Virulence of a Bordetella pertussis strain expressing a mutant adenylyl cyclase with decreased calmodulin affinity

Role of pore-forming toxins in bacterial infectious diseases

Pore-forming toxins (PFTs) are the most common bacterial cytotoxic proteins and are required for virulence in a large number of important pathogens, including Streptococcus pneumoniae, group A and B streptococci, Staphylococcus aureus, Escherichia coli, and Mycobacterium tuberculosis. PFTs generally disrupt host cell membranes, but they can have additional effects independent of pore formation. Substantial effort has been devoted to understanding the molecular mechanisms underlying the functions of certain model PFTs. Likewise, specific host pathways mediating survival and immune responses in the face of toxin-mediated cellular damage have been delineated. However, less is known about the overall functions of PFTs during infection in vivo. This review focuses on common themes in the area of PFT biology, with an emphasis on studies addressing the roles of PFTs in in vivo and ex vivo models of colonization or infection. Common functions of PFTs include disruption of epithelial barrier function and evasion of host immune responses, which contribute to bacterial growth and spreading. The widespread nature of PFTs make this group of toxins an attractive target for the development of new virulence-targeted therapies that may have broad activity against human pathogens.

Adenylyl cyclase inMycobacterium tuberculosis H37Rv-A possible virulence factor

Eukaryotic-like adenylyl cyclase has been identified inMycobacterium tuberculosis H37Rv. TheM. tuberculosis adenylyl cyclase gene (cya) was cloned by complementation of a cAMP dependent expression of maltose operon in acya deletionE. coli strain. The nucleotide sequence analysis of thecya gene revealed an open reading frame that coded for 443 amino acids. A comparison ofM. tuberculosis adenylyl cyclase with the protein sequences in the data bank revealed its homology to the eukaryotic Type I and the calmodulin responsive adenylyl cyclases with an average of about 40% identical and 60% similar amino acids in the catalytic domain. The occurrence of eukaryotic-like adenylyl cyclase inM. tuberculosis suggests a role for this important enzyme in cell signaling and perhaps in the pathogenesis ofM. tuberculosis. We suggest that the human pathogenM. tuberculosis might have acquired the eukaryoticcya by a recombination event.

Probing the function of Bordetella bronchiseptica adenylate cyclase toxin by manipulating host immunity

We have examined the role of adenylate cyclase-hemolysin (CyaA) by constructing an in-frame deletion in the Bordetella bronchiseptica cyaA structural gene and comparing wild-type and cyaA deletion strains in natural host infection models. Both the wild-type strain RB50 and its adenylate cyclase toxin deletion (DeltacyaA) derivative efficiently establish persistent infections in rabbits, rats, and mice following low-dose inoculation. In contrast, an inoculation protocol that seeds the lower respiratory tract revealed significant differences in bacterial numbers and in polymorphonuclear neutrophil recruitment in the lungs from days 5 to 12 postinoculation. We next explored the effects of disarming specific aspects of the immune system on the relative phenotypes of wild-type and DeltacyaA bacteria. SCID, SCID-beige, or RAG-1(-/-) mice succumbed to lethal systemic infection following high- or low-dose intranasal inoculation with the wild-type strain but not the DeltacyaA mutant. Mice rendered neutropenic by treatment with cyclophosphamide or by knockout mutation in the granulocyte colony-stimulating factor locus were highly susceptible to lethal infection by either wild-type or DeltacyaA strains. These results reveal the significant role played by neutrophils early in B. bronchiseptica infection and by acquired immunity at later time points and suggest that phagocytic cells are a primary in vivo target of the Bordetella adenylate cyclase toxin.