Viability Of Bacteriophage Research Articles

Application of bacteriophage MS2 in preliminary simulation of inactivation rate of pathogenic viruses in commercial beef and chicken packaging

SummaryIn response to the growing concern of transmitting pathogenic viruses through food, this research aimed to assess the impact of various factors on the commercial packaging of meat (chicken and beef) on the inactivation of bacteriophage MS2 which was scrutinised by examining the influence of packaging type, bacteriophage spiking levels, temperature, as well as the meat shape and type. The findings revealed that the recovery of bacteriophage MS2 from minced beef was lower in modified atmosphere packaging (MAP) compared with air packaging (AP) at both storage times, spiking levels, and freezing and refrigerating temperatures. On the other hand, the recovery of the bacteriophage from chopped beef was lower in AP than in MAP in refrigerating conditions at both spiking levels during the 3 days of storage. According to our findings, the recovery levels of bacteriophage MS2 from chicken had statistically significant differences in both packaging types at different spiking levels. Storage conditions and packaging type were the most essential parameters in bacteriophage MS2 viability. The lowest bacteriophage viability belonged to MAP.

Bacteriophage-Based Detection of Staphylococcus aureus in Human Serum.

Bacteriophages have been investigated for clinical utility, both as diagnostic tools and as therapeutic interventions. In order to be applied successfully, a detailed understanding of the influence of the human matrix on the interaction between bacteriophage and the host bacterium is required. In this study, a cocktail of luciferase bacteriophage reporters was assessed for functionality in a matrix containing human serum and spiked with Staphylococcus aureus. The inhibition of signal and loss of sensitivity was evident with minimal amounts of serum. This phenotype was independent of bacterial growth and bacteriophage viability. Serum-mediated loss of signal was common, albeit not universal, among S. aureus strains. Immunoglobulin G was identified as an inhibitory component and partial inhibition was observed with both the f(ab’)2 and Fc region. A modified bacteriophage cocktail containing recombinant protein A was developed, which substantially improved signal without the need for additional sample purification. This study highlights the importance of assessing bacteriophage activity in relevant host matrices. Furthermore, it identifies an effective solution, recombinant protein A, for promoting bacteriophage-based detection of S. aureus in matrices containing human serum.

Waterline Disinfectants Reduce Dental Bioaerosols: A Multitracer Validation

Oral microbes are dispersed during dental treatment and reduction methods have been proposed, but dental unit waterline (DUWL) disinfectants have received little attention; specifically, the effect on viruses has not been studied. This study aims to 1) investigate the effect of DUWL disinfectants on viral dispersion in dental bioaerosols and 2) establish a dual-tracer system using live bacteriophage and fluorescein supported by optical particle measurement. Bacteriophage MS2 was used as a viral tracer and fluorescein as a fluorescent tracer. Validation experiments were conducted to exclude interference of one tracer with the other or of DUWL disinfectants on detection methods. Simulated “saliva” containing the tracers was infused into the mouth of a dental mannequin during 10-min dental procedures with an air turbine handpiece (n = 3 replicates). Aerosols and droplets were sampled in an enclosed dental operatory using air samplers and settlement onto sterile filter papers. Bacteriophage was quantified using plaque assays and reverse transcription quantitative polymerase chain reaction (RT-qPCR). Fluorescein was quantified fluorometrically. The effect of DUWL disinfectants on total aerosol concentration was assessed in separate experiments using an optical particle counter. DUWL disinfectants reduced bacteriophage viability, and interference between tracers was not observed. In simulated clinical procedures, the disinfectant ICX reduced bacteriophage detection substantially (P < 0.001; 2-way analysis of variance). MS2 RNA was detected in all experimental samples but not negative controls. Samples positive on RT-qPCR but not plaque assays may indicate that virions at distant sites are nonviable. Fluorescein tracer showed good agreement with the bacteriophage tracer. DUWL disinfectants designed for continuous presence in irrigants reduce the dispersion of viable virus in dental bioaerosols during simulated procedures. Their use may therefore be important for routine infection control and as a mitigation factor during infectious disease outbreaks. Future studies should explore this using a range of viruses and other microbes.

