Evaluation of the Evolution and Clonal Expansion Through Phenotypic and Genotypic Characterization of Salmonella Enterica I 4,[5],12:I:- Isolated from Swine in the United States
Abstract
The National Antimicrobial Resistance Monitoring System has reported a rise in
multidrug-resistant Salmonella I 4,[5],12:i:- in both humans and animals. Salmonella I
4,[5],12:i:- is antigenically similar to Salmonella Typhimurium yet lacks the phase 2
flagellar antigen. The cause of the increased prevalence of Salmonella I 4,[5],12:i:-
remains unknown; however, swine have been identified as an important reservoir. The
aim of this study was to determine unique phenotypic and genotypic traits of Salmonella
I 4,[5],12:i:- that have allowed this serovar to evolve and expand in swine and their
environment. Salmonella I 4,[5],12:i:- was compared to Salmonella Typhimurium and
other monophasic serovars to identify differences associated with monophasic expression
that may affect virulence or survival.
Salmonella was isolated from head trim and cheek meat collected from healthy
swine at a pork processing plant in the United States. Antimicrobial susceptibility patterns
were identified by the Sensititre® system. Bacterial growth curves were determined using
a BioScreen C under different antibiotic concentrations and bacterial fitness was analyzed
using a 3-parameter Gompertz-model in Stata®. Motility and biofilm formation assays
were used to assess swimming/swarming and biofilm production. Whole genome
sequencing was performed to determine point mutations, resistance, heavy metal
tolerance, and biofilm-related genes. Deletions/insertions/mutations in the fljBA locus
were detected via alignment. The evolutionary relationship between Salmonella I 4,[5],12:i:- and Salmonella Typhimurium strains in our study, along with publicly
available genomes, was evaluated via core-genome phylogenetic analyses.
All Salmonella I 4,[5],12:i:- isolates were multidrug-resistant and harbored the
blaTEM-1, strA-strB, sul2, and tet(B) genes encoding resistance to the common ASSuT
phenotype. Salmonella I 4,[5],12:i:- had less fitness cost associated with qnrB, blaSHV-12
and tet genes and had greater fitness than Salmonella Typhimurium under antibiotic
pressure. Monophasic expression was shown to affect swimming motility but not
swarming, while biofilm production was not affected but positively influenced by the
presence of sdiA. This study is important to determining the characteristics of Salmonella
I 4,[5],12:i:- that have led to an increased prevalence in swine for preventing salmonellosis
linked to swine and pork products. Our results suggests the lack of FljB does not affect
the success of Salmonella I 4,[5],12:i:- in swine.
Citation
Gonzalez, Selma (2021). Evaluation of the Evolution and Clonal Expansion Through Phenotypic and Genotypic Characterization of Salmonella Enterica I 4,[5],12:I:- Isolated from Swine in the United States. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /196476.