The role of certain electrolytes in the adsorption of staphylococcal bacteriophages

Survival of Bacteriophage T4 in Quasi-Pure Ionic Solutions

The preservative qualities of individual ionic compounds impacting the infectivity of T4 virions were elucidated. T4 virions were immersed in quasi-pure ionic solutions prior to the adsorption process, and the plaque forming unit (pfu) values of these were measured following the conventional method. In neutral ionic solutions, the minimum and the optimum concentrations of preservative qualities corresponded with the results obtained from the multi-ionic media/buffers. In acid and alkali solutions, phages show tolerances at a pH range of 5-11 in multi-ionic media/buffers. T4 virions show no tolerance in quasi-pure acid, neutral, and weak alkaline conditions. The preservative quality of T4 virions increased in over 10-1 mM OH- solution, equivalent to a pH value over 10, which corresponds to the pKa of the deprotonation of the DNA bases G and T. Infectivity was lost below 10-1 mM OH- and higher than 10 mM OH-. These results imply that maintaining infectivity of a virion may need the flexibility of the intra-capsid DNA by deprotonation.

L-form conversion in Gram-positive bacteria enables escape from phage infection

At the end of a lytic bacteriophage replication cycle in Gram-positive bacteria, peptidoglycan-degrading endolysins that cause explosive cell lysis of the host can also attack non-infected bystander cells. Here we show that in osmotically stabilized environments, Listeria monocytogenes can evade phage predation by transient conversion to a cell wall-deficient L-form state. This L-form escape is triggered by endolysins disintegrating the cell wall from without, leading to turgor-driven extrusion of wall-deficient, yet viable L-form cells. Remarkably, in the absence of phage predation, we show that L-forms can quickly revert to the walled state. These findings suggest that L-form conversion represents a population-level persistence mechanism to evade complete eradication by phage attack. Importantly, we also demonstrate phage-mediated L-form switching of the urinary tract pathogen Enterococcus faecalis in human urine, which underscores that this escape route may be widespread and has important implications for phage- and endolysin-based therapeutic interventions.

Practical methods for determining phage growth parameters

Bacteriophage growth may be differentiated into sequential steps: (i) phage collision with an adsorption-susceptible bacterium, (ii) virion attachment, (iii) virion nucleic acid uptake, (iv) an eclipse period during which infections synthesize phage proteins and nucleic acid, (v) a "post-eclipse" period during which virions mature, (vi) a virion release step, and (vii) a diffusion-delimited period of virion extracellular search for bacteria to adsorb (1). The latent period begins at the point of virion attachment (ii) and/or nucleic acid uptake (iii) and ends with infection termination, spanning both the eclipse (iv) and the post-eclipse maturation (v) periods. For lytic phages, latent-period termination occurs at lysis, i.e., at the point of phage-progeny release (vi). A second compound step is phage adsorption, which, depending upon one's perspective, can begin with virion release (vi), may include the virion extracellular search (vii), certainly involves virion collision with (i) and then attachment to (ii) a bacterium, and ends either with irreversible virion attachment to bacteria (ii) or with phage nucleic acid uptake into cytoplasm (iii). Thus, the phage life cycle, particularly for virulent phages, consists of an adsorption period, virion attachment/nucleic acid uptake, a latent period, and virion release ((2), p. 13, citing d'Herelle). The duration of these steps together define the phage generation time and help to define rates of phage population growth. Also controlling rates of phage population growth is the number of phage progeny produced per infection: the phage burst size. In this chapter we present protocols for determining phage growth parameters, particularly phage rate of adsorption, latent period, eclipse period, and burst size.

SEROLOGY AND TRANSDUCTION IN STAPHYLOCOCCAL PHAGE

Dowell, C. E. (The University of Texas, Dallas) and E. D. Rosenblum. Serology and transduction in staphylococcal phage. J. Bacteriol. 84:1071-1075. 1962.-A triply lysogenic strain of Staphylococcus aureus was shown to carry a serological group B phage capable of transduction. Three typing phages (53, 80, 42D), either belonging to serological group B or having a close association with it, were also shown to have transducing ability. A rapid screening method was used to isolate two new transducing phages, both of which belonged to serological group B. Propagating strain 42B/47C was found to carry a transducing phage that was neutralized by both group B and group F antisera. Nine other phages belonging to serological groups other than group B did not have generalized transducing ability, nor did three group B typing phages that were atypical in their calcium requirement. It was postulated that transducing ability is associated with staphylococcal phages of serological group B and with related phages of group F.

