Observable Effects of Microbial Attack on Pharmaceutical Products

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Chapter: Pharmaceutical Microbiology : Microbial Spoilage, Infection Risk And Contamination Control

Microbial contaminants usually need to attack formulation ingredients and create substrates necessary for biosynthesis and energy production before they can replicate to levels where obvious spoilage becomes apparent.


OBSERVABLE EFFECTS OF MICROBIAL ATTACK ON PHARMACEUTICAL PRODUCTS

 

Microbial contaminants usually need to attack formulation ingredients and create substrates necessary for biosynthesis and energy production before they can replicate to levels where obvious spoilage becomes apparent. Thus, for example, 106 microbes will have an overall degradative effect around 106 times faster than one cell. However, growth and attack may well be localized in surface moisture films or very unevenly distributed within the bulk of viscous formulations such as creams. Early indications of spoilage are often organoleptic, with the release of unpleasant smelling and tasting metabolites such as ‘sour’ fatty acids, ‘fishy’ amines, ‘bad eggs’, bitter, ‘earthy ’ or sickly tastes and smells. Products may become unappealingly discoloured by microbial pigments of various shades. Thickening and suspending agents such as tragacanth, acacia or carboxymethylcellulose can be depolymerized, resulting in loss of viscosity and sedimentation of suspended ingredients. Alternatively, microbial polymerization of sugars and surfactant molecules can produce slimy, viscous masses in syrups, shampoos and creams, and fungal growth in creams has produced ‘gritty’ textures. Changes in product pH can occur depending on whether acidic or basic metabolites are released, and become so modified as to permit secondary attack by microbes previously inhibited by the initial product pH. Gaseous metabolites may be seen as trapped bubbles within viscous formulations.

 

When a complex formulation such as an oil-in-water emulsion is attacked, a gross and progressive spoilage sequence may be observed. Metabolism of surfactants will reduce stability and accelerate ‘creaming’ of the oil globules. Lipolytic release of fatty acids from oils will lower pH and encourage coalescence of oil globules and ‘cracking’ of the emulsion. Fatty acids and their ketonic oxidation products will provide a sour taste and unpleasant smell, while bubbles of gaseous metabolites may be visible, trapped in the product, and pigments may discolour it.


 

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