Autoclaves and Sterilizers

Introduction

An autoclave sterilizes medical or laboratory equipment to kill viruses, bacteria, fungi, and spores. It is the most thorough kind of decontamination that employs saturated steam at a high temperature (typically 121°C) for 15-20 minutes for sterilization (Panta, Richardson, Shaw, Chambers, & Coope, 2019). 

The steam must come into direct contact with the materials at the required temperature and pressure to be completely effective against microbes. This steam is highly pressurized, which allows its temperature to exceed  100°C, accounting for its efficiency. The amount of pressure and temperature the autoclave utilizes is inversely proportional to the time taken for sterilization. When the pressure is 108 kilopascals (kPa), the temperature of the steam is 121°C, and the time needed for sterilization is 20 minutes. On the other hand, at 206 kPa, the steam is 134°C, and it only takes 10 minutes for sterilization. (Dockery, 2012).

Charles Chamberland invented the autoclave in 1879. Researchers began to recognize the benefits of antiseptic surgery around the 1850s. Since then autoclaves have found usage in several fields such as research laboratories and animal labs. 

Principle

The autoclave operates on the principle of moist heat sterilization, in which the material inside the chamber is sterilized by steam under high pressure. 

How does it work?

The Autoclave is made to cater to sterilization requirements while being safe and fully automated. 

• Place materials such as different media, lab instruments, and other experimental laboratory equipment in the autoclave. 
• Use the touch-screen feature to pick the required program, shut the door, and push the start button. 
• The sterilizing duration should be changed depending on the load. However, it is often set at a single length of 20 minutes.
• For an additional drying time after the session, pick the “Dry Only” option. 

All of the settings can be changed as per the laboratory’s needs. 

Applications

Inadequate sterilization of medical and lab equipment increases the risk of infection from human to human and from the environment. Therefore, effective sterilization of lab and medical equipment is required. 

Although autoclaves are typically used to decontaminate laboratory instruments and biological waste, they are also widely used for sterilizing animal feed, bedding, and enrichment items. Rodent meal is sterilized to prevent the entry of possibly harmful microbes that can cause diseases or latent infections, affecting physiological response. This method became popular as the requirement for specific pathogen-free animals grew. 

Scientists have isolated gastrointestinal microorganisms from unsterilized, raw content rodent meals on some instances, notably Salmonella spp., E. coli, and Clostridium spp. Moreover, several recent reports involved the continuity of mouse parvovirus in mouse territories due to the use of an unsterilized diet. Organizations that autoclave their animal diets, on the other hand, should think about the temperatures required for feed sterilization as well as the kind of research in which these autoclaved diets are utilized (Kurtz et al., 2018).

Precautions

Following are some of the precautions recommended while working with an autoclave:

• Wear suitable Personal Protective Equipment (PPE) such as a lab coat, flame-resistant gloves, and protective eyewear.
• If water starts coming out from the bottom of the autoclave, do not open the door. A buildup of boiling water can be caused by obstructed steam lines, equipment breakdown, or clogged drains.
• Look for cracks in the glass tubes and containers. If there are any cracks, get rid of them. Any known cracked glass equipment should never be autoclaved.
• Do not make contact between the material and the autoclave’s internal walls while loading.
• To avoid steam injuries and broken glassware, wait until the pressure has dropped to zero and the temperature has dropped to or below 121°C while opening the door after a cycle.
• Unload the autoclave carefully. When liquids reach a temperature over their typical boiling point yet do not appear to boil, this is known as superheating. Any movement of the fluid could cause it to flare into steam and spray violently. The overheated liquids can boil out of their containers or burst if staff are in a rush to remove flasks or bottles from the autoclave.
• Sharp materials (needles, syringes, shattered glass, etc.), hazardous chemicals, bleach-associated material, low molecular weight biotoxins, and pathogenic wastes should never be autoclaved.

Strengths and Limitations:

Strengths:

The autoclave effectively sterilizes lab equipment using saturated steam. However, it also has a safety mechanism to avoid excessive pressure buildup. The water in the autoclave is brought to a lower temperature by the cooling system before being discharged to minimize damage to the facility’s sewerage system. Some autoclaves additionally have a suction mechanism to eliminate air before injecting steam. As materials containing water cannot be sterilized by dry heat sterilization, autoclaves are essential for ensuring their sterilization. Surgical tools, equipment, pharmaceutical instruments, microbial growth media, and other laboratory items are commonly sterilized using it. Solids and fluids can also be sterilized using this apparatus.

Limitations:

Although an autoclave is a trusted sterilizer, it may not be the best solution for every sterilization need. It cannot be used for heat-sensitive materials or sharp-edged instruments, especially high-grade carbon steel scissors and scalpel blade edges. Some things, such as fabric and linens, cannot be sterilized without being destroyed by the autoclave. High heat can cause some plasticware to melt, and sharp equipment can become dull. Furthermore, many compounds degrade during sterilization, and oily substances cannot be handled since they do not combine with water. Certain high-protein solutions, such as urea, vaccinations, and serums may need to be filtered without heat since they degrade in excessive heat.

Summary

An autoclave is an efficient and economical instrument used for sterilizing purposes in labs, healthcare, and dental settings. It works on the principle of steam sterilization. This high-pressurized steam is effective in killing microbes, including endospores. Although it is effective and recommended for many materials, it is not suitable for heat-sensitive, biological substances, plastic ware, and sharp objects.

References

Dockery, G. D. (2012). Chapter 7 – Aseptic techniques. In G. D. Dockery & M. E. Crawford (Eds.), Lower Extremity Soft Tissue & Cutaneous Plastic Surgery (Second Edition) (pp. 53-68). Oxford: W.B. Saunders.

Gillespie, E. H., & Gibbons, S. A. (1975). Autoclaves and their dangers and safety in laboratories. The Journal of hygiene, 75(3), 475-487. doi:10.1017/s0022172400024517

Kurtz, D. M., Glascoe, R., Caviness, G., Locklear, J., Whiteside, T., Ward, T., . . . Kissling, G. E. (2018). Acrylamide Production in Autoclaved Rodent Feed. Journal of the American Association for Laboratory Animal Science: JAALAS, 57(6), 703-711. doi:10.30802/AALAS-JAALAS-18-000011

Panta, G., Richardson, A. K., Shaw, I. C., Chambers, S., & Coope, P. A. (2019). Effectiveness of steam sterilization of reusable medical devices in primary and secondary care public hospitals in Nepal and factors associated with ineffective sterilization: A nation-wide cross-sectional study. PloS one, 14(11), e0225595-e0225595. doi:10.1371/journal.pone.0225595

Rutala, W. A., & Weber, D. J. (2015). Disinfection, Sterilization, and Control of Hospital Waste. Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases, 3294-3309.e3294. doi:10.1016/B978-1-4557-4801-3.00301-5

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