Sher et al. 2025 — Antibiotic resistance in Shewanella species and heavy-metal co-selection (narrative review)

Narrative review in Microorganisms (MDPI) of the genus Shewanella as an emerging multi-drug-resistant pathogen in clinical and aquatic environmental settings. For HMI purposes the relevance is the paper’s Section 5 on heavy-metal co-selection of antibiotic resistance: arsenic, mercury, cadmium, and chromium exposure is shown across cited studies to drive antibiotic-resistance acquisition in Shewanella via co-resistance (linked genes), cross-resistance (shared efflux systems), and co-regulation (shared promoter regions). The paper contains no primary food-contamination measurements and no ppb-level occurrence data; it is microbiome/AMR context for the heavy-metal-driven selection pressure that contaminated estuaries and aquaculture environments place on resistant pathogen reservoirs.

Key numbers

All values below are secondary citations the review pulls from prior literature, not primary measurements. The paper does not measure heavy metals in food or environmental matrices itself.

Heavy-metal co-selection mechanisms in Shewanella (Section 5, pp. 4–5, citing refs [46–55]):

• Three co-selection mechanisms named: co-resistance (genes for both heavy metal and antibiotic resistance located in proximity on the same promoter region of the bacterial genome), cross-resistance (a single system such as an efflux pump confers resistance to both heavy metals and antibiotics — the efflux system is most common in Shewanella spp.), and co-regulation (resistance genes for metals and antibiotics co-regulated by transcription; in Shewanella and Vibrio strains, genes for co-selection phenotypes are on chromosomes).
• “Bacteria that are resistant to arsenic and mercury are more resistant to antibiotics than bacteria that are sensitive to these metals” (p. 5, citing Lloyd et al. 2018 [ref 54] — whole-genome sequencing of mummichog fish gut Shewanella).
• Mummichog (Fundulus heteroclitus) gut Shewanella whole genome sequence: phenotypic resistance to β-lactam antibiotics and to multiple metals including mercury and arsenic; genome analysis detected the carbapenemase gene blaOXA-48; efflux-pump gene homologs identified (p. 5, ref [54]).
• Shewanella resistance to heavy metals Cd, Cr, Cu, Co, and Zn reported; two strains (SY1, SY2) of fifteen tested were resistant to those metals and to gentamicin, rifampicin, erythromycin, vancomycin, cephalothin, ampicillin, and streptomycin (p. 11, citing ref [96] — Kang and So 2016, Shewanella putrefaciens from shellfish, West Sea, Korea).

Clinical-epidemiology numbers (Section 7 — Shewanella in human infections, pp. 5–6):

• Hong Kong regional hospital, 10-year retrospective (April 2010–December 2020): 128 patients with Shewanella infection; 61.7% male; age range 65–87; S. algae 92.2%, S. putrefaciens 7.8%; >93% of isolates sensitive to ceftazidime, gentamicin, and ciprofloxacin; 76.6% sensitive to imipenem (ref [40]).
• University Hospital of Gran Canaria, Spain (2001–2016): 31 patients (23 male, 8 female); mean age 50.7 (range 15–87); 15 S. putrefaciens, 16 S. algae; 18 isolates from skin/soft tissue, 8 blood, 2 peritoneal, 1 bronchial, 1 bile, 1 ear swab (ref [43]).
• Retrospective analysis published 2024: 51 cases over 10 years; 68.8% S. putrefaciens, 31.4% S. algae; isolates resistant to ticarcillin-clavulanic acid (23.5%), cefoperazone-sulbactam (19.6%), cefotaxime (17.6%), ciprofloxacin (17.6%) (ref [70]).

Antimicrobial resistance gene context (Sections 8–9):

• Five efflux-pump structural families enabling MDR in Shewanellaceae: ABC superfamily, MTE (multidrug and toxic compound extrusion), SMR (small multidrug resistance), MFS (major facilitator superfamily), and RND (resistance/nodulation/division) superfamily (p. 8, refs [11,63,65]).
• Five common porin proteins in Gram-negative outer membrane: OmpA, OmpC, OmpF, OmpW, OmpX (p. 7, ref [73]).
• Shewanella oneidensis contains seven genes expected to encode β-lactamases including AmpC and class D β-lactamase BlaA (also OXA-54); BlaA proposed as progenitor of carbapenem-hydrolyzing oxacillinases (p. 8, refs [80–82]).
• S. algae MARS 14 colistin resistance: 27-fold increase in EptA (ethanolamine phosphotransferase) expression in functional-genomics library screen at 8 mg/L colistin on LB agar (p. 11, ref [69]).
• S. xiamenensis NUITM-VS2 Vietnamese drainage isolate: one chromosome + five plasmids; tet(X4) and tmexC3.2D3.2-toprJ1 tigecycline-resistance genes on 152.2 kb IncC plasmid pNUITM-VS2_2; blaNDM-1 on 24.8 kb untypeable plasmid pNUITM-VS2_4 (p. 11, ref [57]).
• Algerian hospital-waste isolate S. xiamenensis T1: 268.4 kb plasmid pSx1 carrying Tn6297 transposon and blaOXA-416 (blaOXA-48-like) (p. 10, ref [11]).

