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Outbreaks of food poisoning caused by Salmonella enteritidis have become more common in recent years, and eggs are often the source of the infection. In the past, cracked eggs were the source of the salmonella, but recent cases have apparently been transmitted by intact eggs. A salmonella epidemic in Tennessee provided convincing evidence for intact egg transmission of salmonella. Confirmed or probable cases of salmonellosis were documented in 81 patrons of a Knoxville, Tennessee, restaurant, all of whom had eaten at the restaurant on April 8, 1989, and nearly all of whom recalled eating a meal served with either hollandaise or bernaise sauce. The hollandaise sauce had been prepared that evening using two dozen intact eggs, with butter and lemon juice, and then heated briefly. The bernaise sauce was made from the hollandaise sauce with some wine and spices added. The restaurant met local health department standards for cleanliness. The eggs were traced to a farm in Illinois. The chickens on that farm tested positive for a strain of salmonella that was indistinguishable from that cultured from the victims of food poisoning. Eleven of the victims required hospitalization for their symptoms; unlike other salmonella outbreaks of recent years, none died. Prevention of salmonellosis will require destruction of flocks infected with the bacterium, proper cooking of eggs, and may require the use of pasteurized egg products, rather than fresh eggs. (Consumer Summary produced by Reliance Medical Information, Inc.)

Restriction fragment length polymorphisms of ribosomal DNA (ribotyping) of many bacterial species has been useful for both epidemiologic subtyping and species identification. However, the use of ribotyping has been confined to major research and reference laboratories due to two factors: (a) the procedure must be carefully optimized for each organism one wishes to investigate and (b) most currently available protocols use hazardous chemicals or radioisotopes. The purpose of this study is to suggest an overall scheme that a clinical or research microbiologist could apply to ribotyping of any organism. In general, we recommend using a guanidium extraction method for DNA extraction, careful optimization of restriction conditions, and hybridization with non-radioactive digoxigenin-labelled probes; these procedures do not use hazardous chemicals or radioisotopes.

Since October 1992, > 150,000 cases of cholera have been reported from India and Bangladesh; the great majority of Vibrio cholerae isolates belong to the newly established serogroup O139. To better understand the interaction of genetic and epidemiologic factors responsible for their sudden appearance and rapid spread, representative toxigenic V. cholerae O139 isolates were molecularly characterized and compared with a set of toxigenic V. cholerae O1 and non-O1/non-O139 strains. DNA sequences of the cholera toxin B subunit gene and multilocus enzyme electrophoresis markers of V. cholerae O139 strains were identical to those of V. cholerae O1 isolates of the seventh pandemic. Two distinct ribotypes and four pulsed-field gel electrophoretic patterns were observed for O139 strains. V. cholerae O139 strains were very similar to V. cholerae O1 strains of the seventh pandemic but clearly different from the toxigenic V. cholerae strains of serogroups other than O1 and O139.

An outbreak of gastrointestinal illness with clinical and epidemiologic features of enterotoxigenic Escherichia coli (ETEC) occurred among patrons of a restaurant during April 1991. Illnesses among several groups of patrons were characterized by diarrhea (100%) and cramps (79%–88%) lasting a median of 3–5 days. Median incubation periods ranged from 50 to 56 h. A nonmotile strain of E. coli (E. coli O39), which was negative for heat-labile (LT) and heatstable (STa, STb) ETEC toxins, was isolated only from ill patrons. This organism produced enteroaggregative E. coli heat-stable enterotoxin 1 and contained the enteropathogenic E. coli gene locus for enterocyte effacement; it did not display mannose-resistant adherence, but produced attaching and effacing lesions in the absence of mannose on cultured HEp-2 cells. E. coli that are not part of highly characterized but narrowly defined groups may be important causes of foodborne illness.

Since the Latin American cholera epidemic began in 1991, 447 isolates of Vibrio cholerae 01 from the Western Hemisphere have been assayed by multilocus enzyme electrophoresis (MEE) to determine allelic variation among 16 enzyme-encoding genes. Two electrophoretic types (ETs) were identified among toxigenic isolates from Latin America: 323 were ET 4, the ET associated with the Latin American epidemic, and 29 were ET 3. Twenty-three of these ET 3 isolates had a distinctive antimicrobial resistance pattern also seen in isolates imported into the United States from Latin America and Southeast Asia. These resistant isolates had an identical ribotype and nearly identical pulsed-field gel electrophoresis (PFGE) patterns. Most nontoxigenic isolates analyzed were not precursors or descendants of toxigenic epidemic strains. MEE provided a population genetic framework for the interpretation of PFGE and ribotype data from the isolates in this study. All three methods identified 2 distinct strains of toxigenic V. cholerae 01 currently epidemic in Latin America.

During 1994–1996, Shigella sonnei outbreaks occurred in 8 North American traditionally observant Jewish communities. These communities remain relatively separate from neighboring populations while maintaining close contact by travel with coreligionists in other cities. Epidemiologic investigations suggested community-to-community transmission via travel. Outbreak-related and control isolates of S. sonnei from each city were subtyped by pulsed-field gel electrophoresis (PFGE) to confirm an epidemiologic linkage between outbreaks. Forty-three (94%) of 46 outbreak-related isolates had closely related PFGE patterns, constituting a single subtype; 33 (94%) of 35 control isolates demonstrated unrelated PFGE patterns. Several patterns differing by 3 bands were identified within the outbreak subtype; one of these accounted for 65% of outbreak isolates. Hence, a single subtype of S. sonnei caused an international outbreak involving 8 traditionally observant Jewish communities, but not neighboring populations, over a 2-year period, suggesting sustained propagation of the epidemic strain between communities.