New possibility of application of bacteriophages to prevent infectious complications in free skin grafting (bacteriophages in skin grafting)

Aim . To prevent infectious processes in the area of a recipient wound in free skin grafting with a split-graft. Materials and methods. A method was developed for immobilizing bacteriophages in the area of split thickness skin grafts through transferring a solution containing bacteriophages into a gel form. Microbiological and clinical studies of the effectiveness of the proposed method were performed. Results. The viability of bacteriophages in a gel dressing for up to 4 days was confirmed, as well as the reduced likelihood of local infectious complications in skin grafting. Conclusion . The gel composition containing bacteriophages allows quick response to changes in current hospital microflora and effectively counteract the dangers of nosocomial infection.

Viability of Bacteriophages in the Complex Hydrogel Wound Dressings in vitro.

Using bacteriophages to overcome the increasing resistance of microorganisms to antibiotics is a novel research venue of clinical importance. Among other challenges, this technique is expected to create and maintain an adequate local concentration of bacteriophages at the site of application. In addition, the possibility of combining the phage preparation with antioxidants and anesthetics may provide new options for stimulating the reparative process.The aim of the study was to assess the viability and lytic activity of bacteriophages incorporated into a hydrogel-based wound dressing that contains polyvinyl alcohol, phosphate buffer, with optional additions of succinic acid and lidocaine.Materials and MethodsA technique for incorporating bacteriophages into the complex hydrogel wound dressing ex tempore has been proposed. The bacteriolytic activity of phages inside the hydrogel was determined using standard microbiological techniques. Specifically, we used nutrient media with lawn cultures of Staphylococcus aureus added with the following antibacterial combinations: bacteriophages + succinic acid, bacteriophages + lidocaine, and bacteriophages + succinic acid + lidocaine. The lytic activity of bacteriophages was assessed within 1 to 7 days after the formation of the hydrogel.ResultsIn all samples containing bacteriophages, the presence of viable and lytically active phages was noted within 1 to 7 days, as evidenced by the “negative colonies” on the culture lawns. On days 1 to 3, no secondary growth was recorded in the phage-containing samples. In hydrogel samples containing phages, succinic acid, and lidocaine, secondary bacterial colonies were detected starting from day 4 indicating some reduction in the lytic activity.ConclusionThe results suggest that bacteriophages immobilized in the hydrogel maintain their viability and lytic activity, and this activity persists when the phages are combined with succinic acid and lidocaine.

The Influence of Polyanions and Polycations on Bacteriophage Activity.

Phage therapy is a great alternative to antibiotic drugs, but it can’t effectively overcome the over-acidic medium of the stomach. We offer the use of polyelectrolyte microcapsules as a protective means of bacteriophage. It is necessary to understand the influence of polyelectrolytes on bacteriophage survival. The work studied the effect of polyanions and polycations on the coliprotetic bacteriophage’s viability. We have shown that polyallylamine decreased bacteriophage’s viability during increasing polyelectrolyte concentration and polyarginine had a lower inhibitory effect (then PAH) on the activity of the bacteriophage due to polyelectrolyte concentration from 0.05 to 5 mg/mL. It was shown that the inhibition of the bacteriophage by polyallylamine had an electrostatic nature and the use of high ionic strength prevented the formation of the PAH-protein capsid complex. Polystyrene sulfonate does not affect bacteriophage viability during increasing polyelectrolyte concentration from 0.05 mg/mL to 1 mg/mL. Polystyrene sulfonate decreases the viability of bacteriophage from 5 mg/mL of polyelectrolyte concentration. Dextran sulfate inhibits bacteriophage activity at 20–30%. Dextran inhibits bacteriophage activity by 80% at diapason concentration from 0.05 to 5 mg/mL and loses the inhibition effect from a concentration of 5 mg/mL.

The varying effects of a range of preservatives on Myoviridae and Siphoviridae bacteriophages formulated in a semi-solid cream preparation.

