Importance Of Sterilization By Saturated Steam Biology

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While micro-organisms are found on about every surface conceivable, certain industries such as the medical, and the nutrient production industry depend on being able to minimise the inauspicious effects associated with some of these bugs. This is most easy accomplished by the obliteration of these beings, before they pose a job. This is what is known as sterilisation, or more right “ the riddance or devastation of all signifiers of microbic life ” ( Rutala and Weber, 2002 ) . Sterilization may be performed by agencies of dry or damp heat ( steam ) , chemicals, or radiation ( Dutta, 2008 ) . However in the instance of micro-organism ‘death ‘ is a phenomenon that is difficult to categorise ( Phillips and Warshowsky, 1958 ) . This is because some of these methods meant to be bactericidal are simply bacteriostatic ( Phillips and Warshowsky, 1958 ) . In add-on there are many drawbacks associated with a figure of these methods, such as toxicity jeopardies, physical harm to equipment and disbursal in transporting out process ( Bruch, 1961 ) . As a consequence heat in the signifier of dry or damp heat ( steam ) is made usage of for sterilisation intents ( Dutta, 2008 ) . Heat at 60oC is sufficient to kill most vegetive micro-organisms such as bacteriums, Fungis and viruses. However bacterial endospores are known as thermoduric, as they are able to last long term exposure to utmost temperatures, beyond the boiling point of H2O. These thermoduric bacteriums most normally “ belong to the genera Bacillus, Clostridium, Mycobacterium, Micrococcus, Streptococcus and Lactobacillus ” ( Edema and Akingbade 2007 ) . A important concern with such thermoduric spores is that they are the causal beings of diseases such as splenic fever, caused by Bacillus anthracis ( Lemieux et al. , 2006 ) . Furthermore these thermoducric spores besides lead to important negative economic effects ( Rajput et al. , 2009 ) . For case by the spoilage of nutrient merchandises such as milk due to their heat immune nature, enabling them to last the procedure of pasteurization ( Edema and Akingbade, 2007 ) . Pasturisation involves heating milk to 63A° C for 30 min ( Edema and Akingbade, 2007 ) , and therefore this method, successfully destroys vegetive micro-organisms but non the thermoduric spores. In add-on to these concerns, there is besides high hazard of of taint due to inadequate sterilisation in practical facets such as in the medical field, particularly in a surgical context. For case the transmittal of mycobacteria infections in assorted surgeries, as discussed by Wulc and Edmonson, 2006. Due to these grounds at that place needs to accurate and effectual steam sterilisation, this is done by agencies of machine known as an sterilizer. The autoclave utilizations steam under force per unit area to sterilise stuffs, and it destroys bugs by “ by denaturing proteins of import to the beings endurance ” for case enzymes and proteins ( Wulc and Edmonson, 2006 ) . Steam is used within the sterilizer as it is an ideal sterilant. This is because compared to other sterilising media discussed antecedently steam is non toxic in nature, the procedure of sterilisation by agencies of steam is rapid and effectual. In add-on it is inexpensive and readily available, and relatively easy to utilize. Furthermore the steam sterilisation rhythm is in 2 stages, the incursion stage and the keeping stage. The temperature that is maintained in the keeping stage is built up in the incursion stage. These belongingss of steam make it the sterilant of pick to be used within the sterilizer, and it is this operation of moist air in correlativity with the sterilizer that will be explored in this probe.


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Appreciate the mechanisms and rules by which steam sterilisation takes topographic point within an sterilizer

Understand the significance of moist heat ( steam ) in the procedure of sterilisation, when compared to dry heat

Analyze the methods of measuring successful steam sterilisation, within a practical industry application.


