Abstract
Multi-drug resistant bacteria (particularly those producing extended-spectrum β-lactamases) have become a major health concern. The continued exposure to antibiotics, biocides, chemical preservatives, and metals in different settings such as the food chain or in the environment may result in development of multiple resistance or co-resistance. The aim of the present study was to determine multiple resistances (biocides, antibiotics, chemical preservatives, phenolic compounds, and metals) in bacterial isolates from seafoods. A 75.86% of the 87 isolates studied were resistant to at least one antibiotic or one biocide, and 6.90% were multiply resistant to at least three biocides and at least three antibiotics. Significant (P < 0.05) moderate or strong positive correlations were detected between tolerances to biocides, between antibiotics, and between antibiotics with biocides and other antimicrobials. A sub-set of 30 isolates selected according to antimicrobial resistance profile and food type were identified by 16S rDNA sequencing and tested for copper and zinc tolerance. Then, the genetic determinants for biocide and metal tolerance and antibiotic resistance were investigated. The selected isolates were identified as Pseudomonas (63.33%), Acinetobacter (13.33%), Aeromonas (13.33%), Shewanella, Proteus and Listeria (one isolate each). Antibiotic resistance determinants detected included sul1 (43.33% of tested isolates), sul2 (6.66%), blaTEM (16.66%), blaCTX−M (16.66%), blaPSE (10.00%), blaIMP (3.33%), blaNDM−1 (3.33%), floR (16.66%), aadA1 (20.0%), and aac(6′)-Ib (16.66%). The only biocide resistance determinant detected among the selected isolates was qacEΔ1 (10.00%). A 23.30 of the selected isolates were able to grow on media containing 32 mM copper sulfate, and 46.60% on 8 mM zinc chloride. The metal resistance genes pcoA/copA, pcoR, and chrB were detected in 36.66, 6.66, and 13.33% of selected isolates, respectively. Twelve isolates tested positive for both metal and antibiotic resistance genes, including one isolate positive for the carbapenemase gene blaNDM−1 and for pcoA/copA. These results suggest that exposure to metals could co-select for antibiotic resistance and also highlight the potential of bacteria on seafoods to be involved in the transmission of antimicrobial resistance genes.
Highlights
The global world fish market reached 175 million tons in 2016 (Food and Agriculture Organization (FAO), 2016)
Lowest viable counts were reported for blue shark, and highest counts were found in refrigerated raw salmon slices packed in trays
Biocide tolerance and antibiotic resistance were detected among bacteria isolated from seafoods
Summary
The global world fish market reached 175 million tons in 2016 (Food and Agriculture Organization (FAO), 2016). There is a growing concern in the fisheries sector about the increasing prevalence of multidrug-resistant bacterial strains in the food chain (EFSA, 2010; ECDC, 2012, 2013; EFSA-ECDC, 2013; Watts et al, 2017). Resistance genes for antimicrobials such as β-lactams, quinolones, and fluoroquinolones may be associated with plasmids. Plasmids of fluoroquinolone resistance in Enterobacteriaceae are widespread, and are often associated with resistance to β-lactams in strains with multidrug resistant phenotypes (Crémet et al, 2011). Some genes, such as the variant aac(6′)-Ib-cr simultaneously confer resistance to aminoglycosides, and fluoroquinolones (Kim et al, 2011). Others like the efflux pump oqxAB described in Escherichia coli, confer resistance to various antibiotics and biocides (Hansen et al, 2007; Wong and Chen, 2013)
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