Molecular and Phenotypic Characterization of Virulent, Multidrug- Resistant, and Biofilm-Forming Salmonella spp. in Retail Fish
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Date
2025-12-15
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Abstract
Fish is a widely consumed protein source in Bangladesh, yet retail markets often operate
without adequate microbiological monitoring, increasing the risk of foodborne infections.
Salmonella spp., a major zoonotic pathogen, is frequently associated with aquatic environments
and poses a significant public health threat, particularly when antimicrobial resistance (AMR)
and virulence factors converge. A total of 100 fish samples from six major retail markets in
Noakhali, Bangladesh, were examined for the presence of Salmonella. Presumptive isolates
were identified based on cultural and biochemical characteristics, followed by molecular
confirmation using PCR targeting invA. Virulence genes (hilA, fimA), antimicrobial
susceptibility against 14 antibiotics, AMR genes (blaTEM-1, blaCTX-M-1, tetA, sul1), and
biofilm-forming ability were also assessed to evaluate pathogenic and resistance profiles.
Among 145 presumptive isolates, 24 (16.55%) were confirmed as Salmonella spp. All 24
isolates carried the invA gene, while 95.8% and 79.2% possessed hilA and fimA, respectively,
indicating substantial virulence potential. Antibiogram profiling revealed multidrug resistance,
including complete resistance to ceftazidime (100%) and high resistance to ampicillin (75%)
and levofloxacin (50%). PCR detection showed universal carriage of blaTEM-1 (100%), along
with blaCTX-M-1 (50%), tetA (29.2%), and sul1 (29.2%). Biofilm assays demonstrated diverse
adherence capacities, with several isolates classified as strong biofilm formers, suggesting
enhanced environmental persistence and increased risk of cross-contamination. The
identification of virulent, multidrug-resistant, and biofilm-forming Salmonella spp. in retail
fish markets highlights significant risks to public health and food safety in Bangladesh. The
coexistence of virulence genes, AMR determinants, and biofilm-forming capacity underscores
the urgent need for improved hygiene practices, regulated antibiotic use in aquaculture, and
enhanced surveillance of foodborne pathogens. Although serotyping and whole genome
sequencing (WGS) could not be performed due to limited funding and time constraints, these
advanced analyses are planned for future work to better understand the genetic diversity and
epidemiology of circulating strains.