Molecular Characterization and Antimicrobial Resistance Profiling of Salmonella spp. from Onion Leaves Collected from Wet Markets in Metro Manila, Philippines

Abstract

Salmonella spp. is the causative agent of salmonellosis outbreaks in poultry and meats, but recent studies have implicated this pathogen in foodborne outbreaks associated with vegetables. Salmonellosis is commonly managed with antibiotics, but antimicrobial resistance has complicated the treatment of the disease. The pathogenesis of Salmonella spp. is based on virulence factors such as plasmid-encoded genes and lipopolysaccharide moieties, which can be detected by PCR and serotyping, respectively. Thirteen (13) isolates previously identified and confirmed as Salmonella spp. using invA gene-targeting assay were isolated from onion leaf samples collected from wet markets in Metro Manila, Philippines. The isolates were characterized based on the presence of plasmid-encoded virulence gene, serogroup and serotype, and antibiotic resistance profiles using the VITEK®2 system. All 13 Salmonella spp. isolates were spvC-negative. O-serotyping revealed the presence of isolates belonging to serogroups C1 (30.8%), C2 (23.0%), and E1 (30.8%). Two isolates (15.4%) did not belong to the serogroups examined in the study. Further, sequence analysis revealed the presence of serovars Newport, Weltevreden, Tennessee, and Anatum. All the isolates were resistant to at least five antimicrobial agents. To our knowledge, this is the first study in the Philippines to establish baseline data for the molecular features and antibiogram profiles of Salmonella spp. isolated in onion leaf samples from selected wet markets in Metro Manila, Philippines. Furthermore, this study is the first report on the occurrence of four different Salmonella serovars from onion leaves. The data obtained in this study could be used as baseline information and guidance in the implementation of the GAP, monitoring programs of the Department of Agriculture, and the formulation of laws and regulations by policymakers that will address safety issues in fresh produce and quality management principles in farm operations.