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Salmonella enterica serovar Infantis from Food and Human Infections, Switzerland, 2010-2015: Poultry-Related Multidrug Resistant Clones and an Emerging ESBL Producing Clonal Lineage.

ABSTRACT: Objectives: The aim of this study was to characterize a collection of 520 Salmonella enterica serovar Infantis strains isolated from food (poultry meat), human infections and environmental sources from the years 2010, 2013 and 2015 in Switzerland. Methods: We performed antimicrobial susceptibility testing and pulsed-field gel electrophoresis (PFGE) analysis on all 520 S. Infantis isolates, and whole genome sequencing (WGS) on 32 selected isolates. Results: The majority (74.8%) of the isolates was multidrug resistant (MDR). PFGE analysis revealed that 270 (51.9%) isolates shared an identity of 90%. All isolates subjected to WGS belonged to sequence type (ST) 32 or a double-locus variant thereof (one isolate). Seven (21.9%) of the sequenced isolates were phylogenetically related to the broiler-associated clone B that emerged in Hungary and subsequently spread within and outside of Europe. In addition, three isolates harboring bla_CTX-M-65 on a predicted large (∼320 kb) plasmid grouped in a distinct cluster. Conclusion: This study documents the presence of the Hungarian clone B and related clones in food and human isolates between 2010 and 2015, and the emergence of a bla_CTX-M-65 harboring MDR S. serovar Infantis lineage.

SUBMITTER: Hindermann D

PROVIDER: S-EPMC5507995 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Salmonella enterica subsp. enterica serovar Infantis is the most prevalent serovar found in broilers and broiler meat and is among the top five serovars responsible for human infections in Europe. In 2008, a multidrug-resistant S. Infantis isolate emerged in Israel with a mosaic megaplasmid named pESI, associated with increased virulence, biofilm formation, and multidrug resistance. Since then, S. Infantis clones with pESI-like plasmids have been reported worldwide, replacing pESI-free clones. Here, we typed 161 S. Infantis isolates of poultry (n = 133) and human clinical (n = 28) origin using whole-genome sequencing. The isolates were collected between 2007 and 2021. In addition, we performed PacBio/Illumina sequencing for two representative pESI-like plasmids and compared them with publicly available sequences. All isolates belonged to sequence type 32 (ST32), except for one isolate that represented a novel single-locus variant of ST32. Core genome MLST (cgMLST) analysis revealed 14 clusters of genetically closely related isolates, of which four suggested broiler-to-human transmission of S. Infantis. pESI-like plasmids were present in 148/161 (91.9%) isolates; all were highly similar to the publicly available pESI-like sequences but lacked extended-spectrum beta-lactamase (ESBL) genes. PacBio/Illumina hybrid assembly allowed the reconstruction of two novel complete pESI variants. The present study revealed that the multidrug-resistant, pESI-positive S. Infantis clone became the predominant S. Infantis clone in Slovenian broilers and humans during the last decade. Continued surveillance of resistant S. Infantis clones along the food chain is needed to guide public health efforts. IMPORTANCE Salmonella Infantis clones with pESI-like plasmids harboring several virulence and resistance genes have been reported worldwide. In the present study, we compared the population structure of 161 Salmonella Infantis isolates obtained from humans and broilers in Slovenia from 2007 to 2021. Whole-genome sequencing showed that most human isolates clustered apart from broiler isolates, suggesting an alternative source of infection. Most isolates were multidrug resistant due to the presence of pESI-like plasmids, of which two variants (pS89 and pS19) were fully reconstructed using long-read sequencing. Both exhibited high similarity with the original Israeli pESI plasmid and German p2747 plasmid. The prototype plasmid pS89 harbored the typical pESI-associated resistance genes aadA1, qacEΔ1, sul1, and tet(A), which were absent in the truncated plasmid pS19.

Project description:BACKGROUND:Salmonella Infantis (S. Infantis) is one of the most frequent Salmonella serovars isolated from human cases of salmonellosis and the most detected serovar from animal and food sources in Europe. The serovar is commonly associated with poultry and there is increasing concern over multidrug resistant clones spreading worldwide, as the dominating clones are characterized by presence of large plasmids carrying multiple resistance genes. Increasing the knowledge of the S. Infantis population and evolution is important for understanding and preventing further spread. In this study, we analysed a collection of strains representing different decades, sources and geographic locations. We analysed the population structure and the accessory genome, in particular we identified prophages with a view to understand the role of prophages in relation to the evolution of this serovar. RESULTS:We sequenced a global collection of 100?S. Infantis strains. A core-genome SNP analysis separated five strains in e-Burst Group (eBG) 297 with a long branch. The remaining strains, all in eBG31, were divided into three lineages that were estimated to have separated approximately 150?years ago. One lineage contained the vast majority of strains. In five of six clusters, no obvious correlation with source or geographical locations was seen. However, one cluster contained mostly strains from human and avian sources, indicating a clone with preference for these sources. The majority of strains within this cluster harboured a pESI-like plasmid with multiple resistance genes. Another lineage contained three genetic clusters with more rarely isolated strains of mainly animal origin, possibly less sampled or less infectious clones. Conserved prophages were identified in all strains, likely representing bacteriophages which integrated into the chromosome of a common ancestor to S. Infantis. We also saw that some prophages were specific to clusters and were probably introduced when the clusters were formed. CONCLUSIONS:This study analysed a global S. Infantis population and described its genetic structure. We hypothesize that the population has evolved in three separate lineages, with one more successfully emerging lineage. We furthermore detected conserved prophages present in the entire population and cluster specific prophages, which probably shaped the population structure.

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Salmonella enterica serovar Infantis from Food and Human Infections, Switzerland, 2010-2015: Poultry-Related Multidrug Resistant Clones and an Emerging ESBL Producing Clonal Lineage.

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