Prevalence, species diversity, and antimicrobial resistance profile of Listeria monocytogenes in retail meat and dairy products in Southern Ethiopia

Abstract

Listeriosis, caused by Listeria monocytogenes (L. monocytogenes), is an important foodborne disease characterized by low incidence but high case fatality rates. Its prevalence varies across regions and is influenced by hygiene practices, food handling, and environmental conditions. In developing countries like Ethiopia, data on L. monocytogenes is often limited due to a lack of awareness. This study aims to assess the prevalence of L. monocytogenes in retail meat and dairy products and evaluate their antimicrobial profiles. A total of 422 food samples were collected from May 2022 to March 2023 using a cross-sectional study design. The Listeria species were isolated and identified using culture-based methods and PacBio sequencing. Antimicrobial susceptibility testing of L. monocytogenes was performed using the standard disk diffusion method on Mueller Hinton agar against six antibiotics commonly used in both veterinary and human medicine. Among the 422 food samples analyzed, 69 (16.4%) tested positive for Listeria species, of which 25 (5.9%) were identified as L. monocytogenes. The highest prevalence was observed in cheese (12.9%, 95% CI: 7.4–21.7%), followed by raw fish (9.8%, 95% CI: 5.0–18.1%) and raw meat (4.7%, 95% CI: 1.8–11.5%). Among the isolated Listeria species, L. monocytogenes (36%) was the most predominant, followed by L. innocua (25%) and L. seeligeri (16%) in the study area. L. monocytogenes isolates were susceptible to gentamicin, vancomycin, sulfamethoxazole, and amoxicillin, while exhibiting the highest resistance rate (100%) to penicillin. This finding indicates the presence of Listeria species in meat and dairy products, with particular concern for L. monocytogenes, which, despite its low prevalence, requires special attention due to its high case fatality rate. Therefore, training in hygienic handling practices for meat and dairy products is essential to minimize the risk of foodborne diseases. Moreover, reducing antibiotic resistance requires regulating and promoting the prudent use of antibiotics in food-producing animals.

Introduction

Listeria species are Gram-positive bacteria widely distributed across diverse environments¹. To date, approximately twenty-eight species have been identified within the genus, broadly categorized into Listeria sensu stricto and Listeria sensu lato groups. Among these, L. monocytogenes is of greatest public health concern as the causative agent of human listeriosis, a sporadic foodborne disease primarily associated with the consumption of contaminated foods^2,3. The public health significance of L. monocytogenes is largely attributed to its remarkable resilience; the pathogen can survive and multiply under adverse conditions such as low pH, high salt concentrations, and refrigeration temperatures. Additionally, its ability to form biofilms and tolerate sanitizers enables persistence in food processing environments, making it a persistent challenge for food safety and the food industry^1,4,5.

Listeriosis ranges from a mild, self-limiting illness in healthy individuals to severe systemic infections in high-risk populations⁶. Clinical manifestations vary depending on the host’s immune status; healthy individuals typically experience mild flu-like symptoms or febrile gastroenteritis, whereas vulnerable groups, including pregnant women, neonates, the elderly, immunocompromised individuals, and patients with malignancies who may develop invasive diseases such as meningitis, septicemia, and pregnancy-related complications^7–10. Listeriosis is associated with a high mortality rate of approximately 20–30%, which may be even higher among susceptible populations². Notably, pregnancy-associated listeriosis is particularly devastating, with approximately 20% of cases resulting in spontaneous abortion or stillbirth, and many surviving infants developing neonatal listeriosis^11,12.

Globally, L. monocytogenesis an important foodborne pathogen responsible for severe outbreaks associated with a wide range of contaminated foods¹³. Reported prevalence varies considerably across food types, including raw milk (2–12%), poultry (0–85%), fish products (4–60%), and ready-to-eat foods, meat, and vegetables^14–16. Although listeriosis outbreaks are well documented in developed regions such as Europe and the United States, surveillance systems and reporting capacity remain limited in many African countries, including Ethiopia. Despite this gap, available Ethiopian studies consistently report notable levels of contamination, with Listeria species detected in approximately 20% to 38.6% of examined food samples^6,17,18. Collectively, these findings highlight a substantial knowledge gap in the occurrence, distribution, and antimicrobial susceptibility of L. monocytogenes within Ethiopia’s food safety and public health systems. Furthermore, data on the prevalence of L. monocytogenes in retail meat and dairy products in the study area are limited, and local antibiotic resistance patterns remain poorly understood. Therefore, this study was conducted in Arba Minch and surrounding towns in southern Ethiopia to assess the prevalence and antimicrobial susceptibility of L. monocytogenes isolated from retail meat and dairy products. The baseline data generated are expected to support estimation of the local listeriosis burden and provide evidence to guide public health interventions, strengthen food safety policies, and inform clinically relevant therapeutic decisions.

