Intranasal immunization with Yersinia enterocolitica O:8 cellular extract protects against local challenge infection

The route less taken: pulmonary models of enteric Gram-negative infection

Many pathogens are capable of causing a fulminant infection in pulmonary tissues of mammals. Animal models have provided an extensive understanding of the genetic and molecular mechanisms of bacterial pathogenesis as well as host immune response in the lungs. Many clinically relevant Gram-negative bacteria are host-restricted. Thus, the powerful, informative tools of mouse models are not available for study with these organisms. However, over the past 30 years, enterprising work has demonstrated the utility of pulmonary infection with enteric pathogens. Such infection models have increased our understanding host-pathogen interactions in these organisms. Here, we provide a review and comparison of lung models of infection with enteric, Gram-negative bacteria relative to naturally occurring lung pathogens.

Intranasal inoculation of mice with Yersinia pseudotuberculosis causes a lethal lung infection that is dependent on Yersinia outer proteins and PhoP

Yersinia pseudotuberculosis infects many mammals and birds including humans, livestock, and wild rodents and can be recovered from the lungs of infected animals. To determine the Y. pseudotuberculosis factors important for growth during lung infection, we developed an intranasal model of infection in mice. Following intranasal inoculation, we monitored both bacterial growth in lungs and dissemination to systemic tissues. Intranasal inoculation with as few as 18 CFU of Y. pseudotuberculosis caused a lethal lung infection in some mice. Over the course of 7 days, wild-type Y. pseudotuberculosis replicated to nearly 1 x 10(8) CFU/g of lung in BALB/c mice, induced histopathology in lungs consistent with pneumonia, but disseminated sporadically to other tissues. In contrast, a Delta yopB deletion strain was attenuated in this model, indicating that translocation of Yersinia outer proteins (Yops) is essential for virulence. Additionally, a Delta yopH null mutant failed to grow to wild-type levels by 4 days postintranasal inoculation, but deletions of any other single effector YOP did not attenuate lung colonization 4 days postinfection. Strains with deletions in yopH and any one of the other known effector yop genes were more attenuated that the Delta yopH strain, indicating a unique role for yopH in lungs. In summary, we have characterized the progression of a lung infection with an enteric Yersinia pathogen and shown that YopB and YopH are important in lung colonization and dissemination. Furthermore, this lung infection model with Y. pseudotuberculosis can be used to test potential therapeutics against Yersinia and other gram-negative infections in lungs.

Nasal vaccines

The nasal route for vaccination offers some important opportunities, especially for the prophylaxis of respiratory diseases. Vaccination via the respiratory tract is reviewed and the deposition and clearance of antigens in the deep lung and nose are described and contrasted. Lymphoid structures in the respiratory tract differ according to species; the rat and mouse have a well developed nose-associated lymphoid tissue, while in man, the structure known as Waldeyer's ring (that includes the tonsils), is important as an induction site. The immune response following intranasal administration can provide protection at the administration site and at various effector sites as part of the common mucosal immune system. A number of formulation considerations are important when designing novel systems for nasal administration as are physiological factors such as mucociliary clearance.

Bacterial infections of the small intestine and colon

Bacterial infections of the small and large intestine are widespread and continue to be topics of active research. Surveys document the importance of diarrheal disease in many settings. Major breakthroughs in the understanding of pathogenic mechanisms (especially the interactions of bacteria and intestinal cells) continue, particularly with respect to shigella, salmonella, Yersinia species, and enteropathogenic Escherichia coli. Pathogenic mechanisms of other bacteria, such as campylobacter and entero-aggregative E. coli, are not well defined. Vaccines for cholera and typhoid fever are available, and new vaccines are in various stages of development ranging from synthesis of novel constructs to large-scale field trials. Several candidate vaccines are being exploited as carriers of antigens from other pathogens. Extraintestinal complications from salmonella, shigella, campylobacter, Yersinia species, and Shiga toxin-expressing E. coli are receiving much attention. Genomic sequencing of several of these pathogens is underway. The impact of this work is hard to predict, but expectations are high.