Amino acid residues in the tail fiber differentiate the host specificity of Cronobacter sakazakii bacteriophage.

Cronobacter sakazakii is a Gram-negative pathogen that causes severe infections such as neonatal meningitis and sepsis. Bacteriophages (phages) rely on tail fibers for host recognition and infection, but the mechanisms of how phages recognize their bacterial hosts are not completely elucidated. In this study, two lytic C. sakazakii phages belonging to the Drexlerviridae family, CRES7 and CRES9, were isolated from sewage in South Korea. The genomes of both phages are almost the same, with only two nucleotide differences in the gene encoding a putative tail fiber, causing two amino acid differences at amino acid residues 400 and 550 of the tail fiber. The predicted structure of the tail fiber revealed that the two amino acid residues are located on the surface of the tail fiber, suggesting that these two amino acid residues may affect receptor binding. These amino acid differences resulted in differential host ranges, adsorption rates, and burst sizes of CRES7 and CRES9; CRES7, which could infect only the C. sakazakii serotype O1 strain, exhibited a higher adsorption rate and larger burst size compared to CRES9, whereas CRES9 could infect both serotypes O1 and O3 strains. These findings provide insights into how the mutations in the tail fiber gene contribute to the fitness of phages within natural environments and help develop phage-based strategies with expanded host range or enhanced specificity for targeted biocontrol of C. sakazakii.IMPORTANCEAccurate recognition and attachment to the bacterial host, mediated by tail fibers, are crucial for successful phage infection. Understanding the mechanisms underlying host specificity of phages is essential for developing targeted biocontrol applications. This study identified specific amino acid residues responsible for host specificity in the tail fibers of two newly isolated Cronobacter sakazakii phages, CRES7 and CRES9. Differences in these residues showed variation in O serotype recognition, leading to differences in host range, adsorption efficiency, and burst size. These findings provide valuable insights into tail fiber-mediated host specificity, facilitating the development of more effective phage-based strategies against C. sakazakii.