Bacteriophage therapy: practicability and clinical need meet in the multidrug-resistance era

On the potential of microscale electrokinetic cascade devices

Phages used for phage therapy of multidrug resistant bacteria must be highly purified prior to use. There are limited purification approaches that are broadly applicable to many phage types. Electrokinetics has shown great potential to manipulate phages, but obstructions from the cell debris produced during phage propagation can severely diminish the capacity of an electrokinetic device to concentrate and purify phage samples. A multipart insulator-based electrokinetic device is proposed here to remove the larger, undesirable components of mixtures from phage preparations while transferring the freshly purified and concentrated sample to a second stage for downstream analysis. By combining the large debris prescreen and analysis stages in a streamlined system, this approach simultaneously reduces the impact of clogging and minimizes the sample loss observed during manual transferring of purified samples. Polystyrene particles were used to demonstrate a diminished sample loss of approximately one order of magnitude when using the cascade device as opposed to a manual transfer scheme. The purification and concentration of three different phage samples were demonstrated using the first stage of the cascade device as a prescreen. This design provides a simple method of purifying and concentrating valuable samples from a complex mixture that might impede separation capacity in a single channel.

To Be or Not To Be T4: Evidence of a Complex Evolutionary Pathway of Head Structure and Assembly in Giant Salmonella Virus SPN3US

Giant Salmonella phage SPN3US has a 240-kb dsDNA genome and a large complex virion composed of many proteins for which the functions of most are undefined. We recently determined that SPN3US shares a core set of genes with related giant phages and sequenced and characterized 18 amber mutants to facilitate its use as a genetic model system. Notably, SPN3US and related giant phages contain a bolus of ejection proteins within their heads, including a multi-subunit virion RNA polymerase (vRNAP), that enter the host cell with the DNA during infection. In this study, we characterized the SPN3US virion using mass spectrometry to gain insight into its head composition and the features that its head shares with those of related giant phages and with T4 phage. SPN3US has only homologs to the T4 proteins critical for prohead shell formation, the portal and major capsid proteins, as well as to the major enzymes essential for head maturation, the prohead protease and large terminase subunit. Eight of ~50 SPN3US head proteins were found to undergo proteolytic processing at a cleavage motif by the prohead protease gp245. Gp245 undergoes auto-cleavage of its C-terminus, suggesting this is a conserved activation and/or maturation feature of related phage proteases. Analyses of essential head gene mutants showed that the five subunits of the vRNAP must be assembled for any subunit to be incorporated into the prohead, although the assembled vRNAP must then undergo subsequent major conformational rearrangements in the DNA packed capsid to allow ejection through the ~30 Å diameter tail tube for transcription from the injected DNA. In addition, ejection protein candidate gp243 was found to play a critical role in head assembly. Our analyses of the vRNAP and gp243 mutants highlighted an unexpected dichotomy in giant phage head maturation: while all analyzed giant phages have a homologous protease that processes major capsid and portal proteins, processing of ejection proteins is not always a stable/defining feature. Our identification in SPN3US, and related phages, of a diverged paralog to the prohead protease further hints toward a complicated evolutionary pathway for giant phage head structure and assembly.

Polar flagella rotation in Vibrio parahaemolyticus confers resistance to bacteriophage infection

Bacteriophage has been recognized as a novel approach to treat bacterial infectious diseases. However, phage resistance may reduce the efficacy of phage therapy. Here, we described a mechanism of bacterial resistance to phage infections. In Gram-negative enteric pathogen Vibrio parahaemolyticus, we found that polar flagella can reduce the phage infectivity. Deletion of polar flagella, but not the lateral flagella, can dramatically promote the adsorption of phage to the bacteria and enhances the phage infectivity to V. parahaemolyticus, indicating that polar flagella play an inhibitory role in the phage infection. Notably, it is the rotation, not the physical presence, of polar flagella that inhibits the phage infection of V. parahaemolyticus. Strikingly, phage dramatically reduces the virulence of V. parahaemolyticus only when polar flagella were absent both in vitro and in vivo. These results indicated that polar flagella rotation is a previously unidentified mechanism that confers bacteriophage resistance.

Phages targeting infected tissues: novel approach to phage therapy

While the true efficacy of phage therapy still requires formal confirmation in clinical trials, it continues to offer realistic potential treatment in patients in whom antibiotics have failed. Novel developments and approaches are therefore needed to ascertain that future clinical trials would evaluate the therapy in its optimal form thus allowing for reliable conclusions regarding the true value of phage therapy. In this article, we present our vision to develop and establish a bank of phages specific to most threatening pathogens and armed with homing peptides enabling their localization in infected tissues in densities assuring efficient and stable eradication of infection.

New perspectives in the management of Pseudomonas aeruginosa infections

ABSTRACT: 

Infections with Pseudomonas aeruginosa are a major health problem, especially for immune-compromised and cystic fibrosis patients, owing to the particular drug resistance of the microorganism. The aim of this review is to provide recent insights into strategies under investigation for prevention and therapy of these infections. In this survey, the approach directed against bacterial biofilm formation and quorum-sensing systems was focused, along with the evaluation of the treatment with bacteriophages. New interesting, developmental studies and clinical trials to prevent or treat infections due to this opportunistic pathogen are based on active and passive immunotherapy. Some monoclonal antibodies and different vaccines against this microorganism have been developed in the last few decades, even though to date none of them have obtained market authorization.

Phage therapy: eco-physiological pharmacology

Bacterial virus use as antibacterial agents, in the guise of what is commonly known as phage therapy, is an inherently physiological, ecological, and also pharmacological process. Physiologically we can consider metabolic properties of phage infections of bacteria and variation in those properties as a function of preexisting bacterial states. In addition, there are patient responses to pathogenesis, patient responses to phage infections of pathogens, and also patient responses to phage virions alone. Ecologically, we can consider phage propagation, densities, distribution (within bodies), impact on body-associated microbiota (as ecological communities), and modification of the functioning of body "ecosystems" more generally. These ecological and physiological components in many ways represent different perspectives on otherwise equivalent phenomena. Comparable to drugs, one also can view phages during phage therapy in pharmacological terms. The relatively unique status of phages within the context of phage therapy as essentially replicating antimicrobials can therefore result in a confluence of perspectives, many of which can be useful towards gaining a better mechanistic appreciation of phage therapy, as I consider here. Pharmacology more generally may be viewed as a discipline that lies at an interface between organism-associated phenomena, as considered by physiology, and environmental interactions as considered by ecology.