Materials and methods

Study area

This study was conducted in Arba Minch and its surrounding towns. Arba Minch is the administrative city of the Gamo Zone, which is located in the Southern region of Ethiopia, approximately 505 km south of Addis Ababa, the capital city of Ethiopia. The Gamo Zone lies between 5°34′16.31′′ N and 7°20′58.01′′ N latitude, and 36°22′13.04′′ E and 37°51′26.31′′ E longitude (Fig. 1). According to the Central Statistical Agency (CSA), the zone has an estimated population of about 1.69 million people and covers an area of approximately 16,530 km². The study was conducted in all supermarkets, butcheries, and dairy shops in the area. The local culture includes a strong consumption of raw meat and ready-to-eat foods, with over 100 butcheries and one municipal abattoir providing slaughtering services.

Fig. 1.

Administrative map of sampling site and Gamo Zone, Southern Ethiopia.

Study design and period

A cross-sectional study was conducted from May 2022 to March 2023 to assess the prevalence of Listeria monocytogenes in retail meat and dairy products in Arba Minch and surrounding towns.

Sample size determination

The current study employed the Cochrane formula¹⁹ to determine the appropriate sample size. Due to the lack of available estimates regarding the prevalence of Listeria species among public dining places in the study locations, a conservative estimate of 50% was used to ensure an adequate sample size.

Where P is the prevalence of L. monocytogenes in susceptible food samples, MOE is the standard deviation of the observation which is allowable with Z α/2 (1.96), 95% confidence interval. (CI)

Sampling technique

Study samples were collected using simple random sampling with proportional allocation from a comprehensive list of public dining establishments in the town of Arba Minch, Shelle, and Birbir.

Sample collection and processing

A total of 422 food samples, consisting of raw meat (n = 85), yoghurt (n = 85), cheese (n = 85), raw fish (n = 82) and cream cake (n = 85) of only Ethiopian products were purchased randomly from retail markets, shops, supermarkets and food vendors of the study area. The samples were collected using the method described by authors (International Organization for Standardization²⁰. About 100gm or ml of each food type with a usual consumer size of the product was purchased and taken as a sample unit. Samples were taken once every three months. All samples were collected aseptically using disposable gloves to minimize the risk of cross-contamination. Collected samples were transported immediately to the Bacteriology Unit of the Microbiology Laboratory, Arba Minch University, and processed within 1–2 h of collection. All information about the sample type, purchasing date/time and, place/site analyzing date/time were recorded. Upon arrival, the samples were stored in a refrigerator at 4 °C until processing began.

Specimen preparation

Each sample unit was thoroughly mixed to achieve uniform content, and approximately 50 g was aseptically collected for testing. For the cream cake, 10 g from each sample units was taken in a sterile Petri dish (Nest Biotechnology, China), concentrating solely on the cream. For the cheese, 50 g was sampled from various locations within the 500-gram batch using a sterile stainless-steel spoon (Thermo Fisher Scientific, USA). In the case of the raw meat and fish, 50 g were cut from different sections of the 500-gram sample with a sterile scalpel and knife (Swann-Morton, UK) and placed into a sterile Petri dish. For the yoghurt, 25 milliliters was extracted from the 500-milliliter sample into an Erlenmeyer flask (Pyrex, USA). Subsequently, the samples were thoroughly mixed: the yoghurt was agitated, the raw meat and fish samples were chopped with a sterile knife, the cream cake samples were blended with a sterile scalpel, and the cheese was homogenized with a sterile scalpel.

