Genomic Characterization of spp. and spp. Strains Isolated From Powdered Infant Formula in Chile.

This study characterized five spp. and six spp. strains that had been isolated from 155 samples of powdered infant formula (PIF) sold in Chile and manufactured in Chile and Mexico in 2018-2020. Two strains of sequence type (ST) ST1 and ST31 (serotypes O:1 and O:2) and one strain of ST60 (O:1) were identified. All strains were identified as Typhimurium ST19 (serotype O:4) by average nucleotide identity, ribosomal multilocus sequence typing (rMLST), and core genome MLST (cgMLST). The and isolates were resistant to cephalothin, whereas the isolates were resistant to oxacillin and ampicillin. Nineteen antibiotic resistance genes were detected in the and isolates; the most prevalent were mcr-9.1, , and . In , 30 genes encoding for aminoglycoside and cephalosporin resistance were identified, including , β-, , and . In the isolates, 32 virulence-associated genes were detected by WGS and clustered as flagellar proteins, outer membrane proteins, chemotaxis, hemolysins, invasion, plasminogen activator, colonization, transcriptional regulator, survival in macrophages, use of sialic acid, and toxin-antitoxin genes. In the strains, 120 virulence associated genes were detected, adherence, magnesium uptake, resistance to antimicrobial peptides, secretion system, stress protein, toxin, resistance to complement killing, and eight pathogenicity islands. The and strains harbored I-E and I-F CRISPR-Cas systems and carried Col(pHHAD28) and IncFIB(pCTU1) plasmids, respectively. The strains harbored type I-E CRISPR-Cas systems and carried IncFII(S) plasmids. The presence of and in PIF is a health risk for infants aged less than 6 months. For this reason, sanitary practices should be reinforced for its production and retail surveillance.