This study aimed to evaluate the risk of Staphylococcus aureus food poisoning associated with ready-to-eat lettuce for the purpose of providing theoretical references for adopting effective risk management measures.

The incidence and level of S. aureus contamination in environmental samples from lettuce planting in greenhouses or open fields were investigated. With regard to hazard recognition, the description of hazard and risk characteristics and exposure estimation, a risk assessment of S. aureus food positioning caused by eating raw lettuce in China was carried out based on residents’ consumption habit survey data from the statistical yearbook of China and the change in S. aureus count in lettuce from farm to table described using a predictive model describing the growth of S. aureus in lettuce.

The detection rate of S. aureus in greenhouse soil was 0.04%, at levels of -8.72 to 3.01 (lg(CFU/g)). The average concentration of S. aureus in lettuce to be consumed, which underwent irrigation, harvest, transportation, sale, purchase, storage and washing was -1.95 (lg(CFU/g)) with a 90% confidence interval of -8.98 to 4.40 (lg(CFU/g)). In China, the probability of S. aureus poisoning caused by the consumption of raw lettuce was estimated to be 2.72 × 10^-4 with a mean probability of 7.7 illness per 10 million servings per year. The sensitivity analysis showed that the initial concentration of S. aureus in the soil had the biggest effect on the contamination level of S. aureus in lettuce, followed by household storage temperature and washing before consumption. It is concluded that controlling lettuce-planting environment, rational use of refrigerators, and washing lettuce in a scientific way can reduce the risk of S. aureus food poisoning caused by the consumption of raw lettuce.

To understand the relationship between the genetic characteristics and the biofilm formation capability of typical strains of Listeria monocytogenes from fresh livestock and poultry meat in order to provide a basis for the precise control of bacteria in foods.

Ten isolates of L. monocytogenes belonging to eight sequence types (ST) were selected for whole genome sequencing, gene functional annotation, virulence factor identification, analysis of mobile genetic elements (prophage, genome island and plasmid), evolutionary analysis and, identification of genes related to biofilm formation. The biofilm formation capability of these strains was determined by crystal violet staining, and its correlation with their genomic characteristics was analyzed.

The virulence islands LIPI-1, LIPI-2 and more than 19 another virulence genes, as well as different numbers of prophages and genome islands, were identified in the genomes of the eight STs. The LIPI-3 genes were only identified in the ST3 isolates, and plasmids were identified in the ST8 and ST1403 isolates. Evolutionary branching coefficients showed that five STs were closely related to the outbreak strains in the database. In addition, the luxS and sigB genes related to biofilm formation were mutated or deleted in six and seven STs, respectively. The ST1403 and ST87 isolates had a stronger ability to form biofilm, while the ST1402 isolates had the weakest biofilm formation capacity.

Fresh livestock and poultry meat contains a variety of L. monocytogenes with pathogenic potential and carrying mobile genetic elements may be related to the biofilm formation capability.