Inoculation and isolation

A 25 g/mL sample from the composite mixture was transferred into 225 mL of Listeria enrichment broth (LEB; Oxoid, UK) and mixed for 30 min on an orbital shaker (IKA KS 4000 i Control, Germany) at 2500 rev/min. The sample was then incubated at 30 °C for 48 h in an incubator shaker (TH 30; Edmund Bühler, Germany). After this enrichment, the LEB suspension was vortexed (VELP Scientifica, Italy), and 0.1 mL was used to inoculate 10 mL of Modified Fraser broth (MFB; Oxoid, UK). The MFB was incubated at 35 °C for 24 h. Tubes showing a black/dark brown or dark green color were considered positive.

A loopful from a positive MFB culture was streaked onto Brain Heart Infusion (BHI; Oxoid, UK). The plates were incubated at 35 °C for 24–48 h. On media, Listeria species form 1–2 mm diameter colonies that are black or grey-green with a black sunken center and a surrounding black halo. Following the method of Falana²¹, 3–5 well-isolated, typical colonies from each medium were picked and suspended in Tryptic Soy Yeast Extract broth (TSY; HiMedia, India). After incubation at 37 °C until slight turbidity appeared, the suspension was streaked onto Tryptose yeast extract agar (TYEA; HiMedia, India) plates to obtain pure cultures, which were incubated for 24 h at 37 °C. Grey-whitish colonies were suspected to be Listeria. Pure colonies were confirmed using standard biochemical tests, including motility, hemolysis, gram staining, carbohydrate utilization test (Carbohydrates Utilisation Broth Base ISO, Condalab, Madrid, Spain) and the CAMP test. The CAMP test was carried out using the standard perpendicular-streak technique on sheep blood agar (Oxoid, UK) plates. Staphylococcus aureus (ATCC 25923) was used as the indicator strain to demonstrate enhanced hemolysis for L. monocytogenes. Plates were incubated at 35–37 °C for 18–24 h and examined for the characteristic arrowhead-shaped zone of enhanced hemolysis at the intersection of the test isolate and S. aureus streak. Isolates showing a positive CAMP reaction consistent with L. monocytogenes were recorded as confirmed. Following biochemical confirmation, positive isolates from each study site were pooled to obtain representative samples for PacBio sequencing using the PacBio Sequel II platform (Pacific Biosciences, USA) to characterize circulating Listeria strains within the study area.

Bacterial DNA extraction

Bacterial DNA extraction was performed using the alkaline heat lysis method following protocols adapted from Michigan State University, College of Human Medicine, with minor modifications. Briefly, well-isolated bacterial colonies grown on agar plates were aseptically transferred and suspended in 0.85% sterile saline solution (Oxoid Ltd., UK). Approximately 1 ml of the bacterial suspension was transferred into sterile 1.5 ml microcentrifuge tubes (Eppendorf, Germany) and centrifuged at 12,000 × g for 3 min using a benchtop microcentrifuge (Eppendorf 5424, Germany). The supernatant was carefully discarded, and the pellet was completely resuspended in 1 ml of 0.85% NaCl solution (Sigma-Aldrich, USA). The suspension was centrifuged again at 12,000 × g for 3 min, and the supernatant was discarded. The resulting pellet was resuspended in 1 ml of sterile nuclease-free water (Thermo Fisher Scientific, USA). The suspension was then subjected to boiling at 100 °C for 10 min using a dry heat block (Bio-Rad Laboratories, USA) to lyse the bacterial cells. Immediately after boiling, the lysate was centrifuged at 12,000 × g for 1 min to pellet cellular debris. The supernatant containing genomic DNA was carefully transferred to sterile microcentrifuge tubes. The extracted DNA was quantified using a Nanodrop (JENWAY-65847) to determine both concentration and purity prior to shipment to South Africa for sequencing on the Pacific Biosciences RSII platform. The extracted DNA was stored at − 20 °C (Haier Biomedical Freezer, China) for subsequent molecular analysis.

