Identification and impact on Pseudomonas aeruginosa virulence of mutations conferring resistance to a phage cocktail for phage therapy

Phage therapy represents a promising strategy for curing bacterial infections refractory to antibiotics. However, the success rate of phage therapy may be lowered by the emergence of bacterial resistance to the phages used for therapy. In this work, we studied the resistance to the CK4 cocktail, which is a mixture composed of four phages able to cure Pseudomonas aeruginosa infections in animal models. CK4-resistant mutants were easily isolated from cultures grown in either a standard laboratory medium or an artificial sputum medium mimicking the composition of the airway fluid of cystic fibrosis (CF) patients, who are highly susceptible to P. aeruginosa chronic lung infections. In both cases, CK4-resistant mutants resulted in being defective in lipopolysaccharide (LPS) biosynthesis. Accordingly, all CK4 phages were unable to infect wzy mutants lacking the O-antigen polymerase. A survey of the other 15 P. aeruginosa phages isolated from different environmental sources showed that they all needed either wzy or the Type IV-pilus (T4P) biosynthetic gene pilQ for the infection. Overall, our data suggest that 16 out of the 19 analyzed Pseudomonas phages may use either the LPS or the T4P as a receptor. Interestingly, CK4-resistant mutants devoid of the O-antigen had strongly attenuated virulence in a zebrafish embryo infection model, and the lack of T4P also decreased virulence in zebrafish. With respect to isolates from patients with CF, phages not reproducing in the Δwzy mutant had a wider host range than those requiring pilQ, suggesting that phages dependent on PAO1-type T4P may have limited therapeutic value for treating CF-related infections

Animal Models to Translate Phage Therapy to Human Medicine

Phagotherapy, the use of bacteriophages to fight bacterial infections as an alternative to antibiotic treatments, has become of increasing interest in the last years. This is mainly due to the diffusion of multi-drug resistant (MDR) bacterial infections that constitute a serious issue for public health. Phage therapy is gaining favor due to its success in agriculture and veterinary treatments and its extensive utilization for human therapeutic protocols in the Eastern world. In the last decades, some clinical trials and compassionate treatments have also been performed in the Western world, indicating that phage therapy is getting closer to its introduction in standard therapy protocols. However, several questions concerning the use of phages in human therapeutic treatments are still present and need to be addressed. In this review, we illustrate the state of art of phage therapy and examine the role of animal models to translate these treatments to humans.</jats:p

Studying Bacteriophage Efficacy Using a Zebrafish Model

The rise of bacteria resistant to the antibiotics currently in use (multiple drug-resistant, MDR) is a serious problem for patients affected by infections. This situation is even more worrying in the case of chronic bacterial infections, such as those caused by Pseudomonas aeruginosa (Pa), in patients with cystic fibrosis (CF). As an alternative to antibiotic treatments, the use of bacteriophages (phages) to fight bacterial infections has gained increasing interest in the last few years. Phages are viruses that specifically infect and multiply within the bacteria without infecting eukaryotic cells. It is well assumed that phage therapy has a high bacterial specificity, which, unlike antibiotics, should limit the damage to the endogenous microbiome. In addition, phages can kill antibiotic-resistant bacteria and perform self-amplification at the site of the infection.The protocol detailed in this chapter describes how the antimicrobial effect of phages can be studied in vivo in the zebrafish (Danio rerio) model infected with Pa. The same procedure can be applied to test the effectiveness of several different phages killing other bacterial species and for the rapid preclinical testing of phages to be used as personalized medicine

Extracellular Vesicles Released by Colorectal Cancer Cell Lines Modulate Innate Immune Response in Zebrafish Model: The Possible Role of Human Endogenous Retroviruses

Extracellular vesicles (EVs) are important components of the metastatic niche and are crucial in infiltration, metastasis, and immune tolerance processes during tumorigenesis. We hypothesized that human endogenous retroviruses (HERV) positive EVs derived from tumor cellsmay have a role in modulating the innate immune response. The study was conducted in two different colorectal cancer cell lines, representing different stages of cancer development: Caco-2, derived from a non-metastatic colorectal adenocarcinoma, and SK-CO-1, derived from metastatic colorectal adenocarcinoma (ascites). Both cell lines were treated with decitabine to induce global hypomethylation and to reactivate HERV expression. EVs were quantified by nanoparticle tracking analysis, and HERV-positive EV concentrations were measured by flow cytometry. The effect of EVs isolated from both untreated and decitabine-treated cells on the innate immune response was evaluated by injecting them in zebrafish embryos and then assessing Interleukin 1β (IL1-β), Interleukin 10 (IL-10), and the myeloperoxidase (mpx) expression levels by real-time qPCR. Interestingly, HERV-K positive EVs concentrations were significantly associated with a reduced expression of IL1-β and mpx, supporting our hypothesis that HERV-positive EVs may act as immunomodulators in tumor progression. The obtained results open new perspectives about the modulation of the immune response in cancer therapy.</jats:p