Draft Genome Sequence of Salmonella enterica subsp. enterica Serovar Infantis Strain SPE101, Isolated from a Chronic Human Infection

Salmonella enterica subsp. enterica serovar Infantis is a nontyphoid emerging serovar showing increased morbidity in humans worldwide. Recent studies have shown that some emergent S. Infantis isolates carry a self-transmissible megaplasmid that confers stress tolerance and promotes pathogenicity, which can be horizontally transferred to the gut microbiota by conjugation (1, 2). S. Infantis plasmids are thus responsible for the dissemination of genes encoding extended spectrum beta-lactamases and quinolone resistance determinants (3). Surveillance studies also reveal an increased presence of S. Infantis in poultry meat (3), as well as prevalence in human persistent infections caused by nontyphoidal Salmonella serovars (4).

S. Infantis strain SPE101 was isolated from the feces of a 5-month-old breast-fed female in a pediatric unit of a public hospital in Lima, Peru, 4 months after initial hospitalization. The patient showed signs of dehydration and malnutrition when hospitalized. The Salmonella infection persisted for 6 months despite several regimens of beta-lactams, quinolone, and trimethoprim-sulfamethoxazole antibiotic treatments. Prior to genome sequencing, the SPE101 isolate was typified as S. Infantis by multiplex PCR (O and H antigens) and determined to belong to sequence type 32 (ST32) by multilocus sequence typing. The plasmid profile of this isolate revealed the presence of an ~250-kb megaplasmid, similar in size to the megaplasmid pESI reported in emergent S. Infantis isolates (1). PCR assays demonstrated the presence of the pESI backbone gene traC (5). Antimicrobial susceptibility tests performed according to the Clinical and Laboratory Standards Institute (6) showed resistance to beta-lactams and quinolones.

Genomic DNA from an overnight culture of SPE101 was obtained using the phenol-chloroform extraction method (7). Paired-end (2 × 150) sequencing was performed using the Illumina MiSeq platform (Illumina, Inc, San Diego, CA, USA). A total of 6,145,442 reads were generated. De novo assembly was conducted using an algorithm based on the de Brujin graphs (8), resulting in 63 contigs ≥ 500 bp with a 168-fold average coverage. The annotation was performed with the RAST algorithm (9). The draft genome of SPE101 contains 4,985,409 bp, with a 52.1% G+C content, and has 4,805 protein coding sequences, 11 rRNAs, 75 tRNAs, and 201 pseudogenes.

The 4,805 predicted SPE101 proteins were searched using tBLASTn in the 75 genomes of S. Infantis isolates deposited in GenBank by April 2017. Seven proteins were not encoded by any other available genome of S. Infantis. Among them were two putative transcriptional regulators, a proline-rich protein, and proteins encoded by a lambdoid phage. Interestingly, 266 of the 286 genes annotated in the pESI megaplasmid of the emergent S. Infantis strain 119944 reported in Israel (1) were found in SPE101.

Further analyses with derivative strains of SPE101 lacking the genes absent in other S. Infantis isolates may provide the foundation toward unraveling novel attributes of this emergent serovar in human salmonellosis.

This work was supported by grants 215RT0493 and BIO2016-77639-P awarded to F.G.-D.P. from the Programa Iberoamericano de Ciencia y Tecnología para el Desarrollo (CYTED) and the Spanish Ministry of Economy and Competitiveness and European Regional Development Funds (FEDER), respectively; by grants FC-2015-2/879 and 239659 awarded to J.L.P. from the Consejo Nacional de Ciencia y Tecnología (CONACyT) of Mexico; and by a grant from the Comisión Sectorial de Investigación Científica (CSIC) from the Universidad de la República Uruguay.

The SalmoIber CYTED Network members associated with this work include Fernando Soncini and Eleonora García-Vescovi (Universidad de Rosario-CONICET, Argentina); Lorena Soleto, Griselda Flores, and José Pedraza (CENETROP, Santa Cruz de la Sierra, Bolivia); Claudia Silva and José Luis Puente (Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Mexico); Laura Betancor, Lucia Yim, and José Alejandro Chabalgoity (Universidad de la República, Montevideo, Uruguay); Coralith García, Lizeth Astocondor, Theresa Ochoa, and Noemí Hinostroza (Instituto de Medicina Tropical Alexander Von Humboldt, Universidad Peruana Cayetano Heredia, Lima, Perú); M. Graciela Pucciarelli (Universidad Autónoma de Madrid, Centro de Biología Molecular “Severo Ochoa,” Madrid, Spain); and Francisco García-Del Portillo (Centro Nacional de Biotecnología [CNB]-CSIC, Madrid, Spain).