PacBio library preparation and sequencing

To amplify the full-length 16 S rRNA gene from genomic DNA, universal primer sets 27 F (AGRGTTYGATYMTGGCTCAG) and 1492R (RGYTACCTTGTTACGACTT) were used. Sample-specific PacBio barcode sequences were added to both the forward and reverse primers to facilitate multiplex sequencing. Twenty-seven cycles of PCR amplification were performed with KAPA HiFi Hot Start DNA Polymerase (KAPA Biosystems), involving denaturation at 95 °C for 30 s, annealing at 57 °C for 30 s, and extension at 72 °C for 60 s. Agilent Technologies provided the Fragment Analyzer for post-amplification quality control. After amplification, the DNA from each sample was combined at equal concentrations before constructing the library. The SMRTbell Express Template Prep Kit 2.0 (PacBio, USA) was used to process the amplified DNA pool, following the specific protocol for multiplexed library preparation and sequencing (Part Number 100–938 − 900 Version 04, PACBIO). The constructed library was purified using AMPure PB beads (Part Number: 100–265-900, PacBio, USA). The fluorescence concentration and average size of the library pool were determined using a fragment analyzer (Agilent Technologies, USA) and a Qubit HS DNA kit (Qubit Fluorometer, Invitrogen, USA). Primer annealing and polymerase binding were conducted with the Sequel II Binding Kit 2.1 and the Sequel II DNA Internal Control Complex 1.0 (PacBio, USA) before loading the pool into the sequencer. Sequencing was performed on the Sequel II PacBio system with the Sequel II Sequencing Kit 2.0 (PacBio, USA)²².

Microbial community analysis using PacBio

The data obtained from Pacific Biosciences were demultiplexed, and circular consensus sequence (CCS) reads were generated using the SMRT Link analysis software (v9). The raw reads from the three samples underwent processing via the HiFi-16 S workflow. Initially, this workflow assessed the quality of each read, eliminating those of low quality. Reads that satisfied the quality criteria were subsequently analyzed using Cutadapt and DADA2 software. These procedures involved reorienting the sequences, excising forward and reverse primers, filtering and trimming based on sequence length and average quality, dereplicating the reads, estimating sequencing errors with PacBio’s error model, and determining the composition of the samples. Chimeric amplicon sequence variants (ASVs) were excluded, and the remaining ASVs were annotated using the VSEARCH classifier from QIIME and DADA2, employing the species training set from the Silva138.2 database with a minimum bootstrap confidence level of 80.

Antimicrobial susceptibility test

Antimicrobial susceptibility of L. monocytogenes isolates was determined for tetracycline (TE 30 µg), vancomycin (VA 30 µg), gentamicin (CN 10 µg), penicillin (P 10 µg), amoxicillin (AML 20 µg), and sulfamethoxazole (SXT 25 µg) (Oxoid Ltd, Basingstoke, Hampshire, England), using the Kirby-Bauer disk diffusion method²³ on Mueller-Hinton agar (Oxoid Ltd., England), following NCCLS guidelines. The selection of antimicrobials was based on their availability and their frequent use in both veterinary and human medicine within the study area. Briefly, 2–3 pure colonies from a tryptone yeast extract agar plate were suspended in Mueller-Hinton broth and incubated at 37 °C for 1–2 h. The turbidity of the suspension was adjusted to match a 0.5 McFarland standard (BioMérieux, HiMedia, Oxoid). A sterile cotton swab (Oxoid, HiMedia, Copan) dipped into the standardized suspension was used to create a lawn on Mueller-Hinton agar plates. Antibiotic discs were then aseptically placed on the inoculated agar. After 24 h of incubation at 37 °C, the zones of inhibition were measured with a digital caliper (Mitutoyo, Fisher Scientific). The susceptible, intermediate, and resistant categories were assigned based on the critical points recommended by the Clinical and Laboratory Standards Institute²⁴ and according to the manufacturer’s leaflet attached to the disks.

Statistical analysis

Data were entered and analyzed using the statistical software SPSS version 20.0. Descriptive statistics were used to summarize the frequency and percentage of Listeria species detected in different food samples. The prevalence of L. monocytogenes and other Listeria species across food categories was compared using the chi-square (χ²) test to determine statistically significant differences. In addition, 95% confidence intervals (CI) were calculated for prevalence estimates. Similarly, frequency and percentage were used to describe L. monocytogenes antimicrobial susceptibility patterns as resistant, intermediate, or susceptible. Statistical significance was considered at a p-value of less than 0.05.

