Plaque forming units

Fig. 11.7 A, diagrammatic representation of plaque assay for evaluating virucidal activity and B, monolayers of baby hamster ki(hiey (BHK) cells C, virus tte untreated virus (o represents a plaque-forming unit, pfu, in BHK cells) D, virus titre disinfectant-treated virus (before plating onto BHK, die disinfectant must be neuh alized in an appropriate manner). Note the greatly reduced nimiber of pfu in D, indicative of fewer iminactivated virus particles than in C. 

For assaying herpes virus, monolayers of baby hamster kidney (BHK) cells are used. Virus titre is expressed as the number of plaque-forming units (pfu) per millilitre before and after exposure to a disinfectant, so that the virucidal efficacy of the test agent can be determined. A diagrammatic representation is given in Fig. 11.7. 

Infectious Dose 1 Plaque forming unit (Injection). 

Count the number of plaques and calculate the number of plaque forming units per ml virus stock. 

Vaccines Varicella virus vaccine, hve, Oka/Merck strain of hve, attenuated varicella virus Varivax Lyophilized, 0.5 ml reconstituted dose contains 1350 plaque forming units (PFU) SC NA NA NA A single 0.5 ml dose (<12yrs old) two 0.5 ml doses (>13yrs old) at 0 and 4-8 weeks NA NA... 

In order to study the virus growth curve a one-step growth cycle is performed. A high multiplicity of infection (m.o.i.) is used to ensure every cell is infected — usually 10 plaque forming units (p.f.u.) per cell is adequate. For virus production, however, the infection is prolonged under conditions where secondary infection can occur and a low m.o.i. is recommended especially where there is a tendency for defective virus particles to be produced. 

CPE). At 50-75% CPE, decant medium, add fetal calf serum to 20% and freeze at -70°C. After freezing, prepare tenfold dilution series down to 10-5 and assay plaque numbers as noted below. Note plaque forming unit titer and dilution to be used for assay. 

Remove the medium and add a virus inoculum at a multiplicity of infection (moi) of 0.002 plaque forming units (PFU)/cell. 

Prepare virus dilution at approx 0.1 plaque forming unit (PFU)/cell. 

Plaque forming unit (pfu) The number of viable phage per unit volume. 

FIG.4. (Top) Nii currents evoked by voltage steps from —SOmVto — 10 in V in control (left) andHSV-infected DRG neurons (right). (Bottom) Normalized (nA/pF) Na current amplitudes with above voltage step in control (filled bar) and at various times after HSV (5 plaque forming units/cell) infection show dramatic loss at 24 h. 

Prepare m DNA from (-) library by adding 4 x 10 plaque-forming units of M13KO7 (e.g., Stratagene) when bacteria in 200 ml attain a density of 0.4 OD. After another hour of shaking at 37°C, add kanamycin sulfate to 70 pg/ml and continue culture overnight (yield will be about 1 jig/ml of rr DNA). 

Live attenuated varicella vaccine contains the Oka-Merck strain of varicella virus, which was attenuated by propagation through several different cell culture lines. Varicella vaccine is a lyophihzed product that must be kept frozen and protected from light. Once reconstituted, it must be administered subcutaneously within 30 minutes. Each 0.5-mL dose contains a minimum of 1350 plaque-forming units of virus, as well as 12.5 mg of hydrolyzed gelatin and trace amounts of neomycin, fetal bovine serum, and residual components from cell culture. ... 

Jordan and Seet studied the antiviral effects of Amphotericin B Methyl Ester (AME), an antimicrobial agent, on several vimses including VACV in a plaque reduction assay [64], The concentration of AME resulting in a 50% inactivation of the plaque forming units, after a 60 min exposure at 35°C, was reported to be 5.0 pg/mL. The authors suggested lipid components in the host cell membrane which incorporate into the viral envelope may serve as a susceptible site for AME. 

The influenza virus host resistance model has been characterized in mice and rats, and has been widely used to evaluate the potential immunotoxicity of therapeutics. Influenza virus is used as the infectious challenge agent and administered intranasally in a 28-day repeat-dose study. Mice or rats are dosed for 7 days, infected and then dosed for an additional 21 days. Viral clearance is quantified by measuring infectious virus (plaque-forming units) at various times following infection. Dexamethasone may be used as a positive immunomodulatory control. This host resistance assay has been used in Balb/c, C57BL/6, and B6C3F1 mice and Fischer 344 (CDF), Brown Norway, and... 

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