One of the approaches to the treatment of infections caused by multiply-(MDR) or extra drugresistant (XDR) pathogenic strains may be application of bacterial viruses (bacteriophages)phage therapy. Results of a long, but quite limited use of phage therapy in several EasternEuropean countries, as well as experiments on animal models in Western countries support the possibility to use phage therapy.However, given the role of phages in the evolution of bacterial pathogens, it is necessary to discuss and evaluate negative consequences of mass introduction of phage therapy, as the measures necessary for its safe use.We discuss some actions in case of transiting to world-wide use of phage therapy with purpose to prolong the active life of phage therapy and to diminish possible complications.

AIMS:Salmonella is a worldwide foodborne pathogen causing acute enteric infections in humans. In the recent years, the use of bacteriophages has been suggested as a possible tool to combat this zoonotic pathogen in poultry farms. This work aims to isolate and perform comparative studies of a group of phages active against a collection of specific Salmonella Enteritidis strains from Portugal and England. Also, suitable phage candidates for therapy of poultry will be selected. METHODS AND RESULTS:The Salm. Enteritidis strains studied were shown to have a significantly high occurrence of defective (cryptic) prophages; however, no live phages were found in the strains. Bacteriophages isolated from different environments lysed all except one of the tested Salm. Enteritidis strains. The bacteriophages studied were divided into different groups according to their genetic homology, RFLP profiles and phenotypic features, and most of them showed no DNA homology with the bacterial hosts. The bacteriophage lytic efficacy proved to be highly dependent on the propagation host strain. CONCLUSIONS:Despite the evidences shown in this work that the Salm. Enteritidis strains used did not produce viable phages, we have confirmed that some phages, when grown on particular hosts, behaved as complexes of phages. This is most likely because of the presence of inactive phage-related genomes (or their parts) in the bacterial strains which are capable of being reactivated or which can recombine with lytic phages. Furthermore, changes of the bacterial hosts used for maintenance of phages must be avoided as these can drastically modify the parameters of the phage preparations, including host range and lytic activity. SIGNIFICANCE AND IMPACT OF THE STUDY:This work shows that the optimal host and growth conditions must be carefully studied and selected for the production of each bacteriophage candidate for animal therapy.

Pseudomonas aeruginosa phage EL is a dsDNA phage related to the giant ϕKZ-like Myoviridae. The EL genome sequence comprises 211,215bp and has 201 predicted open reading frames (ORFs). The EL genome does not share DNA sequence homology with other viruses and micro-organisms sequenced to date. However, one-third of the predicted EL gene products (gps) shares similarity (Blast alignments of 17–55% amino acid identity) with ϕKZ proteins. Comparative EL and ϕKZ genomics reveals that these giant phages are an example of substantially diverged genetic mosaics. Based on the position of similar EL and ϕKZ predicted gene products, five genome regions can be delineated in EL, four of which are relatively conserved between EL and ϕKZ. Region IV, a 17.7kb genome region with 28 predicted ORFs, is unique to EL. Fourteen EL ORFs have been assigned a putative function based on protein similarity. Assigned proteins are involved in DNA replication and nucleotide metabolism (NAD+-dependent DNA ligase, ribonuclease HI, helicase, thymidylate kinase), host lysis and particle structure. EL-gp146 is the first chaperonin GroEL sequence identified in a viral genome. Besides a putative transposase, EL harbours predicted mobile endonucleases related to H–N–H and LAGLIDADG homing endonucleases associated with group I intron and intein intervening sequences.

Recently we have accomplished the entire DNA sequence of bacteriophage phiKZ, a giant virus infecting Pseudomonas aeruginosa. The 280 334-bp of phiKZ genome is a linear, circularly permutated and terminally redundant, AT-rich dsDNA molecule that contains no sites for NotI, PstI, SacI, SmaI, XhoI and XmaIII endonucleases. Limited homology to other bacteriophages on the DNA and protein levels indicated that phiKZ represents a distinct branch of the Myoviridae family. In this work, we analyzed a group of six P. aeruginosa phages (Lin68, Lin21, PTB80, NN, EL, and RU), which are morphologically similar to phiKZ, have similar genome size and low G + C content. All phages have a broad host range among R aeruginosa strains, and they are resistant to the inhibitory action of many P aeruginosa plasmids. The analysis of the genomic DNA by restriction enzymes and DNA-DNA hybridization shows that phages are representative of three phiKZ-Iike species: phiKZ-type (phiKZ, Lin2l, NN and PTB80), EL-type (EL and RU) and Lin68 which has a shorter tail than other phages. Except for related phages EL and RU, all phiKZ-Iike phages have identical N-terminal amino acid sequences of the major capsid protein. Random genome sequencing shows that the EL and RU phages have no homology to the phiKZ-Iike phages on DNA level. We propose that the ( KZ, Lin2l, NN, PTB80 and Lin68 phages can be included in a new ( KZ genus, and that the EL and RU phages belong to a separate genus within the Myoviridae family. Based on the resistance to many restriction enzymes and the transduction ability, there are indications that over the long pathway of evolution, the phiKZ-Iike phages probably inherited the capacity to infect different bacterial species. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.