Swiftlet Bacteriophages Concerning Diversity and Biological Features in South Kalimantan, Indonesia

We aimed to isolate and characterize bacteriophages infecting Nitrobacter spp. from swiftlet house environments and to evaluate their biological properties as potential biocontrol agents to mitigate nitrate accumulation in edible bird’s nest (EBN) production. Environmental samples were collected from multiple swiftlet houses in South Kalimantan, Indonesia. Samples were enriched with Nitrobacter cultures, and bacteriophages were detected using spot assays followed by plaque purification. Plaque morphology was examined using digital microscopy. Host range specificity was assessed against a panel of nitrifying bacterial isolates obtained from different swiftlet houses. Phage replication dynamics, including rise period and burst size, were determined using one-step growth curve assays. Twelve distinct bacteriophages capable of infecting Nitrobacter were successfully isolated. Plaque morphologies varied from small, clear plaques to larger plaques with halos. Host range analysis demonstrated that all phages exhibited specificity toward Nitrobacter isolates. One-step growth curve analysis revealed rise periods ranging from 30 to 90 min and burst sizes spanning from 2.8 to 6429.9 plaque-forming units per infected cell, indicating substantial variability in replication efficiency among the phages. Bacteriophages isolated from swiftlet house environments displayed considerable morphological and biological diversity while maintaining a narrow host range for Nitrobacter. Phages exhibiting higher burst sizes represent promising candidates for targeted biocontrol strategies aimed at improving microbiological safety in EBN production. Further studies are required to evaluate phage stability, application feasibility, and integration into sustainable veterinary hygiene practices.