Evaluation of the Persistence and Characterization of Listeria monocytogenes in Foodservice Operations

Listeriosis: Characteristics, Occurrence in Domestic Animals, Public Health Significance, Surveillance and Control

Listeriosis is a dangerous zoonosis caused by bacteria of the genus Listeria, with Listeria monocytogenes (LM) being the most pathogenic species. Listeria monocytogenes has been detected in various animal species and in humans, and its ability to evolve from an environmental saprophyte to a powerful intracellular pathogen is driven by the invasion mechanisms and virulence factors that enable cell invasion, replication and cell-to-cell spread. Key regulatory systems, including positive regulatory factor A (PrfA) and the stress-responsive sigma factor σB, control the expression of virulence genes and facilitate invasion of host cells. Listeriosis poses a significant threat to cattle, sheep and goat herds, leading to abortions, septicemia and meningoencephalitis, and ruminants are important reservoirs for Listeria, facilitating transmission to humans. Other Listeria species such as Listeria ivanovii and Listeria innocua can also cause disease in ruminants. Resilience of LM in food processing environments makes it an important foodborne pathogen that is frequently transmitted through contaminated meat and dairy products, with contamination often occurring along the food production chain. In humans, listeriosis primarily affects immunocompromised individuals, pregnant women and the elderly and leads to severe conditions, such as meningitis, septicemia and spontaneous abortion. Possible treatment requires antibiotics that penetrate the blood-brain barrier. Despite the relatively low antimicrobial resistance, multidrug-resistant LM strains have been detected in animals, food and the environment. Controlling and monitoring the disease at the herd level, along with adopting a One Health approach, are crucial to protect human and animal health and to minimize the potential negative impacts on the environment.

Formation and recovery of Listeria monocytogenes in viable but nonculturable state under different temperatures combined with low nutrition and high NaCl concentration

The viable but nonculturable (VBNC) state occurs when bacteria lose their ability to grow and multiply on conventional media when stressed by adverse environmental factors, but they remain active and can revive under certain conditions, posing a food safety risk. In this study, the VBNC state of Listeria monocytogenes was induced with different temperatures combined with low nutrient conditions; the VBNC state of L. monocytogenes was confirmed in conjunction with the housekeeping gene abcZ using a molecular biology assay (PMA-qPCR) to calculate the viable bacterial count; The resuscitation conditions for the VBNC state of L. monocytogenes were investigated utilizing various nutrients in the culture medium and pasteurized milk. Four strains of L. monocytogenes reached the VBNC stage after 14, 21, 21, and 35 days at 20°C with 20% (or 30%) NaCl. Resuscitation studies indicate that Trypticase Soy Broth (TSB) combined with Tween 80 and sodium pyruvate is more effective for resuscitation. The Chinese national standard technology GB 4789.30-2016 was used to inoculate lettuce, chicken, and pasteurized milk with L. monocytogenes ATCC 19115 VBNC state. This research has significant implications for commercial food processing, long-term storage, disinfection, disease prevention, and control.

Evaluation of the Effects of Food Safety Training on the Microbiological Load Present in Equipment, Surfaces, Utensils, and Food Manipulator's Hands in Restaurants

Training food handlers is essential to ensure food safety. However, the efficacy of training programs relying solely on theoretical information remains uncertain and often fails to induce significant changes in inadequate food practices. Training programs in good hygiene and food safety practices that integrate theoretical and practical approaches have emerged as a vital tool, enabling food handlers to apply their knowledge during work hours and clarify doubts. This study aimed to assess the impact of food safety training based on theoretical and on-the-job training on the microbiological counts of equipment, surfaces, utensils, and food handler (FH) hands. The hygiene and food safety conditions of four restaurants were analyzed through facility checklists, employee questionnaires, and microbiological analyses conducted before and after training. Eight sample collection moments were conducted at each restaurant before and after training. The pre-training results indicate that 15% and 26% of analyses for Enterobacteriaceae and total mesophilic aerobic bacteria (TMB), respectively, did not comply with hygiene safety limits. Additionally, 31% and 64% of Enterobacteriaceae and TMB values, respectively, exceeded safety limits on food handler hands. Positive cases of coagulase-positive Staphylococcus (CoPS) resulted from unprotected wounds on some FH hands. The presence of Listeria monocytogenes in drains was also identified as a concern. Following training, significant differences in results were observed. In many cases, there was a reduction of over 80% in microbial load for Enterobacteriaceae and TMB collected from equipment, surfaces, utensils, and food handler hands. The presence of L. monocytogenes in drains was also eliminated after food safety training. In conclusion, this study underscores the importance of effective training in improving food safety practices.

Characterization and Antibiotic Resistance of Listeria monocytogenes Strains Isolated from Greek Myzithra Soft Whey Cheese and Related Food Processing Surfaces over Two-and-a-Half Years of Safety Monitoring in a Cheese Processing Facility

Listeriosis is a serious infectious disease with one of the highest case fatality rates (ca. 20%) among the diseases manifested from bacterial foodborne pathogens in humans, while dairy products are often implicated as sources of human infection with Listeria monocytogenes. In this study, we characterized phenotypically and genetically by whole-genome sequencing (WGS) 54 L. monocytogenes strains isolated from Myzithra, a traditional Greek soft whey cheese (48 isolates), and swabs collected from surfaces of a cheese processing plant (six isolates) in the Epirus region of Greece. All but one strain of L. monocytogenes belonged to the polymerase chain reaction (PCR) serogroups IIa (16.7%) and IIb (81.5%), corresponding to serotypes 1/2a, 3a and 1/2b, 3b, 7, respectively. The latter was identified as a PCR-serogroup IVb strain (1.8%) of serotypes 4b, 4d, 4e. Bioinformatics analysis revealed the presence of five sequence types (STs) and clonal complexes (CCs); ST1, ST3, ST121, ST 155, ST398 and CC1, CC3, CC121, CC155, CC398 were thus detected in 1.9, 83.3, 11.0, 1.9, and 1.9% of the L. monocytogenes isolates, respectively. Antibiograms of the pathogen against a panel of seven selected antibiotics (erythromycin, tetracycline, benzylpenicillin, trimethoprim-sulfamethoxazole, ampicillin, ciprofloxacin, and meropenem) showed that 50 strains (92.6%), the six surface isolates also included, were intermediately resistant to ciprofloxacin and susceptible to the rest of the six antimicrobial agents tested, whereas strong resistance against the use of a single from three implicated antibiotics was recorded to four strains (7.4%) of the pathogen isolated from Myzithra cheese samples. Thence, the minimum inhibitory concentrations (MICs) were determined for erythromycin (MIC = 0.19 μg/mL), ciprofloxacin (MIC ≥ 0.19 μg/mL), and meropenem (MIC = 0.64 μg/mL), and finally, just one strain was deemed resistant to the latter antibiotic. The phylogenetic positions of the L. monocytogenes strains and their genetic variability were determined through WGS, whilst also stress response and virulence gene analysis for the isolates was conducted. Findings of this work should be useful as they could be utilized for epidemiological investigations of L. monocytogenes in the food processing environment, revealing possible contamination scenarios, and acquired antimicrobial resistance along the food production chain.