Evaluation of Virucidal activity and Preservatives

Evaluation of virucidal activity and preservatives

Intended
learning objectives

At the end of this lecture, the student will be able to:

• List the methods for determination of virucidal activity
of disinfectants

• Explain the methods for the determination of virucidal
activity

• Describe the challenge test for evaluation of
preservatives

Evaluation
of Virucidal Activity

• The testing of disinfectants for virucidal activity is not
easy      

• Viruses are obligate intracellular parasites and are
unable in artificial culture media to grow

• They require some other system employing living cells                              

Suggested test viruses include

• Rotavirus, adenovirus, poliovirus, herpes simplex viruses,
human immunodeficiency virus, pox viruses and papovavirus

• Appropriate facilities for handling such pathogens are
essential

• The virus is grown in an appropriate cell line that is
then mixed with water containing an organic load and the disinfectant under
test

• After appropriate time, residual viral infectivity is
determined using a

         • Tissue
culture/plaque assay

         • Other
system (e.g. animal host, molecular assay for some specific viral component)

         • Tissue
culture or egg inoculation

         •
Bacteriophage evaluation method

         • Plaque
assays

         • Duck hepatitis
B virus (DHVB) method

         • Acceptable
animal model

• A reduction of infectivity by a factor of 104 has been
regarded as evidence of acceptable virucidal activity

• For viruses which cannot be grown in the laboratory (e.g.
hepatitis B), naturally infected cells/tissues must be used

Limitations

• Such procedures are costly

• Time-consuming

• Must be appropriately controlled to exclude factors such
as disinfectant killing of the cell system or test animal

Evaluation
of Preservatives

• Preservatives are widely employed in the cosmetic and
pharmaceutical industries as well as in a variety of other manufacturing
industries

• The inhibitory or bactericidal activity of the chemical to
be used as the preservative can be evaluated using an appropriate in vitro test
system

• Its continued activity when combined with the other
ingredients in the final manufactured product must be established

Evaluation of
Preservatives – Challenge test

• The final preserved product is deliberately inoculated
with a suitable environmental microorganism

• Fungal, e.g. 
candida,  or  bacterial, 
e.g.  Staphylococcus  aureus, Escherichia coli, Pseudomonas
aeruginosa

• For preparations with a high sucrose content, the
osmophilic yeast Zygosaccharomyces rouxii is a consideration

• The subsequent survival (inhibition), death or growth of
the inoculum is then assessed using viable count techniques

Evaluation
of Mycobactericidal activity

• They are hydrophobic in nature, hence difficult to prepare
homogeneous suspensions of mycobacteria

• M.tuberculosis are slow growing pathogenic strains hence a
non- pathogenic M.terrae is used as an indicator organism

• General bacteriostatic and bactericidal evaluations are
carried out

Evaluation
of Sporicidal activity

• Sporicidal activity can be determined against spores in
liquid suspension or against spores dried on carriers

• General bacteriostatic and bactericidal evaluations are
carried out

• Since they are spores, sufficient germination time must be
given considering that damaged spores require even more time for germination

Evaluation
of Antifungal activity

• Fungi may be potential pathogens, which occurs as contaminants
in pharmaceutical products

• Fungicidal activity – general procedure, suitable culture
media

• Fungitatic activity – Solid dilution test Liquid dilution
test Gradient – plate technique

Summery

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