खाद्य सुरक्षा, गुणवत्ता मानक व पैकेजिंग

The plaque assay (developed by Renato Dulbecco in 1952) is the gold standard virological technique used to quantitatively enumerate infectious viral particles. A serial dilution of virus is inoculated onto a confluent monolayer of susceptible host cells under an agarose overlay; each infectious viral particle causes localized lysis forming a clear zone called a 'plaque', quantified as Plaque Forming Units per mL ($PFU/mL$).

Option analysis:

• Ion exchange assay: Chromatographic separation based on electrical charge, not a viral count assay.
• MPN assay: Most Probable Number, statistical method used for coliform and bacterial enumeration.
• Plaque assay: Correct, the standard quantitative assay for infectious virus particles ($PFU$).
• Selective medium assay: Used for culturing specific bacterial taxa, not viruses which require host cells.