Extensive genetic variability linked to IS26 insertions in the fljB promoter region of atypical monophasic variants of Salmonella enterica serovar Typhimurium.
Fifty-nine monophasic Salmonella enterica serovar Typhimurium isolates, collected in Belgium during the period from 2008 to 2011, have been serotyped as 4,[5]:i:- and shown to harbor an fljB coding sequence. The genetic differences between these strains and phenotypically biphasic Salmonella Typhimurium were analyzed through PCR and DNA sequencing. Genetic alterations in the fljB promoter region affecting expression of the phase 2 flagellin were observed in 53 isolates. Other genetic events in the invertible region carrying the fljB promoter were observed in 2 isolates. For the remaining 4 isolates, no molecular differences with a reference biphasic Salmonella Typhimurium strain could be observed. Next-generation sequencing of one representative isolate affected in the fljB promoter region revealed a 26-kb IS26 composite transposon insertion along with a local genomic rearrangement. Several other IS26 element-mediated alterations of this genomic region were observed. This group of monophasic Salmonella Typhimurium isolates was genetically heterogeneous, as revealed by multilocus variable-number tandem-repeat analysis (MLVA), PCR, and sequencing. Pigs and pork represented a major source of such monophasic isolates in Belgium, as reported in other countries. Three out of 5 isolates of human origin presented genetic profiles identical to those of food isolates, demonstrating the pathogenic potential of the newly characterized variants and potential dissemination along the food chain. This study highlighted the key role played by IS26 insertions in the loss of phase 2 flagellin expression and the subsequent generation of multiple monophasic variant lineages from biphasic Salmonella Typhimurium ancestors.
Veterinary & Agrochemical Research Centre, Foodborne Bacterial Zoonoses & Antibiotic Resistance Unit, Brussels, Belgium Faculty of Bioscience Engineering, Earth and Life Institute, Université catholique de Louvain, Louvain-la-Neuve, Belgium.
Cécile
C
Boland
National Reference Centre for Salmonella and Shigella, Bacterial Diseases Division, Communicable and Infectious Diseases, Scientific Institute of Public Health, Brussels, Belgium.
Sophie
S
Bertrand
National Reference Centre for Salmonella and Shigella, Bacterial Diseases Division, Communicable and Infectious Diseases, Scientific Institute of Public Health, Brussels, Belgium.
Wesley
W
Mattheus
Scientific Service Food-borne Pathogens, Communicable and Infectious Diseases, Scientific Institute of Public Health, Brussels, Belgium.
Katelijne
K
Dierick
Veterinary & Agrochemical Research Centre, Foodborne Bacterial Zoonoses & Antibiotic Resistance Unit, Brussels, Belgium.
Vicky
V
Jasson
Veterinary & Agrochemical Research Centre, Molecular Platform Unit, Brussels, Belgium.
Toon
T
Rosseel
Veterinary & Agrochemical Research Centre, Molecular Platform Unit, Brussels, Belgium.
Steven
S
Van Borm
Faculty of Bioscience Engineering, Earth and Life Institute, Université catholique de Louvain, Louvain-la-Neuve, Belgium.
Jacques
J
Mahillon
Veterinary & Agrochemical Research Centre, Foodborne Bacterial Zoonoses & Antibiotic Resistance Unit, Brussels, Belgium Pierre.Wattiau@coda-cerva.be.
Pierre
P
Wattiau
D000818:Animals; D001530:Belgium; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D005408:Flagellin / Q000235:genetics*; D014644:Genetic Variation; D008460:Meat / Q000382:microbiology; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D012480:Salmonella Infections / Q000382:microbiology; D012481:Salmonella Infections, Animal / Q000382:microbiology; D012486:Salmonella typhimurium / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification; D017422:Sequence Analysis, DNA; D013552:Swine
D004251:DNA Transposable Elements; D004269:DNA, Bacterial; C094427:FljB protein, Salmonella; D005408:Flagellin