Aseptic and Sterile Conditions: Do You Know the Difference?

It is obvious that microbial cultures need to be handled in a safe manner in order to avoid the risk of infection. It is therefore essential to fully understand the meaning of words used in descriptions of safety procedures.

Two of these words, sterile and aseptic, are commonly used both in relation to safety and in the context of manufacturing and dispensing of medicines. Unfortunately, the words are often misunderstood and used incorrectly as if they mean the same thing – they don’t!

Sterile, in a pharmaceutical context, means the complete absence of life. So any medicine or surgical device, or, indeed, any object that is sterile, has no living organisms at all in it or on it.

It is an absolute term, so an object is either sterile or it is not; there are no levels of microbial contamination that are so low as to be regarded as insignificant and therefore acceptable.

If a medicine is contaminated with a single organism it is not sterile, so phrases like ‘almost sterile’ or ‘more sterile’ should be avoided because they simply display a lack of understanding of the concept.

Several categories of medicines, notably injections and eye products, are required to be sterile, and there are two manufacturing strategies available: the preferred method, known as terminal sterilization, is where the medicine is made from non-sterile raw materials and subjected to a heat, radiation or other sterilization procedure at the end of the manufacturing process.

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The alternative used when the product cannot withstand the high temperatures or radiation doses of a terminal sterilization process, is to start with raw materials that are individually sterilized – often bypassing solutions of them through bacteria proof filters – and then mixing them together under conditions that do not allow the entry of microorganisms, followed by filling into presterilized containers; this is termed ‘aseptic manufacture’.

Aseptic, therefore, is a word used to describe a procedure that is intended to avoid the unwanted transfer of microorganisms from one object or location to another.

It works both ways: it can be a procedure designed to avoid the introduction of organisms into a medicine whilst it is being made, dispensed, or administered to a patient, but it also describes procedures for handling hazardous organisms which pose an infection risk to operators.

In this case, therefore, the aseptic procedure is intended to keep the organism in its container and avoid it being dispersed into the atmosphere and inhaled, or transferred onto the body of the person handling it.

Regardless of whether the intention is to protect the product or protect the operator, aseptic procedures would normally require gowns, gloves, facemasks, disinfectants, and the use of safety cabinets or isolators supplied with filtered decontaminated air.

Source

• Hanlon, G. and Hodges, N. (2013). Essential Microbiology for Pharmacy and Pharmaceutical Sciences. UK: John Wiley & Sons, Ltd.

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