Attachment characteristics and kinetics of biofilm formation by Staphylococcus aureus on ready-to-eat cooked beef contact surfaces.

Staphylococcus aureus is a food-borne pathogen that quickly forms biofilm on meat contact surfaces and thus poses a serious threat to the safety of the meat industry. This study evaluated the attachment, survival, and growth of S. aureus biofilm with exposure to environmental factors in the meat industry by simulated ready-to-eat (RTE) cooked beef product contamination scenarios. The results indicated that the meat-borne S. aureus biofilm formation dynamic could be divided into four different phases: initial adhesion (4-12 h), exponential (12-24 h), slow growth (1-3 days), and stationary (3-7 days). Meat-borne S. aureus has strong adhesion and biofilm formation ability, and its biofilm exhibits persistence, high-intensity metabolic activity, aerotaxis, and strain heterogeneity. This study has also demonstrated that in the long-term existence of meat-borne S. aureus biofilm on stainless steel and plexiglass surfaces (>7 days, 7.2-8.8 log CFU/cm2 ), expose to RTE cooked beef products, may cause it to become high-risk contaminated food. Meat-borne S. aureus that forms a dense and rough concave-convex in the shape of biofilm architecture was observed by scanning electron microscopy, consisting of complex components and adhesion of living and dead cells. This was further confirmed by the meat-borne S. aureus biofilm on the stainless steel surface by attenuated total reflectance Fourier transformed infrared spectroscopy, and the dominant peaks in biofilm spectra were mainly associated with proteins, polysaccharides, amino acid residues, and phospholipids (>50%). These findings may help in the identification of the main sources of contamination within the meat industry and the subsequent establishment of strategies for biofilm prevention and removal. PRACTICAL APPLICATION: This study revealed the meat-borne S. aureus biofilm formation mechanism and found that it exhibited strong colonization and biofilm-forming ability, which can persist on the contact surfaces of ready-to-eat beef products. These initial findings could provide information on the behavior of meat-borne S. aureus biofilm attached to meat contact surfaces under conditions commonly encountered in meat environments, which help to support the determination of the main sources of contamination within the meat industry and the subsequent establishment of strategies for biofilm prevention and removal. It was also helpful in controlling biofilm contamination and improving meat safety to minimize it.

Application of interaction models in predicting the simultaneous growth of Staphylococcus aureus and different concentrations of background microbiota in Chinese-style braised beef.

This study aimed to investigate the growth kinetics of S. aureus and different concentrations of background microbiota in Chinese-style braised beef (CBB). A one-step analysis method was applied to develop predictive model to describe the simultaneous growth and interaction of S. aureus with different concentrations of background microbiota in CBB. The results show that a one-step method successfully models the growth of S. aureus and background microbiota in CBB and the competing interactions between the two. In sterile CBB, the estimated minimum growth temperatures (Tmin,S) and the maximum growth concentrations (Ymax,S) were 8.76 °C and 9.58 log CFU/g for S. aureus. Under competition, the growth of background microbiota was not affected by S. aureus, the estimated Tmin,B and Ymax,B was 4.46 °C and 9.94 log CFU/g. The background microbiota in CBB did not affect the growth rate of S. aureus (α1 = 1.04), but had an inhibitory effect on the number of S. aureus (α2 = 0.69) at the later growth stage. The Root Mean Square Error (RMSE) of the modeling data was 0.34 log CFU/g, with 85.5% of the residual errors within ±0.5 log CFU/g of experimental observations. The one-step analysis and dynamic temperatures (8 °C-32 °C) verification indicated that the RMSE of prediction was <0.5 log CFU/g for both S. aureus and background microbiota. This study demonstrates that microbial interaction models are a useful and promising tool for predicting and evaluating the spatiotemporal population dynamics of S. aureus and background microbiota in CBB products.

SdiA Enhanced the Drug Resistance of Cronobacter sakazakii and Suppressed Its Motility, Adhesion and Biofilm Formation.

Cronobacter sakazakii is a common foodborne pathogen, and the mortality rate of its infection is as high as 40-80%. SdiA acts as a quorum sensing regulator in many foodborne pathogens, but its role in C. sakazakii remains unclear. Here, we further determined the effect of the sdiA gene in C. sakazakii pathogenicity. The SdiA gene in C. sakazakii was knocked out by gene editing technology, and the biological characteristics of the ΔsdiA mutant of C. sakazakii were studied, followed by transcriptome analysis to elucidate its effects. The results suggested that SdiA gene enhanced the drug resistance of C. sakazakii but diminished its motility, adhesion and biofilm formation ability and had no effect on its growth. Transcriptome analysis showed that the ΔsdiA upregulated the expression levels of D-galactose operon genes (including dgoR, dgoK, dgoA, dgoD and dgoT) and flagella-related genes (FliA and FliC) in C. sakazakii and downregulated the expression levels of related genes in the type VI secretion system (VasK gene was downregulated by 1.53-fold) and ABC transport system (downregulated by 1.5-fold), indicating that SdiA gene was related to the physiological metabolism of C. sakazakii. The results were useful for clarifying the pathogenic mechanism of C. sakazakii and provide a theoretical basis for controlling bacterial infection.