A low-pH medium in vitro or the environment within a macrophage decreases the transcriptional levels of fimA, fimZ and lrp in Salmonella enterica serovar Typhimurium.
Many Salmonella Typhimurium isolates produce type 1 fimbriae and exhibit fimbrial phase variation in vitro. Static broth culture favours the production of fimbriae, while solid agar medium inhibits the generation of these appendages. Little information is available regarding whether S. Typhimurium continues to produce type 1 fimbriae during in vivo growth. We used a type 1 fimbrial phase-variable strain S. Typhimurium LB5010 and its derivatives to infect RAW 264.7 macrophages. Following entry into macrophages, S. Typhimurium LB5010 gradually decreased the transcript levels of fimbrial subunit gene fimA, positive regulatory gene fimZ, and global regulatory gene lrp. A similar decrease in transcript levels was detected by RT-PCRwhen the pH of static brothmediumwas shifted frompH 7 to amore acidic pH 4. A fimA-deleted strain continued to multiply within macrophages as did the parental strain. An lrp deletion strain was unimpaired for in vitro growth at pH 7 or pH 4, while a strain harboring an lrp-containing plasmid exhibited impaired in vitro growth at pH 4. We propose that acidic medium, which resembles one aspect of the intracellular environment in a macrophage, inhibits type 1 fimbrial production by down-regulation of the expression of lrp, fimZ and fimA.
Graduate Institute of Medical Sciences, College of Medicine, Taipei Medical University, Taipei, Taiwan.
Ke-Chuan
KC
Wang
Yuan-Hsun
YH
Hsu
Yi-Ning
YN
Huang
Ter-Hsin
TH
Chen
Jiunn-Horng
JH
Lin
Shih-Ling
SL
Hsuan
Maw-Sheng
MS
Chien
Wei-Cheng
WC
Lee
Kuang-Sheng
KS
Yeh
D000942:Antigens, Bacterial / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics*; D015536:Down-Regulation; D036781:Fimbriae Proteins / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D006863:Hydrogen-Ion Concentration; D008264:Macrophages / Q000378:metabolism*; D011485:Protein Binding; D012486:Salmonella typhimurium / Q000235:genetics* / Q000254:growth & development / Q000472:pathogenicity; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic
D000942:Antigens, Bacterial; D001426:Bacterial Proteins; C110675:SEF21 protein, Salmonella enteritidis; D014157:Transcription Factors; D036781:Fimbriae Proteins