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

Abstract

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.

Genomic variations leading to alterations in cell morphology of Campylobacter spp

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The infectious intracellular lifestyle ofSalmonella entericarelies on the adaptation to nutritional conditions within theSalmonella-containing vacuole

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Growth of healthy and sanitizer-injured Salmonella cells on mung bean sprouts in different commercial enrichment broths

“…These results suggest that the acidic condition of LB during enrichment might inhibit the growth of bacteria but not cause membrane damage. Thus, the growth inhibition in LB may be explained by the decrease in the transcript levels of some life cycle regulated genes, such as fim, under low pH conditions (Wang et al, 2013) or by the inactivation of some pH-sensitive enzymes in cytoplasm (Stratford et al, 2009).…”