The industry criterion for sterilisation by agencies of moist heat, 121oC ( 101 kpa ) for 15 mins is successful in its disinfectant nature, and does non merely map in a bacteriostatic mode. Furthermore industry methods of mensurating effectual sterilisation by agencies of chemical planimeters and biological indexs

Materials and Methods

As per practical manual, pp 35 – 38 ( BMS 2052, Class Notes, 2010 )


Observation of Thermalog strips

Two ‘Thermalog ‘ sterilisation index strips were placed within 2 Schott bottles, one incorporating 2ml of H2O and slackly capped, while the other empty and tightly capped. These 2 bottles along with the ‘Thermalog ‘ strips were placed within the sterlizer and maintained at 121oC for 15 proceedingss. Immediately on completion of the sterilising rhythm the coloring material alteration on the ‘Thermalog ‘ strips was examined and noted down.

Table 1: ‘Thermalog ‘ sterilisation index strips sterilised at 121oC for 15 proceedingss within Schott bottles in either dry or damp heat ( concentrated steam ) .





‘Safe ‘ zone


‘Unsafe ‘ zone



Successful Sterilization


YES+ : Coloring material of the ‘safe ‘ or ‘unsafe ‘ zones on the ‘Thermalog ‘ strips changed coloring material.

On completion of the sterilization rhythm the ‘Thermalog ‘ strip exposed to moist heat ( concentrated steam ) changed from transparent to blue in both the ‘unsafe ‘ and ‘safe zones ‘ . In comparing the ‘Thermalog ‘ strip exposed to dry heat merely changed coloring materials within the ‘unsafe ‘ zone.

Observation of Sterikon plus Bioindicator phials

One of the Sterikon plus Bioindicator phials was placed in the autoclave, and maintained at 121oC for 15 proceedingss. The 2nd Sterikon plus Bioindicator phial was non sterilized. On completion of sterilisation both phials were incubated at 56oC for 3 yearss. Following this the color alterations of each phial were observed.

Table 2: Sterikon plus Bioindicator phials incubated at 56oC for 3 yearss, with or without anterior sterilisation at 121oC for 15 proceedingss.










Coloring material









NO+ : Sterilization/incubation performed – : Sterilization/incubation non performed

It was seen that vial 1 remained pink ( showed no color alteration ) , while vial 2 which was non sterilized prior to incubation changed coloring material from pink to yellow.

Observation of spore impregnated strips in TSB

Strips of paper impregnated with Bascillus stearothermophilus were placed in bottles 1 to 4. Several beads of H2O were added to bottle 2, while paraffin oil was added to bottle 4 until the spore strip was wholly immersed in oil. The caps of bottles 2,3 and 4 were screwed on tightly and sterilized at 121oC for 15 proceedingss, bottle 1 was non sterilized. On completion of sterilisation 3ml of tryptone soy stock ( TSB ) media were added to bottles 1,2,3 and 5. The spore strip from bottle 4 was so aseptically transferred to bottle 5, and bottles 1,2,3 and 5 were incubated at 56oC for 3 yearss. Upon completion the turbidness of each of the bottles was examined and recorded.

Table 3: Bascillus stearothermophilus spore impregnated strips in tryptone soy stock

media ( TSB ) , incubated at 56oC for 3 yearss with or without anterior sterilisation in

different conditions at 121oC for 15 proceedingss.












of ‘Thermalog ‘ strip


( Moist heat/steam )

Few beads of H2O

( Moist heat/

steam )

Tightly Capped

( Dry heat )

Paraffin oil

( Dry heat )





( None )




( LOW )






NO+ : Sterilization performed – : Sterilization non performed

Upon observation it was seen that bottle 1 had the highest sum of turbidness of all the bottles. Both bottles 3 and 5 showed turbidness, but to a lesser grade when compared to bottle 1. Of these bottle 3 showed the lowest turbidness. In contrast bottle 2 showed no marks of turbidness.


Bioindicators such as Sterikon plus Bioindicator phials and Chemical indexs such as ‘Thermalog ‘ strips are used in sterilizers, in order to guarantee satisfactory sterilisation has taken topographic point. This is because the gages on the sterilizer used to mensurate temperature and force per unit area are non accurate on their ain, due to the possibility of pockets of air organizing or escapes in the sterilizer that alter temperature within the sterilizer. ( Lee et al.,1979 ) .

