Epsilon Open Archive

Abstract

The bacterium Listeria monocytogenes can cause the disease listeriosis in both humans and animals. For humans, the infection is mainly foodborne. Since the bacterium is able to grow even at refrigerator temperature, a food product may constitute a possible vehicle of infection although stored in cold environment. Meningoencephalitis and septicaemia are clinical manifestations of listeriosis. Infection in a pregnant woman may lead to abortion of the foetus or the birth of a seriously ill child. Risk groups for L. monocytogenes infection are immunocompromised persons, the elderly, pregnant women and infants. Different methods for visualising the genetic diversity among strains of L. monocytogenes were used in this thesis. L. monocytogenes can be established in food processing plants for long periods. Investigation of genetic diversity among strains isolated from a dairy during several years by pulsed-field gel electrophoresis (PFGE) showed indistinguishable restriction patterns. This indicated a common source for the L. monocytogenes contamination. The PFGE method was also used to investigate the diversity among strains isolated from faeces from clinically healthy cows. Polymerase chain reaction and restriction enzyme analysis (PCR-REA) of a segment of a virulence gene region could divide strains of serovar 1/2a into two groups. Strain diversity was also visualised by sequencing. Both conventional sequencing of 1500 bp of the virulence gene inlB and the sequencing-by-synthesis method pyrosequencing of two positions of this gene, grouped L. monocytogenes strains in a similar way. Strains of serovars 1/2a and 1/2c formed one group, strains of serovar 1/2b and 3b another and strains of serovar 4b were divided into two groups. Based on nucleotide polymorphisms in the inlB gene the strain diversity within serovar 4b was more distinct than within the other investigated serovar