[Salmonella multiphasic flagellar antigen]

In the Salmonella antigenic pattern, more than one phase of flagellar antigen is observed. The phase of flagellar antigen depends of the gene which encodes the protein building the filament of flagella. The fliC gene encodes the 1st phase of flagellar antigen and the fljB gene encodes the 2nd phase of flagellar antigen. The third phase of flagellar antigen is encoded by one of the genes localized on the plasmid. Expression of the fljB gene (part of the hinfljBA operon) is regulated by a mechanism of DNA fragment sequence inversion. The hin gene, which encodes Hin invertase, flanked by two regions - hixL and hixR - is inverted by Hin invertase together with Fis protein. This process turns on or turns off of the hinfljBA operon. When this operon is turned on, FljB protein is produced (structural protein of flagella filament), and also FljA protein, which is a transcriptional repressor of the fliC gene. This means that one Salmonella cell could have only one phase flagellar antigen--1st or 2nd phase. Sometimes, due to mutation in one of the mentioned genes, naturally diphasic Salmonella strains have the ability to produce only one phase of flagellar antigen. Mostly monophasic Salmonella with an active fliC gene are observed. In recent years such a strain, Salmonella enterica with the antigenic formula 1,4,[5],12: i: -, is one of the most often isolated strains from human cases in many European countries.