100% lethal within 14 days postinfection. These results confirm that the predicted ABC transporter is required for the full virulence and survival of B. ovis in vivo.Brucella ovis is one of the main causes of reproductive failure in sheep (6). The disease is characterized by chronic epididymitis, orchitis, and infertility in sexually mature rams and occasional abortion and stillbirth in ewes (4,15,46). B. ovis has a worldwide distribution in economically important sheep-raising areas, with the exception of Great Britain (6). This organism may affect as much as 46% of a herd (41), leading to significant economic losses for the sheep industry due to infertility and early culling (8). B. ovis is a stable, rough, Gramnegative coccobacilli that belongs to the Alpha-2-Proteobacteriacea family (4, 17), and it is one of the few classical Brucella species that are not pathogenic to humans (4, 47).Brucella spp. are facultative intracellular bacteria that are able to survive and replicate in phagocytic and nonphagocytic cells and to establish chronic infections in animals and humans (18,46). Virulence factors are required for the invasion of host cells by Brucella spp. and for their survival and replication in host cells. Although classical virulence factors, such as capsules and fimbriae, are absent in Brucella species (18), pathogenic mechanisms specific to Brucella spp. have been identified (20,29,39,42). The mouse is often used as an animal model to investigate the pathogenesis of animal and human brucellosis (2, 13, 28). The murine model also allows studies that may reveal mech...

Evasion of host immune responses is a prerequisite for chronic bacterial diseases; however, the underlying mechanisms are not fully understood. Here, we show that the persistent intracellular pathogen Brucella abortus prevents immune activation of macrophages by inducing CD4+CD25+ T cells to produce the anti-inflammatory cytokine interleukin-10 (IL-10) early during infection. IL-10 receptor (IL-10R) blockage in macrophages resulted in significantly higher NF-kB activation as well as decreased bacterial intracellular survival associated with an inability of B. abortus to escape the late endosome compartment in vitro. Moreover, either a lack of IL-10 production by T cells or a lack of macrophage responsiveness to this cytokine resulted in an increased ability of mice to control B. abortus infection, while inducing elevated production of pro-inflammatory cytokines, which led to severe pathology in liver and spleen of infected mice. Collectively, our results suggest that early IL-10 production by CD25+CD4+ T cells modulates macrophage function and contributes to an initial balance between pro-inflammatory and anti-inflammatory cytokines that is beneficial to the pathogen, thereby promoting enhanced bacterial survival and persistent infection.

No abstract

Visceral leishmaniasis (VL) is primarily transmitted by an invertebrate vector, but transmission in the absence of the vector has been reported. Vertical transmission of VL has been described in man and dogs. The aim of this study was to evaluate the distribution of Leishmania amastigotes in fetal organs and histopathologic changes associated with parasitism and to determinate the frequency of transplacental transmission and potential of vertical transmission by symptomatic and asymptomatic pregnant bitches. Symptomatic (n=4) and asymptomatic (n=4) pregnant bitches, serologically and parasitologically positive for Leishmania sp., carrying a total of 53 fetuses (26 from symptomatic and 27 from asymptomatic bitches) were selected at the Veterinary Hospital of the National University of Asuncion, Paraguay. Samples of placenta and fetal organs such as liver, spleen, lymph nodes, bone marrow, kidney and heart were histologically evaluated and processed for immunodetection of amastigotes and PCR. There were no lesions compatible with VL in fetal tissues in spite of the presence of amastigotes, particularly in lymphoreticular tissues. However, fetal hepatocytes had marked degenerative changes that were independent of the presence of amastigotes in liver. Twenty-six out of 53 placentas (13 symptomatic and 13 asymptomatic) and a total of 17 fetuses out of 53 (nine symptomatic and eight asymptomatic) were PCR positive. Together these findings indicate a high frequency of transplacental transmission and no differences in the potential of transmission when symptomatic were compared to asymptomatic pregnant bitches.

No abstract