Use of pulsed-field gel electrophoresis to characterize the genetic diversity and clonal persistence of Salmonella senftenberg in mussel processing facilities

Salmonella senftenberg was detected in association with persistent contamination events in mussel processing facilities between 1998 and 2002 in Spain. A total of 110 isolates from 8 facilities were subjected to molecular typing by Pulsed-Field Gel Electrophoresis (PFGE). Additionally, a selection of epidemiologically unrelated isolates of this serovar originating from human, animal, feed and environmental sources was included in the study. PFGE analysis proved to be a useful tool for studying the persistence and dissemination of S. senftenberg in factory environments. Facilities that used brine in their processing lines had greater genetic diversity among their S. senftenberg populations, which supports the hypothesis that imported salt used for brine preparation could have been the origin of the contamination. The XbaI type X19 was the most prevalent among the panel, and it was found persisting exclusively in one facility during the 5-year study. In general, isolates from mussel processing plants were clearly different from those of clinical and environmental sources. However, one of the human isolates showed an indistinguishable restriction pattern to an isolate from a frozen mussel sample, this could indicate the potential for food-borne transmission of this serovar via consumption of contaminated seafood products. Isolates in the study were largely sensitive to antimicrobials. Only 9 isolates (6 from mussel processing facilities, 1 from soy flour and 2 from meat meal) showed antimicrobial resistance.