The Salmonella typhimurium fimA gene is controlled by several ancillary fim genes. One of these genes, fimZ, appears to be involved in increasing the expression of fimA. A fimZ mutant of S. typhimurium was constructed by allelic exchange, and this mutant was found to be nonfimbriate. The fimZ mutant demonstrated decreased levels of fimA expression compared with the parental strain when both were grown under conditions favoring fimbrial expression. An examination of the predicted amino acid sequence, deduced from the nucleotide sequence of fimZ, indicated that the FimZ polypeptide possessed a DNA binding motif. Bacterial lysates, derived from strains transformed with recombinant plasmids possessing a fimZ gene, demonstrated DNA binding activity with a fragment containing the fimA promoter. Lysates without a FimZ polypeptide did not exhibit any binding activity. These data are consistent with FimZ being a transcriptional activator of fimA, and FimZ acts by binding to the promoter region.Initial investigations of the Salmonella typhimurium fim gene cluster have suggested that the gene encoding the major fimbrial subunit, fimA, is regulated in part by fim genes that are not immediately adjacent to fimA within the gene cluster (2, 23). Four genes, fimZ, -Y, -W, and -U, have been implicated in affecting fimA expression in S. typhimurium (4, 25), and one of these genes (fimU) encodes a tRNA molecule (25). The precise mechanism by which FimZ, -Y, and -W control fimA expression is unknown, but initial evidence indicates that fimZ encodes a positive activator of fimA (4, 23). The mechanism of action of the fimZ, fimY, and fimW determinants has yet to be elucidated.In Escherichia coli, the control of fimA expression is a complex process involving a number of different proteins (6,9,13,14). It is likely that the regulation of fimA expression in S. typhimurium is also under the control of numerous gene products. However, the two fimA genes do appear to be controlled, in part, by different and unrelated mechanisms. Evidence for this is as follows. Firstly, there are no fimB or fimE homologs in the S. typhimurium fim gene cluster. Conversely, genes related to the Salmonella fimY or fimW are not found within the E. coli gene cluster. Secondly, fimbriate E. coli strains lysogenized with an S. typhimurium fimA-lacZ fusion molecule demonstrate poor ␤-galactosidase activity (23). Therefore, under conditions in which the E. coli fimA gene is expressed in these strains, the S. typhimurium fimA gene is not. Thirdly, none of the E. coli fim genes affect the expression of the S. typhimurium fimA in its natural host, whereas ancillary Salmonella fim genes that alter fimA expression have been identified (4, 23).Since we have demonstrated that the S. typhimurium fimZ gene appears to alter fimA expression (23), we decided to investigate further the mechanism of action of the fimZ gene product. The following describes the construction and characterization of an S. typhimurium fimZ mutant and the ability of FimZ to bind to the promoter region...

No abstract

The FimZ protein, an activator of FimA production in Salmonella typhimurium, acts in conjunction with FimY to facilitate the expression of type 1 fimbriae. The predicted amino acid sequence of FimZ suggests that this protein may be a DNA‐binding protein related to BvgA, a sensory regulator of virulence gene expression in Bordetella pertussis. Purification of FimZ following overexpression of the protein by a strong inducible promoter and gel mobility shift assays confirm that FimZ is a 25‐kDa polypeptide that binds to the promoter region of fimA. The region of DNA protected from DNase I digestion by FimZ binding is located between 47 and 98 nucleotides upstream from the fimA transcription initiation site. This region possesses a pair of 7‐base pair tandem repeats, of which at least one is necessary for FimZ binding. One copy of the 7‐base pair sequence is also located in the fimZ promoter region. In addition, expression from a fimZ‐lacZ reporter construct confirms that FimZ plays a role in its own expression. Both FimZ and FimY are required for high‐level expression of FimZ, which suggests that these two fimbrial proteins are involved in regulating both FimA and FimZ.

The pH 6 antigen of Yersinia pestis is a virulence protein whose gene, psaA, is positively regulated at the transcriptional level by low pH, mammalian temperature, and an upstream locus, psaE. Low pH appears to be required for initial psaA transcription, although increased temperature is necessary for full expression of the gene. In addition, psaA is monocistronic and its transcript has a relatively long 5 nontranslated region.

The domestic pig is an important source of human salmonellosis, and houseflies are potential mechanical vectors of foodborne Salmonella pathogens. In 2005, we recovered 144 Salmonella isolates from flies and swine stool samples from 11 farms in Taoyuan County and Hsin Chu County (northwestern Taiwan). A total of 71.5% of the isolates were resistant to at least three antibiotics. There were a total of 14 serotypes, and 8 of these serotypes were present in both flies and swine stool samples. Some multidrug-resistant Salmonella strains coming from different swine farms were found to have identical pulsed-field gel electrophoresis (PFGE). Among four common serotypes, we identified 18 PFGE patterns, 8 of which were present in flies and swine stools. The similarity in PFGE profiles between isolates from swine and flies in different farms indicate the potential of flies to serve as a vector for transmission.