Molecular follow-up of Salmonella enterica subsp. enterica serovar Agona infection in cattle and humans

Abstract

Salmonella enterica subsp. enterica serovar Agona was not frequently encountered in Finland until an increase in rates of isolation among animal and feed was seen in 1994. A small outbreak among cattle farms in the regions of Oulu and Vaasa in northwestern Finland in 1994-1995 included eight farms. After the outbreak, an increase in the number of serovar Agona infections in humans was seen in 1999: the number of annual microbiologically confirmed cases in humans increased from about 10 from 1990 to 1998 to 84 in 1999, including an outbreak in which more than 50 people were infected. To gather epidemiological data on serovar Agona and to trace the origin of the human infections, 110 serovar Agona isolates isolated from animal, feed, and other sources as well as from humans with cases of salmonellosis of domestic and foreign origin, which were recovered from 1984 to 1999, were analyzed for their pulsed-field gel electrophoresis (PFGE), plasmid, and IS200 profiles and antibiograms. Of these typing methods, PFGE with restriction endonucleases XbaI, BlnI, NotI, and SpeI was the most useful. The PFGE profile of the strain causing an outbreak among cattle in Finland in 1994-1995 was not seen previously. The strain with this profile was later only sporadically found in human infections. The profile of the strain causing the human outbreak in 1999 was not found among isolates from cattle or any other sources. Molecular typing was valuable in showing that although the outbreaks in cattle and humans seemed to be related regionally, they were not related otherwise.

FIG. 1.

Occurrence of domestic (○) and imported (⧫) human cases of Salmonella serovar Agona infection from 1999 through 2000.

FIG. 2.

Dendrogram showing 39 pf profiles of Salmonella serovar Agona after XbaI restriction of chromosomal DNA followed by PFGE. Dice similarity coefficients are shown at the upper left; the molecular sizes (in kilobases) of the fragments are shown at the upper middle. XbaI profiles pf1 to pf40 and the number of isolates with the XbaI profile, as well as the human and cattle outbreak profiles, are indicated on the right.