Attempts to establish phage typing as an epidemiological marker for Salmonella enteritidis

Phage restriction and the presence of small plasmids in Salmonella enteritidis

Between 1990-1994, a total of 16,505 S. enteritidis strains of human, animal and food origin were phage-typed, using the Hungarian scheme and the changes of incidence of the dominant phage types were monitored. The incidence of PT1 (corresponding to Ward's PT1 was very high between 1990 and 1992 (67.9-71.0% of the total S. enteritidis isolates), later, it decreased. The prevalence of PT6 (corresponding to Ward's PT4) was rare until 1992, then it gradually increased. The phage type and plasmid content of 78 Salmonella enteritidis strains were determined. Small plasmids were present in 59% of the isolates, together with a serotype-specific (38 MDa) plasmid. A correlation was found between the presence of the small plasmid and phage restriction to two phages used for subdividing the Hungarian phage types 1 (PT1) and 6 (PT6) of S. enteritidis (corresponding to PT1 and PT4 in Ward's typing scheme, respectively).

Correlation of conversion of Salmonella enterica serovar enteritidis phage type 1, 4, or 6 to phage type 7 with loss of lipopolysaccharide

Studies of pairs of Salmonella enterica serovar Enteritidis isolates from different poultry flocks showed that phage type (PT) 7 may be derived from PT 1, 4, and 6. The conversion appeared to be associated with loss of lipopolysaccharide. It is concluded that PT 7 may be of little value as an epidemiological marker of S. enterica serovar Enteritidis.

Differentiation of strains from a food-borne outbreak of Salmonella enterica by phenotypic and genetic typing methods

A combination of typing methods was used to identify the strains and the infection source in a food-borne outbreak of Salmonella enterica occurring in a summer camp and affecting 25 children. All isolates tested were found to be serovar Enteritidis, with an identical biotype API 20E and ribotype. However, they differed in their plasmid profiles and/or antibiograms, and were grouped into three strains. One strain was found in human stools, another in a hen's egg, and the third in both stools and another egg pointing to large Spanish omelettes to be the contaminated food source.

The characterization of Danish isolates of Salmonella enterica serovar Enteritidis by phage typing and plasmid profiling: 1980-1990

Plasmid profiling, phage typing and antimicrobial resistance typing have been carried out on 736 isolates of Salmonella enterica serovar Enteritidis collected in Denmark during the period 1980 to 1990. Strains originated from cases of human salmonellosis, broiler poultry flocks, layer poultry flocks, quarantined imported poultry, environmental samples from hatchery units, and from bovines. Phage type (PT) 1 was found to be the most common type among isolates of poultry origin (57.6%) followed by PT4 (28.8%). Isolates belonging to PT8 were found exclusively in imported birds. Phage typing of a representative sample of human isolates revealed the predominance, as in most other Western European countries, of PT4 (61.8%). PT1, however, was found in 17.0% of human strains, a much higher incidence than expected. Antibiotic resistance was observed in 4 out of 107 human isolates (3.7%) and 2 out of 205 non-human isolates (1%) tested.

Distribution of Salmonella enteritidis phage types in Canada

The distribution of Salmonella enteritidis phage types in Canada is described; 606 of 674 strains examined were of human origin. Typable strains of all sources, constituted 99.6% (671/674) of all strains examined, and were representative of 15 different phage types. Five phage types (8, 13, 4, 13a and 1) accounted for 92.4% of the total. Phage type 8 consistently showed the highest incidence in human (69.96%) and non-human (72.05%) sources and appeared to be the most common in North America. Phage type 4, the most prevalent in the UK, is infrequent in Canada (38/674). The distribution of phage types showed regional variation among infrequent phage types, whereas the common type, 8, was observed in different frequencies in all provinces. Examination of 29 outbreaks of S. enteritidis representing 254 isolates for humans revealed 5 different phage types, the highest number of outbreaks (11) were type 8. A study of these outbreaks and the animal-host-associations of the common phage types, 8 and 13, indicated that contaminated poultry appeared to be the most common source of human infection in Canada.