Bacterial typing methods suitable for epidemiological analysis. Applications in investigations of salmonellosis among livestock.

The ability to subtype bacteria by typing methods provides the bacteriologist with a powerful means to identify relationships between bacteria. This knowledge is used to identify routes of disease transmission among livestock and from livestock to humans. In the present paper, the principles of bacterial typing and the most commonly applied typing methods for use in veterinary public health are discussed in the context of their application in the investigation of salmonella epidemiology. Typing methods are now routinely used in most investigations on this subject and have provided insight into routes of transmission, reservoirs of infection and mechanisms of persistent infection. Under the EC order on zoonotic diseases, extended surveillance on the presence of zoonotic bacteria in livestock must be expected. To receive the maximum benefits of this surveillance, selected typing methods must be applied to all isolates of e.g. salmonella. At present, serotyping, and phage typing where applicable, are the most obvious choices for continuous surveillance of this organism. Random amplification of polymorphic DNA (PCR based typing) may have the potential for allocating strains into relevant groups quicker and without the requirement for additional manpower, and this method may be preferred in future.