an epidemiological study of listeriosis in dairy cattle

etween increased anti-LLO antibodies and faecal excretion has also been suggested in
an experimental infection of L. monocytogenes (Mietinnen and others 1991).
The sources of infection on these farms were investigated using RAPD test. One
criticism of RAPD is its lack of reproducibility (Wernars and others 1996). The RAPD
technique used in this study had been validated in another laboratory (O’Donoghue and
others 1995). The use of 6 primers allowed internal validation and the experiments
showed that the technique was repeatable. Similar results were reported by other
researchers (Mazurier and Wernars 1992, MacGowan and others 1993, O’Donoghue
and others 1995). Alternative typing methods such as serotyping, ribotyping, restriction
enzyme analysis (REA) multilocus enzyme electrophoresis (MEE) and pulsed field gel
electrophoresis (PFGE), have been used for L. monocytogenes (Ralovich 1993) and a
comparison with RAPD has also been made (Boerlin and others 1995, Louie and others
1996). RAPD was compared with serotyping, ribotyping, MEE and REA by Boerlin and
others (1995). They acknowledged the superiority of RAPD. RAPD was also compared
with ribotyping and PFGE. RAPD and PFGE were found to be the most discriminating
typing methods and their ability to differentiate between strains was comparable (Louie
and others 1996). However PFGE may take several days, it is costly and sophisticated
laboratory equipment is required to perform it. RAPD, on the other hand, is cheap, rapid
(results are obtained within several hours) and easy to perform (O’Donoghue and others
1995, Louie and others 1996).
The wide diversity of L. monocytogenes found on five study farms makes it
difficult to link environmental strains with faecal strains. Because of the lack of
understanding of the population dynamics of strains of L. monocytogenes it is also not
known if temporal distribution of strains occurs (Low and Donachie 1997). This was
also the case in this study.
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