Bacteriophages may be formulated into semi-solid bases for therapeutic delivery. This work investigated the effects of a range of preservatives on the viability of Myoviridae and Siphoviridae bacteriophages when these were formulated into a standard semi-solid cream base. The six preservatives tested included: benzoic acid (0·1%), chlorocresol (0·1%), combination hydroxybenzoates (propyl 4-hydroxybenzoates with methyl 4-hydroxybenzoates) (0·1%), methyl 4-hydroxybenzoate (0·08%), 2-phenoxyethanol (1%) and propyl 4-hydroxybenzoate (0·02%). These were each formulated into cetomacrogol cream aqueous to generate six individual semi-solid bases into which Myoviridae and Siphoviridae bacteriophages were added and tested for stability. Optimal bacteriophage stability was seen when the preservative chlorocresol was used. Bacteriophage in the acidic benzoic acid were the least stable, resulting in complete loss of viability after 4-5weeks. Of the bacteriophages tested, the Myoviridae KOX1 was significantly more stable than the Siphoviridae PAC1 after 91days in formulations with each of the preservatives. Our results suggest the need for individual testing of specific bacteriophages in pharmaceutical formulations, as their efficacy when exposed to preservatives and excipients in these delivery forms may vary. SIGNIFICANCE AND IMPACT OF THE STUDY: Bacteriophages are being increasingly investigated as alternatives to antibiotics. While bacteriophages can be formulated in diverse ways for therapeutic delivery, there has been scant work on how excipients and preservatives in these formulations affect stability of different bacteriophages. We demonstrate that the nature of preservatives in formulations will affect bacteriophage stability, and that in these formulations, viability of bacteriophage differs according to their morphology. Our work highlights the need for individual testing of specific bacteriophages in pharmaceutical formulations, as efficacy when exposed to preservatives and excipients in these delivery forms may vary.

Protozoa and Virus Disinfection by Silver- and Copper-Embedded Ceramic Tablets for Water Purification

Point-of-use water treatment (PoUWT) technologies have been shown to reduce incidences of waterborne diseases. However, their effectiveness is limited against the most harmful pathogens, such as protozoa and viruses, due to the inability to deliver effective and safe levels of disinfectant. This paper studies disinfection mechanisms and efficiency of silver and copper against Cryptosporidium parvum, Giardia lamblia, and MS2 bacteriophage through a novel PoUWT method, a ceramic tablet embedded with metallic ions. Results demonstrate that the PoUWT method can deliver safe and effective levels of silver and copper to inhibit sporozoite metabolic ability, and thus disinfect protozoa. Excystation reduced from 74% to 14% for Cryptosporidium parvum oocysts treated with silver-embedded ceramic tablets. Similar results were observed among Giardia lamblia oocysts and copper-treated oocysts. Fluorescence microscopy demonstrated two mechanisms for protozoa disinfection by metallic ions: (1) structural damage of oocyst walls, and (2) alteration of sporozoite structure. Also, MS2 bacteriophage viability reduced by 89% when treated with ceramic tablet treatment. Using the PoUWT method in this study, silver and copper show promise as disinfecting agents for protozoa.

A sandwich-type bacteriophage-based amperometric biosensor for the detection of Shiga toxin-producing Escherichia coli serogroups in complex matrices.

Immuno-based biosensors are a popular tool designed for pathogen screening and detection. The current antibody-based biosensors employ direct, indirect, or sandwich detection approaches; however, instability, cross-reactivity, and high-cost render them unreliable and impractical. To circumvent these drawbacks, here we report a portable sandwich-type bacteriophage-based amperometric biosensor, which is highly-specific to various Shiga toxin-producing Escherichia coli (STEC) serogroups. Environmentally isolated and biotinylated bacteriophages were directly immobilized onto a streptavidin-coated screen-printed carbon electrode (SPCE), which recognized and captured viable target cells. Samples (50 μL) were transferred to these bacteriophage-functionalized SPCEs (12 min, room temp) before sequentially adding a bacteriophage–gold nanoparticle solution (20 μL), H2O2 (40 mM), and 1,1′-ferrocenedicarboxylic acid for amperometric tests (100 mV s−1) and analysis (ANOVA and LSD, P < 0.05). The optimum biotin concentration (10 mM) retained 94.47% bacteriophage viability. Non-target bacteria (Listeria monocytogenes and Salmonella Typhimurium) had delta currents below the threshold of a positive detection. With less than 1 h turn-around time, the amperometric biosensor had a detection limit of 10–102 CFU mL−1 for STEC O157, O26, and O179 strains and R2 values of 0.97, 0.99, and 0.87, respectively, and a similar detection limit was observed in complex matrices, 10–102 CFU g−1 or mL−1 with R2 values of 0.98, 0.95, and 0.76, respectively. The newly developed portable amperometric biosensor was able to rapidly detect viable target cells at low inoculum levels, thus providing an inexpensive and improved alternative to the current immuno- and laboratory-based STEC screening methods.

