No abstract

The enteropathogenicity of Providencia alcalifaciens, a member of the family Enterobacteriaceae, has not yet been well established. In November 1996, a large outbreak of foodborne infection occurred in Fukui, Japan. In this study, the etiology of the outbreak was investigated. No other recognized enteropathogens were detected in patient fecal samples, but P. alcalifaciens was detected in 7 of 18 samples. The isolates were found to be clonal by pulsed-field gel electrophoresis. The patients who presented with gastroenteritis had elevated levels of specific antibody against the isolated P. alcalifaciens. The isolates showed invasion of Caco-2 cells and fluid accumulation in rabbit ileal loops. This study strongly suggests that the outbreak was caused by P. alcalifaciens. This is the first report of a large outbreak of foodborne infection attributed to the organism and provides definitive evidence that P. alcalifaciens is a causative agent of gastroenteritis.

Vibrio parahaemolyticus, a halophilic gram-negative rod, causes seafood-borne gastroenteritis in humans. Infections caused by this organism have been associated with diverse serovars: 13 O serotypes and 75 K serotypes have been identified. Recent studies, however, have revealed the emergence and pandemic spread of a single serovar, O3:K6 (1-6). Strains belonging to the O3:K6 serovar abruptly appeared in India in 1996 and have since been isolated in Southeast Asian countries, from travelers at quarantine stations in Japan, and from foodborne outbreaks in the United States (1-5). This serovar accounts for more than half of the V. parahaemolyticus isolates from diarrheal patients in Japan (6). Such widespread occurrence of a single serovar of V. parahaemolyticus had not previously been reported. Since 1998, V. parahaemolyticus strains belonging to other two serovars, O4:K68 and O1:K untypeable (KUT), have also been isolated with increasing frequency from diarrheal patients (2,6,7). The genetic background of the O4:K68 and O1:KUT isolates is almost indistinguishable from that of the recent O3:K6 strains, suggesting a common origin (2,7).In a previous study, we reported on a filamentous phage that is specifically associated with the recent O3:K6 serovar strains of V. parahaemolyticus (8). This phage, f237, has several genes in common with and a similar genomic structure to another filamentous phage, CTX (9), which is known to carry the genes for cholera enterotoxin (ctxAB), the most important virulence factor of V. cholerae. Instead of ctxAB, f237 possesses a unique open reading frame, ORF8, which has no homology with other sequences in DNA databases (8). In this study, we examined the distribution of f237 in recent clinical isolates of V. parahaemolyticus.

Vibrios are gram-negative ␥-proteobacteria which are ubiquitous in marine and estuarine environments. Recently, we demonstrated that some, if not all, Vibrio species have two circular chromosomes. The whole genome sequence of Vibrio cholerae N16961 has been reported. In this study, we constructed a physical and genetic map of the genome of Kanagawa phenomenon-positive Vibrio parahaemolyticus strain KX-V237 and compared it with those of V. parahaemolyticus AQ4673 and V. cholerae N16961. The genome of KX-V237 comprised two circular chromosomes (3.3 and 1.9 Mb), similar to the structure of the AQ4673 genome. The relative positions of the genes on the genomes were well conserved in the two strains, but a large inversion on the large chromosomes, probably symmetric around the replication origin, was suggested. Although the sizes of the large chromosomes of KX-V237 and V. cholerae N16961 were similar, the sizes of the small chromosomes were very different. Unlike N16961, the superintegron of KX-V237 was located on the large chromosome. Comparison of the genetic maps of the chromosomes of KX-V237 and V. cholerae N16961 revealed that most of the open reading frames (ORFs) present on the large chromosome of the V. cholerae strain had homologues on the large chromosome of the V. parahaemolyticus strain and that most of the ORFs on the small chromosome of N16961 were present on the small chromosome of KX-V237. The difference in the orders of the ORFs on the chromosomes of N16961 and KX-V237 implies that numerous and frequent genetic exchanges have occurred intrachromosomally rather than interchromosomally.

The dif site is located in the replication terminus region of bacterial chromosomes, having a function of resolving dimeric chromosomes formed during replication. We demonstrate that filamentous bacteriophages of vibrios, such as f237 (Vibrio parahaemolyticus) and CTX (V. cholerae), are integrated into the dif-like site of host chromosome.