Plasmid-Curing Potential of Silkworm-Derived Moricins against Multidrug-Resistant Salmonella Typhi from Fish Pond Water

Abstract

Salmonella enterica subspecies enterica serovar Typhi (ST) remains a major public health concern in Nigeria, with water bodies serving as potential reservoirs for the transmission of multidrug-resistant strains to humans. Despite reports of environmental Salmonella in Anambra State, there is a paucity of data on the molecular identity, resistance profile, and plasmid-mediated resistance of ST from water bodies in Uli community, creating a critical knowledge gap for targeted control. This study aimed to isolate, characterize, and determine the antibiotic resistance and plasmid-curing profiles of ST using silkworm-derived moricins. One hundred fish pond water samples were collected from five locations in Uli, and screened for ST using colonial, morphological, and biochemical tests, followed by 16S rRNA sequencing. Antibiotic susceptibility was determined by disk diffusion, and plasmid curing was assessed using moricins at concentrations of 30–90%. Data were analyzed using appropriate statistical tools. The morphological, biochemical and 16S rRNA sequencing confirmed 100% identity to ST strains BKQU3X, R19.2839, ERL082358, 311189_214186, and 311189_256186. Of 72 screened isolates, 49 (68%) were resistant to at least one antibiotic, with ST strains BKQU3X (STBK) showing the highest resistance (86%). SXT, PN, CEP, S, and CPX were most implicated. Curing agent concentration significantly decreased resistance (p < 0.05), with a strong negative dose-response trend. Complete curing was achieved at 80%, with ST strains R19.2839 (STR1) most persistent up to 70%. Multidrug-resistant S. typhi is prevalent in Uli fishpond water, and resistance is largely plasmid-mediated and cu rable at 80% silkworm-derived moricin concentration.