Different sterilization methods
To date, there are different sterilization methods. They are cited and commented on in the international guides relating to Good Manufacturing Practices (GMP) annexed to the respective Pharmacopoeias:
- European Pharmacopoeia
- US Pharmacopoeia
- Japanese Pharmacopoeia
The choice of sterilization method falls to the manufacturer, who must be able to demonstrate its merits, suitability for the product and expected effectiveness.
Definition of sterilization
With regard to public health, from hospitals to canneries or from cosmetics to medical device manufacturers, many sectors of ultra-cleanliness and in particular the pharmaceutical industry, are faced with the absence of viable micro-organisms. both in a manufacturing stage and in terms of quality of the finished product.
Not only does the elimination of all biological contamination, generating a pathogenic or non-pathogenic infectious risk, appear obvious, but the search for sterility is also motivated by the obligation to control all the required interactions and stabilities. Many sterilization methods exist for this.
Since the awareness of the existence of micro-organisms in the infinitely small with Louis Pasteur and the first techniques of Nicolas Appert to control them in a given environment, the collective unconscious and therefore the authorities have been worried, s question, doubt in the face of this sometimes unrecognized invisible. The available literature being prolific even verbose, our aim will be limited to presenting an exhaustive overview of the concepts and treatment methods most used currently.
LEXICON
Viable micro-organism: being microscopic capable of living as a unicellular type, such as bacteria, viruses, fungi, yeasts and protists (algae and protozoa)
Sterility: absolute state, probably demonstrable(1), ensuring the absence of viable micro-organisms.
Sterile: probably(1) free of viable micro-organisms (EN 556-1: 2001 def 3.4)
Sterilization: validated process aimed at making a product free of viable micro-organisms (according to ISO 11139:2001 def 2.42). Sterilization is therefore a treatment aimed at achieving a state of sterility, that is to say being able to guarantee, with a controlled risk, the absence of viable micro-organisms.
(1) A properly sterilized product is not “sterile” but “probably sterile” or heat treated with a Probability of Survival of a Microorganism/unit less than 10-6 (PSMO).
AVAILABLE STERILIZATION METHODS
There is no good or bad sterilization technology: they all give excellent results if they are well adapted to the material to be treated (including packaging, loading, environment, etc.). However, certain technologies provide thermal treatments that reduce the bioburden without being able to achieve the sterility requirements required by the European, Japanese and American pharmacopoeias.
THE CHEMICAL WAY
Contact of the germ under specific conditions with one or more molecules generally destroying the metabolism and especially the nucleus of the micro-organism. These treatments are called “cold” although sometimes using temperature as a catalyst accelerating the reaction. They exist in continuous or discontinuous flow.
1. Greening/chlorination
Either by immersion in bleached water, or by adding gaseous or liquid sodium hypochlorite to the surfaces or environments to be treated. High oxidizing potential. Corrosion even on austeinitic stainless steel.
2. Ethylene oxide
Very rarely pure, more often in a low or high pressure mixture, with carbon dioxide (CO2) or nitrous oxide, ethylene oxide under very strict humidity and temperature conditions ensures sterilization. , according to a gas concentration/exposure time cut. Exploitation is becoming rarer in the industry due to draconian environmental controls given the dangers of exploitation. Desorption is always very long (24 to 48 hours).
3. Propylene oxide
Generally used in the food industry, it provides surface decontamination.
4. Hydrogen peroxide (H2O2)
High oxidizing potential: in liquid medium by dissolution or misting or by vaporization (VHP) on surfaces (non-penetrating). Leaves no residue. Recommended concentration of 1 to 2% (M/V); duration of 2 to 24 hours.
Applications: SIP machines, reverse osmosis insulators, material airlocks, ZAC atmosphere.
| Température (°C) | Concentration H2O2 (mg/L) | PPM | Valeur D en minutes |
| 4 | 0,3 à 0,5 | 350 | 8 à 12 |
| 25 | 1 à 2 | 700 à 1500 | 1 à 2 |
| 37 | 3 à 4 | 2000 à 3000 | 0,5 à 1 |
5. Ozone
Produced by electric discharge in a very dry air atmosphere (pure O2), this unstable gas (O3) is very reactive at low concentrations but also irritating, toxic and smelly. Strong oxidant used as a bleaching agent (waxes, oils, textiles, etc.) its germicidal action is used to disinfect air and water in the pharmaceutical industry.
Operation requires ultraviolet (253 nm) through residual degradation. Disinfection and decontamination agent, usually it does not guarantee sterilization with SAL 10-6.
6. Peracetic acid in vapor
Mainly used for the decontamination of insulators, it is easy to eliminate but is limited to a decontamination action (some spores resist). Recommended concentration: 0.2 to 0.8% (M/V); 1 to 2 hours.
7. Hydrogen peroxide plasma gas
Strong germ oxidation techniques. This patented discontinuous process (sterrad) is accepted by the AFSSAPS and validated in the hospital sector as a sterilization technique and not yet in industry given the difficulty of guaranteeing the homogeneity of the plasma concentration of gases enriched with oxidizing species, throughout the duration of exposure, due to absorption or state transformation by the charge.
Plasma being a gas very energetically enriched in unstable elements, after their reaction, they regain their stability by emitting radiation and recombining into H2O2 + O2.
8. Formalin (formaldehyde)
Despite powerful biocidal activity, exploitation generates carcinogenic, mutagenic and reprotoxic (CMR) risks for humans. Also, by decision of the European Commission 2011/391/EU and the Ministry of Ecology in France (JO: 09/14/2011), its marketing is now prohibited from 07/01/2012 and its use from 01/01/2013.
