A comparison of Listeria monocytogenes serovar 4b isolates of clinical and food origin in Austria by automated ribotyping and pulsed-field gel electrophoresis

Abstract number: 1134_04_62

Heller I., Grif K., Dierich M.P., Wuerzner R.

Objectives:  

In this study, automated ribotyping and pulsed-field gel electrophoresis (PFGE) were evaluated in an epidemiological study of Listeria monocytogenes serotype 4b strains from patients and food samples collected in Austria. These isolates were compared with isolates from foodborne incidents which have occurred in other European countries and North America.

Methods:  

The L. monocytogenes serovar 4b isolated were comprised of isolates from listeriosis patients in Austria, isolates from food and environmental samples in Austria as well as isolates from foodborne listeriosis in other European countries and North America. Automated ribotyping was performed using the RiboPrinter microbial characterisation system according to manufacturer's instructions using EcoRI as restriction enzyme. PFGE was performed according to the standardized protocol for molecular subtyping of L. monocytogenes by PulseNet USA using restriction enzymes AscI and ApaI.

Results:  

Two PFGE subtypes dominated among human isolates, and these PFGE subtypes were also found among food isolates. Some ribotypes contained different PFGE types, but PFGE types were also assigned to different ribotypes. The largest group of Austrian clinical isolates was of the same PFGE subtype as those isolated from foodborne outbreaks in the United Kingdom and in the USA. Another subtype of clinical isolates from Austria was indistinguishable to that obtained from isolates responsible for foodborne outbreaks in Canada, Switzerland, the USA and France.

Conclusion:  

Although the discriminatory power of PFGE is believed to be higher than that of ribotyping, some PFGE types included several ribotypes. Thus, combining data obtained by ribotyping and PFGE increases the likelihood of strains discrimination. Nevertheless, many of the Austrian strains remain indistinguishable from strains of foodborne outbreaks in other countries. This complies to previous results which show the highly clonal nature of the serotype 4b clonal group.