Quality control

Reference strains of Staphylococcus aureus (ATCC 25923) and Listeria monocytogenes (ATCC 19111) were obtained from the Ethiopian Public Health Institute (EPHI), Addis Ababa, and were included as positive controls to verify the performance of both the culture method and the antimicrobial susceptibility testing procedures.

Result

Prevalence of Listeria monocytogenes and other Listeria species in food items

A total of 422 samples were analyzed, L. monocytogenes was detected in 25 samples, representing 5.9% of the total, while other Listeria species were identified in 44 samples (10.4%). Combined, Listeria contamination was observed in 69 samples, yielding a total prevalence of 16.4%. The prevalence of L. monocytogenes differed significantly across food types (χ² = 17.19, df = 4, p = 0.0018) (Table 1). The prevalence ranged from 0.0% in cream cake to 12.9% in cheese. The highest prevalence was observed in cheese (12.9%, 95% CI: 7.4–21.7%), followed by raw fish (9.8%, 95% CI: 5.0–18.1%) and raw meat (4.7%, 95% CI: 1.8–11.5%). Lower prevalence was observed in yoghurt (2.3%, 95% CI: 0.6–8.2%), while no L. monocytogenes was detected in cream cake (0.0%, 95% CI: 0.0–4.3%). Similarly, the prevalence of other Listeria species varied significantly among food types (χ² = 22.58, df = 4, p < 0.001). The highest contamination rate was observed in raw fish (23.2%, 95% CI: 15.4–33.4), followed by raw meat (10.6%, 95% CI: 5.7–18.9) and yoghurt (9.4%, 95% CI: 4.8–17.5). Cheese samples showed moderate contamination (8.2%, 95% CI: 4.0–16.0), while cream cake exhibited the lowest prevalence (1.2%, 95% CI: 0.2–6.4). These findings indicate that raw fish may represent a major potential reservoir for other Listeria species in the study area (Table 1).

Table 1.

Prevalence of L. monocytogenes and other Listeria species in retail meat and dairy products in Arba Minch and the surrounding towns.

Variable	Raw fish (n = 82)	Cheese (n = 85)	Raw meat (n = 85)	Yoghurt (n = 85)	Cream cake (n = 85)	Total (N = 422)	χ²	P-value
L. monocytogenes	8 (9.8%)	11 (12.9%)	4 (4.7%)	2 (2.3%)	0 (0.0%)	25 (5.9%)	χ² = 17.19	P < 0.001
95% CI	5.0–18.1%	7.4–21.7%	1.8–11.5%	0.6–8.2%	0.0–4.3%
Other Listeria spp.	19 (23.2%)	7 (8.2%)	9 (10.6%)	8 (9.4%)	1 (1.2%)	44(10.4%)	χ² = 22.58	P < 0.001
95% CI	15.4–33.4%	4.0–16.0%	5.7–18.9%	4.8–17.5%	0.2–6.4%
Total	27 (32.9%)	18 (21.2%)	13 (15.3%)	10 (11.7%)	1 (1.2%)	69(16.4%)

Sequence preprocessing

Comprehensive 16 S rRNA amplicon sequencing generated significant raw datasets from three sampling sites: Arba Minch (29,264 sequences), Shelle (48,335 sequences), and Birbir (17,627 sequences). These datasets underwent a thorough preprocessing workflow that included several quality control steps: trimming low-quality regions, removing ambiguous bases, eliminating adapter sequences, denoising to correct sequencing errors, and filtering out chimeras to discard any artificial recombinant sequences. This meticulous curation process resulted in final high-quality sequence counts of 8,921 for Arba Minch, 11,412 for Shelle, and 6,732 for Birbir, corresponding to retention rates of about 30.5%, 23.6%, and 38.2%, respectively.

