Ewingella americana

Ewingella americana is a gram-negative, facultatively anaerobic, rod-shaped member of the order Enterobacterales (family Yersiniaceae), first isolated from clinical specimens in 1983 and formerly placed in Enterobacteriaceae before reclassification. Until recently it was a microbiological curiosity — an occasional opportunistic pathogen of immunocompromised patients, most often hospital-acquired, and a pathogen of cultivated mushrooms and some marine animals. It gained aging and oncology relevance in 2025 when Iwata et al. demonstrated that an E. americana strain isolated from the gut microbiota of the Japanese tree frog Dryophytes japonicus achieves 100% complete response in a murine syngeneic colorectal carcinoma model after a single intravenous dose — outperforming anti-PD-L1 antibody (20% CR) and liposomal doxorubicin (0% CR), with immunological memory persisting ≥60 days ¹. This page anchors the species; the primary-source claims are detailed in iwata-2025-ewingella-americana-antitumor.

Taxonomy and identification

Field	Value
Species	Ewingella americana Grimont et al. 1983
NCBI Taxonomy ID	41202
Domain	Bacteria
Phylum	Pseudomonadota (formerly Proteobacteria)
Class	Gammaproteobacteria
Order	Enterobacterales
Family	Yersiniaceae (current)
Gram stain	Negative
Morphology	Rod-shaped (rods/coccobacilli); motile via peritrichous flagella
Oxygen tolerance	Facultative anaerobe
Type strain	ATCC 33852 (= DSM 4580 = CCUG 14506 = LMG 7869 = NCTC 12157 = JCM 5911 = CIP 81.94)
Genome size	~4.87 Mb (GCF_000735345.1, contig-level assembly)
GC content	~54%
Protein-coding genes	4,386 predicted (GCF_000735345.1)
Nomenclatural validation	IJSEM Validation List 13, 1984
Biosafety level	Risk Group 2 (Canada, Switzerland, Germany)

Family reclassification note. E. americana was originally placed in Enterobacteriaceae ² and this placement persists in some older references. Adeolu et al. 2016 (Int J Syst Evol Microbiol) reorganized Enterobacterales using multilocus phylogenomics and established Yersiniaceae as a distinct family; NCBI Taxonomy now places Ewingella within Yersiniaceae. LPSN (List of Prokaryotic names with Standing in Nomenclature) also reflects this assignment. Both family names appear in the clinical literature; Yersiniaceae is the current valid placement. needs-replication — the 2016 reclassification is not universally adopted in clinical microbiology; some contemporary clinical case reports still cite Enterobacteriaceae affiliation.

The genus Ewingella is monotypic — E. americana is its only recognized species. The genus name honors William H. Ewing, an American bacteriologist at the CDC who contributed extensively to Enterobacteriaceae taxonomy ². The species was formerly designated “CDC Enteric Group 40” before Grimont and colleagues formally named the genus and species ².

Identification. Routine clinical microbiology identifies E. americana by biochemical profiling (API 20E or equivalent) and, increasingly, by MALDI-TOF mass spectrometry or 16S rRNA gene sequencing. Misidentification as other Enterobacterales members is reported; mNGS has been used to confirm cases where conventional culture yielded ambiguous results ³.

Discovery and clinical relevance

Grimont et al. 1983 described the genus and species from clinical specimens collected primarily from hospital environments — blood, wounds, and respiratory secretions — in the United States ². The original isolates were obtained from humans, fitting the historical perception of E. americana as a rarely-pathogenic commensal/contaminant of healthcare settings. Formal nomenclatural validation occurred in 1984 via IJSEM Validation List 13.

Documented human infections

Ioannou et al. 2024 (Antibiotics) conducted the most comprehensive review of human E. americana infections, analyzing 19 cases across 16 studies ³. Key patterns:

Median patient age: 55 years; infections not restricted to elderly but consistently associated with immunocompromise
Infection sites: Bloodstream infections (bacteremia/sepsis) most common; also respiratory tract, peritoneal cavity (peritoneal dialysis-associated peritonitis), urinary tract, conjunctiva, and musculoskeletal (vertebral lesion confirmed by mNGS in an ankylosing spondylitis patient ⁴)
Predisposing conditions: Malignancy, chemotherapy, dialysis, neonatal prematurity, structural cardiac anomalies, chronic inflammatory disease
Contamination source: Hospital water systems, sinks, blood product contamination (platelet transfusions, red blood cell transfusions). A 2025 case report documented sepsis developing during red blood cell transfusion in a chemotherapy patient ⁵
Antibiotic susceptibility: Generally susceptible to fluoroquinolones, aminoglycosides, third-generation cephalosporins, and trimethoprim-sulfamethoxazole. One isolate from carbapenem-resistant swine screening showed extended-spectrum resistance ⁶. Overall mortality low — single fatal case (bacteremia) in the Ioannou 2024 series
Mortality: Low; outcome generally favorable with appropriate antimicrobial therapy ³

