Till Örebro universitet

Since 1986, 68% of the Listeria monocytogenes isolates from human cases of invasive listeriosis in Sweden are available for retrospective studies. The aim of the present study was to characterize 601 human invasive isolates of L. monocytogenes in Sweden from 1986 to 2007 by using serotyping and pulsed-field gel electrophoresis. Since 1996, serovar 4b was permanently reduced to the second or third most common serovar in human cases in Sweden. During the latter period, 2000-2007, only 13% belonged to serovar 4b and 71% to 1/2a. The dendrogram, based on pulsovars, reveals two clusters with different serovars. Cluster 1 exhibits serovars 4b and 1/2b, whereas cluster 2 consists of serovar 1/2a. Serovar 1/2a seems to be more heterogeneous than serovar 4b.

The incidence of Listeria species in the seafood of markets in Goa, India was studied. One hundred and fifteen raw/fresh seafoods bought at the fish markets were sampled and tested for presence of Listeria spp. using a two step enrichment procedure, followed by plating on two selective agars. The confirmation of the isolates was based on biochemical identification. Twenty eight seafood samples were positive for Listeria spp. and in 10 samples Listeria monocytogenes was detected. L.innocua was the most common Listeria species recovered and was detected in 18 samples. L. monocytogenes in raw seafood may pose a health risk in kitchen if contaminating ready-to-eat food.

Gravad (Gravlax) and cold-smoked salmon are associated with human listeriosis in Sweden. The present investigation of Listeria monocytogenes in salmon was a follow-up of a similar study in the middle of the 1990s. Since our first study, there has been an increasing focus on food hygiene in general and specially on self-inspection and Hazard Analysis and Critical Control Points from the authorities and food producers. L. monocytogenes was isolated from 11 (three manufacturers) of the 56 products analyzed. The highest level of L. monocytogenes was 1500 cfu/g from a cold-smoked salmon product; however, the level was low (<100 cfu/g) in most products. Serovar 1/2a was predominant, followed by 4b. restriction enzyme analysis/ pulsed-field gel electrophoresis typing of the 56 salmon isolates identified five types of L. monocytogenes. One type was identical to a human type, whereas two other were closely related. These findings suggest that gravad and coldsmoked salmon are still possible sources of listeriosis in Sweden.

Listeria species were isolated from farm bulk milk (n=123) at the receiving dairy plant and cervico-vaginal samples (n=20) collected from dairy cows with reproductive disorders. Following enrichment and plating on two selective agar media, confirmation of the isolates was based on standard tests. Isolates were subjected to a PCR assay for detection of the hlyA gene. Overall, Listeria spp. were isolated from 30(24.4%) bulk milk samples and four (20%) cervico-vaginal swabs. Listeria monocytogenes was isolated from 17.9%, L. innocua from 1.6%, L. seeligeri from 3.3% and L. welshimeri from 1.6% bulk milk samples. Only L. monocytogenes (10%) and L. innocua (10%) could be isolated from cervico-vaginal swabs. The hlyA gene was detected in all L. monocytogenes isolates. These findings represent a public health risk where homemade unpasteurised milk and milk products are largely consumed.