Molecular characterization of endemic salmonella infections ... - Evira

4. MATERIAL AND METHODS
4.1 MATERIAL
The Salmonella isolates were mainly obtained from the collections belonging to the Finnish Food
Safety Authority Evira (the former National Veterinary and Food Research Institute, EELA, is a part
of Evira), Helsinki, Finland, and to the National Public Health Institute, Laboratory of Enteric
Pathogens, Helsinki, Finland. Phage typing of S. Typhimurium isolates was carried out at the
National Public Health Institute in Finland, where it began by the Colindale method in March 1968.
Escherichia coli strains V517 (35.6, 4.8, 3.7, 3.4, 1.8, 1.4 MDa) (Macrina et al 1978) and 39R861
(98.0, 42.0, 23.9, 4.6 MDa) (Threlfall et al 1986b) were used as plasmid reference strains.
4.1.1 S. Infantis isolates (I, II)
The isolates (total no = 659) were obtained from the Finnish Food Safety Authority Evira in
Helsinki, Finland. This includes the former National Veterinary and Food Research Institute (EELA)
in Helsinki, and its regional laboratories in Oulu, Seinäjoki and Kuopio (n=655; 636 isolates from
cattle from 478 farms, and 19 isolates from feed). The Plant Production Inspection Centre in
Vantaa (n=4) is also now part of Evira.
In the former province of Vaasa (where most S. Infantis isolations from cattle were made in the
1990s) as early as 1971 the first isolations were found in: imported soya feed, hygiene samples in
local slaughterhouses, pig, cattle, and a broiler rearing facility. In the subsequent years, isolations
were obtained from poultry slaughterhouses and in 1976 from imported slaughterhouse waste.
From 1978 onwards, cattle isolations have been obtained every year (Aho et al 1996; National
Veterinary and Food Research Institute 1965-2005) (II: table 1).
The analysed S. Infantis isolates from cattle originated from farms (n=588; 382 faecal and 206
other isolates), slaughterhouses (n=15) and slaughter transportation vehicles (n=33) from 1985 to
2003. Apart from carcass-samples from the slaughterhouse, the farm isolates were mostly found in
faecal samples. The samples from slaughterhouses and cattle transportation vehicles were
hygiene samples and therefore not to be traced to any specific farm. The cattle feed isolates
originated from the feed production plant (n = 5) and cattle farms (n = 18). The cattle farm isolates
were representative of the geographical distribution of S. Infantis positive farms (II: figure 2). Two
or more isolates taken from 142 farms during the eradication of the infection were available for
analysis. If available, isolates from faecal samples were analysed. The isolates were either
obtained over the same year or from several years. All isolates had been serologically confirmed to
be S. Infantis and stored at -70°C, except for the isolates obtained during the 1980s, which were
stored on egg agar slopes prior to analysis.
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