A review of the global emergence of multidrug-resistant Salmonella enterica subsp. enterica Serovar Infantis

Salmonella enterica serovar Infantis is an emergent foodborne and zoonotic Salmonella serovar with critical implications for global health. In recent years, the prevalence of S. Infantis infections has increased in the United States, Europe, and Latin America, due to contaminated chicken and other foods. An essential trait of S. Infantis is its resistance to multiple antibiotics, including the critically important third-generation cephalosporins and quinolones, undermining effective medical treatment, particularly in low-resource settings. We describe the emergence of multidrug-resistant (MDR) S. Infantis, focusing on humans, animals, the environment, and food. We conducted a systematic review (1979-2021), selected 183 studies, and analyzed the origin, source, antimicrobial resistance, and presence of a conjugative plasmid of emerging S. Infantis (pESI) in reported isolates. S. Infantis has been detected worldwide, with a substantial increase since 2011. We found the highest number of isolations in the Americas (42.9 %), Europe (29.8 %), Western Pacific (17.2 %), Eastern Mediterranean (6.6 %), Africa (3.4 %), and South-East Asia (0.1 %). S. Infantis showed MDR patterns and numerous resistant genes in all sources. The primary source of MDR S. Infantis is broiler and their meat; however, this emerging pathogen is also present in other reservoirs such as food, wildlife, and the environment. Clinical cases of MDR S. Infantis have been reported in children and adults. The global emergence of S. Infantis is related to a plasmid (pESI) with antibiotic and arsenic- and mercury-resistance genes. Additionally, a new megaplasmid (pESI-like), carrying bla_CTX-M-65 and antibiotic-resistant genes reported in an ancestral version, was detected in the broiler, human, and chicken meat isolates. Strains harboring pESI-like were primarily observed in the Americas and Europe. MDR S. Infantis has spread globally, potentially becoming a major public health threat, particularly in low- and middle-income countries.