Bacteriophage PUTH1: Isolation & Characterization of a Pseudomonas aeruginosa Virus
# Unveiling the Secrets of a Novel Bacteriophage: Characterization and Growth Dynamics
## Introduction
The relentless rise of antibiotic resistance poses a notable threat to global public health, necessitating the exploration of alternative therapeutic strategies. Bacteriophages, viruses that specifically infect and lyse bacteria, have emerged as a promising avenue in combating bacterial infections. this study focuses on the complete characterization of a novel bacteriophage, detailing its optimal infection conditions, environmental stability, and growth kinetics. By understanding these fundamental aspects, we aim to pave the way for its potential application in phage therapy.
## Materials and Methods
### Bacterial Strain and Phage Preparation
A virulent strain of *Pseudomonas aeruginosa* was cultured in Luria-Bertani (LB) liquid medium at 37 °C untill it reached the logarithmic growth phase. The bacteriophage, obtained from a previous isolation, was amplified by infecting the host bacteria at a low multiplicity of infection (MOI). Following incubation, the mixture was centrifuged to remove bacterial debris, and the supernatant containing the phages was filtered through a 0.22 µm membrane to obtain a purified phage stock. This stock was then serially diluted and plated on LB agar to determine the phage titer in plaque-forming units per milliliter (PFU/mL).
### Determination of Optimal Multiplicity of Infection (MOI)
To ascertain the optimal MOI for phage infection, the phage stock was diluted to achieve a titer of 107 PFU/mL. This diluted phage suspension was then mixed with an equal volume of the host bacterial solution. various MOI values, including 10, 1, 0.1, 0.01, and 0.001, were tested by adjusting the bacterial concentration accordingly. Each phage-bacterial mixture was transferred to sterilized LB liquid culture medium and incubated at 37 °C for 4 hours.
Following incubation, the mixtures were centrifuged at 5,000 × g for 2 minutes to pellet the bacterial cells. The supernatant, containing any released phages, was carefully collected. The phage titers in the supernatant for each MOI were subsequently persistent using the double-layer agar (DLA) method. The MOI that yielded the highest phage titer was identified as the optimal MOI for this phage. This experiment was meticulously repeated in triplicate, and the mean phage titer was calculated for each MOI to ensure statistical robustness.
### Temperature and pH Stability
The thermal stability of the bacteriophage was evaluated by incubating 1 mL aliquots of a phage suspension (107 PFU/mL) in a water bath at a range of temperatures: 37 °C, 40 °C, 50 °C, 60 °C, and 70 °C. After a 1-hour incubation period at each temperature, the remaining phage potency was measured using the double-layer plate assay. This entire procedure was replicated in triplicate to confirm the observed stability profiles.
To assess the phage’s stability under varying pH conditions, phage suspensions at a concentration of 105 PFU/mL were added to a series of buffer solutions spanning a wide pH range, from 1.0 to 12.0, in increments of one pH unit.These included pH values of 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0,11.0, and 12.0. After incubation in a 37 °C water bath for 1 hour, the phage titer was determined for each pH condition using the DLA method.For all stability experiments, the phage titers obtained at 37 °C (for temperature stability) and pH 7.0 (for pH stability) were designated as the reference baselines. These baseline values served as the standard against which the phage’s performance at other temperatures and pH levels was compared.Control titers were established under standard experimental conditions,yielding approximately 3 × 108 CFU/mL for bacterial viability at 37 °C and 2 × 108 CFU/mL at pH 7.0, ensuring the integrity of the experimental setup.### Adsorption Curve
The adsorption efficiency of the bacteriophage to its host bacteria was investigated by preparing a mixture