Detection and functionality of the CdtB, PltA, and PltB from Salmonella enterica serovar Javiana

Salmonella infection is one of the major foodborne illnesses in the United States. Several Gram-negative bacterial pathogens, including Salmonella Typhi, produce cytolethal distending toxin (CDT), which arrests growth, induces apoptosis of infected host cells and extends persistence of pathogenic bacteria in the host. The aim of this study was to characterize the functionality of CDT (cdtB, pltA and pltB) from nontyphoidal Salmonella isolates. Fifty Salmonella enterica serovar Javiana isolates from food, environmental, and clinical samples were screened for cdtB, pltA, and pltB genes by PCR, and all were positive for all three genes. Nucleotide sequence analysis of all amplified PCR products showed 100% identity to S. Typhi cdtB. To understand the roles of CdtB, PltA, and PltB in S. Javiana, cdtB, pltA, and pltB deletion mutants were constructed using a lambda Red-based recombination system. In vitro-cultured HeLa cell lines were infected with a wild-type strain and its isogenic ∆cdtB, ∆pltA, and ∆pltB to determine whether the strains of S. Javiana are responsible for invasion and cytolethal distending intoxication, including cell cycle arrest, cytoplasmic distension, and nuclear enlargement of host target cells. The results showed that HeLa cells infected with S. Javiana wild type were arrested in G2 /M and had distended cytoplasm and nuclei that were larger than those infected with S. Javiana ∆cdtB and ∆pltA strains. The S. Javiana ∆pltB strain retained the ability to induce cytoplasmic distension and cell cycle arrest, whereas the complemented ∆cdtB and ∆pltA S. Javiana strains showed activity like the wild-type strains. CdtB and pltA from S. Javiana had apparent effects on the distension of both cytoplasm and nucleus as well as cell cycle arrest of HeLa cell lines after 72 h of infection. Our data show a significant difference between the wild-type cdtB strain and its isogenic ∆cdtB for invasion of the cell lines. Therefore, CdtB produced from S. Javiana strains may play an important role in pathogenesis in host cells.