Molecular identification in monophasic and nonmotile variants of S almonella enterica serovar T yphimurium

Variant strains of S almonella enterica serovar T yphimurium, lacking one or both flagellar phases have been widely reported. The monophasic S . 1 ,4,[5],12:i:‐ variant has emerged worldwide in the past few years and has become one of the most frequently encountered in many countries. In contrast, monophasic S . 1 ,4,[5],12:‐:1,2 and nonmotile S . 1 ,4,[5],12:‐:‐ strains are rarely described. This study investigated seven molecular markers to identify and delineate monophasic S . 1 ,4,[5],12:i:‐ ( n  = 90), S . 1 ,4,[5],12:‐:1,2 ( n  = 25), nonmotile S . 1 ,4,[5],12:‐:‐ ( n  = 17) strains, and some serovar T yphimurium strains ( n  = 124) collected through the F rench S almonella network between 2001 and 2010. Three markers were commonly detected in serovar T yphimurium and in all variant strains: STM 2757, mdh and fliA‐B . Monophasic S . 1 ,4,[5],12:i:‐ were genotypically confirmed by the absence of the fljB , fljA , and hin genes. Nevertheless, 13 (14.5%) of them were positive for these last three genes, revealing monophasic strains named “inconsistent” as previously described. All nonmotile 1 ,4,[5],12:‐:‐ strains had the fliC , fljA , fljB , and hin genes and the fliC gene was detected in 88% of monophasic S . 1 ,4,[5],12:‐:1,2 strains. The combination of the seven markers detection enables to recognize eight different genotypes within the S . 1 ,4,[5],12:i:‐ collection, among which the S panish and the U.S. clones previously described could be distinguished and assigned to a genotype. Based on this molecular approach, 71% of the F rench S .1,4,[5],12:i:‐ collection belonged to the S panish clone, whereas only 2% were assigned to the U.S. clone. This study highlights the usefulness of these molecular markers and genotypes for identifying lineages, especially among the epidemiologically important monophasic S . 1 ,4,[5],12:i:‐ variant.