Non-human reservoir contexts

Beyond human clinical isolation, E. americana has a notably broad environmental and host range:

Cultivated mushrooms: A clinically distinct context — E. americana causes brown blotch and discoloration lesions on button mushrooms (Agaricus bisporus) and other edible species. Strains isolated from Iranian button mushroom farms in 2023 showed variable aggressiveness ⁷. The bacterium produces volatile organic compounds including 2,4-di-tert-butylphenol that are toxic to fungal hosts ⁸
Marine animals: Isolated from a sub-adult loggerhead sea turtle (Caretta caretta) with osteolytic lesions and bacteremia; successfully treated with enrofloxacin ⁹
Plant-associated: An Antarctic isolate (L47) produces L-arabinose isomerase and β-galactosidases ¹⁰; insect gut isolates have been shown to promote tomato plant growth ¹¹
Amphibian gut (Iwata 2025 context): Isolated from the gut microbiota of Dryophytes japonicus (Japanese tree frog) — the specific context that yielded the antitumor strain ¹

This ecological breadth suggests E. americana is a generalist opportunist with metabolic versatility, rather than a host-specialist pathogen.

Genomic and virulence features

The reference genome GCF_000735345.1 (ATCC 33852 type strain) is a contig-level assembly of ~4.87 Mb with ~54% GC content and 4,386 predicted protein-coding genes ¹². This is notably larger than Akkermansia muciniphila (2.66 Mb) and reflects a broader metabolic repertoire consistent with an environmental generalist.

Iwata et al. 2025 analyzed the virulence-factor profile of E. americana using the reference genome against the Virulence Factor Database (VFDB), categorizing predicted virulence factors across multiple functional classes ¹:

Nutritional/Metabolic factors — iron acquisition (siderophores), nutrient uptake systems
Effector delivery system — type III secretion system (T3SS) components; enables translocation of effector proteins into host cells
Immune modulation — capsule and surface polysaccharide components that interfere with complement and phagocytosis
Motility — flagellar apparatus (peritrichous flagella; confirmed motile)
Adherence — fimbriae and outer-membrane adhesins
Regulation — gene-regulatory factors (virulence-gene expression control)
Biofilm — biofilm formation machinery (relevant to hospital-environment persistence)
Stress survival — oxidative-stress response; relevant for TME (tumor microenvironment) survival
Invasion — putative invasin-class proteins enabling epithelial invasion
Exotoxin — hemolysin(s) and secreted cytolysins proposed as direct cytolytic effectors against tumor cells ¹

needs-strain-genome — Iwata et al. 2025 analyzed GCF_000735345.1 (the ATCC 33852 type strain), not the actual Dryophytes japonicus-derived antitumor isolate. Whether the antitumor isolate’s virulence-factor profile matches the reference genome exactly is unknown; strain-level genomic differences may contribute to (or detract from) antitumor efficacy. The paper discusses this limitation.

Aging and oncology context (Iwata 2025)

The Iwata 2025 Gut Microbes study is the primary reason E. americana appears in this wiki ¹. Full mechanistic and experimental detail is in iwata-2025-ewingella-americana-antitumor; summary here for cross-referencing:

Key experimental findings

Model: 4-week-old female BALB/c mice bearing subcutaneous Colon-26 syngeneic colorectal carcinoma; single intravenous injection of 200 µL at 5×10⁹ CFU/mL (= 1×10⁹ CFU per mouse)

Efficacy (n=5 per group, comparative experiment):

Complete response (CR) rate at day 30: 100% (5/5; E. americana, single IV dose) vs 20% (1/5; anti-PD-L1 antibody, 4 doses every other day at 2.5 mg/kg) vs 0% (0/5; liposomal doxorubicin, 4 doses every other day at 2.5 mg/kg)
CR status confirmed histologically at day 30; tumor-free status maintained ≥60 days post-treatment with no recurrence in complete responders ¹

Immunological memory: Animals that achieved CR rejected rechallenge with Colon-26 cells at day 60 (0/10 tumors developed in cured animals vs 10/10 in naïve controls), demonstrating durable adaptive immune memory — consistent with a vaccine-like antitumor effect ¹ needs-replication

Safety: No significant weight loss, overt organ toxicity, or mortality attributable to bacterial treatment in the primary tumor model. The antibiotic-susceptibility profile means treatment could be terminated with standard antibiotics if toxicity emerged — a key regulatory de-risking feature compared to genetically-modified strains ¹

Proposed dual mechanism

Iwata 2025 proposes E. americana’s antitumor activity operates through two converging axes ¹:

