DNA from two bacteria was detected in many of the pooled table-egg samples examined in Assiut City, Egypt. Listeria monocytogenes DNA appeared in 32 of 58 samples, or 55.2%, while Salmonella enteritidis DNA appeared in 29, or 50%. The reported overall difference was not statistically significant.
In stool samples from diarrheic patients, Salmonella enteritidis DNA was detected in 41.17% of samples, compared with 11.76% for Listeria monocytogenes. That difference was reported as statistically significant. The result is a DNA-detection prevalence, not confirmation of viable bacteria or direct transmission.
The signal was strongest on the shell
For both organisms, detections were more concentrated on egg shells than in the egg contents. Listeria monocytogenes DNA was found on 44.82% of farm-egg shells and 58.62% of Baladi-egg shells, but in only 3.44% and 10.34% of their contents, respectively. Salmonella enteritidis DNA was detected on 34.48% of farm shells and 65.51% of Baladi shells, with none detected in either content group.
The Salmonella shell results varied significantly by egg type, while the Listeria results showed a significant shell-content difference. That pattern identifies where the DNA was found, but it does not establish direct zoonotic transmission.
What the researchers tested
The cross-sectional study included 58 pooled fresh hen-egg samples, split between 29 farm pools and 29 Baladi pools. Each pool represented three eggs. It also included 34 stool samples from diarrheic patients aged from 5 months to 16 years, including 20 males and 14 females.
Eggs were selected through systematic random sampling at multiple supermarkets on different days and times between June and November 2025. Cracked, improperly stored, contaminated, unlabeled, or inadequately collected samples were excluded. The researchers extracted DNA from shells, contents, and stool samples, then stored the extracts at minus 20 degrees Celsius.
The laboratory testing used PCR, a method that looks for specific genetic material. The assay targeted the Listeria monocytogenes hemolysin hlyA gene and Salmonella enteritidis phage type 4. The team summarized prevalence with descriptive statistics and used chi-square tests for categorical comparisons, treating a p-value below 0.05 as statistically significant.
Differences by age, sex and symptoms were tentative
The patient data showed descriptive differences by sex and age, but none of those comparisons was statistically significant. Listeria monocytogenes detection was 15% in males and 7.14% in females, while Salmonella enteritidis detection was 35% in males and 50% in females. Listeria was highest in the 5-month-to-1-year group at 20%, whereas Salmonella was highest in the group older than 5 and up to 10 years at 54.54%.
Among cases in which Salmonella enteritidis DNA was detected, abdominal pain was reported in 60%, compared with 40% for vomiting and fever and 50% for dehydration. Among cases with detected Listeria monocytogenes DNA, vomiting and abdominal pain were each reported in 20%, while dehydration and fever were reported in 0%. Detection rates according to accompanying symptoms were not significantly different, and these exploratory patterns cannot establish that a pathogen caused a particular symptom.
A warning about what PCR can show
The central limitation is that the researchers did not follow PCR with culture-based isolation or confirmation. The tests therefore showed the presence of pathogen DNA, not whether live bacteria were still present. The study also did not include serotyping, virulence-gene testing, antimicrobial susceptibility testing, or whole-genome sequencing, so it could not assess the organisms in those ways.
The authors describe the findings as a potential public-health concern, but explicitly say that pathogen DNA does not confirm viable bacteria or direct zoonotic transmission. The results should therefore be read as detection findings from the sampled eggs and patients, not proof that eggs caused the patients’ illness.
The protocol was approved by the relevant Assiut University scientific and ethics committees, and written informed consent was obtained from the human participants. The authors declare no competing interests. The paper states that open-access funding came from STDF in cooperation with EKB, while also saying that the study itself received no funding from governmental or private institutions.
Paper data and sources
Original title: Molecular investigation on Listeria monocytogenes and Salmonella enteritidis in table eggs and diarrheic patients.
Authors: Asmaa A Rayan, Reem M Alsaadawy, Marwa G Abd El Kader
Journal/Repository: Scientific reports
Status: Peer-reviewed
First online: 2026-08-20
DOI: 10.1038/s41598-026-66486-1
Original paper · Full text