Bioburden Determinations

BIOBURDEN  DETERMINATIONS         

The term bioburden is used to describe the concentration of microorganisms in a material; this may be either a total number of organisms per millilitre or per gram, regardless of type, or a breakdown into such categories as aerobic bacteria or yeasts and moulds. Bioburden determinations are normally undertaken by the supplier of the raw material, whose responsibility it is to ensure that the material supplied conforms to the agreed specification, but they may also be checked by the recipient. The maximum permitted concentrations of contaminants may be those specified in various pharmacopoeias or the levels established by the manufacturer during product development.

The level of sterility assurance that is achieved in a terminally sterilized product is dependent on the design of the sterilization process itself and on the bioburden immediately prior to sterilization. However, the adoption of high standards for the quality of the raw materials is not, in itself, a strategy that will ensure that the product has an acceptably low bioburden immediately prior to sterilization. It is necessary also to ensure that the opportunities for microbial contamination during manufacture are restricted (see below), and that those organisms that are present initially do not normally find themselves in conditions conducive to growth. It is for these reasons that manufacturing processes are designed to utilize adverse temperatures, extreme pH values and organic solvent exposures in order to prevent an increase in the microbial load. For example, water is the most common, and potentially the most significant, source of contamination in the manufactured product, and maintenance of water at elevated temperatures is commonly employed as a means of limiting the growth of organisms such as Pseudomonas spp., which can proliferate during storage, even in distilled or deionized water. Precautions such as these ensure that chemically synthesized raw materials have bioburdens that are generally much lower than those found in ‘natural’ products of animal, vegetable or mineral origin.