Identification of Listeria species and Multilocus Variable-Number Tandem Repeat Analysis (MLVA) Typing of Listeria innocua and Listeria monocytogenes Isolates from Cattle Farms and Beef and Beef-Based Products from Retail Outlets in Mpumalanga and North West Provinces, South Africa

Immunogenicity of culture filtrated proteins and whole-cell killed formalin of Listeria monocytogenes to induced cellular immune response in vivo

Background

Listeria monocytogenes (LM) is a life-threatening bacterium affecting many individuals worldwide, including elderly people, pregnant women, and immune-deficient patients.

Aim

Whole-cell killed formalin of LM antigens (WKLMAgs) and Listeria culture filtrated proteins (LCFPs) against challenge-attenuated LM after two booster doses (0 and 14 days) of immunization act as an antigen activating a high level of IgG3, IgM, CXCL2, and IL-1 beta.

Methods

Forty male rats were randomly assigned to four groups. The first group served as a control negative, while the second positive (+) control was inoculation orally 1 ml with virulent (1 × 107 colony forming unit CFU/ml) of LM on day 28, whereas the other two groups were injected with 1-ml WKLMAgs and 1-ml LCFPs in two subcutaneously doses with day 14 intervals, with at day 28 a challenged effective dose (1 × 107 CFU/ml) of virulent LM. Serum blood parameters were measured. During the 35 days, the euthanized animal histopathology studies were performed on the spleen, liver, small intestine, and brain.

Results

The current study indicated a significant difference between WKLMAgs and LCFPs for serological tests Immunoglobulin (Ig) M, chemokine (C-X-C motif) ligand 2, Ig G3, and interleukin-1 beta compared to both negative and positive controls at P < 0.001. Additionally, the WKLMAgs and LCFPs led to a decrease in the histopathological changes of organs such as (brain, spleen, liver, and intestine) compared to the positive control, which affected the organs with microgranuloma, with a pathological difference between the WKLMAgs and LCFPs compared to the negative control group.

Conclusion

Both WKLMAgs and LCFPs are capable to be as a vaccine candidate antigen for the induction of protective immunity against L. monocytogenes.

Prevalence, virulence potential, antibiotic resistance profile, heavy metal resistance genes of Listeria innocua: A first study in consumed foods for assessment of human health risk in Northern Turkey

Listeria (L.) innocua is typically considered a non-pathogenic bacterium that can sometimes act as an opportunistic pathogen in severely immunocompromised patients. However, it plays an important role in food safety because it acts as an indicator organism for potential contamination and the effectiveness of sanitation methods. The aim of this study was to determine the prevalence, virulence genes, antibiotic resistance profiles, heavy metal and disinfectant resistance genes of L. innocua isolates from animal-derived foods. In this study, we isolated and characterized 39 L. innocua strains recovered from commonly 400 consumed beef meat, fresh fish meat, raw cow milk, and traditional cheese samples collected in Giresun, Turkey. The occurrence of virulence-associated genes was detected, such as plcA (97.4%), iap (35.8%), and hlyA (15.3%). A high incidence of resistance was recorded for fusidic acid (100%), followed by oxacillin (97.4%), clindamycin (82%), trimethoprim/sulfamethoxazole (69.2%), benzylpenicillin (41%), nitrofurantoin (35.8%), and fosfomycin (35.8%). Overall, 100% (39/39) of the isolates were resistant to at least one antibiotic, while 92.3% (36/39) of the isolate strains were multidrug resistant in the antimicrobial susceptibility tested. Among the L. innocua isolates (n = 39), 51.2%, 38.4%, 20.5%, 7.6%, 5.1%, 2.5%, and 2.5% were positive for qacH, cadA1, qacE, qacEΔ1-sul, qacJ, qacF, and qacG heavy metal and disinfectant resistance genes, respectively. The results highlight the need for more comprehensive studies to understand the monitoring and surveillance of L. innocua and their potential hazards to both humans and animals.

A review of the literature of Listeria monocytogenes in Africa highlights breast milk as an overlooked human source

According to the latest WHO estimates (2015) of the global burden of foodborne diseases, Listeria monocytogenes is responsible for one of the most serious foodborne infections and commonly results in severe clinical outcomes. The 2013 French MONALISA prospective cohort identified that women born in Africa has a 3-fold increase in the risk of maternal neonatal listeriosis. One of the largest L. monocytogenes outbreaks occurred in South Africa in 2017-2018 with over 1,000 cases. Moreover, recent findings identified L. monocytogenes in human breast milk in Mali and Senegal with its relative abundance positively correlated with severe acute malnutrition. These observations suggest that the carriage of L. monocytogenes in Africa should be further explored, starting with the existing literature. For that purpose, we searched the peer-reviewed and grey literature published dating back to 1926 to date using six databases. Ultimately, 225 articles were included in this review. We highlighted that L. monocytogenes is detected in various sample types including environmental samples, food samples as well as animal and human samples. These studies were mostly conducted in five east African countries, four west African countries, four north African countries, and two Southern African countries. Moreover, only ≈ 0.2% of the Listeria monocytogenes genomes available on NCBI were obtained from African samples, contracted with its detection. The pangenome resulting from the African Listeria monocytogenes samples revealed three clusters including two from South-African strains as well as one consisting of the strains isolated from breast milk in Mali and Senegal and, a vaginal post-miscarriage sample. This suggests there was a clonal complex circulating in Mali and Senegal. As this clone has not been associated to infections, further studies should be conducted to confirm its circulation in the region and explore its association with foodborne infections. Moreover, it is apparent that more resources should be allocated to the detection of L. monocytogenes as only 15/54 countries have reported its detection in the literature. It seems paramount to map the presence and carriage of L. monocytogenes in all African countries to prevent listeriosis outbreaks and the related miscarriages and confirm its association with severe acute malnutrition.

Genomic Characterization of Listeria innocua Isolates Recovered from Cattle Farms, Beef Abattoirs, and Retail Outlets in Gauteng Province, South Africa

Whole-genome sequencing (WGS) was used for the genomic characterization of one hundred and ten strains of Listeria innocua (L. innocua) isolated from twenty-three cattle farms, eight beef abattoirs, and forty-eight retail outlets in Gauteng province, South Africa. In silico multilocus sequence typing (MLST) was used to identify the isolates' sequence types (STs). BLAST-based analyses were used to identify antimicrobial and virulence genes. The study also linked the detection of the genes to the origin (industries and types of samples) of the L. innocua isolates. The study detected 14 STs, 13 resistance genes, and 23 virulence genes. Of the 14 STs detected, ST637 (26.4%), ST448 (20%), 537 (13.6%), and 1085 (12.7%) were predominant, and the frequency varied significantly (p < 0.05). All 110 isolates of L. innocua were carriers of one or more antimicrobial resistance genes, with resistance genes lin (100%), fosX (100%), and tet(M) (30%) being the most frequently detected (p < 0.05). Of the 23 virulence genes recognized, 13 (clpC, clpE, clpP, hbp1, svpA, hbp2, iap/cwhA, lap, lpeA, lplA1, lspA, oatA, pdgA, and prsA2) were found in all 110 isolates of L. innocua. Overall, diversity and significant differences were detected in the frequencies of STs, resistance, and virulence genes according to the origins (source and sample type) of the L. innocua isolates. This, being the first genomic characterization of L. innocua recovered from the three levels/industries (farm, abattoir, and retail) of the beef production system in South Africa, provides data on the organism's distribution and potential food safety implications.