Bacteriophage 2851 is a prototype phage for dissemination of the Shiga toxin variant gene 2c in Escherichia coli O157:H7.

The production of Shiga toxin (Stx) (verocytotoxin) is a major virulence factor of Escherichia coli O157:H7 strains (Shiga toxin-producing E. coli [STEC] O157). Two types of Shiga toxins, designated Stx1 and Stx2, are produced in STEC O157. Variants of the Stx2 type (Stx2, Stx2c) are associated with high virulences of these strains for humans. A bacteriophage designated 2851 from a human STEC O157 encoding the Stx2c variant was described previously. Nucleotide sequence analysis of the phage 2851 genome revealed 75 predicted coding sequences and indicated a mosaic structure typical for lambdoid phages. Analyses of free phages and K-12 phage 2851 lysogens revealed that upon excision from the bacterial chromosome, the loss of a phage-encoded IS629 element leads to fusion of phage antA and antB genes, with the generation of a recombined antAB gene encoding a strong antirepressor. In wild-type E. coli O157 as well as in K-12 strains, phage 2851 was found to be integrated in the sbcB locus. Additionally, phage 2851 carries an open reading frame which encodes an OspB-like type III effector similar to that found in Shigella spp. Investigation of 39 stx(2c) E. coli O157 strains revealed that all except 1 were positive for most phage 2851-specific genes and possessed a prophage with the same border sequences integrated into the sbcB locus. Phage 2851-specific sequences were absent from most stx(2c)-negative E. coli O157 strains, and we suggest that phage 2851-like phages contributed significantly to the dissemination of the Stx2c variant toxin within this group of E. coli.

Broad-host-range Yersinia phage PY100: genome sequence, proteome analysis of virions, and DNA packaging strategy.

PY100 is a lytic bacteriophage with a broad host range within the genus Yersinia. The phage forms plaques on strains of the three human pathogenic species Yersinia enterocolitica, Y. pseudotuberculosis, and Y. pestis at 37 degrees C. PY100 was isolated from farm manure and intended to be used in phage therapy trials. PY100 has an icosahedral capsid containing double-stranded DNA and a contractile tail. The genome consists of 50,291 bp and is predicted to contain 93 open reading frames (ORFs). PY100 gene products were found to be homologous to the capsid proteins and proteins involved in DNA metabolism of the enterobacterial phage T1; PY100 tail proteins possess homologies to putative tail proteins of phage AaPhi23 of Actinobacillus actinomycetemcomitans. In a proteome analysis of virion particles, 15 proteins of the head and tail structures were identified by mass spectrometry. The putative gene product of ORF2 of PY100 shows significant homology to the gene 3 product (small terminase subunit) of Salmonella phage P22 that is involved in packaging of the concatemeric phage DNA. The packaging mechanism of PY100 was analyzed by hybridization and sequence analysis of DNA isolated from virion particles. Newly replicated PY100 DNA is cut initially at a pac recognition site, which is located in the coding region of ORF2.

A cryptic plasmid of Yersinia enterocolitica encodes a conjugative transfer system related to the regions of CloDF13 Mob and IncX Pil.

Yersinia enterocolitica 29930 (biotype 1A; O : 7,8), the producing strain of the phage-tail-like bacteriocin enterocoliticin, possesses a plasmid-encoded conjugative type IV transfer system. The genes of the conjugative system were found by screening of a cosmid library constructed from total DNA of strain 29930. The cosmid Cos100 consists of the vector SuperCos1 and an insert DNA of 40 303 bp derived from a cryptic plasmid of strain 29930. The conjugative transfer system consists of genes encoding a DNA transfer and replication system (Dtr) with close relationship to the mob region of the mobilizable plasmid CloDF13 and a gene cluster encoding a mating pair formation system (Mpf) closely related to the Mpf system of the IncX plasmid R6K. However, a gene encoding a homologue of TaxB, the coupling protein of the IncX system, is missing. The whole transfer region has a size of approximately 17 kb. The recombinant plasmid Cos100 was shown to be transferable between Escherichia coli and Yersinia with transfer frequencies up to 0.1 transconjugants per donor. Mutations generated by inserting a tetracycline cassette into putative tri genes yielded a transfer-deficient phenotype. Conjugative transfer of the cryptic plasmid could not be demonstrated in the original host Y. enterocolitica 29930. However, a kanamycin-resistance-conferring derivative of the plasmid was successfully introduced into E. coli K-12 by transformation and was shown to be self-transmissible. Furthermore, Southern blot hybridization and PCR experiments were carried out to elucidate the distribution of the conjugative transfer system in Yersinia. In total, six Y. enterocolitica biotype 1A strains harbouring closely related systems on endogenous plasmids were identified.