Evaluation of the Virulence Potential of Listeria monocytogenes through the Characterization of the Truncated Forms of Internalin A.

Listeria monocytogenes is a widespread Gram-positive pathogenic bacterium that causes listeriosis, a rather rare but severe foodborne disease. Pregnant women, infants, the elderly, and immunocompromised individuals are considered particularly at risk. L. monocytogenes can contaminate food and food-processing environments. In particular, ready-to-eat (RTE) products are the most common source associated with listeriosis. L. monocytogenes virulence factors include internalin A (InlA), a surface protein known to facilitate bacterial uptake by human intestinal epithelial cells that express the E-cadherin receptor. Previous studies have demonstrated that the presence of premature stop codon (PMSC) mutations naturally occurring in inlA lead to the production of a truncated protein correlated with attenuate virulence. In this study, 849 L. monocytogenes isolates, collected from food, food-processing plants, and clinical cases in Italy, were typed and analyzed for the presence of PMSCs in the inlA gene using Sanger sequencing or whole-genome sequencing (WGS). PMSC mutations were found in 27% of the isolates, predominantly in those belonging to hypovirulent clones (ST9 and ST121). The presence of inlA PMSC mutations in food and environmental isolates was higher than that in clinical isolates. The results reveal the distribution of the virulence potential of L. monocytogenes circulating in Italy and could help to improve risk assessment approaches.

Transfer of Mycotoxins from Lactation Feed to Colostrum of Sows.

Studies regarding the transfer of mycotoxins from sow feed to colostrum are scarce. A sample of in-house produced lactation feed and one of colostrum were collected from two or three sows per farm (total 49) from 19 farms. The feed contents of aflatoxins (AFs), fumonisins (FUs), deoxynivalenol (DON) and zearalenone (ZEA) were assessed using ELISA and confirmed by liquid chromatography-mass spectrometry (LC-MS), The values were very low (10, 12, 17 and 2 positive samples for AFs, FUs, DON and ZEA, respectively), except for two samples (one AF, one DON). Based on feed values, colostrum samples from 13 farms were tested for at least one mycotoxin (Total 35). Aflatoxins were not found in any sample. A signal for FUs was observed in 5 of 11 colostra, despite low feed values; DON was frequently present in the colostrum (10/14). On the farm where the feed exceeded the DON suggested limits, a higher colostrum content was seen, 10.9 µg/kg, approximately 1/69 of the value showing toxicity in young pigs. The absence of reference values for neonate pigs, and the risk of higher and longer ingestion of DON by sows suggested considering routine checks of sow feed; more research on DON transfer and toxicity in piglets is needed.

Fate of Methicillin-resistant Staphylococcus aureus (MRSA) under simulated acidic conditions of the human stomach.

A known amount (107 cfu/ml) of animal origin Methicillin-resistant Staphylococcus aureus (MRSA) ST398/t011/V and of human origin MRSA ST1/t127/IVa strains were individually inoculated into ricotta cheese and hamburger samples. The pH of each food matrix was gradually decreased from 6.0 down to 2.0 during a period of about 2 hr, under conditions simulating the mechanical digestion of the human stomach. Afterward, the MRSA strains were recovered by using a MRSA-specific plating medium. Although both strains showed a certain acidic resistance, they showed different responses at low pH values during the experiment: ST398 survived unharmed during the course of the experiments to the last stage at pH 2 where counts of 6.4 cfu/g for the hamburger and 7.5 log cfu/g for ricotta cheese assays were obtained. In contrast, the ST1 population was no longer detectable at pH 3 in the hamburger and at pH 2 in the ricotta cheese assays. To the best of our knowledge, this is the first study that investigates the ability of MRSA to overcome the acidic conditions of the human stomach and that adds new evidence that might contribute to expand the scientific knowledge on the significance of MRSA in the food safety debate.

Global Emergence of Colistin-Resistant Escherichia coli in Food Chains and Associated Food Safety Implications: A Review.

Antimicrobial resistance in bacteria represents one of the most important challenges for public health worldwide. Human infections from antimicrobial-resistant bacteria can be transmitted from person to person, via the environment (especially in the hospital environment), or via handling or eating contaminated foods. Colistin is well known as a last-resort antibiotic for the treatment of human infections; a recent study performed in the People's Republic of China has revealed that colistin resistance is also conferred by the plasmid-mediated mcr-1 gene in Escherichia coli. After that discovery, further plasmid-mediated, colistin resistance genes have been detected. However, to date, only reports on E. coli carrying the mcr-1 gene (E. coli mcr-1+) in foodstuff are available. E. coli mcr-1+ has been isolated from food of animal origin and vegetables; this discovery has opened a debate among food safety experts. This review aims to provide a critical overview of the currently available scientific literature on the presence of the plasmid-mediated, colistin resistance gene E. coli mcr-1 in foodstuffs, focusing on the main implications and future perspectives for food safety.