CALCIUM ION REQUIREMENT FOR PROLIFERATION OF BACTERIOPHAGE PHI MU-4

Shafia, Fred (University of Nebraska, Lincoln), and T. L. Thompson. Calcium ion requirement for proliferation of bacteriophage phimu-4. J. Bacteriol. 88:293-296. 1964.-Divalent ions are essential for proliferation of phage phimu-4. Small amounts of citrate interfere with efficient adsorption of phage to the host cells. Penetration of phage material into the cell is strictly dependent on divalent ions and is inhibited by low levels of citrate. Inhibition of infection can be partially reversed, in early latent period, by calcium ions. Synthesis of new phage particles is also dependent on divalent ions. Addition of citrate to infected cell suspensions significantly reduced the number of phage progeny produced. Chelates such as phosphate and citrate rapidly inactivated the free phage particles at 65 C. Chelate inactivation of phage is not reversible; however, it can be prevented to some degree by calcium ions.

Conjugative transfer of staphylococcal antibiotic resistance markers in the absence of detectable plasmid DNA

Eleven Staphylococcus aureus clinical isolates were tested for transfer of resistance markers by transduction and filter mating. The resistance markers of six of the strains could be transferred only by transduction; however, the five remaining strains transferred their resistance both by transduction and filter mating. The resistance markers that were cotransferred in filter matings (transfer of resistance to penicillin and streptogramin A was accompanied, in each case, by the transfer of one or more markers, i.e., resistance to aminoglycosides, cadmium, or tetracycline, depending on the donor) were not cotransduced. The filter mating transfers were recA independent and were observed with both Staphylococcus aureus and Staphylococcus epidermidis recipients. Experiments to elucidate the mechanism of transfer by filter mating suggested that conjugation requiring cell-to-cell contact may have been involved. These transfers occurred in the absence of detectable plasmid DNA.

[Effectivity of murein preparations in the phage inhibition test--effect of Ca++ions and EDTA]

The inactivating efficacy for the typing phages 54, 83A, and 187 of the peptidoglycan of Staphylococcus aureus is decreased by increasing the Ca++-content of the medium; the irreversible inhibition of phage 187 becomes reversible. The percentage of its inhibition is proportional to the Ca++-content of the medium. Minute amounts of phage 187 bound irreversibly under Ca++-deprivation can be loosened by addition of Ca++-ions. Addition of EDTA up to the equivalence concentration of Ca++ present in the medium has no influence. Addition of EDTA up to the tenfold equivalence causes a significant increase of the inactivating efficacy of the peptidoglycan.

EFFECT OF SODIUM CHLORIDE ON STAPHYLOCOCCUS-PHAGE RELATIONSHIPS

West, B. (University of Oklahoma Medical Center, Oklahoma City), Florene C. Kelly, and Doris A. Shields. Effect of sodium chloride on staphylococcus-phage relationships. J. Bacteriol. 86:773-780. 1963.-Phage patterns of 21 phage-propagating strains of staphylococci on medium with high NaCl content appeared to be an expression of the staphylococcal cells, as well as of the salt tolerance of the phages. Serological group A phages, previously found to be NaCl-tolerant in the free state, were capable of lysing susceptible staphylococci on 3, 7.5, and 10% NaCl Trypticase Soy Agar. None of the other phages tested was active when the medium contained 7.5 and 10% NaCl. Increasing the NaCl content of the medium rarely resulted in nonspecific reactions; rather the effect was, generally, a narrowing of the phage spectrum of the cells, with persistence in the phage pattern of the phage, or phages, which were propagated on the cells being tested. Although NaCl tolerance of the phages was the chief limiting factor of phage activity in the presence of 7.5 and 10% NaCl, reactions on salt medium also depended on the degree of susceptibility of cells to phage on routine typing medium and to certain other unexplained factors. In some instances, under the influence of increased NaCl, significant lysis at 1000 RTD was replaced by thinning of growth (inhibition), with or without the presence of plaques. Conversely, certain phage-cell combinations, which gave inhibition at 1000 RTD on standard medium produced some degree of lysis when the NaCl concentration was increased. Studies of phage 81 and its propagating strain showed that replication of phage occurred in 10% NaCl medium, although adsorption diminished as salt concentration was increased, and the time required to reach maximal lytic activity was delayed.