Microbial Spoilage

Microbial Spoilage


• Spoilage of pharmaceutical products

• Pharmaceutical ingredients which are susceptible to
microbial attack

• Factors affecting microbial spoilage

• Sources and control of contamination

• The extent of microbial contamination

• Factors determining the extent of microbial contamination

Learning objectives

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

• Describe Spoilage of pharmaceutical products and ways to
minimize them

• Discuss different pharmaceutical ingredients which are
susceptible to microbial attack

• Discuss factors affecting microbial spoilage

• Explain various sources and control of contamination

• Describe effects of microbial contamination in
pharmaceutical product

• Summarise factors determining the extent of microbial


• Spoilage is a process where the product gets deteriorated
to such an extent that it is considered as unfit for the human consumption

• It is a complex event, which may be combination of
microbial and biochemical activities

• Spoilage process led to the addition of preservatives into
the product to extend its shelf-life


• Microbial Spoilage include the contamination of
pharmaceutical products with the microbes which lead to spoilage of the product
affecting drug safety and quality

• Microorganisms have the ability to degrade compounds at
mild physicochemical conditions

• Mixture of microbial species are effective biodeteriogens

• The rate of degradation of materials varies from product
to product

• The overall rate of deterioration of a pharmaceutical
compound depends on:

– Its molecular structure

– The physicochemical properties of a particular environment

– Type & quantity of microbes present

– Whether the metabolites produced can serve as source of
usable energy & precursor for biosynthesis

Pharmaceutical ingredients susceptible to microbial attack

• Therapeutic agents

• Surface active agents

• Organic polymer: Starch, CMC, pectin -Agar –Polystyrene

• Humectant: Glycerin, sorbitol

• Oil & Fats

• Organoleptic additives

• Preservatives, disinfectants

– When used in concentration less than the effective
concentration, Gram negative organisms can attack

affecting microbial spoilage

1. Types and size of contaminant inoculum

2. Nutritional factors                      

3. Moisture content: water activity (Aw)              

4. Redox potential                          

5. Storage temperature               

6. pH                     

7. Packaging design                        

8. Protection of microorganism’s products within

1. Types and
size of contaminant inoculum

• While designing formulation, the formulator should
consider the environment  and  usage 
to  which  the 
product  is  likely 
to  be subjected

• Very low levels of contaminants which are unable to
replicate in a product might not cause appreciable spoilage

• Inoculum size alone is not always a reliable indicator of

• For  example, a  very 
low  level  of, 
aggressive pseudomonas in  a
weakly preserved solution may suggest a greater risk than tablets containing
fairly high numbers of fungal and bacterial spores

• When an aggressive contaminant enters a medicine, there
may be a lag period before significant spoilage begins

• Since there is usually a long delay between manufacture and
administration of medicines, growth and attack could start during this period unless additional steps are taken to
prevent it like addition of preservation

2. Nutritional

• Many common spoilage microorganisms have simple
nutritional requirements and metabolic adaptability which enable them to
utilize many of the components of medicines as substrates for biosynthesis and

• The use of crude vegetable or animal products in a
formulation provides an additionally nutritious environment

• Even demineralized water prepared by good ion-exchange
methods normally contains sufficient nutrients to allow significant growth of
many water-borne Gram-negative bacteria such as Pseudomonas species                                                                                     

3. Moisture content: water activity

• Microorganisms require water in appreciable quantities for

• Although some solute-rich medicines such as syrups appear
to be ‘wet’, microbial growth in them may be difficult since the microbes have
to compete for water molecules with the large numbers of sugar and other
molecules of the formulation which also interact with water via hydrogen

• The greater the solute concentration, the lower is the
water activity

• Hygroscopic medicines (tablets, capsules, powders) will
require suitable packaging to prevent resorption of water and consequent
microbial growth

• Dilute aqueous films formed on the surface of viscous
products such as syrups and creams can lead to surface yeast and fungal

4. Redox

• The ability of microbes to grow in an environment is influenced
by its oxidation-reduction balance

• The redox potential in viscous emulsion may be quite high
due to the high solubility of oxygen in most fats & oils

5. Storage

• Spoilage of pharmaceuticals could occur over the range of
about -20° to 60°C

• Storage in a deep freeze at -20°C or lower is used for
long- term storage of foodstuffs and some pharmaceutical raw materials, to even
further minimize the risk of growth of any contaminants

• Reconstituted suspensions and multi-dose eye drop packs
are sometimes dispensed with the instruction to ‘store in a cool place’
(8°-12°C), or “store in refrigerator”