Shewanella genus context (Section 2 and Table 1):

• 114 species identified in genus (GenBank, accessed November 2024) (p. 2).
• Table 1 (p. 4) — genome assemblies and sizes for 15 Shewanella species, NCBI accessed 10 January 2024; sample rows:
  • S. putrefaciens: 22 assemblies, 1 chromosome, 3 plasmids, 4.38–5.05 Mb, GC 44.30–47.90%, ~4055 genes, ~3820 proteins
  • S. algae: 230 assemblies, 1 chromosome, 1 plasmid, 4.60–5.20 Mb, GC 52.50–53.2%, ~4185 genes, ~4450 proteins
  • S. oneidensis: 7 assemblies, 1 chromosome, 1 plasmid, 3.71–5.13 Mb, GC 45.93–46.50%, ~4438 genes, ~4261 proteins
• Most clinically important species: S. putrefaciens and S. algae (p. 4).

Evidence fitness

This source supports microbiome and AMR context only. It is a narrative review with no primary contamination data; all numerical claims are pulled from secondary sources without independent measurement. The paper does not measure heavy metals in any food matrix and contributes nothing to ingredient or product contamination_profile values. It can be cited for:

• The three co-selection mechanisms (co-resistance, cross-resistance, co-regulation) by which heavy-metal contamination of aquatic environments drives antibiotic-resistance acquisition in environmental bacteria — relevant to any HMI discussion of why heavy-metal contamination of estuaries, aquaculture, and seafood is a public-health concern beyond direct dietary exposure.
• The efflux-pump cross-resistance mechanism specifically as a Shewanella-relevant example of how a single bacterial system can be selected for by either metals or antibiotics and confer resistance to both.
• Mummichog-fish-gut Shewanella as a documented case of co-selection between mercury/arsenic resistance and β-lactam/carbapenem resistance in a coastal aquatic environment (the underlying primary source is Lloyd et al. 2018, Marine Pollution Bulletin, ref [54]).
• Background for WikiBiome federation work on metal–antibiotic-resistance co-selection in aquatic and gut microbiomes.

It does not support occurrence percentiles, regulatory-limit derivations, ingredient/product contamination-profile values, or any quantitative wiki claim that needs primary metal-concentration provenance. Where the review cites a specific underlying study (Lloyd 2018 for mummichog gut; Kang and So 2016 for Korean shellfish Shewanella; Gupta et al. 2022 [ref 46] for UK/India urban-river co-selection; Berg et al. 2005 [ref 97] for copper-amended agricultural soil; Akinbowale et al. 2007 [ref 98] for rainbow-trout-farm motile Aeromonas/Pseudomonas), those primary sources should be ingested directly rather than via this review.

Methods (brief)

Narrative literature review with no PRISMA protocol; no search strategy, database list, inclusion/exclusion criteria, or quality-assessment framework reported. Authors are at Florida A&M University School of the Environment (lead author), USDA Agricultural Research Service / Delaware State University, and University of Maryland Eastern Shore Department of Agriculture, Food and Resource Science. The paper is organized by topic (Background → Microbiological characteristics → Molecular identification → Heavy metals’ role in AMR acceleration → Antibiotic reservoirs in aquatic environments → Shewanella in human infections → Mechanisms of antibiotic resistance → Transmission of resistance genes → Conclusions). Figures 1 (six resistance mechanisms) and 2 (three HGT mechanisms) drawn in ChemBioDraw. Table 1 compiles NCBI genome-assembly statistics for 15 species. No new data created or analyzed (Data Availability Statement, p. 12). No external funding; no IRB or informed-consent requirements stated. Conflicts-of-interest statement notes that the use of trade names is for identification purposes and does not imply USDA endorsement.

Implications

• Certification: No direct HMT&C input. The heavy-metal co-selection mechanism is relevant background when scoping seafood, shellfish, or aquaculture-derived product categories — the argument that heavy-metal-contaminated estuaries propagate antibiotic-resistant pathogens compounds the case for monitoring metal contamination in seafood beyond direct human-exposure terms — but no certification threshold derives from this review.
• Courses: Useful as a secondary reading for courses on environmental microbiology, AMR, or seafood safety. The three co-selection mechanisms (co-resistance, cross-resistance, co-regulation) and the efflux-pump-as-shared-defense framing are pedagogically clean. Figures 1 and 2 are clear teaching graphics.
• App: No contamination_profile changes warranted. This source does not support quantitative ingredient values.
• Microbiome: This is the primary HMI-relevant angle. The review is a candidate for WikiBiome federation as a citation source for the metal–antibiotic-resistance co-selection axis in aquatic and gut microbiomes. The mummichog-fish-gut case (ref [54]) is a concrete worked example for how environmental metal pollution shapes the resistome of coastal microbial communities.

Provenance notes

PDF dropped into raw/Manual Fetch Kimi /June 2 Manual Fetches/ by Karen on 2026-06-02 under the original journal filename microorganisms-13-01115.pdf. Open access under Creative Commons Attribution (CC BY 4.0) per the MDPI copyright statement on the title page. SHA256 recorded in frontmatter. No external funding (Funding statement, p. 12). No declared conflicts of interest beyond the USDA trade-name disclaimer.

Wiki pages this source may touch

• cadmium
• arsenic
• arsenic-total
• mercury
• mercury-total
• chromium
• copper
• cobalt
• zinc

Page history

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