Diversity in biofilm formation and production of curli fimbriae and cellulose of Salmonella Typhimurium strains of different origin in high and low nutrient medium.

The biofilm forming behavior of 51 Salmonella Typhimurium strains was determined in Tryptone Soya Broth (TSB) and 20 times diluted TSB (1/20TSB) at 25°C and 37°C. The results indicated that biofilm forming behavior is influenced by environmental conditions and associated with the origin of the strains. Clinical, outbreak-associated and retail product isolates showed dense biofilm formation in both media at 25°C, and in TSB also at 37°C. However, industrial isolates only showed dense biofilm formation in 1/20TSB at 25°C. By enumeration of biofilm cells, LIVE/DEAD staining and SEM analysis of biofilms it was found that the ratio of cells and extracellular matrix is affected by environmental conditions. Indeed, the genes involved in curli fimbriae and cellulose production are highly induced during biofilm formation at 25°C in 1/20TSB. This indicates that these are important matrix components during biofilm formation in 1/20TSB at 25°C and that other factors contribute to biofilm formation of clinical, outbreak-associated and retail product isolates at 37°C and/or nutrient-rich conditions.

Sources and transmission routes of campylobacteriosis: A combined analysis of genome and exposure data.

OBJECTIVES: To determine the contributions of several animal and environmental sources of human campylobacteriosis and identify source-specific risk factors. METHODS: 1417 Campylobacter jejuni/coli isolates from the Netherlands in 2017-2019 were whole-genome sequenced, including isolates from human cases (n = 280), chickens/turkeys (n = 238), laying hens (n = 56), cattle (n = 158), veal calves (n = 49), sheep/goats (n = 111), pigs (n = 110), dogs/cats (n = 100), wild birds (n = 62), and surface water (n = 253). Questionnaire-based exposure data was collected. Source attribution was performed using core-genome multilocus sequence typing. Risk factors were determined on the attribution estimates. RESULTS: Cases were mostly attributed to chickens/turkeys (48.2%), dogs/cats (18.0%), cattle (12.1%), and surface water (8.5%). Of the associations identified, never consuming chicken, as well as frequent chicken consumption, and rarely washing hands after touching raw meat, were risk factors for chicken/turkey-attributable infections. Consuming unpasteurized milk or barbecued beef increased the risk for cattle-attributable infections. Risk factors for infections attributable to environmental sources were open water swimming, contact with dog faeces, and consuming non-chicken/turkey avian meat like game birds. CONCLUSIONS: Poultry and cattle are the main livestock sources of campylobacteriosis, while pets and surface water are important non-livestock sources. Foodborne transmission is only partially consistent with the attributions, as frequency and alternative pathways of exposure are significant.

Rapid detection and differentiation of Salmonella species, Salmonella Typhimurium and Salmonella Enteritidis by multiplex quantitative PCR.

A multiplex quantitative PCR (qPCR) was developed and evaluated for the simultaneous detection of Salmonella spp., S. enterica serovar Typhimurium and S. enterica serovar Enteritidis in various (food) matrices. Early and fast detection of these pathogens facilitates effective intervention and prevents further distribution of contaminated food products on the market. Three primer and probe sets were designed to target the invA gene, the STM4200 gene, and the SEN1392 gene to detect and differentiate Salmonella spp., S. Typhimurium, and S. Enteritidis, respectively. The multiplex qPCR targeting these three genes was optimized for efficiency and linearity. By testing 225 Salmonella isolates and 34 non-Salmonella isolates from various sources the inclusivity and exclusivity were determined. The inclusivity of the multiplex qPCR was 100% for all Salmonella isolates, including 72 S. Typhimurium isolates, and 53 S. Enteritidis isolates. The exclusivity for Salmonella spp., S. Typhimurium, and S. Enteritidis was 100%, 94.6%, and 100%, respectively. No positive results were reported for non-Salmonella isolates. The limit of detection (LOD) for the qPCR was determined for the matrices poultry, minced meat, egg, herbs/spices, powdered milk, fish, animal feed, boot-socks with chicken feces and chicken down. LOD values for qPCR and the conventional culture methods were similar, except for the matrix boot-socks and down, for which the LOD for the conventional culture methods performed better than the qPCR method. In conclusion, the multiplex qPCR assay developed allows for rapid screening of Salmonella spp., S. Typhimurium, and S. Enteritidis in various (food) matrices.

Surface behaviour of S. Typhimurium, S. Derby, S. Brandenburg and S. Infantis.

Cross-contamination due to Salmonella on the surface of processing equipment greatly contributes to contamination of pork products. Therefore, a clear understanding of surface and survival behaviour of relevant Salmonella serovars in pork processing environments is needed to develop better strategies for Salmonella control. Within this study the biofilm forming behaviour of S. Typhimurium, S. Derby, S. Brandenburg and S. Infantis isolates was analysed using the crystal violet assay. This assay, commonly used to analyse total biofilm formation, revealed variation in biofilm forming capacity between and within serovars. This has not been shown before for S. Derby, S. Brandenburg and S. Infantis. From each serovar, isolates with different biofilm forming capacity were selected to analyse biofilm formation on stainless steel. This revealed no significant differences between biofilm formation on polystyrene compared to stainless steel. Furthermore a relation was observed between biofilm forming capacity of an isolate and survival on stainless steel surfaces. On such surfaces, biofilms showed greater and longer survival than planktonic cells, and they were less susceptible to peracetic acid disinfection treatments. However, the latter effect was marginal and only observed in the presence of organic material, which drastically decreased the activity of peracetic acid. With the obtained results a hierarchical cluster was also performed to identify differences and similarities between the four different serovars. This indicated that the surface behaviour of S. Typhimurium was more comparable to S. Infantis than to S. Derby or S. Brandenburg.