Influence of environmental factors and human activity on the presence of Salmonella serovars in a marine environment.

The temporal and spatial distribution of Salmonella contamination in the coastal waters of Galicia (northwestern Spain) relative to contamination events with different environmental factors (temperature, wind, hours of sunlight, rainfall, and river flow) were investigated over a 4-year period. Salmonellae were isolated from 127 of 5,384 samples of molluscs and seawater (2.4%), and no significant differences (P < 0.05) between isolates obtained in different years were observed. The incidence of salmonellae was significantly higher in water column samples (2.9%) than in those taken from the marine benthos (0.7%). Of the 127 strains of Salmonella isolated, 20 different serovars were identified. Salmonella enterica serovar Senftenberg was the predominant serovar, being represented by 54 isolates (42.5%), followed by serovar Typhimurium (19 isolates [15%]) and serovar Agona (12 isolates [9.4%]). Serovar Senftenberg was detected at specific points on the coast and could not be related to any of the environmental parameters analyzed. All serovars except Salmonella serovar Senftenberg were found principally in the southern coastal areas close to the mouths of rivers, and their incidence was associated with high southwestern wind and rainfall. Using multiple logistic regression analysis models, the prevalence of salmonellae was best explained by environmental parameters on the day prior to sampling. Understanding this relationship may be useful for the control of molluscan shellfish harvests, with wind and rainfall serving as triggers for closure.

Detection of Salmonella Senftenberg associated with high saline environments in mussel processing facilities.

A contamination by Salmonella Senftenberg in frozen mussels was detected in 1998 during a routine analytical surveillance. From June 1998 to December 2001, a total of 3,410 samples of steamed frozen mussels and items related to their manufacture were analyzed for the presence of Salmonella. Salmonella Senftenberg was isolated in 573 (16.8%) samples, and no other serovar was detected. The contamination episodes extended for several months. Salmonella Senftenberg colonies from the first contamination events showed a rugose morphology on agar with a shiny crystalline layer and limited colony formation on microbiological media. These contaminations were mainly associated with brine (300 g of NaCl per liter), while the live molluscs that were being processed were free of Salmonella. When the brine contaminations were nearly controlled, new episodes were detected that were associated with live mussels. In the new episodes, colonies showed the typical characteristics of Salmonella and normal growth on agar. Salmonella Senftenberg presented a high resistance to unfavorable environments and showed a preference for clean environments. While Salmonella Senftenberg could be isolated from mussels after steam treatment, it could not survive after immersion in water at 80 degrees C for 1 min. This fact was used to develop a process to remove contamination from products, minimizing the health risk associated with frozen mussel consumption. The general incidence of Salmonella Senftenberg in facilities and mussels was reduced from 31.2% in 1998 to 2.5% in 2001. During this study, no cases of illness from consumption of frozen mussels were reported, indicating a possible lack of virulence of Salmonella Senftenberg in these contamination events.