• Pharmacopoeial Water for Injections is recommended to be held
at 80°C or above

6. pH

• Extremes of pH prevent microbial attack

• Around neutrality bacterial spoilage is more likely, with
reports of pseudomonas and related Gram-negative bacteria growing in antacid
mixtures, flavoured mouth washes and in distilled or demineralised water

• Above pH 8, e.g with soap-based emulsions, spoilage is

  For  products 
with  low  pH 
levels  such  as 
the  fruit  juice-flavoured syrups (pH 3-4) mould or
yeast attack is more

• Yeasts can metabolize organic acids and raise the pH to
levels where secondary bacterial growth can occur

• In food industry low pH adjustment can be made to preserve
foodstuffs (pickles, yoghurt) but not suitable for pharmaceutical products

7. Packaging

• Packaging should be made in a way to control the entry of contaminants
during both storage and use

• The most important dosage form to be protected are the
parenteral drugs because of the high risks of infection by this route of

• Self-sealing rubber closures must be used to prevent
microbial entry into multi-dose injection containers following withdrawals with
a hypodermic needle

• Wide-mouthed cream jars are now replaced with narrow
nozzle and flexible screw capped tubes to remove the likelihood of
operator-introduced contamination during use

• For medicines which rely on their low Aw to prevent
spoilage, packaging such as strip foils must be of water vapour-proof materials
with fully efficient seals

• Cardboard outer packaging and labels   are potential means microbial attack in
humid conditions

8. Protection
of microorganisms within pharmaceutical products

• The survival of microorganisms in particular environments
is influenced by the presence of various relatively inert materials

• Microbes can be more resistant to heat or desiccation in
the presence of some polymers such as starch, acacia or gelatin

• Presence of suspended particles such as kaolin, magnesium
trisilicate or aluminium hydroxide gel may influence contaminant longevity in

• Presence of some surfactants, suspending agents and
proteins can increase the resistance of microorganisms to preservatives, over
and above their direct inactivating effect on the agents

Sources and
control of contamination

During manufacturing

– Hospital manufacture

– Water

– Environment

– Packaging

In use

– Human sources

– Environmental sources

– Equipment sources


Microbiological quality of the finished product will be
determined by

– The formulation components used,

– The environment in which they are manufactured and

– The manufacturing process itself

Quality should not be only inspected at the end of manufacturing
but must be built into the product at all stages of the process

• Raw materials, like water and ingredients of natural

• All processing equipment should be subject to planned
preventive maintenance and should be properly cleaned after use to prevent
cross-contamination between batches

• Cleaning equipment should be appropriate for the task in
hand and should be thoroughly cleaned and properly maintained

• Manufacture should take place in suitable premises,
supplied with filtered air, for which the environmental requirements vary
according to the type of product being made

• Staff involved in manufacture should not only have good
health but also a good knowledge of the importance of personal and production

• The end-product requires suitable packaging which will protect
it from contamination during its shelf-life and is itself free from


• Manufacture in hospital premises increases contamination issues


• Wet areas are sources of microorganisms

• Cleaning equipment, such as mops, buckets, cloths and
scrubbing machines, may be responsible for distributing these organisms around
the pharmacy

• Good manufacturing practices minimises contamination


• Cardboard, card liners, corks and papers are unsuitable
for packaging pharmaceuticals, as they are heavily contaminated with bacterial or
fungal spores

• Re-usable containers must be thoroughly washed and dried

• Common practice in hospitals is the repackaging of
products purchased in bulk into smaller containers increasing the chances of


• Water for pharmaceutical manufacture requires some
treatment such as distillation, reverse osmosis, deionization or a combination
of these

• Gram-negative opportunist pathogens can survive on traces
of organic matter present in treated water and will readily multiply to high
numbers at room temperature

• Water should therefore be stored at a temperature in
excess of 80°C and circulated in at a flow rate of 1–2 m/s to prevent the build-up
of bacterial biofilms in the piping

In use

• All multi-dose products are vulnerable to contamination
during use

• The risk of contamination during product use has been much
reduced in recent years due to improvements in packaging and changes in nursing


• During normal usage, patients may contaminate their
medicine with their own microbial flora

• Topical 
products  are  considered 
to  be  most 
at  risk,  as  the
product will probably be applied by hand thus introducing contaminants from the

• In hospitals, multi-dose products, once contaminated, may
serve as a vehicle of cross contamination or cross-infection between patients

• These contaminations can be minimised by effective hand


• Small numbers of airborne contaminants may settle in
products left open to the atmosphere