Encapsulation of bacteriophage T4 in mannitol-alginate dry macrospheres and survival in simulated gastrointestinal conditions

In recent years application of bacteriophages in the reduction of bacterial pathogens that may contaminate the food supply has become of growing interest. The aim of this study was to produce dried macrospheres ensuring viability of bacteriophages during exposure to adverse conditions of the digestive system after storage for an extended period of time. The viability of phages entrapped in mannitol-alginate wet and dried formulations was investigated for up to 4 weeks of storage at room temperature. Phage-loaded beads were exposed to an acidic environment (pH 2.5) of simulated gastric fluid and directly transferred to intestinal medium to dissolve. During the period from 1 to 4 weeks the survival of bacteriophage T4 in dried macrospheres under simulated gastrointestinal conditions revealed only a slight decrease and resulted in a final survival of 5.02 log10 pfu/ml. The results of this study show that the addition of 0.3 M mannitol may improve phage protection against gastrointestinal conditions and enable a large proportion of bacteriophage T4 to remain active. The potential of the developed technology can be considered in oral application of bacteriophages to reduce intestinal colonization of pathogenic bacteria via prolonged stability of phages in a dry state.

Manufacturing and ambient stability of shelf freeze dried bacteriophage powder formulations

The severity of multidrug resistance to antibiotics has urged development of alternative treatment approaches, including bacteriophage therapy. Given the complexity of the bacteriophage structure, formulation and stability are primary concerns. Our present work optimized process and formulations of phage powder manufacturing and investigated the stability of lyophilized bacteriophage powders under ambient storage. The model phage M13 was formulated with trehalose, mannitol, sucrose and PEG6000 and lyophilized in different conditions. Bacteriophage viability was examined by titering and was considered as the assessment of phage stability. Less titer loss of trehalose and sucrose formulations were observed compared to mannitol and PEG groups both immediately after lyophilization and upon long term storage. When evaluating lyophilization conditions, an additional 1 log titer was preserved by reduction of product drying stress. Trehalose was stabilized in the amorphous state whereas mannitol stayed in crystalline state in lyophilized powders. Increased moisture content was demonstrated to have a positive impact on viability of phage after lyophilization and upon storage. Overall, 2% trehalose or sucrose (w/v) can sufficiently stabilize phage during lyophilization process and storage in ambient conditions. There is a positive correlation between residual water and stability of phage. These collective findings highlight the potential of long-term, ambient storage of bacteriophage towards their successful use in diverse healthcare settings.

Antibacterial Activity of Novel Strains of Bacteriophages: An Experimental Approach.

The evolution of antibiotic resistance in bacteria has increased research in the development of alternative therapies to conventional drugs. In this study, isolated phages were characterized and antibacterial activity was determined by standard agar disc diffusion method. The phages showed maximum propagation at 37°C to 40°C and highest viability at pH 7. Sugars influenced the bacteriophage viability. Sodium chloride decreased the phage propagation. Calcium chloride and magnesium chloride increased the phage propagation up to a certain limit. SDS-PAGE analysis confirmed the presence of protein cover and showed the various bands ranging from 10 to 200 kDa. Nucleic acid analysis confirmed the presence of RNA with a size of approximately 20 kb. Transmission electron microscopy indicated that the phages belong to Siphoviridae, Leviviridae, and Podoviridae families.

Preparation and characterization of transdermal mediated microemulsion delivery of T4 bacteriophages against E.coli bacteria: a novel anti-microbial approach

The objective of this study was to design a novel microemulsion system for transdermal delivery of natural antimicrobial agent, i.e. bacteriophage (T4) specifically lysing E. coli bacteria. Pseudoternary phase diagrams were constructed and various formulations were prepared using a combination of ethyl oleate (oil), Tween 80:Span 20 (surfactant mixture) and water (aqueous phase). Developed formulations were subjected to physicochemical characterization, ex vivo and thermodynamic stability studies, skin irritation and histology studies. All the formulations had small droplet size (150–320nm), uniform size distribution (PI < 0.4), adequate viscosity and surface tension. 4 × 105, 6.02 × 106 and 6.7 × 106 PFU/mL was the cumulative amount of bacteriophage permeated from ME1-3, respectively. Results from permeation studies suggested the synergistic effect of oil and surfactant mixture on the permeation profile (p < 0.05), on increasing surfactant concentration with respect to oil, the bacteriophage permeation was increasing and so, the flux was increases too. ME2 was found to be thermodynamically stable, non-irritant and followed zero order kinetics. The bacteriophage viability to lyse E. coli was significantly affected at various temperatures, pH and dilution. Histological findings revealed the effect of formulation variables on the skin, necessary for permeation. These results indicate that microemulsion-based transdermal delivery of bacteriophage can be a promising approach to treat the infections caused by antibiotic-resistant bacteria but needs thorough clinical investigations.

