No abstract

Escherichia coli mRNA interferases, such as MazF and ChpBK, are sequence-specific endoribonucleases encoded by toxin-antitoxin (TA) systems present in its genome. A MazF homologue in Staphylococcus aureus (MazF Sa ) has been shown to inhibit cell growth when induced in E. coli. Here, we determined the cleavage site for MazF Sa with the use of phage MS2 RNA as a substrate and CspA, an RNA chaperone, which prevents the formation of secondary structures in the RNA substrate. MazF Sa specifically cleaves the RNA at a pentad sequence, U2ACAU. Bioinformatics analysis revealed that this pentad sequence is significantly abundant in several genes, including the sraP gene in the S. aureus N315 strain. This gene encodes a serine-rich protein, which is known to play an important role in adhesion of the pathogen to human tissues and thus in endovascular infection. We demonstrated that the sraP mRNA became extremely unstable in comparison with the ompA mRNA only when MazF Sa was induced in E. coli. Further bioinformatics analysis indicated that the pentad sequence is also significantly abundant in the mRNAs for all the pathogenic factors in S. aureus. This observation suggests a possible regulatory relationship between the MazEF Sa TA module and the pathogenicity in S. aureus.

The data suggest that pregnancy, especially in the early periods, promotes the proliferation of microorganisms in the oral cavity and facilitates a colonization of periodontal pathogens.

Staphylococcus aureus produces many virulence factors, including toxins, immune-modulatory factors, and exoenzymes. Previous studies involving the analysis of virulence expression were mainly performed by in vitro experiments using bacterial medium. However, when S. aureus infects a host, the bacterial growth conditions are quite different from those in a medium, which may be related to the different expression of virulence factors in the host. In this study, we investigated the expression of virulence factors in S. aureus grown in calf serum. The expression of many virulence factors, including hemolysins, enterotoxins, proteases, and iron acquisition factors, was significantly increased compared with that in bacterial medium. In addition, the expression of RNA III, a global regulon for virulence expression, was significantly increased. This effect was partially restored by the addition of 300 M FeCl 3 into serum, suggesting that iron depletion is associated with the increased expression of virulence factors in serum. In chemically defined medium without iron, a similar effect was observed. In a mutant with agr inactivated grown in serum, the expression of RNA III, psm, and sec4 was not increased, while other factors were still induced in the mutant, suggesting that another regulatory factor(s) is involved. In addition, we found that serum albumin is a major factor for the capture of free iron to prevent the supply of iron to bacteria grown in serum. These results indicate that S. aureus expresses virulence factors in adaptation to the host environment.Staphylococcus aureus is one of the major pathogens of humans; it causes various suppurative diseases, food poisoning, pneumonia, and toxic shock syndrome (11,20). In addition, S. aureus, especially methicillin-resistant S. aureus (MRSA), often causes serious problems via nosocomial infection in hospitals (10, 16). Furthermore, community-acquired MRSA has recently emerged and has been reported to cause serious infectious diseases, sepsis, and pneumonia (3, 9).It is well known that S. aureus produces many virulence factors, such as hemolysins, leukocidins, proteases, enterotoxins, exfoliative toxins, and immune-modulatory factors (11,12,21,31). The expression of these factors is tightly regulated during growth. The agr system, known as the quorum-sensing system, is known to play a central role in the regulation of virulence factors (5,26,27). AgrAC is a two-component system (TCS) that consists of a histidine kinase and a response regulator. The Agr system regulates the expression of the gene coding for small RNA, known as RNA III, which is localized divergently at the agr operon and regulates the expression of many virulence factors, such as hemolysins, leukocidins, and protein A (26, 27). In addition, RNA III, known as hld, encodes delta-hemolysin. The mechanisms of RNA III regulation for the expression of several virulence factors and regulatory factors, including alpha-hemolysin, coagulase, protein A, Map, and Rot, have been demonstrated to occur at the posttran...

Novel N-substituted phthalimides (2-substituted 1H-isoindole-1,3-diones) were prepared, and their effects on tumor necrosis factor-alpha (TNF-alpha) production by human leukemia cell line HL-60 stimulated with 12-O-tetradecanoylphorbol 13-acetate (TPA) or okadaic acid (OA) were examined. A structure-activity relationship study of the N-phenylphthalimides and N-benzylphthalimides revealed that their enhancing effect on TPA-induced TNF-alpha production by HL-60 cells and their inhibiting effect on OA-induced TNF-alpha production by HL-60 cells are only partially correlated.