• Larger numbers of waterborne contaminants may be
accidentally introduced into topical products by wet hands or by a ‘splash-back
mechanism’ if left at the side of a basin

• When to hospitals, there are fewer opportunities for
contamination in the home, as patients are generally issued


• Disposable applicators or swabs should be used

• Reused applicators such as sponges, brushes, spatulas are
main reasons of contaminations

• Humidifiers, incubators, ventilators, resuscitators and
other apparatus require proper maintenance and decontamination after use

• Chemical disinfectants minimises the spread of
cross-infection among hospital patients

of microbial contamination and spoilage

Observable effects of microbial attack on pharmaceutical products
are –

• Early indications of spoilage are organoleptic (smell
& taste) Example: sour, fishy, bad eggs, bitter, earthy taste and smells

• Discoloration to products by microbial pigments

• Loss of viscosity due to depolymerization of thickening
& suspending agent like acacia, carboxy methyl cellulose (CMC) resulting in
sedimentation of suspended ingredients

• Microbial polymerization of sugars and surfactant
molecules can produce slimy, viscous, masses in syrups, shampoos and creams, fungal
growth in creams produce ‘gritty’ textures

• Acidic or basic microbial metabolites change pH of the
formulation & enhance microbial growth

• Gaseous metabolites may be seen as trapped bubbles within
viscous formulations

• When emulsions are attacked, it reduces the stability and
accelerates creaming, coalescence and cracking of emulsion

The extent
of microbial contamination

Medicament-borne contamination have become very common these

• A wide range of non-streile products were found to be
contaminated with Bacillus subtilis, Staph. albus, yeasts and moulds, and large
numbers of coliforms soon after manufacture

• Under Medicines Act 1968, pharmaceutical products made in
industry were expected to conform microbiological and chemical quality

• Higher rates of contamination are seen in products after opening
and using

• Medicines used in hospitals are more likely to be contaminated
than those used in the general community

• Medicines used in the home are not only less often
contaminated but also contain lower levels of contaminants and fewer pathogenic

determining the extent of microbial contamination

• Type and degree of microbial contamination

• Resistance of the patient

• The route of administration

Type and
degree of microbial contamination

• Microorganisms that contaminate medicines and cause
disease in patients may be classified as true pathogens or opportunist

• Pathogenic organisms like Clostridium tetani and
Salmonella spp. rarely occur in products, but when present cause serious

• Opportunist pathogens like Ps. aeruginosa, Klebsiella,
Serratia require simple nutritional requirements when enable them to survive in
a wide range of pharmaceuticals

• Opportunist pathogens can survive in disinfectants and antiseptic
solutions that are normally used in the control of hospital cross-infection

of the patient

• A patient’s resistance is important in determining the
outcome of a medicament-borne infection

• Hospital patients are more exposed and susceptible to
infection than those treated in the general community

• Neonates, the elderly, diabetics and patients traumatized
by surgery or accident may have impaired defence mechanisms

• People suffering from leukaemia and those treated with immunosuppressants
are most vulnerable to infection   

• The critical dose of microorganisms that will initiate an
infection is largely unknown and varies between species but also within a

• Animal and human volunteer studies have indicated that the
infecting dose reduces significantly in the presence of trauma or foreign
bodies or if accompanied by a drug having a local vaso-constrictive action.


The route
of administration

• Contaminated products injected directly into the
bloodstream or instilled into the eye cause the most serious problems

• Injectable and ophthalmic solutions are often simple
solutions and provide Gram-negative opportunist pathogens   with sufficient nutrients to multiply during

• Contaminants in topical products may cause harm when deposited
on broken skin

• Patients treated with topical steroids are also prone to
local infections due to contaminations

• Eye when damaged through the improper use of contact
lenses or scratched by fingernails or cosmetic applicators, infections due to ophthalmic

• The acidity of the stomach provides a good barrier for
contaminants ingested orally in medicines


• Spoilage is a process where the product gets deteriorated
to such an extent that it is considered as unfit for the human consumption

• Spoilage of pharmaceutical products are of two types-

– Chemical deterioration

– Physicochemical deterioration

Factors affecting
microbial spoilage

1. Types and size of contaminant inoculum

2. Nutritional factors

3. Moisture content: water activity (Aw)              

4. Redox potential                          

5. Storage temperature               

6. pH                     

7. Packaging design                        

8. Protection of microorganism’s products within pharmaceutical

 Factors determining the extent of microbial contamination

• Type and degree of microbial contamination

• Resistance of the patient

• The route of administration

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