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Open Access Research article

Identification of the genetic determinants of Salmonella enterica serotype Typhimurium that may regulate the expression of the type 1 fimbriae in response to solid agar and static broth culture conditions

Yin-Ching Chuang1, Ke-Chuan Wang2, Yi-Tseng Chen2, Chia-Huei Yang2, Shang-Chin Men2, Chia-Chun Fan2, Li-Huan Chang2 and Kuang-Sheng Yeh23*

Author Affiliations

1 Department of Medical Research, Chi Mei Medical Center, 901 Chung Hwa Road, Yong Kang City, Tainan 710, Taiwan

2 Graduate Institute of Medical Sciences, College of Medicine, Taipei Medical University, 250 Wu-Hsing Street, Taipei 110, Taiwan

3 Department of Microbiology and Immunology, School of Medicine, College of Medicine, Taipei Medical University, 250 Wu-Hsing Street, Taipei 110, Taiwan

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BMC Microbiology 2008, 8:126  doi:10.1186/1471-2180-8-126

Published: 25 July 2008

Abstract

Background

Type 1 fimbriae are the most commonly found fimbrial appendages on the outer membrane of Salmonella enterica serotype Typhimurium. Previous investigations indicate that static broth culture favours S. Typhimurium to produce type 1 fimbriae, while non-fimbriate bacteria are obtained by growth on solid agar media. The phenotypic expression of type 1 fimbriae in S. Typhimurium is the result of the interaction and cooperation of several genes in the fim gene cluster. Other gene products that may also participate in the regulation of type 1 fimbrial expression remain uncharacterized.

Results

In the present study, transposon insertion mutagenesis was performed on S. Typhimurium to generate a library to screen for those mutants that would exhibit different type 1 fimbrial phenotypes than the parental strain. Eight-two mutants were obtained from 7,239 clones screened using the yeast agglutination test. Forty-four mutants produced type 1 fimbriae on both solid agar and static broth media, while none of the other 38 mutants formed type 1 fimbriae in either culture condition. The flanking sequences of the transposons from 54 mutants were cloned and sequenced. These mutants can be classified according to the functions or putative functions of the open reading frames disrupted by the transposon. Our current results indicate that the genetic determinants such as those involved in the fimbrial biogenesis and regulation, global regulators, transporter proteins, prophage-derived proteins, and enzymes of different functions, to name a few, may play a role in the regulation of type 1 fimbrial expression in response to solid agar and static broth culture conditions. A complementation test revealed that transforming a recombinant plasmid possessing the coding sequence of a NAD(P)H-flavin reductase gene ubiB restored an ubiB mutant to exhibit the type 1 fimbrial phenotype as its parental strain.

Conclusion

Genetic determinants other than the fim genes may involve in the regulation of type 1 fimbrial expression in S. Typhimurium. How each gene product may influence type 1 fimbrial expression is an interesting research topic which warrants further investigation.