Characterization of the emerging Salmonella 4,[5],12:i:- in Danish animal production

The monophasic Salmonella variant with the antigenic formula Salmonella 4,[5],12:i:- has emerged in the last decade as one of the main serotypes related to human salmonellosis. In the present study, a collection of 94 isolates of the S. 4,12:i:- and S. 4,5,12:i:- coming from Danish farm animals, swine (86), cattle (7), and poultry (1), with well-defined identification was further typed by polymerase chain reaction serotyping, phage typing, and molecular typing (polymerase chain reaction and multilocus variable-number tandem-repeat analysis [MLVA]). Moreover, the determination of antimicrobial resistance pattern of each isolate was tested. In 68 of the isolates the fljB gene was absent (i.e., they were true monophasic strains), whereas in 26 isolates, the gene was present despite the fact that the isolates did not express it. The results clustered the isolates in three main pulse-types. The predominant cluster was compatible with the previously described pattern STYMXB.0131. All the isolates included in this cluster lacked the fljB gene, and all the isolates except one belonged to phage type DT 193 with the AMP-STR-SMX-TET resistance pattern. MLVA analysis divided the clusters in several MLVA profiles previously reported by other studies. Finally, antimicrobial resistance and multiresistance was frequent, although no resistance was detected in critical compounds: fluoroquinolones and cephalosporins. The present study demonstrates the presence of monophasic Salmonella Typhimurium-like strains in Danish food animal production with well-characterized clones that are described by previous studies, demonstrating the emergence and spread of this serotype in Denmark.