Detection of mcr-1 Gene in Undefined Vibrio Species Isolated from Clams
Christian Valdez1, Cátia Costa1, Marco Simões1
1MARE-Marine and Environmental Sciences Centre, ESTM, Polytechnic of Leiria, 2520-630 Peniche, Portugal.
Abstract:
The increase of antimicrobial resistant strains is leading to an emerging threat to public health. Pathogenic Vibrio are responsible for human and animal illness. The Enterobacteriaceae family includes microorganisms that affect humans, causing several infections. One of the main causes of human infection is related to the ingestion of undercooked seafood. Due to their filter-feeding habit, marine invertebrates, such as clams, are known to be a natural reservoir of specific microbial communities. In the present study, Vibrionaceae and coliforms microorganisms were isolated from clams. A microbial susceptibility test was performed using the disk diffusion method. From 43 presumptive Vibrio spp. and 17 coliforms, three Vibrio spp. with MICs to colistin >512 mg L-1 were found. From the 23 antimicrobial resistance genes investigated, only the three isolates that showed phenotypic resistance to colistin contained the mcr-1 gene. Genotypic analysis for virulence genes in EB07V indicated chiA gene presence. The results from the plasmid cure and transformation showed that the resistance is chromosomally mediated. Biochemical analysis and MLSA, on the basis of four protein-coding gene sequences (recA, rpoB, groEL and dnaJ), grouped the isolates into the genus Vibrio but distinguished them as different from any known Vibrio spp.
Insights
Antimicrobial resistance is a growing public health concern. Researchers found colistin-resistant Vibrio species in clams, carrying the mcr-1 gene, indicating a potential threat from seafood consumption.
Area of Science:
- Microbiology
- Public Health
- Food Safety
Background:
- Antimicrobial resistance (AMR) poses a significant global public health threat.
- Pathogenic Vibrio and Enterobacteriaceae species cause human and animal infections, often linked to seafood consumption.
- Marine invertebrates like clams serve as reservoirs for microbial communities, potentially harboring resistant bacteria.
Purpose of the Study:
- To investigate the presence of antimicrobial-resistant Vibrionaceae and coliforms in clams.
- To characterize the resistance mechanisms and genetic elements associated with resistance in isolated Vibrio strains.
- To determine the taxonomic classification of the identified Vibrio isolates.
Main Methods:
- Isolation and identification of Vibrionaceae and coliforms from clam samples.
- Antimicrobial susceptibility testing using the disk diffusion method and determination of Minimum Inhibitory Concentrations (MICs) for colistin.
- Detection of antimicrobial resistance genes (e.g., mcr-1) and virulence genes (e.g., chiA) using molecular methods.
- Plasmid curing, transformation experiments, and Multi-Locus Sequence Analysis (MLSA) for genetic characterization.
Main Results:
- Three Vibrio isolates exhibited high-level colistin resistance (MICs >512 mg L⁻¹).
- The mcr-1 gene, conferring resistance to colistin, was detected in the three resistant isolates.
- Genotypic analysis revealed the presence of the chiA virulence gene in one isolate (EB07V).
- Plasmid curing and transformation experiments indicated that colistin resistance is chromosomally mediated.
- MLSA and biochemical analyses identified the isolates as belonging to the Vibrio genus but as novel species.
Conclusions:
- Clams can harbor colistin-resistant Vibrio species carrying the mcr-1 gene, posing a potential risk through seafood consumption.
- The identified Vibrio strains represent novel species with chromosomally mediated colistin resistance.
- Further research is needed to understand the prevalence and public health implications of these resistant Vibrio strains.
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