To investigate the molecular basis for heat-stable antigenic diversity in Campylobacter jejuni, lipopolysaccharides (LPSs) from serotype reference strains and serotyped isolates were examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis coupled with silver staining and immunoblotting. By silver staining, only low-Mr components, consisting of one major band and as many as three minor bands ranging in Mr from 4,500 to 5,000, were detected. However, by immunoblotting with homologous antisera, 10 of 34 strains were shown to have a series of high-Mr LPS components characteristic of molecules with 0 side chains of various lengths. Isolates of the same serotype as the reference strain that had high-Mr LPS molecules were also found to have high-Mr LPS and in one case of cross-reacting strains it was found that the cross-reaction was associated with antibodies against high-Mr LPS. The reactions of LPSs with homologous and heterologous antisera indicated that both high-and low-Mr-type LPSs were strain-specific antigens, but in some cases cross-reactions were noted. Evidently, all C. jejuni strains possess low-Mr LPS that is readily detectable by silver staining, but some serotypes also possess high-Mr LPS components that can be visualized by immunoblotting.

A cluster of four cases of haemolytic uraemic syndrome in children occurred in Northern Bohemia, Czech Republic, between 15 June and 7 July, 1995. All the cases had significantly elevated titres of anti-O157 lipopolysaccharide (LPS) antibodies as detected by the indirect haemagglutination assay. All but one of them had drunk unpasteurized goat's milk from the same farm within the week before the disease. Evidence of E. coli O157 infection was subsequently found in 5 of 15 regular drinkers of the farm's raw goat's milk; four of them were asymptomatic, 1 had mild diarrhoea at the end of June. Verocytotoxin 2-producing E. coli O157:H7 strains of phage type 2 and of identical pulsed-field gel electrophoresis patterns were isolated from 1 of 2 farm goats and from 1 of the asymptomatic goat's milk drinkers. The frequency of anti-O157 LPS antibodies found among regular drinkers of the farm's raw goat's milk (33%; 5 of 15) was significantly higher than that found in control population (0%; none of 45) (P = 0.0005; Fisher's exact test). Our findings indicate that goats may be a reservoir of E. coli O157:H7 and a source of the infection for humans; raw goat's milk may serve as a vehicle of the pathogen transmission.

Some strains of Campylobacter jejuni react with more than one reference antiserum from the serotyping scheme based on heat-stable lipopolysaccharide antigens. To investigate the molecular basis of these cross-reactions, lipopolysaccharides from the reference strains for serotypes 4, 13, 16, 43, and 50 and isolates recovered during two different outbreaks of C. jejuni enteritis were analyzed by passive haemagglutination and sodium dodecyl sulphate-polyacrylamide gel electrophoresis coupled with silver staining or immunoblotting. The results showed that lipopolysaccharides from the reference strains and the isolates reacted with antisera prepared against heterologous strains in various combinations and that both silver-stainable, low Mr and non-silver-stainable, high Mr lipopolysaccharide components provided the antigenic determinants associated with the cross-reactions. There were strain-to-strain differences in the structural and antigenic properties of these macromolecules and shared antigenic determinants were not always provided by a common structure. Analysis of the silver-stained lipopolysaccharide profiles, outer membrane protein patterns, and chromosomal DNA restriction patterns indicated that strains with the same lipopolysaccharide profile could have the same outer membrane protein pattern and the same DNA restriction pattern. These results provided evidence for the presence of clones within this antigenic complex and implicated antigenic variation in some strains as the phenomenon responsible for the multiplicity of cross-reactions.

In September 1994, a complaint was registered at a public health unit concerning a cheese product. In addition, public health laboratories in Ontario reported an increase in the number of isolates of Salmonella berta from patients with diarrhoeal illness. A clinical, environmental and laboratory investigation was initiated to determine the nature of this outbreak. Isolates of Salmonella berta were compared using large fragment genomic fingerprinting by pulsed-field gel electrophoresis (PFGE). By late October, 82 clinical cases had been identified including 35 confirmed, 44 suspected and 3 secondary. The investigation linked illness to consumption of an unpasteurized soft cheese product produced on a farm and sold at farmers' markets. Subtyping results of patient, cheese and chicken isolates were indistinguishable, suggesting that the cheese was contaminated by chicken carcasses during production. The outbreak illustrates the potential role of uninspected home-based food producers and of cross-contamination in the transmission of foodborne bacterial pathogens.

Phage typing and DNA macrorestriction fragment analysis by pulsed-field gel electrophoresis (PFGE) were evaluated for use in the epidemiological subtyping of Escherichia coli serogroup O157 strains isolated in Ontario, Canada. Among 30 strains isolated from patients with sporadic cases of infection, 22 distinct XbaI macrorestriction patterns were identified and 17 strains exhibited unique PFGE patterns. In contrast, phage typing identified only seven different phage types and 17 strains belonged to the same phage type. A total of 25 phage type-macrorestriction pattern combinations were identified among the strains from patients with sporadic cases of infection. PFGE subtyping differentiated between unrelated strains that exhibited the same phage type, and in one group of strains, phage typing differentiated between strains of the same PFGE subtype. Both typing procedures correctly identified outbreak-related isolates as belonging to the same type in four separate outbreaks. Each outbreak strain was characterized by a distinct macrorestriction pattern, while phage typing subdivided the outbreak strains into only three different types. A small percentage of outbreak-related isolates had PFGE patterns that differed slightly (one or two DNA fragment differences) from that of the outbreak strain. On the other hand, each isolate from the same outbreak belonged to the same phage type as that of the outbreak strain. We conclude that phage typing and PFGE fingerprinting represent complementary procedures for the subtyping of E. coli serogroup O157 and that the combined use of these procedures provides optimal discrimination.