Phage typing in the diagnostic of Salmonella Enteritidis occurring in Poland

Phage typing has a long history with regard to the differentiation of Salmonella serovars of human and animal origin. This method provides the fast and cheap characterization of frequent serovars on the sub-serovar level and is especially useful for primary epidemiological analysis before investigation by other, more expensive molecular techniques. Since the discovery of bacteriophages many different Salmonella typing schemes have been developed. More than one typing scheme may have been developed for a serovar. Several phage-typing schemes have been published for Salmonella Enteritidis. The most widely used is that of Ward et al. In Poland a different typing scheme is used - the Lalko et al. scheme. It employs eight typing phages for differentiation more than 20 phage types. Basing on the results of Salmonella Enteritidis phage typing, which has been conducted in Poland for many years, it can be noted that Salmonella Enteritidis infections reported in our country during the last fifty years were associated with two serious epidemics. Among the strains isolated during the first epidemic, phage types 2, 5, 7, 8 and 12 were predominant and the great majority of the strains were represented by types 8 and 5. Phage types 1, 6 and 7 were found to be dominated during 27 years of the second Salmonella Enteritidis epidemic in Poland. The strains of type 7 were the most numerous ones. The results of phage typing indicate that sources of infections of these two Salmonella Enteritidis epidemics are quite different. However, a relationship between them exists: Salmonella Enteritidis type 7 organisms occur in both. During the first epidemic they were isolated in a relatively small percentage and only from humans. The great majority of sources of Salmonella Enteritidis infections associated with the second epidemic were dominated by them. They were also prevalent in human isolates. Generally, during the last 27 years, no significant changes in the distribution of Salmonella Enteritidis phage types in Poland have been observed. Although, it is noteworthy that except the same, permanent phage types continuously existing in the environment, the new types start to appear. They can suggest an appearance of new sources of Salmonella Enteritidis infections, unknown yet in our country, which is very possible as a result of effective elimination of currently existing ones.