The first portion of the probe focused on the sterilization of the ‘Thermalog ‘ strips within Schott bottles, from this it can be seen that the ‘Thermalog ‘ strip exposed to moist air/saturated steam ( Table 1 ) changed coloring material within both the ‘unsafe ‘ and ‘safe ‘ zones. The coloring material alteration within the ‘safe ‘ zone indicates that the right standards for sterilization have been met, and the conditions of moist heat are equal for sterilization. In comparing the ‘Thermalog ‘ strip exposed to dry heat ( Table 1 ) merely changed coloring materials within the ‘unsafe ‘ zone, it can be seen that the right standards for sterilisation has non been met.

In the portion of the probe that focused on the use of Sterikon plus Bioindicator phials, each vial consists of the medium known as the stock, a pH index, sugar and spores from Geobacillus stearothermophilus, which are non-pathogenic in nature ( Merck,12th edn ) . The heat opposition of the Geobacillus stearothermophilus spores is such that they are destroyed if exposed to compressed steam at temperatures of 121oC or higher and force per unit areas of for about 15 proceedingss ( Merck, 12th edn ) . The temperature within the sterilizer used for the experiment is 121oC and the exposure clip is 15 proceedingss, and therefore any phial of Sterikon plus Bioindicator should be decently sterilized. If nevertheless the clip or temperature the spores were subjected to was lower than this degree, a little proportion of the spores will be able to last and go active in favorable conditions ( Merck, 12th edn ) . After being autoclaved the adequateness of sterilisation is investigated by agencies of incubation ( Merck, 12th edn ) . This is besides done to guarantee that these beings have been killed and non merely been immobilised, that is, after sterilisation it is observed if they multiply to organize new offspring when placed in a favorable environment, presented during incubation ( Phillips and Warshowsky, 1958 ) .

Upon completion of incubation vial 1, which was sterilized prior to incubation ( Table 2 ) remained red-violet ( showed no color alteration ) . This deficiency of coloring material alteration is declarative of no spore activity, significance that successful sterilisation has taken topographic point and that all the Geobacillus stearothermophilus bacterial spores have been destroyed ( Merck, 12th edn ) . Hence the media of vial 1 does non alter coloring material on incubation.

In comparing phial 2 which was non sterilized prior to incubation ( Table 2 ) changed coloring material from red-violet to yellow, which is declarative of bacterial spore growing. This is due to the fact that the spores were non autoclaved and therefore non sterilised. Therefore these spores, when exposed to more favorable conditions for bacterial growing become active and produced the coloring material alteration in the medium of the phial. This color alteration is brought approximately by an acid produced during the agitation of the sugars by the bacteriums. The acid is detected by the pH index, and the turbid yellow coloring material associated with bacterial activity is produced. ( Merck, 12th edn ) .

Therefore it can be seen that sterilisation of bacterial spores within an sterilizer has a negative consequence on bacterial growing, even if environmental conditions following sterilisation go more favorable to growing.

From the portion of the probe which focused on the usage of strips impregnated with Bascillus stearothermophilus spores, placed in tryptone soy broth media ( TSB ) , it can be seen that bottle 1 was non sterilized prior to incubation ( Table 3 ) . This unsterilised ( unexposed ) spore strip was used within the probe as it acts as a positive control, exhibiting the normal growing of the spores. This growing is of import for demoing that the right medium was used for the growing of the spores, extinguishing any possible jobs of the spore and medium non being compatible with each other. Furthermore the presence of feasible spores is necessary for the successful reaction that consequences in turbidness ( Table 3 ) .

