Tailspike with EPS-depolymerase activity, encoded by a phage belonging to a new genus, makes Providencia stuartii 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 with 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 β-structure migrating close to the expected trimer in a non-denaturing 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 anti-virulence agents that could complement the immune system in the fight with P. stuartii. IMPORTANCE The pace at which multidrug-resistance 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 substrate specificity spectra and by acting as anti-virulent but not bactericidal agents they do not cause the selection of resistant bacteria.