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With the increased demand for lightly preserved and/or ready-to-eat (RTE) food products, the prevalence of the foodborne pathogen Listeria monocytogenes has increased, which is a public health concern. The goal for this review is to discuss the incidence, epidemiological importance, and contamination routes of L. monocytogenes in various aquatic ecosystems, seafood products, and processing environments and to summarize the data obtained since the 1990s. L. monocytogenes primarily enters the food-production chain by cross-contamination in production plants, making this pathogen a major threat to the seafood industry. This pathogen generally contaminates food products at low or moderate levels, but the levels involved in listeriosis outbreaks are significantly higher. The majority of isolates from aquatic products belong to serotype 1/2a, and outbreaks have been linked to highly similar or even indistinguishable strains. Several seafood-processing plants are colonized by specific "in-house" flora containing special DNA subtypes of L. monocytogenes. In such cases, L. monocytogenes populations can persist and/or multiply despite the inherent obstacles to their growth in food preservation and manufacturing operations. Therefore, food-processing facilities must be designed carefully with an emphasis on effective cleaning and disinfecting operations in the production line.

In this study, shotgun metagenomics was employed to monitor the effect of oxytetracycline, administered at a therapeutic dose, on the dynamics of the microbiota and resistome in the feces of weaned pigs. Sixteen weaning pigs were assigned to one of two treatments including standard starter diet for 21 days or antibiotic-supplemented diet (10 g oxytetracycline/100 kg body weight/day) for 7 days, followed by 14 days of standard starter diet. Feces were collected from the pigs on days 0, 8, and 21 for microbiota and resistome profiling. Pigs receiving oxytetracycline exhibited a significantly greater richness (ANOVA, P = 0.034) and diversity (ANOVA, P = 0.048) of antibiotic resistance genes (ARGs) than the control pigs. Antibiotic administration significantly enriched the abundances of 41 ARGs, mainly from the tetracycline, betalactam and multidrug resistance classes. Compositional shifts in the bacterial communities were observed following 7 days of antibiotic adminstration, with the medicated pigs showing an increase in Escherichia (Proteobacteria) and Prevotella (Bacteroidetes) populations compared with the nonmedicated pigs. This might be explained by the potential of these taxa to carry ARGs that may be transferred to other susceptible bacteria in the densely populated gut environment. These findings will help in the optimization of therapeutic schemes involving antibiotic usage in swine production.