RADIATION
The radiation provides bombardment (electromagnetic radiation of varying high energy) thus destroying the internal structures of the nucleus of micro-organisms. The treatments are carried out cold continuously or discontinuously on site or more often at a specialized service provider.
1. Germicidal UV radiation 253 nm
Exposure to the radiation of ultraviolet lamps under very specific conditions (often poorly respected) ensures the reduction of a large quantity of germs but cannot in any way guarantee the term of sterilization.
2. β (beta) radiation
Carried out in a specialized center, off the production site, this bombardment of a beam of accelerated electrons degrades the structure of the nucleus according to a dose-effect law. Articles packaged in waterproof packaging receive a dose of energetic radiation expressed in megarads and therefore controlled by a dosimeter qualifying the quantified absorption.
3. γ (gamma) radiation
Always produced outside, the energy comes from and depends on a radioactive source. The exposure time is therefore several hours and the yield lower.
4. X-rays
The energy of the X-rays obtained by braking the accelerated electrons degrades the structure of the chromosomes of the nucleus of the germs. Little exploited industrially due to its yields.
use from 01/01/2013.
STERILIZING MICRO-NANOFILTRATIONS
No action on the germ, the “sieving” effect separates and retains the micro-organisms upstream of the filters, depending on the porosity of the medium.
1. Sterilizing micro-filtration (10-6) on membranes and cartridges
Cartridges with a porosity generally less than one micrometer are used: < 0.2 μm
Widely used in aseptic filling
Viruses are not retained
2. Ultra-filtration (10-7) and Nano-filtration (10-9)
Filtration threshold allowing virus retention. However, these techniques are generally limited to fluids (air and water) because they could also retain pharmaceutical molecules.
3. Single or double reverse osmosis
Different from filtration, applied to water, this technique known as solubilization (high pressure diffusion), simple or repeated twice, purifies the water of its ions, microbes and pyrogens by forced passages over special membranes.
Some operations in the agri-food sectors, particularly for fruit juices.
THERMAL TREATMENTS
Thermal treatments are carried out via sterilization autoclaves. Several technologies can be used: dry heat autoclave, moist heat autoclave, air/steam autoclave, saturated steam autoclave, superheated water autoclave, steam autoclave, etc.
1. Dry heat
It is oxidation by combustion in the presence of energy and oxygen. The integrity of molecular structures is degraded. It is carried out continuously or discontinuously with the most common heat transfer fluids: air and steam.
Continuous: Hot air through tunnel in the pharmaceutical industry
Discontinuous: Air – oven/oven technique with 3 stages of absolute air filtration heated to 200 – 225°C by specific resistances. This technique also allows depyrogenation.
2. Damp heat
The sterilizing effect results from a reaction between the germ to be sterilized and the moist heat present in contact with it. Saturated steam, superheated water or air-steam mixtures are hydro-energetic complexes, which in the presence of colder mass, will transfer their calories, which themselves will degrade the chromosomal structures of the nucleus of microorganisms.
In the presence of dry saturated steam, slightly humid but very energetic, heating will be faster and condensation will be intense until the load + chamber assembly is thermally homogeneous.
Continuous :
Steam in complete sterilization tower in the food industry for products in cartons, and in particular baby nutrition, and occasionally in the pharmaceutical industry if production rates allow (bottles and bags). Ensuring a pressure of 1 bar in immersion, these 10 to 15m towers, horizontal or vertical, manage the different phases using continuous mechanization crossing siphon-type hydraulic barriers.
Ultra high temperature technique allowing the treatment of high temperature liquid in continuous flow carried out in plate or tube bundle exchangers supplied with steam or by infrared heating (Fo +2 Z).
Discontinuous:
Subaqual: Consists of total immersion of the load in superheated water
Superheated water: by trickling of superpressurized, superheated and sterile water from top to bottom over the entire load passing in continuous circulation on an exchanger supplied with steam for heating and water for cooling.
Air/steam autoclave: Technique allowing the mixing of two gases of different densities, very suitable in the pharmaceutical industry for products that do not require a vacuum technique.
Saturated steam autoclave: Sterilization is independent of the steam strength (saturated wet or dry).
S.I.P. : In-place sterilization of a process device, generally by timed injection of pure steam; the system being at atmospheric pressure (so-called fluent steam disinfection) or under pressure of 1 to 2 bars (so-called “dynamic” steam sterilization).
OTHER METHODS
There are many other sterilization methods, discover a non-exhaustive list of other sterilization processes below.
1. Pulsed light energy
Pure Bright process: Approximately 20,000 times more energetic than solar light, the repetition (1 to 10) of pulsed flashes of light (450 nm) of 0.5 to 2 J/cm3 for a few millionths of a second ensures, by accumulation of energy on the targets, without the possibility of dissipation, a photolysis irreversibly denaturing the nucleic acids and proteins.
Liquids and containers must be transparent.
Rapid action and absence of residue.
Process currently being validated in the pharmaceutical industry.
2. Pascalization
So-called “hyper-bar” treatment varying from 2000 to 7000 bars (<70°C) for the destruction of bacteria, yeasts and filamentous fungi in the food industry. The mechanism is considered to be diffusion, expansion, rupture and degradation of these micro-organisms but it should be noted that bacterial spores can withstand pressures of 10,000 bars.
3. Microwaves
In the current state of scientific knowledge, they are never sterilizing agents as such, however they allow the production of plasma very enriched in oxidizing elements in the air or the production of steam when they heat the air very quickly. ‘water.
Widely used in the treatment of baby bottles and in the food industry, the treatment is assimilated to decontamination except in the case of steam production in accordance with steam sterilization.