Direct cytolysis — hemolysin(s) and secreted cytolysins (exotoxins) directly kill tumor cells; caspase-3-mediated apoptosis and TUNEL-positive cell death confirmed in Colon-26 3D tumor spheroids in vitro and in tumor sections in vivo (IHC). Intratumoral bacterial load increased ~3000-fold between 3 h and 24 h post-injection (colony assay), confirming selective tumor colonization driven by the hypoxic tumor microenvironment — the same tropism described for Bifidobacterium, Salmonella, and Clostridium strains in bacterial cancer therapy.
PAMP-driven immune activation — bacterial PAMPs stimulate innate immune sensors in the TME, triggering recruitment of B cells (CD19+; +3% vs PBS), T cells (CD3+; +5%), and neutrophils (CXCR4+; +30%; the dominant responding population); IFN-γ and TNF-α expression elevated in tumor tissue at 6 h post-injection (qPCR). This immune arm likely underlies the immunological memory and rechallenge rejection ¹

Dimension	Status
Pathway conserved in humans?	partial — caspase-3 apoptosis and PAMP/TLR axes are conserved; tumor-hypoxia tropism likely conserved; direct human tumor cytolysis not demonstrated
Phenotype conserved in humans?	unknown — no human tumor data; Colon-26 is a murine syngeneic model
Replicated in humans?	no — single preclinical paper; no human clinical trial registered as of 2026-05-21

Comparison to other bacterial cancer therapies

E. americana’s natural (non-engineered) origin distinguishes it from the dominant paradigm in bacterial cancer therapy ¹:

Agent	Status	Genetic modification	Key limitation
Salmonella VNP20009	Phase 1 clinical trials; limited efficacy in humans	Attenuated (msbB deletion)	Attenuation reduced cytolytic potency; engineering risk
Listeria-based (ADXS-HPV, axalimogene filolisbac)	Phase 2/3 (cervical cancer)	Attenuated Lm + antigen expression	Requires complex genetic engineering; regulatory complexity
E. coli Nissle 1917 variants	Preclinical	Variable; quorum-sensing kill switches proposed	No natural antitumor activity; requires engineered effectors
E. americana (Iwata 2025)	Preclinical (murine only)	None	Single model; single dose schedule; no human data

The naturally-occurring antitumor activity of E. americana, combined with antibiotic susceptibility providing a “kill switch,” is proposed to lower the regulatory barrier compared to genetically-modified bacterial therapies ¹. See bacterial-cancer-therapy for the broader intervention class context.

Relevance to cancer hallmarks and aging

Cancer incidence rises exponentially with age, making effective cancer therapy directly relevant to the aging wiki’s scope (see cancer). The gut-microbiome-aging-shifts page documents how the aging gut microbiome loses beneficial commensals and gains potentially pro-inflammatory species — the discovery of a gut-derived bacterium with potent antitumor activity adds a new dimension to the microbiome-aging-cancer axis. Whether gut E. americana abundance changes with age, or whether age-related gut microbiome shifts affect the efficacy of E. americana as a therapeutic, are completely unexplored. unsourced

Recency literature search (R25)

Query: “Ewingella americana,” PubMed, 2020–2026-05-21. Results: 22 records. Triage:

Iwata et al. 2025 (PMID 41376334; Gut Microbes) — antitumor; must-include; integrated above
Ioannou et al. 2024 (PMID 38927225; Antibiotics) — narrative review of 19 human infections; most comprehensive clinical reference; integrated above
Rivero et al. 2026 (PMID 41596769; IJMS) — Antarctic isolate; lactose-transforming enzymes; not aging-relevant
Wei et al. 2025 (PMID 41003513; Toxins) — volatile organic compounds; mushroom pathogenicity; not aging-relevant
Jafarova Ayik et al. 2025 (PMID 40636648; Cureus) — sepsis case report; low-tier (Cureus; single case); noted in clinical section with appropriate weighting
Manan et al. 2024 (PMID 39741595; Front Microbiol) — mushroom microbiome survey; not aging-relevant
Salehi et al. 2023 (PMID 36131391; Phytopathology) — mushroom pathogen; not aging-relevant
Fahrimal et al. 2024 (PMID 39033154; BMC Musculoskelet Disord) — mNGS case report in ankylosing spondylitis; integrated as clinical breadth example
Ioannou 2022 (PMID 35223116) — peritoneal dialysis peritonitis case; cited as fourth documented human case at that time
Remaining hits: carbapenem-resistance screening (PMID 35740183), plant growth promotion (PMID 36362334), sea turtle osteomyelitis (PMID 38731321), other case reports and environmental isolates

No meta-analyses or RCTs exist — field is too early-stage. No Iwata 2025 findings are contradicted by other sources in the recency window. The clinical infection literature (19 cases as of Ioannou 2024 review) is entirely case-report/case-series level — Cureus case reports noted but included only as illustrative rather than weight-bearing. The antitumor finding is, as of 2026-05-21, a single-paper result.

