Biofilm-Forming and Multidrug-Resistant Salmonella Thompson Strains Isolated from Edible Cipangopaludina cathayensis: An Emerging Food Safety Concern in Southern China

Abstract

Salmonella enterica Thompson (S. Thompson) is a zoonotic foodborne pathogen causing infection in humans and animals, yet limited data exist on isolates from edible Cipangopaludina cathayensis (C. cathayensis), a key ingredient of Liuzhou Luosifen. In the present study, seven S. Thompson isolates recovered from edible C. cathayensis in southern China (2021–2022) were characterized in terms of antimicrobial resistance, biofilm formation, resistance and virulence genes, and pathogenicity in mice. All seven isolates showed resistance to at least one antimicrobial agent for which valid interpretive criteria exist. Since no Clinical and Laboratory Standards Institute (CLSI) interpretive criteria exist for vancomycin, clindamycin, lincomycin, erythromycin, penicillin, and oxacillin, these agents were excluded from multiple drug resistance (MDR) classification; after reclassification, two isolates, 2/7 (28.6%), fulfilled the criteria for MDR. Five isolates, 5/7 (71.4%), formed biofilms in vitro and carried csgA and/or csgD; the two non-biofilm-forming isolates lacked both genes. All isolates harbored blaTEM-1 and blaOXA; blaCTX-M, blaPSE-1, blaCMY-2, and blaNDM were detected in 5/7 (71.4%) and blaSHV in 4/7 (57.1%). All isolates carried stn, fimA, invA, sseL, and virK; siiE was present in six of seven isolates. In mice, the biofilm-forming isolate C6469 induced hepatic necrosis and intestinal injury. Microbiome and metabolomic analyses indicated a reduction in beneficial gut bacteria, an increase in pathogenic bacteria, and enhanced phosphatidylcholine (PC) (14:0-P-18:0) metabolism, which in turn promotes liver inflammation. These correlational findings warrant further functional validation. This study highlights food safety implications and the strengthening of surveillance for biofilm-forming S. Thompson.