Listeria monocytogenes in faeces from clinically healthy dairy cows in Sweden

Faecal samples from 102 clinically healthy dairy cows, representing 34 farm s in the Swedish province of Uppsala, were analysed for the presence of Lis teria spp. using an enrichment procedure. Listeria monocytogenes was isolat ed from six ((6%) and L. innocua from 2 (2%) cows. From each of the 6 sampl es positive for L. monocytogenes, 5 isolates were further characterised by restriction enzyme analysis using the 3 enzymes Apa I, Sma I, and Asc I, fo llowed by pulsed-field gel electrophoresis. Three of the L. monocytogenes p ositive cows lived at the same farm, and they all harboured the same clonal type. One of these 3 cows also harboured a further clonal type of L. monoc ytogenes. The fact that one of the cows harboured 2 different clonal typos of L. monocytogenes is important from an epidemiological point of view when routes of infection are to be investigated.