Shiga toxin-producing Escherichia coli O157:H7 (O157) are significant foodborne pathogens and pose a serious threat to public health worldwide. The major reservoirs of O157 are asymptomatic cattle which harbor the organism in the terminal recto-anal junction (RAJ). Some colonized animals, referred to as “super-shedders” (SS), are known to shed O157 in exceptionally large numbers (>104 CFU/g of feces). Recent studies suggest that SS cattle play a major role in the prevalence and transmission of O157, but little is known about the molecular mechanisms associated with super-shedding. Whole genome sequence analysis of an SS O157 strain (SS17) revealed a genome of 5,523,849 bp chromosome with 5,430 open reading frames and two plasmids, pO157 and pSS17, of 94,645 bp and 37,446 bp, respectively. Comparative analyses showed that SS17 is clustered with spinach-associated O157 outbreak strains, and belongs to the lineage I/II, clade 8, D group, and genotype 1, a subgroup of O157 with predicted hyper-virulence. A large number of non-synonymous SNPs and other polymorphisms were identified in SS17 as compared with other O157 strains (EC4115, EDL933, Sakai, TW14359), including in key adherence- and virulence-related loci. Phenotypic analyses revealed a distinctive and strongly adherent aggregative phenotype of SS17 on bovine RAJ stratified squamous epithelial (RSE) cells that was conserved amongst other SS isolates. Molecular genetic and functional analyses of defined mutants of SS17 suggested that the strongly adherent aggregative phenotype amongst SS isolates is LEE-independent, and likely results from a novel mechanism. Taken together, our study provides a rational framework for investigating the molecular mechanisms associated with SS, and strong evidence that SS O157 isolates have distinctive features and use a LEE-independent mechanism for hyper-adherence to bovine rectal epithelial cells.

ATF5 loss of function has been shown previously to cause apoptotic cell death in glioblastoma and breast cancer cells but not in non-transformed astrocytes and human breast epithelial cells. The mechanism for the cell type-dependent survival function of ATF5 is unknown. We report here that the anti-apoptotic factor BCL-2 is a downstream target of ATF5 that mediates the prosurvival function of ATF5 in C6 glioma cells and MCF-7 breast cancer cells. ATF5 binds to an ATF5-specific regulatory element that is downstream of and adjacent to the negative regulatory element in the BCL-2 P2 promoter, stimulating BCL-2 expression. Highlighting the critical role of BCL-2 in ATF5-dependent cancer cell survival, expression of BCL-2 blocks death of C6 and MCF-7 cells induced by dominant-negative ATF5, and depletion of BCL-2 impairs ATF5-promoted cell survival. Moreover, we found that BCL-2 expression is not regulated by ATF5 in non-transformed rat astrocytes, mouse embryonic fibroblasts, and human breast epithelial cells, where expression of BCL-2 but not ATF5 is required for cell survival. These findings identify BCL-2 as an essential mediator for the cancer-specific cell survival function of ATF5 in glioblastoma and breast cancer cells and provide direct evidence that the cell type-specific function of ATF5 derives from differential regulation of downstream targets by ATF5 in different types of cells.ATF5 (activating transcription factor 5; also known as ATFx) is a member of the ATF/cAMP response element-binding protein (CREB) 2 family of bZIP (basic zipper) proteins (1). It can bind to several transcription regulatory DNA elements that include cAMP response elements (CRE), an amino acid response element, and an ATF5-specific response element (ARE) and regulate gene expression in different types of cells (1-4). ATF5 has been identified as a factor whose down-regulation is essential for differentiation of rat neural progenitor cells and PC12 pheochromocytoma cells (5-7). ATF5 is expressed in a number of cancer cells and down-regulated in those cells following growth factor deprivation; exogenous expression of ATF5 suppresses apoptosis in HeLa cells induced by serum withdrawal and in FL5.12 cells, an IL-3-dependent cell line, by IL-3 deprivation (8). Conversely, dominant-negative ATF5 induces apoptosis of HeLa and FL5.12 cells and a number of glioma and breast cancer cell lines cultured in the presence of growth factors (8 -10). Similar interference of ATF5 function in non-neoplastic breast cells or in non-tumor brain cells, such as mature neurons and glial cells, does not affect their survival (9, 10). The mechanism of such selective survival requirement for ATF5 in different cell types is not understood.The BCL-2 family of proteins includes both anti-apoptotic (BCL-2, BCL-X L , and MCL-1) and apoptotic (BAK, BAX, BID, and BIM) proteins. The regulation and balance of this BCL-2 family of proteins in a particular cell result in inhibition or induction of the apoptotic signaling pathways (11,12). Notably, the expression pattern ...

Recent emergence of antimicrobial resistance of Neisseria gonorrhoeae worldwide has resulted in limited therapeutic choices for treatment of infections caused by this organism. We performed global transcriptomic analysis of N. gonorrhoeae in subjects with gonorrhea who attended a Nanjing, China, sexually transmitted infection (STI) clinic, where antimicrobial resistance of N. gonorrhoeae is high and increasing. We found that N. gonorrhoeae transcriptional responses to infection differed in genital specimens taken from men and women, particularly antibiotic resistance gene expression, which was increased in men. These sex-specific findings may provide a new approach to guide therapeutic interventions and preventive measures that are also sex specific while providing additional insight to address antimicrobial resistance of N. gonorrhoeae.

Cah is a calcium-binding autotransporter protein involved in autoaggregation and biofilm formation. Although is widespread in Shiga toxin-producing (STEC), we detected mutations in at a frequency of 31.3% in this pathogen. In STEC O157:H7 supershedder strain SS17, a large deletion results in a smaller coding sequence, encoding a protein lacking the C-terminal 71 amino acids compared with Cah in STEC O157:H7 strain EDL933. We examined the function of Cah in biofilm formation and host colonization to better understand the selective pressures for mutations. EDL933-Cah played a conditional role in biofilm formation : it enhanced DH5α biofilm formation on glass surfaces under agitated culture conditions that prevented autoaggregation but inhibited biofilm formation under hydrostatic conditions that facilitated autoaggregation. This function appeared to be strain dependent since Cah-mediated biofilm formation was diminished when an EDL933 gene was expressed in SS17. Deletion of in EDL933 enhanced bacterial attachment to spinach leaves and altered the adherence pattern of EDL933 to bovine recto-anal junction squamous epithelial (RSE) cells. In contrast, in expression of EDL933 in SS17 increased its attachment to leaf surfaces, and in DH5α, it enhanced its adherence to RSE cells. Hence, the ecological function of Cah appears to be modulated by environmental conditions and other bacterial strain-specific properties. Considering the prevalence of in STEC and its role in attachment and biofilm formation, mutations might be selected in ecological niches in which inactivation of Cah would result in an increased fitness in STEC during colonization of plants or animal hosts. Shiga toxin-producing (STEC) harbors genes encoding diverse adhesins, and many of these are known to play an important role in bacterial attachment and host colonization. We demonstrated here that the autotransporter protein Cah confers on DH5α cells a strong autoaggregative phenotype that is inversely correlated with its ability to form biofilms and plays a strain-specific role in plant and animal colonization by STEC. Although is widespread in the STEC population, we detected a mutation rate of 31.3% in, which is similar to that reported for and The formation of cell aggregates due to increased bacterium-to-bacterium interactions may be disadvantageous to bacterial populations under conditions that favor a planktonic state in STEC. Therefore, a loss-of-function mutation in is likely a selective trait in STEC when autoaggregative properties become detrimental to bacterial cells and may contribute to the adaptability of STEC to fluctuating environments.