Dehydration of bacteriophages in electrospun nanofibers: effect of excipients in polymeric solutions

Bacteriophages are viruses capable of infecting and lysing target bacterial cells; as such they have potential applications in agriculture for decontamination of foods, food contact surfaces and food rinse water. Although bacteriophages can retain infectivity long-term using lyophilized storage, the process of freeze-drying can be time consuming and expensive. In this study, electrospinning was used for dehydrating bacteriophages in polyvinylpyrrolidone polymer solutions with addition of excipients (sodium chloride, magnesium sulfate, Tris-HCl, sucrose) in deionized water. The high voltage dehydration reduced the infectivity of bacteriophages following electrospinning, with the damaging effect abated with addition of storage media (SM) buffer and sucrose. SM buffer and sucrose also provided the most protection over extended storage (8 weeks; 20 °C; 1% relative humidity) by mitigating environmental effects on the dried bacteriophages. Magnesium sulfate however provided the least protection due to coagulation effects of the ion, which can disrupt the native conformation of the bacteriophage protein coat. Storage temperatures (20 °C, 4 °C and −20 °C; 1% relative humidity) had a minimal effect while relative humidity had substantial effect on the infectivity of bacteriophages. Nanofibers stored in higher relative humidity (33% and 75%) underwent considerable damage due to extensive water absorption and disruption of the fibers. Overall, following storage of nanofiber mats for eight weeks at ambient temperatures, high infective phage concentrations (106–107 PFU ml−1) were retained. Therefore, this study provided valuable insights on preservation and dehydration of bacteriophages by electrospinning in comparison to freeze drying and liquid storage, and the influence of excipients on the viability of bacteriophages.

Application of chitosan–alginate microspheres for the sustained release of bacteriophage in simulated gastrointestinal conditions

SummaryThis study was designed to evaluate the acid stability, release property and antimicrobial efficacy of Escherichia coli O157:H7 bacteriophages encapsulated in chitosan–alginate microspheres under the simulated gastrointestinal conditions. The bacteriophages belonging to Myoviridae family were stable at the pH above 4 in trypticase soy broth. The chitosan–alginate microspheres exhibited protective effect on the viability of bacteriophages in the simulated gastric conditions at pH 2.0 and pH 2.5, showing 4.8 and 5.6 log PFU mL‐1, respectively, after 1 h of incubation at 37 °C. The release per cent of bacteriophages from microspheres gradually increased up to 65% in the simulated intestinal condition (pH 7.5) at 37 °C for 6 h. The lytic efficacy of chitosan‐ and alginate‐encapsulated bacteriophages against E. coli O157:H7 was significantly maintained in the simulated intestinal conditions to 10 h of incubation (1.3 log reduction). The results suggest that the chitosan–alginate microspheres can be used as a reliable delivery system for bacteriophages.

Incorporation of T4 bacteriophage in electrospun fibres

Antibacterial food packaging materials, such as bacteriophage-activated electrospun fibrous mats, may address concerns triggered by waves of bacterial food contamination. To address this, we investigated several efficient methods for incorporating T4 bacteriophage into electrospun fibrous mats. The incorporation of T4 bacteriophage using simple suspension electrospinning led to more than five orders of magnitude decrease in bacteriophage activity. To better maintain bacteriophage viability, emulsion electrospinning was developed where the T4 bacteriophage was pre-encapsulated in an alginate reservoir via an emulsification process and subsequently electrospun into fibres. This resulted in an increase in bacteriophage viability, but there was still two orders of magnitude drop in activity. Using a coaxial electrospinning process, full bacteriophage activity could be maintained. In this process, a core/shell fibre structure was formed with the T4 bacteriophage being directly incorporated into the fibre core. The core/shell fibre encapsulated bacteriophage exhibited full bacteriophage viability after storing for several weeks at +4°C. Coaxial electrospinning was shown to be capable of encapsulating bacteriophages with high loading capacity, high viability and long storage time. These results are significant in the context of controlling and preventing bacterial infections in perishable foods during storage.

