Microbial contamination of medicines arises from three principal sources:
- the raw materials, including water, from which the product is manufactured;
- the manufacturing environment, including thenatmosphere, equipment and work surfaces; and
- manufacturing personnel.
The relative contributions of these three sources vary depending on the type of product in question. It is a known fact that raw materials of different origin may differ significantly in their extent of microbial contamination.
‘Natural’ materials originating from animals (e.g. gelatin), vegetables
(starch, cellulose derivatives, alginates) or minerals (talc, kaolin, magnesium trisilicate, bentonite) usually have much higher bioburdens than synthesized
chemicals, in which organisms are often killed by heat, extremes of pH or organic solvents.
Despite the high levels of microorganisms to be found in locations where many natural materials arise (gelatin, for example, originates in the slaughterhouse, where faecal contamination of animal carcasses is not uncommon), the cleaning and purification procedures currently used mean that contamination levels are
only one or two orders of magnitude higher than those for synthesized chemicals.
This is reflected in the pharmacopoeial limit of not more than 104 colony-forming units of aerobic bacteria per gram for some oral products containing materials of natural origin compared with 102 colony-forming units per gram otherwise.
Generally, the types of contaminating organisms are reflective of the origins of the product and this, in turn, is reflected in the objectionable organisms that must be absent. For example, salmonellae and
Escherichia coli might arise in faeces, so gelatin is subject to tests for the absence of these species. The same organisms might originate from natural fertilizers
used on commercial crops, and so they must be absent too from vegetable drugs, starches, mucilages, etc.
Both vegetable drugs and mined minerals may contain organisms originating from the soil (e.g. Bacillus and Clostridium species), usually as spores. Vegetable drugs may be contaminated with spores of fungal
plant pathogens such as Cladosporium that rarely arise in other circumstances.
Water is the most commonly used raw material for manufacturing medicines. Not only is it obviously present in most liquid medicines, it may be added, then removed, during manufacture of dry products too (e.g. during tablet granulation). It is also used in
the factory for cleaning equipment, work surfaces, mixing vessels and bottles or other product containers.
As a consequence, the microbiological quality of both ingredients and cleaning water can have a profound effect on the final bioburden of the manufactured
product. To those unfamiliar with methods of water purification, it is a paradox that pharmaceutical
purified water is more likely to contain high levels of bacteria (particularly after storage) than the mains water that is used as the source material. This is
simply a consequence of the fact that mains water (potable water) is chlorinated, and the chlorine, which
acts as a preservative, is removed during purification.
Despite this purification process, purified water still contains sufficient dissolved nutrients to support the growth of several species of Gram-negative bacteria to population levels well in excess of 105 per millilitre.
Such levels may be attained within days rather than weeks of room-temperature storage after chlorine removal. The species commonly found are described
as low-demand organisms (i.e. they are metabolically versatile and can efficiently utilize as nutrients low concentrations of a diverse range of carbon-containing compounds).
Pseudomonads (i.e. the organisms
resembling the pathogen Pseudomonas aeruginosa) are good examples of low-demand Gram-negative bacteria, although organisms of other genera, such as Flavobacterium and Alcaligenes, also arise.
Product contaminants originating from the manufacturing environment all tend to have one characteristic in common: they survive well in dry conditions.
The Gram-negative bacteria that are prevalent in water are rarely seen in this situation. Most of these environmental contaminants are spore-formers, both
bacteria and fungi, or Gram-positive bacteria such as micrococci and staphylococci.
All these can persist for long periods while attached to dust particles
suspended in the atmosphere or settled on floors, work surfaces or equipment.
Pharmaceutical factories are supplied with filtered air, so the level of particulate contamination in the atmosphere in a room where there is no activity (i.e. operators are absent) is usually very low. The main component of the dust in a manufacturing area that is in operation is skin scales shed by operational personnel. Humans replace skin constantly and are therefore continually shedding particles with attached skin bacteria; these particles
are typically approximately 20 µm in size and cannot be seen with the naked eye.
The extent to which skin scales are shed depends on many factors, such
as the design and coverage of protective clothing, general health, personal hygiene and, in particular, levels of activity. People standing or sitting normally shed far fewer particles than those who are in motion.
Statistics and estimates of the extent to which humans shed skin scales differ substantially, but approximately
109 per day is a commonly quoted value (Cosslett, 2007).
Swabbing with antiseptics or washing with bactericidal soap reduces the numbers of microorganisms on the skin, but is by no means totally effective. Fig.1 above shows a Petri dish of nutrient medium used to take ‘finger dabs’ from fingers treated in this way.
In the upper left segment, bacterial colonies were cultured from an unwashed finger; the upper right shows the colonies from a finger washed with bactericidal soap and the bottom sector shows those from a finger swabbed for 1 minute with cotton wool soaked in antiseptic.
It is clear that short periods of
exposure to bactericidal soaps cannot be relied on to eliminate contamination, and a recognized antiseptic is far more effective.