Beyond Adsorption: New Insights Into Phage Resistance in Clinical Pseudomonas aeruginosa Isolates

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Source : full video here https://www.canal-u.tv/177442

As phage therapy gains momentum as a potential solution to the global antibiotic resistance crisis, understanding why bacteria resist phage infection has become one of the field's most pressing challenges. For decades, phage resistance was largely viewed through a relatively simple framework: bacteria escape infection by modifying or losing the surface receptors used by phages for attachment. While receptor-mediated resistance remains a fundamental mechanism, recent discoveries suggest that the interaction between bacteriophages and their hosts is considerably more complex.

During a presentation delivered at the Phages 2026 conference, Clarisse Plantady explored the determinants of phage resistance in clinical isolates of Pseudomonas aeruginosa, one of the most problematic opportunistic pathogens encountered in modern healthcare. The study provides a detailed examination of how both extracellular and intracellular mechanisms contribute to phage susceptibility in strains isolated from patients who experienced antibiotic treatment failure.

Pseudomonas aeruginosa remains a major target for phage therapy development. The bacterium is responsible for chronic lung infections in cystic fibrosis patients, ventilator-associated pneumonia, burn wound infections and numerous hospital-acquired infections. Its remarkable capacity to acquire antibiotic resistance has placed it among the pathogens prioritized by global health organizations for alternative therapeutic approaches. Yet the same evolutionary flexibility that enables antibiotic resistance can also generate resistance to bacteriophages.

To better understand these mechanisms, researchers assembled a collection of 125 clinical P. aeruginosa isolates obtained from cases where antibiotic treatment had failed. These strains were challenged against a panel of eight bacteriophages representing multiple taxonomic groups and infection strategies. The experimental design combined high-throughput infectivity screening, adsorption assays, whole-genome sequencing and genome-wide association studies to identify the genetic factors influencing phage susceptibility.

The results confirmed that adsorption remains a dominant barrier to infection. In most resistant strains, phages were unable to efficiently attach to the bacterial surface, preventing the infection cycle from progressing. This finding reinforces the importance of bacterial surface structures such as lipopolysaccharides, type IV pili and outer membrane proteins, all of which can serve as phage receptors. Even minor modifications to these structures may be sufficient to block viral attachment and provide immediate protection against infection.

However, adsorption failure did not explain all observed resistance patterns. A significant proportion of strains displayed more complex phenotypes in which phages successfully attached to the bacterial surface but failed to establish productive infections. These observations point toward the growing importance of intracellular defense systems that act after viral entry.

Over the past decade, researchers have discovered an extraordinary diversity of bacterial immune mechanisms capable of targeting invading phages. These systems include restriction-modification complexes, CRISPR-Cas immunity, abortive infection pathways, CBASS systems, retrons and numerous recently identified defense islands. Many of these mechanisms remain poorly characterized in clinical isolates despite their likely importance in determining therapeutic outcomes.

The study identified a significant negative correlation between the number of defense systems encoded by a bacterial genome and overall phage infectivity. In other words, strains carrying larger repertoires of antiviral defenses were generally more resistant to phage infection. This relationship suggests that bacterial defense load may serve as an important predictor of therapeutic success. Nevertheless, the correlation was not absolute, indicating that additional factors continue to influence susceptibility.

This observation highlights an increasingly recognized concept in phage biology: resistance is not determined solely by the presence or absence of individual defense systems, but by the combined architecture of the bacterial defense network. Two strains may carry similar immune systems yet exhibit dramatically different responses to the same phage depending on gene expression levels, regulatory interactions, metabolic state or the presence of unidentified antiviral mechanisms.

The genomic analyses also revealed substantial unexplained variation. Even after accounting for adsorption efficiency and known defense systems, some strains remained unexpectedly susceptible or resistant. This suggests that a considerable portion of the molecular landscape governing phage-host interactions remains undiscovered. Transcriptional regulators, stress response pathways, membrane physiology and metabolic factors may all contribute to shaping infection outcomes in ways that are not yet fully understood.

From a therapeutic perspective, these findings have important implications. Modern phage therapy increasingly relies on personalized approaches in which phages are selected against individual patient isolates. Understanding not only receptor availability but also the composition of intracellular defense systems could improve phage selection strategies and help anticipate treatment failure before therapy begins.

The work also illustrates how phage susceptibility is becoming a data-rich problem. By combining phenotypic assays with comparative genomics and genome-wide association studies, researchers can begin constructing predictive models capable of estimating the likelihood of successful infection. Such approaches may eventually enable clinicians to identify optimal phage combinations based on the genetic profile of a patient's bacterial pathogen.

As phage therapy progresses toward broader clinical implementation, studies such as this demonstrate that bacterial resistance cannot be reduced to a single mechanism. The interaction between phages and clinical pathogens represents a multilayered conflict involving receptor biology, intracellular immunity, regulatory networks and evolutionary adaptation. Understanding this complexity will be essential for developing robust and durable phage-based treatments against multidrug-resistant infections.

Source ; https://www.canal-u.tv/177442

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