Reintroduction of H5N1 highly pathogenic avian influenza virus by migratory water birds, causing poultry outbreaks in the

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To evaluate DNA fingerprinting as an epidemiologic tool, pulsed-field gel electrophoresis (PFGE) was performed on isolates of Salmonella, including S. typhimurium, S. thompson, and S. enteritidis. Chromosomal DNA was digested with the restriction endonucleases Bln I and Xba I. The patterns of S. thompson and S. typhimurium isolates from various sources were different from one another. There was no correlation between the phage type and the digestion pattern of S. enteritidis isolates. Some strains belonging to one phage type were distinguished by their PFGE pattern in this study. These results suggest that the Bln I and Xba I digestion patterns of chromosomal DNA are useful for epidemiological analysis of an outbreak of Salmonella infection or food poisoning.

Pulsed-field gel electrophoresis (PFGE) of XbaI-digested DNA fragments of enterohemorrhagic Escherichia coli (EHEC) O157:H7 strains showed disappearance of a 70- or 80-kb fragment in their patterns associated with loss of Shiga toxin genes during maintenance or subcultivation. Hybridization experiments with a DNA probe complementary to Shiga toxin sequences revealed that the Shiga toxin genes in the parental strain were located on fragments the same size as the lost fragments from the toxin-negative derivatives. The evidence indicates that PFGE pattern of EHEC O157:H7 may change due to loss of Shiga toxin genes, which is likely to be associated with curing of Shiga toxin gene carrying phages in vitro.

Eggs that harbor Salmonella in their edible contents pose a significant risk of transmitting disease to consumers. Although Salmonella deposition inside yolks does not usually occur at a high frequency in naturally contaminated eggs, bacterial penetration through the vitelline membrane could lead to rapid and extensive multiplication in the nutrient-rich yolk contents. The present study used an in vitro egg contamination model to assess the ability of Salmonella strains to penetrate the vitelline membrane and multiply inside yolks. An S. enteritidis strain and 2 Salmonella heidelberg strains, initially inoculated onto the outside of the vitelline membrane, were able to enter the yolk contents (at frequencies ranging from 10 to 25% of experimentally contaminated eggs) during 24 h of incubation at 30 degrees C. Variants of these parent strains, obtained by in vivo passage into eggs laid by infected hens, penetrated the yolk membrane at significantly higher frequencies. These results demonstrate that pathogens such as S. enteritidis and S. heidelberg can penetrate into and begin to multiply inside the yolks of contaminated eggs during the first day of storage at warm temperatures.

An outbreak due to Shiga toxin-producing Escherichia coli O26:H11 (STEC) occurred at a nursery in southeastern Japan in 1997. Thirty-two children had watery or bloody diarrhoea but none of them suffered from haemolytic-uremic syndrome. All of the STEC O26 were isolated during the period from 23 July to 22 August from 24 children, 3 nurses, and 2 food samples. These organisms had stx1 and eae genes but none of the other genes for which we tested (stx2, bfp, and EAF plasmid). They also possessed multiple antimicrobial resistances, which were encoded by a transmissible plasmid, and showed mostly identical genomic pulsed-field gel electrophoretic patterns. The results of this investigation suggested that contaminated food was the main contributing factor to this multiple antimicrobial-resistant STEC O26 infection, and person-to-person transmission also contributed to the spread of this outbreak.

In order to investigate contamination of chicken farms with Salmonella, feed and eggs were sampled from 16 commercial layer farms in eastern Japan between 1993 and 1998 and cultured for salmonellae. Salmonella enterica subsp. enterica isolates belonging to 19 serovars were obtained from the feed. Six of the 19 serotypes, including Salmonella serovar Enteritidis, were observed in isolates recovered from the eggs. Salmonella serovar Enteritidis strains obtained from a feed sample and egg contents in a layer farm showed pulsed-field gel electrophoresis patterns that were genetically related and belonged to a single phage type, suggesting that the contamination of the farms was linked to the occurrence of salmonellae in feed.

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