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Cytotoxic Escherichia coli strains encoding colibactin and cytotoxic necrotizing factor (CNF) colonize laboratory
Yan Feng1, Anthony Mannion1, Carolyn M Madden1
1Division of Comparative Medicine, Massachusetts Institute of Technology, 77 Massachusetts Avenue, 16-825, Cambridge, MA 02139 USA.
Background:
Many Escherichia coli strains are considered to be a component of the normal flora found in the human and animal intestinal tracts. While most E. coli strains are commensal, some strains encode virulence factors that enable the bacteria to cause intestinal and extra-intestinal clinically-relevant infections. Colibactin, encoded by a genomic island (pks island), and cytotoxic necrotizing factor (CNF), encoded by the cnf gene, are genotoxic and can modulate cellular differentiation, apoptosis and proliferation. Some commensal and pathogenic pks+ and cnf+ E. coli strains have been associated with inflammation and cancer in humans and animals.
Results:
In the present study, E. coli strains encoding colibactin and CNF were identified in macaque samples. We performed bacterial cultures utilizing rectal swabs and extra-intestinal samples from clinically normal macaques. A total of 239 E. coli strains were isolated from 266 macaques. The strains were identified biochemically and selected isolates were serotyped as O88:H4, O25:H4, O7:H7, OM:H14, and OM:H16. Specific PCR for pks and cnf1 gene amplification, and phylogenetic group identification were performed on all E. coli strains. Among the 239 isolates, 41 (17.2%) were pks+/cnf1-, 19 (7.9%) were pks-/cnf1+, and 31 (13.0%) were pks+/cnf1+. One hundred forty-eight (61.9%) E. coli isolates were negative for both genes (pks-/cnf1-). In total, 72 (30.1%) were positive for pks genes, and 50 (20.9%) were positive for cnf1. No cnf2+ isolates were detected. Both pks+ and cnf1+ E. coli strains belonged mainly to phylogenetic group B2, including B21. Colibactin and CNF cytotoxic activities were observed using a HeLa cell cytotoxicity assay in representative isolates. Whole genome sequencing of 10 representative E. coli strains confirmed the presence of virulence factors and antibiotic resistance genes in rhesus macaque E. coli isolates.
Conclusions:
Our findings indicate that colibactin- and CNF-encoding E. coli colonize laboratory macaques and can potentially cause clinical and subclinical diseases that impact macaque models.
Insights
Colibactin (pks) and cytotoxic necrotizing factor (CNF) encoding Escherichia coli strains were found in macaques. These bacteria may cause disease, impacting their use in research models.
Area of Science:
- Microbiology
- Genomics
- Veterinary Medicine
Background:
- Escherichia coli (E. coli) is a common gut bacterium, but some strains possess virulence factors like colibactin (pks island) and cytotoxic necrotizing factor (CNF).
- These genotoxic factors are linked to inflammation and cancer in humans and animals.
- The presence and impact of these virulence factors in macaque models are not fully understood.
Purpose of the Study:
- To investigate the prevalence of colibactin (pks) and CNF-encoding E. coli in macaques.
- To characterize these E. coli strains and assess their potential virulence.
- To evaluate the implications for macaque models in biomedical research.
Main Methods:
- Bacterial cultures from rectal and extra-intestinal macaque samples.
- Biochemical identification, serotyping, and phylogenetic grouping of E. coli isolates.
- Polymerase Chain Reaction (PCR) for pks and cnf1 gene detection.
- HeLa cell cytotoxicity assays and whole genome sequencing.
Main Results:
- 239 E. coli strains were isolated from 266 macaques; 30.1% carried pks genes and 20.9% carried cnf1.
- Colibactin and CNF cytotoxic activities were confirmed in representative isolates.
- pks+ and cnf1+ E. coli strains predominantly belonged to phylogenetic group B2.
- Whole genome sequencing revealed virulence factors and antibiotic resistance genes.
Conclusions:
- Colibactin- and CNF-encoding E. coli strains are present in laboratory macaques.
- These bacteria have the potential to cause clinical and subclinical diseases in macaques.
- Findings highlight the importance of considering E. coli virulence factors in macaque research models.
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