Aerosol Infection of BALB/c Mice with Brucella melitensis and Brucella abortus and Protective Efficacy against Aerosol Challenge

Abstract

Brucellosis is a zoonotic disease with a worldwide distribution that can be transmitted via intentional or accidental aerosol exposure. In order to engineer superior vaccine strains against Brucella species for use in animals as well as in humans, the possibility of challenge infection via aerosol needs to be considered to properly evaluate vaccine efficacy. In this study, we assessed the use of an aerosol chamber to infect deep lung tissue of mice to elicit systemic infections with either Brucella abortus or B. melitensis at various doses. The results reveal that B. abortus causes a chronic infection of lung tissue in BALB/c mice and peripheral organs at low doses. In contrast, B. melitensis infection diminishes more rapidly, and higher infectious doses are required to obtain infection rates in animals similar to those of B. abortus. Whether this difference translates to severity of human infection remains to be elucidated. Despite these differences, unmarked deletion mutants BA⌬asp24 and BM⌬asp24 consistently confer superior protection to mice against homologous and heterologous aerosol challenge infection and should be considered viable candidates as vaccine strains against brucellosis.

Protective Efficacy and Safety of Brucella melitensis 16MΔmucRagainst Intraperitoneal and Aerosol Challenge in BALB/c Mice

“…It has been documented that 10 to 100 organisms are enough to cause disease in humans, and Brucella is therefore considered highly infectious when delivered by this route (7). Previous investigations performed by this laboratory have determined that BALB/c mice receiving an infectious dose of 5 ϫ 10 9 CFU/ml added to the chamber nebulizer inhaled an average of 12,250 organisms per mouse (4.10 logs) and that tissue colonization reached a peak by 4 weeks postexposure (23). The high dose (100-fold more bacteria that actually needed to establish an infection) and the time postvaccination chosen to test efficacy provide us the means to evaluate the vaccine candidate efficacy under the most stringent conditions.…”

“…In order to determine the vaccination efficacy elicited by the 16M⌬mucR mutant against a natural route of exposure, the level of protection provided by the vaccine candidate was evaluated against aerosol B. melitensis 16M wild-type challenge at 20 weeks postvaccination. For aerosol exposure studies, the 4-week postchallenge time point was chosen as the time point of peak splenic colonization (23). Mice that were euthanized within 1 h of aerosol exposure inhaled an average of 2.1 ϫ 10 4 CFU/lungs, as determined by plating their lungs and enumerating the bacteria recovered.…”

Identification of Immune Effectors Essential to the Control of Primary and Secondary Intranasal Infection with Brucella melitensis in Mice

“…Brucella establishes a stealthy infection in mice and constitutes an interesting experimental model that can be used to analyze the relationships between hosts and intracellular stealth pathogens (46,47). Although the aerosol route is a common cause of infection in nature (1), a relatively limited number of Brucella studies (20,22,36,37,48,49) investigated the protective immune response following respiratory infection. In this study, we analyzed the progression of B. melitensis in the lungs, spleen, and liver of C57BL/6 mice, as well as the nature of the protective immune response following primary and secondary i.n.…”

Key Role of Toll-Like Receptor 2 in the Inflammatory Response and Major Histocompatibility Complex Class II Downregulation in Brucella abortus-Infected Alveolar Macrophages

“…and remained high at least until week 8 p.i. (12), suggesting that B. abortus can replicate and persist within the murine lung. It can be speculated that this long-term survival of Brucella in the lung takes place, at least in part, in AM.…”