# Genomic, Functional, and Evolutionary Insights into a Novel T7-like Phage B1 Infecting Multidrug-Resistant Enterobacter cloacae

## TL;DR

A new T7-like phage, B1, was discovered that can effectively kill drug-resistant Enterobacter cloacae, offering potential for phage therapy.

## Contribution

The discovery of a novel lytic phage B1 with high efficiency against MDR E. cloacae and insights into its genomic and evolutionary characteristics.

## Key findings

- Phage B1 has a narrow host range and efficiently lyses MDR E. cloacae with a short latent period and high burst size.
- Genomic analysis shows B1 is a new species within the T7-like phage genus but distinct from other Enterobacter phages.
- B1 lacks lysogeny or virulence genes, making it a safe candidate for phage therapy.

## Abstract

Multidrug-resistant (MDR) Enterobacter cloacae is a growing public health issue worldwide, highlighting the urgent need for alternative antimicrobial strategies. This study reports on a lytic phage, designated B1, isolated from sewage, which exhibits specificity and lytic efficiency against MDR E. cloacae. Morphological observation revealed that B1 possesses an icosahedral head (~54 nm) and a short tail (~13 nm). Phage B1 showed a narrow host range, demonstrated stability within a temperature range of 4–37 °C, tolerance to pH values between 5 and 11, and showed an excellent bacteriolytic capacity with a short latent period of less than 10 min and a burst size of approximately 150 PFU/initially infected cell, indicating a rapid lytic cycle and efficient replication capability. Whole-genome sequencing revealed that the phage genome consists of 40,163 base pairs of double-stranded DNA containing 52 open reading frames (ORFs) with a GC content of 52%. Comparative genome-wide analysis using VIRIDIC revealed that B1 shares 75% to 92% similarity with Escherichia phage IMM-002 (accession: NC_048071), Citrobacter phage SH4, and Cronobacter phage Dev2 (accession: NC_023558), but shares less than 70% similarity with other Enterobacter phages. According to ICTV criteria, B1 represents a new species within the same genus as T7-like phages belonging to Autographiviridae, subfamily Studiervirinae, genus Kayfunavirus. In addition, B1 lacks lysogeny-associated or virulence genes and exhibits potent lytic activity against multidrug-resistant E. cloacae, making it a promising candidate for phage therapy. These findings opened up our understanding of the diversity of T7-like phages and provided insights into their evolutionary adaptability and therapeutic potential.