Listeria spp assessment with PacBio sequencing

The high-quality sequences were used for taxonomic classification against the latest Silva database release. Based on the analysis results, the microbial community from all samples consisted mainly of seven Listeria species, dominated by L. monocytogenes, with average relative abundances of 39% in sample Arba Minch, 31.6% in sample Shelle, and 38% in sample Birbir. As shown in Fig. 2, the predominant Listeria species identified were L. monocytogenes (36%), L. innocua (25%), L. seeligeri (16%), L. welshimeri (12%), L. ilorinensis (5%), L. ivanovii (3%), and L. marthii 21 (3%). Species distribution varied across locations, with Arba Minch Town exhibiting greater diversity. In this location, L. monocytogenes (13%) was the most prevalent species, followed by L. innocua (5%). Other species, including L. ivanovii (4%), L. ilorinensis (3%), L. marthii (3%), L. welshimeri (3%), and L. seeligeri (2%) were detected at lower relative abundances. The presence and varying prevalence of L. monocytogenes, a primary human pathogen, highlight significant food safety concerns and point to different contamination profiles across the retail sources in the study area (Fig. 2).

Fig. 2.

The relative abundance of Listeria at the species level isolated from retail meat and dairy products.

Antimicrobial susceptibility profile of L. monocytogenes

The antimicrobial susceptibility patterns of 25 confirmed L. monocytogenes isolates were evaluated against six commonly used antibiotics. The findings revealed distinct variations in susceptibility, underscoring important implications for treatment and public health. Notably, all 25 (100%) L. monocytogenes isolates exhibited resistance to penicillin, indicating a striking and concerning level of resistance to this traditionally used antibiotic. In contrast, gentamicin, vancomycin, and amoxicillin demonstrated complete susceptibility (100%) among all tested isolates, highlighting their strong therapeutic potential and reliability as effective treatment options for L. monocytogenes infections. Tetracycline showed moderate resistance, with 16% of isolates resistant and 24% exhibiting intermediate, representing a 40% non-susceptibility rate. Similarly, sulfamethoxazole displayed low resistance (4%) and high susceptibility (96%), indicating that it remains a generally effective antimicrobial agent against L. monocytogenes (Table 2).

Table 2.

Antimicrobial resistance profiles of L. monocytogenes isolated from retail meat and dairy products in Arba Minch and the surrounding towns.

Antimicrobial agent	Number of isolates (%)
	Resistance	Intermediate	Susceptible
Sulfamethoxazole	1(4%)	0	24(96%)
Gentamicin	0	0	25(100%)
Tetracycline	4(16%)	6(24%)	15(60%)
Vancomycin	0	0	25(100%)
Amoxicillin	0	0	25(100%)
Penicillin	25(100%)	0	0

Discussion

This study demonstrates a significant prevalence of Listeria species (16.4%) and the pathogen L. monocytogenes (5.9%) in retail meat and dairy products within the study area, highlighting a substantial public health risk. The rate of L. monocytogenes isolation aligns with reports from Ethiopia^18,25 and Chile²⁶ but is lower than findings from Norway²⁷ and Turkey²⁸ and higher than those from Morocco²⁹. These disparities might be due to differences in food composition, processing hygiene, and methodological sensitivities. A critical finding is the identification of high-risk food commodities. Raw fish emerged as the most contaminated product (p < 0.0001), with a total Listeria prevalence of 32.9% (9.7% L. monocytogenes). This finding is higher than the results reported by Derra et al.³⁰. Cheese was also a major concern, with a total prevalence of 21.2%, including a notably high 12.9% for L. monocytogenes. This result is consistent with the report by Seyoum et al.³¹, but the rates exceed previous national reports^30,32, indicating an urgent need for targeted intervention in these supply chains. In contrast, cake samples showed minimal contamination of Listeria species (1.2%), suggesting their composition or processing is less conducive to Listeriasurvival. The finding is consistent with the report by Wei et al.³³. Raw meat products showed a relatively higher level of contamination with Listeria species, consistent with findings from previous studies in Ethiopia^17,30,34. Specifically, the prevalence of L. monocytogenes from raw meat in this investigation was comparable to earlier reports from Ethiopia^31,35 but higher than findings from Korea³⁶. The microbial community structure, elucidated via 16 S rRNA sequencing, revealed study sites consisted mainly of seven Listeria species, dominated by L. monocytogenes, with average relative abundances of 39% in Arba Minch samples, 31.6% in Shelle samples, and 38% in Birbir samples. The relative abundance result is slightly consistent with¹⁸ and³³. In the present study, the predominant identified Listeria species were L. monocytogenes (36%), L. innocua (25%), L. seeligeri (16%), L. welshimeri (12%), and L. ivanovii (5%). This finding is in line with the report of¹⁸, where 27%, 14.48%, 8. 28%, 3.10%, and 2. 7% respectively. In particular, L. innocua, which was the second most abundant species (25%), is often considered an indicator organism for Listeria contamination and may signal inadequate hygiene practices during food processing, handling, and storage³⁷. Species distribution varied across locations, with Arba Minch exhibiting greater diversity. L. monocytogenes and L. innocua were the most prevalent species, followed by L. seeligeri, while L. welshimeri, L. ilorinensis, L. ivanovii, and L. marthii 21 occurred at lower relative abundances. This finding is consistent with the research conducted in Jimma¹⁸ but lower than the research conducted in Nigerian³⁸.

