A Tailspike with Exopolysaccharide Depolymerase Activity from a New Providencia stuartii Phage Makes Multidrug-Resistant Bacteria Susceptible to Serum-Mediated Killing.

Providencia stuartii is emerging as a significant drug-resistant nosocomial pathogen, which encourages the search for alternative therapies. Here, we have isolated Providencia stuartii phage Stuart, a novel podovirus infecting multidrug-resistant hospital isolates of this bacterium. Phage Stuart is a proposed member of a new Autographivirinae subfamily genus, with a 41,218-bp genome, direct 345-bp repeats at virion DNA ends, and limited sequence similarity of proteins to proteins in databases. Twelve out of the 52 predicted Stuart proteins are virion components. We found one to be a tailspike with depolymerase activity. The tailspike could form a highly thermostable oligomeric ß-structure migrating close to the expected trimer in a nondenaturing gel. It appeared to be essential for the infection of three out of four P. stuartii hosts infected by phage Stuart. Moreover, it degraded the exopolysaccharide of relevant phage Stuart hosts, making the bacteria susceptible to serum killing. Prolonged exposure of a sensitive host to the tailspike did not cause the emergence of bacteria resistant to the phage or to serum killing, opposite to the prolonged exposure to the phage. This indicates that phage tail-associated depolymerases are attractive antivirulence agents that could complement the immune system in the fight with P. stuartiiIMPORTANCE The pace at which multidrug-resistant strains emerge has been alarming. P. stuartii is an infrequent but relevant drug-resistant nosocomial pathogen causing local to systemic life-threatening infections. We propose an alternative approach to fight this bacterium based on the properties of phage tailspikes with depolymerase activity that degrade the surface bacterial polymers, making the bacteria susceptible to the immune system. Unlike antibiotics, phage tailspikes have narrow and specific substrate spectra, and by acting as antivirulent but not bactericidal agents they do not cause the selection of resistant bacteria.

A Lytic Providencia rettgeri Virus of Potential Therapeutic Value Is a Deep-Branching Member of the T5virus Genus.

Providencia rettgeri is emerging as a new opportunistic pathogen with high antibiotic resistance. The need to find alternative methods to control antibiotic-resistant bacteria and the recent advances in phage therapy motivate the search for new phages able to infect Providencia spp. This study describes the isolation and characterization of an obligatory lytic phage, vB_PreS_PR1 (PR1), with therapeutic potential against drug-resistant P. rettgeri PR1 is a siphovirus. Its virion DNA size (118,537 bp), transcriptional organization, terminal repeats (10,461 bp), and nicks in the 3'-to-5' strand are similar to those of phage T5. However, sequence similarities of PR1 to phages of the T5virus genus at the DNA and protein levels are limited, suggesting that it belongs to a new species within the Siphoviridae family. PR1 exhibits the ability to kill P. rettgeri antibiotic-resistant strains, is highly specific to the species, and did not present known genomic markers indicating a temperate lifestyle. The lack of homologies between its proteins and proteins of the only other sequenced Providencia prophage, Redjac, suggests that these two phages evolved separately and may target different host proteins.IMPORTANCE The alarming increase in the number of bacteria resistant to antibiotics has been observed worldwide. This is particularly true for Gram-negative bacteria. For certain of their strains, no effective antibiotics are available. Providencia sp. has been a neglected pathogen but is emerging as a multidrug-resistant bacterium. This has revived interest in bacteriophages as alternative therapeutic agents against this bacterium. We describe the morphological, physiological, and genomic characterization of a novel lytic virus, PR1, which is able to kill drug-resistant P. rettgeri clinical isolates. Genomic and phylogenetic analyses indicate that PR1 is a distant relative of T5virus genus representatives. The lack of known virulence- or temperate lifestyle-associated genes in the genome of PR1 makes this phage a potential candidate for therapeutic use. Analysis of its genome also improves our knowledge of the ecology and diversity of T5-like siphoviruses, providing a new link for evolutionary studies of this phage group.

[Comparative study of Morganella and Providencia bacteriophages]. / Sravnitel'noe izuchenie bakteriofagov Morganella i Providencia.

7 strains of M.morganii phages and 7 strains of P.rettgeri phages were isolated from lysogenic cultures and the environment. The main biological properties of these phages were studied. The phages under study formed independent taxonomic groups. These phages were found to be highly specific and capable of being used for the identification of bacteria.