In vitro lung delivery of bacteriophages KS4-M and ΦKZ using dry powder inhalers for treatment of Burkholderia cepacia complex and Pseudomonas aeruginosa infections in cystic fibrosis

To determine the feasibility of formulating and aerosolizing powders containing bacteriophages KS4-M and ΦKZ for lung delivery and treatment of pulmonary Burkholderia cepacia complex and Pseudomonas aeruginosa infections. Endotoxin-removed bacteriophages KS4-M and ΦKZ were lyophilized in lactose/lactoferrin 60 : 40 w/w matrix and deagglomerated in a mixer mill (without beads) to formulate respirable powders. The powders were then aerosolized using an Aerolizer(®) capsule inhaler. Mass median aerodynamic diameter (MMAD) of this inhalable aerosol was determined using Andersen cascade impactor at 60 l min(-1). Measured MMAD for both types of powders was 3·4 μm, and geometric standard deviation was 1·9-2·0. Viability of bacteriophages delivered distal to an idealized mouth-throat replica was determined from bioassays of samples collected on filters placed after the idealized replica. As a percentage of inhaler load, amount of powder delivered distal to the mouth-throat replica, which is a measure of lung delivery, was 33·7 ± 0·3% for KS4-M and 32·7 ± 0·9% for ΦKZ. Titres collected downstream of the mouth throat were (3·4 ± 2·5) × 10(6) PFU for KS4-M with an Aerolizer capsule load of (9·8 ± 4·8) × 10(6) and (1·9 ± 0·6) × 10(7) for ΦKZ with an Aerolizer capsule load of (6·5 ± 1·9) × 10(7). Bacteriophages KS4-M and ΦKZ can be lyophilized without significant loss of viability in a lactose/lactoferrin 60 : 40 w/w matrix. The resulting powders can be aerosolized to deliver viable bacteriophages to the lungs. Development of lactoferrin-based bacteriophage aerosol powders solidifies the ground for future research on developing novel formulations as an alternative to inhaled antibiotic therapy in patients with cystic fibrosis.

Physical mapping of Bacillus subtilis phage rho14 cloning vehicles: heteroduplex and restriction enzyme analyses.

Four deletion mutants of temperate Bacillus subtilis bacteriophage rho14 have been examined utilizing restriction enzyme and DNA heteroduplex methods. This has allowed the orientation and mapping of the deletions on the rho14 physical map. A continuous 15% of the genome contains functions not essential for bacteriophage viability. A 7% subsection of this region contains phage immunity functions. The deletions were found to range in size from about 2.2-3.3 kilobases. In addition, the deletion mutants retain a single Sal I restriction site, which is currently being used as a cloning site for recombinant DNA. We have located the Sal I site to be 400 basepairs from the immunity region. Thus, the clear- and turbid-plaque deletion mutants are all capable of being utilized as molecular cloning vehicles for Bacillus subtilis.

The Viability of Bacteriophage T 4 after Irradiation of Only the Head Component or the Tail Component II. In Aqueous Suspension

Amber mutants of bacteriophage ${\rm T}_{4}{\rm D}$ were used to prepare phage head and tail components. The isolated heads and tails were purified and their response in aqueous suspension to ionizing radiation measured. The radiosensitivities were compared with that of whole bacteriophage. Both the heads and tails were inactivated exponentially. The Do (37% survival) of the tails was 1.6 krad compared with 1.2 krad for whole phage and 5.0 krad for heads. In nutrient broth the DNA containing heads were similar but slightly more sensitive to radiation than whole phage, while the protein tails were considerably more resistant. In dilute suspension however the tails were similar but slightly more resistant to radiation than whole phage but the heads were substantially more resistant than tails or whole phage. The major lethal target for phage irradiated in dilute aqueous solution is probably located in the tail.

The Viability of Bacteriophage T 4 after Irradiation of Only the Head Component or the Tail Component: I. In Nutrient Broth Projected Conditions

Amber mutants of bacteriophage ${\rm T}_{4}{\rm D}$ were used to study the relative radiosensitivity of the head component and of the tail component of the phage under various experimental conditions. In the presence of radical scavenging agents the protein tails were considerably less sensitive to ionizing radiation than the intact, whole phage, whereas the DNA-containing heads were slightly more sensitive than whole bacteriophage. The Do (37% survival) of anoxic tails was 900 krad and 26 krad for heads. Addition of cysteamine reduced the radiosensitivity of phage heads and whole phage but had no effect on the tails. Likewise oxygen had a protective effect on the heads and whole phage but did not alter the radiosensitivity of the tails. Irradiation had no effect on the in vitro assembly method used for measuring the heads and tails.