Diversity in the Characteristics of ST101 of Human, Environmental, and Animal Origin.

BACKGROUND

ST101 is an emerging high-risk clone which exhibits extensive drug resistance. Bacterial strains residing in multiple hosts show unique signatures related to host adaptation. In this study, we assess the genetic relationship of ST101 isolated from hospital samples, the environment, community, and livestock using whole genome sequencing (WGS).

MATERIALS AND METHODS

We selected ten ST101 strains from hospitalized patients in Italy ( = 3) (2014) and Spain ( = 5) (2015-2016) as well as Belgian livestock animals ( = 2) (2017-2018). WGS was performed with 2 × 250 bp paired-end sequencing (Nextera XT) sample preparation kit and MiSeq (Illumina Inc.). Long-read sequencing (Pacbio Sequel I) was used to sequence the two livestock strains and three Italian hospital-associated strains. Furthermore, a public ST101 sequence collection of 586 strains (566 hospital-associated strains, 12 environmental strains, six strains from healthy individuals, one food-associated strain and one pig strain) was obtained. BacPipe and Kleborate were used to conduct genome analysis. ISFinder was used to find IS elements, and PHASTER was utilized to identify prophages. A phylogenetic tree was constructed to illustrate genetic relatedness.

RESULTS

Hospital-associated ST101 showed higher resistance scores than non-clinical isolates from healthy individuals, the environment, food and livestock (1.85 ± 0.72 in hospital-associated isolates vs. 1.14 ± 1.13 in non-clinical isolates, < 0.01). Importantly, the lack of integrative conjugative elements ICE bearing iron-scavenging yersiniabactin siderophores () in livestock-associated strains suggests a lower pathogenicity potential than hospital-associated strains. Mobile genetic elements (MGE) appear to be an important source of diversity in ST101 strains from different origins, with a highly stable genome and few recombination events outside the prophage-containing regions. Core genome MLST based analysis revealed a distinct genetic clustering between human and livestock-associated isolates.

CONCLUSION

The study of ST101 hospital-associated and strains from healthy individuals and animals revealed a genetic diversity between these two groups, allowing us to identify the presence of yersiniabactin siderophores in hospital-associated isolates. Resistance and virulence levels in livestock-associated strains were considerably lower than hospital-associated strains, implying that the public health risk remains low. The introduction of an ICE into animal strains, on the other hand, might pose a public threat over time.