Furthermore, we have shown that deletion of genes involved in LPS assembly affects serum resistance as well mainly because virulence in SCID-beige mice (unpublished results). infection, suggesting neutrophils are crucial to the early inflammatory response to the former but not the second option. was dramatically more active than in mediating the lysis of J774 cells in vitro and in inducing apoptosis of inflammatory cells in mouse lungs. This side-by-side assessment describes phenotypic variations that may be correlated with genetic variations in the comparative analysis of the genomes of these two highly related organisms. and are closely related gram-negative bacteria that cause respiratory tract infections in their respective hosts. Although extensively analyzed in vitro, limitations of the mouse model have hindered a full exploration of the infectious process in vivo. While is definitely highly infectious in humans, mouse infection models require inoculation with high numbers of bacteria delivered in a large liquid volume or in aerosolized form directly to the lungs. The bacteria grow transiently and are cleared from your animals over a period of weeks. These models are likely to bypass many ALK6 of the mechanisms that normally allow small numbers of bacteria to efficiently adhere, grow, and spread throughout the respiratory tract during a natural illness. The mouse model is definitely therefore unlikely to accurately reflect the functions of adhesins and colonization factors that are believed to contribute to the highly infectious nature of in humans. and are so closely related as to be considered subspecies (20). They express a similar set of virulence factors and use a conserved and functionally interchangeable two-component signal transduction system, BvgAS, to regulate the expression of virulence genes (4, 17). They differ, however, in their propensity to cause disease and in their nonoverlapping host ranges. While causes a severe, acute disease E7080 (Lenvatinib) that can be life-threatening in unvaccinated patients, typically establishes asymptomatic infections that persist indefinitely in the upper respiratory tract of infected animals. has a highly restricted host range which is usually exclusively confined to humans. In contrast, has a broad host range which includes rodents, pigs, dogs, and cats but only rarely humans (11, 29). This broad host range has allowed the development of natural host animal models that use and rabbits, rats, and mice (1, 5, 12). The amazing efficiency with which establishes persistent colonization in rodents suggests that relevant virulence factors are functional in these models. In contrast to requires fewer than 10 organisms delivered in a 5-l droplet to the external naris to establish murine infections that last for the life of the animal (12). In the context of this contamination model, interactions between bacteria and host may be dissected at the molecular level with the confidence that E7080 (Lenvatinib) findings are likely to be relevant to natural infections. Here we describe a side-by-side comparison of the and strains whose genomes are currently being sequenced, Tohama I and RB50, respectively (20a). Sequence data will allow future comparative studies to use powerful genome-based techniques to investigate the genetic basis for differences between these closely related organisms. The prerequisite for such studies is a careful comparative analysis of their phenotypic differences. Mice are the most advanced system available to study the role of host immune functions and have been used extensively in the study of and was resistant to serum killing, was highly cytotoxic for J774 cells in vitro, and induced apoptosis of inflammatory cells in the lungs of infected mice. was deficient in all of these virulence characteristics, indicating that this subspecies has a dramatically different virulence strategy E7080 (Lenvatinib) or that this mouse model does not accurately reflect natural contamination of its human host. MATERIALS AND METHODS Bacteria. Bacteria were maintained on Bordet-Gengou (BG) agar (Difco) and were produced to mid-log phase in Stainer-Scholte broth for assays and inoculations. Tohama I was originally isolated from a human patient with whooping cough and has been extensively studied for 4 decades (13). RB50 was isolated from a naturally infected rabbit colony (5). Bvg+ and Bvg? derivatives of RB50 (RB53 and RB54, respectively) and Tohama I (370 and 369, respectively) have been described (5, 18, 25, 26). Animals. test. Histology and apoptosis assays. For histological examination, lungs and trachea were excised as a unit. The trachea was cannulated with a blunt-ended 18-gauge needle attached to a syringe. Lungs were carefully inflated with 10%.