Characteristics of Listeria monocytogenes Strains Isolated from Milk and Humans and the Possibility of Milk-Borne Strains Transmission

Characterization and Preliminary Application of Phage Isolated From Listeria monocytogenes

Listeria monocytogenes (LM) is one of the four major foodborne bacteria that cause bacteremia and meningitis. To explore the control of listeriosis with natural phages, we used the double-layer agar plate method to isolate LM from slaughterhouse sewage and designated LP8. The result of electron microscopy indicated that the phage belonged to the family of Myoviridae. Whole-genome sequencing indicated that the genome size of LP8 is 87,038 bp and contains 120 genes. Mice were infected with LM and treated with penicillin G sodium, LP8, and the combination of these two. From the levels of lymphocyte subsets (CD4+, CD8+), the expression of cytokines (TNF-α, IL1β, IL-10, and IFN-γ), observation of pathological changes in organs (heart, liver, spleen, kidney, and brain), and the bacterial load of the spleen, we concluded the therapeutic effect of LP8 against listeriosis and demonstrate the feasibility of a combined therapy to reduce the use of antibiotics. This provides a new avenue for the treatment of listeriosis.

First substantiation of clinico-molecular investigation of pathogenic Listeria monocytogenes in Nili-Ravi buffaloes

Background

Listeriosis is a zoonotic disease of humans, animals, birds, fish, and crustaceans worldwide. Domestic animals, especially ruminants, are more susceptible to listeriosis. This infectious disease is caused by Listeria monocytogenes, an intracellular bacterium that can cross blood-brain, placental and intestinal barriers. In Pakistan, the incidence and reliable diagnostic tools for the L. monocytogenes are unidentified in Nili-Ravi buffaloes.

Aims

This study was designed to inspect listeriosis in buffaloes through molecular techniques and haemato-biochemical analyses.

Methods

A total of 230 samples (115 milk and 115 faecal samples) were collected from symptomatic listeriosis cases in Nili-Ravi buffaloes of 3 geographical districts (Rawalpindi, Faisalabad, and Muzaffargarh) Punjab, Pakistan. These samples were processed for DNA extraction using commercialized kits, and L. monocytogenes was confirmed by conventional PCR.

Results

The results revealed that 6.08% and 4.34% of the isolates from milk and faecal samples were found positive for L. monocytogenes, respectively. The phylogenetic analysis of these isolates showed 97-100% similarity to isolates from the USA, Switzerland, Japan, and India. The accession numbers on NCBI GenBank appeared as HF558398 (Switzerland), KP965732 (India), EU372032 (USA), and LC259850 (Japan). Haemato-biochemical examinations showed that the values of WBCs, plasma fibrinogen, ALT, and AST significantly increased (P<0.05) in diseased buffaloes compared to healthy ones.

Conclusion

The occurrence of listeriosis in buffaloes urges continuous monitoring and surveillance to prevent this emerging disease in Pakistan.

Prevalence, Antibiogram and Genetic Characterization of Listeria monocytogenes from Food Products in Egypt

World Health Organization classified Listeria monocytogenes as a major notable foodborne pathogen associated with high mortality and hospitalization. The study reports the prevalence, antibiogram, virulence determination and genetic characterization of L. monocytogenes from different food products. A total of 250 food samples, fifty samples each from raw milk, ice cream, minced meat, fish fillet and sausage were collected from the Menoufiya governorate in Egypt. L. monocytogenes was detected in 17 (6.8%) of the tested food samples including minced meat (14%), fish fillet (8%), sausage (6%) and raw milk (6%). The antimicrobial susceptibility assay of 17 L. monocytogenes isolates against seventeen antibiotics belonging to eight antibiotics classes revealed a high susceptibility to norfloxacin (82.3%), amoxicillin-clavulanic acid (76.4%), cefotaxime (70.5%), erythromycin (64.6%), amoxicillin (64.6%), gentamicin (58.7%) and vancomycin (58.7%). While, high resistance was observed against oxytetracycline (76.4%), trimethoprim-sulfamethoxazole (76.4%), chloramphenicol (70.5%), doxycycline (64.6%), levofloxacin (41.2%) and azithromycin (41.2%). Of note, all L. monocytogenes isolates were multidrug-resistant. The multiplex PCR successfully amplified L. monocytogenes in all tested isolates. Screening of the five virulence-related genes revealed the hlyA and iap as the most prevalent genes followed by actA gene, however, the inlA and prfA genes were not detected in any of the studied isolates. The partial 16S rRNA gene sequencing of three L. monocytogenes isolates showed a high nucleotide similarity (99.1–99.8%) between the study isolates and various global clones, and phylogenetic analysis clustered these L. monocytogenes strains with other Listeria species including L. welshimeri, L. seeligeri and L. innocua. This study demonstrates the impact of L. monocytogenes as a major contaminant of various food products and suggests more attention to the awareness and hygienic measures in the food industry.