The antimicrobial susceptibility profile of the isolates is a paramount concern. A striking 100% of L. monocytogenes isolates were resistant to penicillin. This high resistance rate is consistent with observations in other studies^17,18 and may be correlated with the widespread, uncontrolled use of this low-cost antibiotic in the community^17,18,39. In stark contrast, high susceptibility was maintained to gentamicin, vancomycin, and amoxicillin, confirming their therapeutic utility. This finding is more in line with findings from Jimma¹⁸. The presence of multi-drug resistant profiles in 16% of isolates, alongside moderate resistance to tetracycline, signals a troubling trend that complicates potential clinical management. This finding is slightly contrary to the work from Mekelle²⁵.

Conclusion and recommendation

This study demonstrated the presence of Listeria species in retail meat and dairy products, confirming that foodborne contamination represents a potential public health concern in the study area. Overall, Listeria species were detected in 16.4% of samples, with L. monocytogenes identified in 5.9%, highlighting its clinical importance. Contamination varied across food types, with raw fish (32.9%) and cheese (21.2%) showing the highest prevalence, indicating that these foods may serve as key exposure sources. The detection of L. innocua further suggests environmental contamination within the food production and handling chain. Antimicrobial susceptibility testing revealed that L. monocytogenes isolates exhibited resistance to penicillin while remaining susceptible to amoxicillin, vancomycin, gentamicin, sulfamethoxazole, and tetracycline. These findings indicate the circulation of resistant L. monocytogenes strains alongside heterogeneous contamination across food types, emphasizing the need for strengthened food safety practices, improved hygiene throughout the food supply chain, and prudent antimicrobial use to mitigate public health risks. We recommend immediate strengthening of retail-level food safety surveillance through routine microbiological testing, regular sanitary inspections, and targeted training for food handlers, led by regulatory and public health authorities, with food retailers implementing improved hygiene and safe handling practices.

Limitations of the study

This study has several limitations related to its design and scope. The cross-sectional nature of the study provides only a snapshot of contamination and does not capture potential temporal or seasonal variations. In addition, sampling was limited to retail food outlets, which may introduce sampling bias and does not allow assessment of contamination sources across the entire food production chain. Molecular confirmation was also limited, as only three isolates were subjected to sequencing, which may not adequately represent the genetic diversity of the detected pathogens. Also, the relatively limited sample size and geographic coverage may affect the generalizability of the findings. Future studies incorporating longitudinal designs, broader geographic coverage, larger sample sizes, and advanced molecular characterization are recommended to better understand pathogen distribution and associated public health risks.

Abbreviations

CAMP

Christe atkins munch peterson

LAB

Lactic acid bacteria

LPM

Lithium chloride phenylethanol moxacalatam medium

C I

Confidence interval

NCCLS

National committee for clinical laboratory standards

RTE

Ready to eat

CSA

Central statistical agency

Author contributions

Alemu Chemeda, study design, performed research, analyzed data and wrote the paperBikila Wodajo, study design, Review the paper,

Data availability

The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.

Declarations

Competing interests

The authors declare no competing interests.

Ethical approval

Ethical clearance was obtained from the Ethical Review Board of School of Health Science, Arba Minch University. Written consent was received from public dining house owners who participated in this study. Confidentiality of the information was maintained throughout the study.