Limitations and gaps

needs-replication — Iwata 2025 is a single-lab, single-tumor-model result. Independent replication across additional syngeneic models (MC38, CT26, B16F10) and orthotopic models required before mechanistic conclusions can be firmed
needs-human-replication — No human tumor data. ClinicalTrials.gov search (2026-05-21) finds no registered trials of E. americana as a cancer therapeutic
needs-strain-genome — Antitumor efficacy was demonstrated with a D. japonicus-derived isolate, but virulence-factor analysis used the ATCC 33852 type strain genome. Strain-level genomic comparison is lacking
dose-response-unclear — Single dose schedule (1×10⁹ CFU IV per mouse, once; concentration 5×10⁹ CFU/mL in 200 µL) tested; dose–response, optimal dosing interval, and route alternatives (intraperitoneal, intratumoral, oral) unexplored
long-term-unknown — No long-term safety data in any animal model; Risk Group 2 classification warrants rigorous pharmacokinetics and biodistribution studies in immunocompetent and immunocompromised hosts before human translation
no-mechanism — The specific molecular target(s) responsible for tumor-selective colonization and the identity of the cytolytic hemolysin(s) have not been biochemically characterized
unsourced — Whether E. americana is a normal (if rare) component of the human gut microbiome and whether its abundance changes with aging is unknown; no human gut microbiome abundance data cited here
The oral delivery format required for a scalable therapeutic requires development; Iwata 2025 discusses but does not solve the challenge of protecting bacteria through gastric acid to enable oral dosing

Footnotes

iwata-2025-ewingella-americana-antitumor · doi:10.1080/19490976.2025.2599562 · PMID 41376334 · in-vivo + in-vitro · n=5/group (comparative efficacy experiment, Fig. 3); n=3/group (initial antitumor screening, Fig. 2) · 4-week-old female BALB/c mice, Colon-26 syngeneic model · Iwata S, Yamasita N, Asukabe K, Sakari M, Miyako E · Gut Microbes 2025;17(1):2599562 · PDF locally available · OA: gold (CC BY-NC 4.0) ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹²
doi:10.1016/0769-2609(83)90102-3 · Grimont PAD et al. · Annales de l’Institut Pasteur / Microbiologie 1983 · original description of genus Ewingella and species E. americana from clinical specimens; nomenclatural validation: IJSEM Validation List 13, 1984 · cited_by_count: 72 · no-fulltext-access (closed-access; claims about original isolation context derived from LPSN + NCBI Taxonomy + secondary literature) ↩ ↩² ↩³ ↩⁴
doi:10.3390/antibiotics13060559 · PMID 38927225 · Ioannou P, Baliou S, Kofteridis D · Antibiotics 2024;13(6):559 · narrative review · n=19 documented human infection cases across 16 studies · University of Crete · OA: gold (download pending in a local paper archive) ↩ ↩² ↩³
PMID 39033154 · doi to be confirmed · Fahrimal et al. · BMC Musculoskeletal Disorders 2024 · case report · n=1 · mNGS detection of E. americana in Andersson lesion vertebral biopsy in ankylosing spondylitis patient · needs-replication (single case) ↩
PMID 40636648 · doi to be confirmed · Jafarova Ayik et al. · Cureus 2025 · case report · n=1 · E. americana sepsis during RBC transfusion in chemotherapy patient; treated successfully with ceftriaxone · low-tier (Cureus); weight accordingly ↩
PMID 35740183 · Antibiotics 2022 · survey · E. americana in carbapenem-resistant swine isolates; potential zoonotic significance ↩
PMID 36131391 · Salehi et al. · Phytopathology 2023 · observational (mycology) · 40 E. americana isolates from Iranian button mushroom farms; variable aggressiveness ↩
PMID 41003513 · Wei et al. · Toxins (Basel) 2025 · in-vitro + in-vivo (mushroom) · 16 volatile compounds identified; 2,4-di-tert-butylphenol most potent ↩
PMID 38731321 · Animals (Basel) 2024 · case report (veterinary) · E. americana bacteremia in loggerhead sea turtle; responsive to enrofloxacin ↩
PMID 41596769 · Rivero et al. · IJMS 2026 · in-vitro · Antarctic isolate; lactose-to-tagatose conversion enzymes (~18% tagatose yield) ↩
PMID 36362334 · IJMS 2022 · in-vivo (plant model) · insect gut-derived E. americana with plant growth-promoting properties; 41% increase in tomato fruit yield ↩
NCBI RefSeq GCF_000735345.1 · Ewingella americana ATCC 33852 · contig-level assembly · total sequence ~4.87 Mb · GC 54% · 4,386 protein-coding genes · 55 pseudogenes · queried 2026-05-21 via NCBI Datasets v2 API ↩

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