[Molecular Characterization of Salmonella enterica subsp. enterica Serovar 4: b: -]

Salmonella is a major causative agent of food borne diseases. Recently, monophasic strains of Salmonella, such as S. enterica 4: i: -, have been frequently reported. Here, we investigated the genetic background of S. enterica 4: b: - using multilocus sequence typing (MLST) and pulsed-field gel electrophoresis. A total of 10 strains of S. enterica (I) 4: b: - were examined and compared with 34 strains including serovar Paratyphi B and Paratyphi B var Java, Schleissheim, and II b: -. All I 4: b: - strains were negative for hin which encodes an invertase that converts the H phases, and six were also negative for fljB, which encodes the second phase of the H antigen. An MLST analysis identified 12 sequence types (ST) and 6 ST complexes (STC) from the 44 strains. A clustering analysis of PFGE patterns almost corresponded to the STC. The monophasic I 4: b: - strains were assigned to 3 STCs (19, 32 and 155), corresponding to those of Paratyphi B var. Java or a monophasic strain according to the data of this and previous studies. These findings suggest that the monophasic strains examined in this study might have been derived from multiple clones of Paratyphi B var Java. This study shows the usefulness of molecular typing as complementation tools of the conventional serotyping system.