Salmonella enterica requires a type III secretion system, designated Spi/Ssa, to survive and proliferate within macrophages. The Spi/Ssa system is encoded within the SPI-2 pathogenicity island and appears to function intracellularly. Here, we establish that the SPI-2-encoded SpiC protein is exported by the Spi/Ssa type III secretion system into the host cell cytosol where it interferes with intracellular trafficking. In J774 macrophages, wild-type Salmonella inhibited fusion of Salmonella-containing phagosomes with lysosomes and endosomes, and interfered with trafficking of vesicles devoid of the microorganism. These inhibitory activities required living Salmonella and a functional spiC gene. Purified SpiC protein inhibited endosome-endosome fusion in vitro. A Sindbis virus expressing the SpiC protein interfered with normal trafficking of the transferrin receptor in vivo. A spiC mutant was attenuated for virulence, suggesting that the ability to interfere with intracellular trafficking is essential for Salmonella pathogenesis.

The rfb gene cluster of Escherichia coli O9 directs the synthesis of the O9-specific polysaccharide which has the structure 32-␣-Man- (132) (18,55), and the O3-and O5-specific polysaccharides of Klebsiella strains are identical to the O8 and O9 polysaccharides of E. coli (8,18,29). Mannans of algal origin were found to exert antitumor activity (37). Such an activity could later be attributed also to the mannan-containing LPS of E. coli and Klebsiella strains (13, 37).The genetics of LPS biosynthesis in enteric bacteria is well documented in recent reviews (33,43,48,55). Two mechanisms, block and monomeric, have been described for O-polysaccharide synthesis (49). In the block mechanism, observed for Salmonella typhimurium and related Salmonella serotypes, the oligosaccharide repeating units are assembled on undecaprenol phosphate (antigen carrier lipid [ACL]) under the direction of rfb genes. The first sugar transferred was found to be galactose-1-phosphate, and the corresponding transferase gene was termed rfbP (48). The repeating units are polymerized under the direction of the rfc gene, which may be located outside of or within the rfb gene cluster (41). The chain length is controlled by the rol gene, located between gnd and his (3, 4). The monomeric mechanism, experimentally proven only for E. coli O8 and O9 (18, 55), consists of the direct and sequential transfer of the monosaccharide residues from their nucleotideactivated precursors to the nonreducing end of the growing polysaccharide chain.The synthesis of some O polysaccharides requires the rfe gene. According to this requirement, LPS biosynthesis can also be divided into rfe-dependent and rfe-independent pathways. The rfe gene, first described by Mäkelä et al. (31), was found to be essential for the synthesis of the O polysaccharide in Salmonella strains of O groups C1 and L, and E. coli O8 and O9 (18, 33) and more recently in E. coli O4, O7, O18, O75, and O111 (1, 23a). It was reported to determine the tunicamycinsensitive transfer of N-acetylglucosamine (GlcNAc)-1-phosphate from UDP-GlcNAc to undecaprenol monophosphate

Mycobacterium avium complex (MAC) infections are increasing annually in various countries, including

A novel virulence gene (virA) was identified upstream of the virG gene on the large plasmid of Shigella flexneri 2a YSH6000. Characterization of virA mutants infecting MK2 epithelial cell monolayers revealed that their invasive capacity was decreased to less than one fifth of the wild-type level. Nevertheless, the bacteria were capable of expressing and secreting IpaB, IpaC and IpaD proteins. The virA mutants were also impaired in their ability to spread intercellularly, since the bacteria gave rise to a small number of foci in a focus-plaque-forming test with MK2 cells. Although virG expression was slightly decreased in the virA mutants, introduction of a cloned virG gene into a virA mutant, N1945, failed to restore spreading ability. Although, introduction of a cloned virA gene into N1945 restored invasiveness and spreading ability, the reduced virG transcription level was not affected, indicating that the reduced virG expression in virA mutants does not play a major role in defective intercellular spreading. The nucleotide sequence of the virA region revealed that the virA gene was located 528 bp upstream of the virG gene, in the opposite orientation. The deduced amino acid sequence of the VirA protein indicated a 44.7 kDa protein with no homology to known proteins. The VirA protein was secreted into the culture supernatant, a process that required the Mxi and Spa loci. The expression of virA was under the control of the virB gene, the positive regulator of the ipa, mxi and spa operons. These results indicate that virA is a new member of the invasion regulon directed by virB and that the VirA function is involved in invasion and intercellular spreading.

Mycobacterium avium complex (MAC) infection causes disseminated disease in immunocompromised hosts, such as human immunodeficiency virus (HIV)-positive patients, and pulmonary disease in persons without systemic immunosuppression, which has been increasing in many countries. In Japan, the incidence of pulmonary MAC disease caused by M. avium is about 7 times higher than that caused by M. intracellulare. To explore the bacterial factors that affect the pathological state of MAC disease caused by M. avium, we determined the complete genome sequence of the previously unreported M. avium subsp. hominissuis strain TH135 isolated from a HIV-negative patient with pulmonary MAC disease and compared it with the known genomic sequence of M. avium strain 104 derived from an acquired immunodeficiency syndrome patient with MAC disease. The genome of strain TH135 consists of a 4,951,217-bp circular chromosome with 4,636 coding sequences. Comparative analysis revealed that 4,012 genes are shared between the two strains, and strains TH135 and 104 have 624 and 1,108 unique genes, respectively. Many strain-specific regions including virulence-associated genes were found in genomes of both strains, and except for some regions, the G+C content in the specific regions was low compared with the mean G+C content of the corresponding chromosome. Screening of clinical isolates for genes located in the strain-specific regions revealed that the detection rates of strain TH135-specific genes were relatively high in specimens isolated from pulmonary MAC disease patients, while, those of strain 104-specific genes were relatively high in those from HIV-positive patients. Collectively, M. avium strains that cause pulmonary and disseminated disease possess genetically distinct features, and it suggests that the acquisition of specific genes during strain evolution has played an important role in the pathological manifestations of MAC disease.