This bottle 1 ( Table 3 ) showed the highest turbidness, bespeaking highest bacterial spore activity. The favorable environment provided during the incubation period offers a really favorable environment to the unsterilised bacterial spores, which become active and makes the TSB media turbid due to to the agitation of foods within the TSB media

Of the bottles sterilised bottles 3 and 5 showed turbidness, with bottle 5 demoing greater turbidness that bottle 3. Bottle 5 contained the spore strip from bottle 4 which was filled with paraffin oil. The presence of the oil along with the palpebra being capped tightly meant that no moist heat ( steam ) could make the spore strip, and so it was merely exposed to dry heat. Furthermore the presence of paraffin oil World Health Organization boiling point is 220oC ( and therefore in liquid signifier while in the sterilizer at 121oC ) means that the spore strip is besides slightly protected by the dry heat due to the liquid nature of the oil. Together this meant that while it was placed in the sterilizer and sterilized, the sterilisation was non equal as it did non kill all the spores. These lasting spores when placed in the favorable environment during the incubation period became active and made the media turbid.

Bottle 3 was tightly capped before being placed in the sterilizer. This meant that the moist heat ( steam ) could non make the spore strip, and so the spores were merely exposed to dry heat, this once more meant that one time conditions became more suitable to bacterial growing the spores became active and made the media turbid as in the instance of bottle 5, although to a lesser grade than was in bottle 5 due to less figure of spores lasting in bottle 3.

Bottle 2, showed no marks of turbidness in the TSB media, which is declarative of no bacterial spore activity. As was mentioned in the consequences subdivision, before being placed in the autoclave several beads of H2O were added to bottle 2. These droplets of H2O holding a boiling point of 100oC rapidly boiled over and turned to steam within the sterilizer, which was at 121oC. This meant that although the cap on this bottle was screwed on tightly, forestalling moist heat ( steam ) from the sterilizer making the spore strip, the H2O vapor within the bottle functioned as its beginning of steam sterilising the spores in the spore strip. Furthermore the fact that the bottle was tightly capped meant that none of the steam could get away the bottle and were contained within it. As the spores were wholly sterilized, even when the conditions became more favorable during the incubation period, there were no lasting spores to go active and do the media turbid, and therefore the media remained clear, and it can be seen that this bottle has been successfully sterilized.

These findings lead to an of import issue, that of the biocidal nature of moist and dry heat. It is when compared to dry heat that the significance of moist heat ( steam ) can truely be understood. The temperature and clip parametric quantities for successful steam sterilisation are 121A°C for 15 proceedingss ( Wulc and Edmonson, 2006 ) . In comparing the minimum parametric quantities for successful dry heat sterilisation is 160A°C for 2 H ( Wulc and Edmonson, 2006 ) . Hence the usage of steam enables faster sterilisation instead than the usage of dry heat. ( 3M Technical information sheet ) . Furthermore steam is a more efficient autoclave when compared to dry heat as “ the intrinsic heat resistence ” of bacterial cells is much higher “ in a wholly dry province ” ( Dutta, 2008 ) . Therefore as a consequence of this rate of decease of cells in a dry status are lower than those in a damp status ( Dutta, 2008 ) .

However an of import characteristic associated with sterilisation by agencies of moist heat, is that for steam to be a successful sterilant there needs to be physical contact between the stuff being sterilized and steam. This is because concentrated steam demands to distill onto a surface, when it does this it releases its latent heat to the stuff, which consequences in devastation of any microbes nowadays.


The industry criterion for sterilisation by moist heat set out in the hypothesis ( 121oC,101 kpa for 15 mins ) was successful in sterilising micro-organisms, every bit good as thermoduric bacterial endospores. This success or failiure of sterilisation was readily discernible by agencies of the indexs used in concurrence with moist or dry heat sterilisation within the sterilizer. The success observed with the sterilizer in this little graduated table probe is declarative of the utility of sterilisation by agencies of moist heat in concurrence of sterilizers in big scale industrial procedures. With a more effectual research and development, the usage of steam sterilisation utilizing higher temperatures and greater force per unit area could be explored, taking to greater practical applications.

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