No abstract

During recent years, interest in the use of bacteriophages as biocontrol agents against foodborne pathogens has increased, particularly for members of the family Enterobacteriaceae, with pathogenic Escherichia coli, Shigella, and Salmonella strains among them. Here, we report the isolation and characterisation of 12 novel T5-like bacteriophages from confiscated food samples. All bacterophages effectively lysed E. coli K-12 strains and were able to infect pathogenic E. coli strains representing enterohaemorrhagic (EHEC), enteropathogenic (EPEC), enterotoxigenic (ETEC), and enteroinvasive (EIEC) pathotypes, Shigella dysenteriae, S. sonnei strains, as well as multidrug-resistant (MDR) E. coli and multiple strains representing different Salmonella enterica serovars. All the bacteriophages exhibited Siphoviridae morphology. Whole genome sequencing of the novel T5-like bacteriophages showed that they represent two distinct groups, with the genome-based grouping correlating to the different host spectra. As these bacteriophages are of food origin, their stability and lack of any virulence genes, as well as their broad and mutually complementary host spectrum makes these new T5-like bacteriophages valuable candidates for use as biocontrol agents against foodborne pathogenic enterobacteria.

cCytolethal distending toxins (CDT) are potent cytotoxins of several Gram-negative pathogenic bacteria, including Escherichia coli, in which five types (CDT-I to CDT-V) have been identified so far. CDT-V is frequently associated with Shiga-toxigenic E. coli (STEC), enterohemorrhagic E. coli (EHEC) O157 strains, and strains not fitting any established pathotypes. In this study, we were the first to sequence and annotate a 31.2-kb-long, noninducible P2-like prophage carrying the cdt-V operon from an stx-and eae-negative E. coli O157:H43 strain of bovine origin. The cdt-V operon is integrated in the place of the tin and old phage immunity genes (termed the TO region) of the prophage, and the prophage itself is integrated into the bacterial chromosome between the housekeeping genes cpxP and fieF. The presence of P2-like genes (n ‫؍‬ 20) was investigated in a further five CDT-V-positive bovine E. coli O157 strains of various serotypes, three EHEC O157:NM strains, four strains expressing other variants of CDT, and eight CDT-negative strains. All but one CDT-V-positive atypical O157 strain uniformly carried all the investigated genomic regions of P2-like phages, while the EHEC O157 strains missed three regions and the CDT-V-negative strains carried only a few P2-like sequences. Our results suggest that P2-like phages play a role in the dissemination of cdt-V between E. coli O157 strains and that after integration into the bacterial chromosome, they adapted to the respective hosts and became temperate.

No abstract

We isolated and characterized two novel rV5-like lytic bacteriophages from independently collected food samples. Nucleotide sequence analysis revealed that these phages have linear double-stranded DNA genomes comprising 138,073 bp with 213 CDS and 5 tRNA genes. The two genomes contain completely identical nucleotide sequence, albeit there is a 10,718 bp-long shift in the sequence. The GC content of the phage genomes was 43.7% and they showed high general homology to rV5-like phages. The new phages were termed C203 and P206. The genome of both phages contains a unique ORF that encodes for a putative phage homing endonuclease. The phage produced clear plaques with a burst size of approx. 1000 viral particles and a latent period of 60 min. Morphological investigation indicated that the new phages are members of the family Myoviridae with an approximate head length of 85 nm, tail length of 75 nm, and a head width of 96 nm. C203 and P206 exhibit a broad and uniform host range, which included enterohemorrhagic Escherichia coli strains of serogroup O157, multi drug resistant (MDR) E. coli strains of various sero- and pathotypes, and both Shigella sonnei and S. dysenteriae strains. C203 and P206 both effectively reduced the number of living EHEC O157:H7 Sakai in experimentally inoculated minced meat. The same broad host range, the lack of any virulence related genes, the stability and its short latent period suggest that these newly found phages could be suitable candidates as a bio-control agents against food-borne pathogenic Enterobacteria.

Here we report the draft genome sequence of an Escherichia coli O157:H43 strain, designated T22, with an atypical virulence gene profile and isolated from healthy cattle. T22 produces cytolethal distending toxin V (CDT-V) and belongs to phylogenetic group B1 and sequence type 155 (ST155).

Shigella strains are important agents of bacillary dysentery, and in recent years Shigella sonnei has emerged as the leading cause of shigellosis in industrialized and rapidly developing countries. More recently, several S. sonnei and Shigella flexneri strains producing Shiga toxin (Stx) have been reported from sporadic cases and from an outbreak in America. In the present study we aimed to shed light on the evolution of a recently identified Shiga toxin producing S. sonnei (STSS) isolated in Europe. Here we report the first completely assembled whole genome sequence of a multidrug resistant (MDR) Stx-producing S. sonnei (STSS) clinical strain and reveal its phylogenetic relations. STSS 75/02 proved to be resistant to ampicillin, streptomycin, tetracycline, chloramphenicol, thrimetoprim, and sulfomethoxazol. The genome of STSS 75/02 contains a 4,891,717 nt chromosome and seven plasmids including the 214 kb invasion plasmid (pInv) harboring type III secretion system genes and associated effectors. The chromosome harbors 23 prophage regions including the Stx1 converting prophage. The genome carries all virulence determinants necessary for an enteroinvasive lifestyle, as well as the Stx1 encoding gene cluster within an earlier described inducible converting prophage. In silico SNP genotyping of the assembled genome as well as 438 complete or draft S. sonnei genomes downloaded from NCBI GenBank revealed that S. sonnei 75/02 belongs to the more recently diverged global MDR lineage (IIIc). Targeted screening of 1131 next-generation sequencing projects taken from NCBI Short Read Archive of confirms that only a few S. sonnei isolates are Stx positive. Our results suggest that the acquisition of Stx phages could have occurred in different environments as independent events and that multiple horizontal transfers are responsible for the appearance of Stx phages in S. sonnei strains.

Enterohemorrhagic Escherichia coli (EHEC) isolates of serotype O157:H7 are serious foodborne zoonotic pathogens and prime targets for biocontrol using bacteriophages. We report on the complete genome sequences of 11 novel lytic bacteriophages, representing three viral genera, isolated from cattle in Hungary that target E. coli O157 strains.