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SUMMARYUsing pulsed-field gel electrophoresis (PFGE) and 168 rRNA (rrn) analysis (ribotyping), the in vivo derivation of strains of Salmonella enteritidis PTs 9a and 7 from a strain of S. enteritidis PT 4 has been demonstrated. All strains were isolated from a single patient over a 6-week period. Further studies have demonstrated that in terms of pulsed-field profile and ribotype, the genotypes of the patient-derived strains differed from those of the reference strains of the respective phage types. It is concluded that when used in combination, these methods can provide evidence of phylogenetic relationships in apparently unrelated S. enteritidis phage types isolated during pathogenesis of disease.

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Five phage types have been identified in 38 strains of Salmonella enteritidis isolated in Turkey in the 20-month period June 1992-January 1994. Strains belonging to phage type 4 predominated. Within phage type 4, plasmid profile typing has proved a useful method of strain discrimination and has confirmed the identity of a putative outbreak involving canteen workers in an industrial complex.

An analogue, for ferrimagnetism, of the Curie–Weiss model ferromagnet is introduced. The resulting structure, the Curie–Weiss–Néel model, is based on a two sublattice description in which spins of one magnitude occupy one sublattice and spins of another magnitude occupy the other. Attention is concentrated on the case in which spins on the different sublattices tend to align in an anti-parallel fashion. Many properties of the new model are similar to those of the Curie–Weiss ferromagnet. Artificially long-ranged interactions connect spins on the different sublattices. The complete thermodynamics can be obtained exactly by relatively elementary methods. The exact solution of the model is essentially identical with the appropriate mean field results (of Néel). Attention is given to the Néel point and associated critical phenomena. Many standard critical exponents are calculated and, of course, classical exponent values result. Novel features of critical phenomena in ferrimagnets are considered. These are associated with the fact that, theoretically, the staggered magnetization and staggered fields are important while, experimentally, the total magnetization and uniform fields are usually employed. It is shown that, within the present context, corresponding staggered and uniform properties have identical exponent values.