Some observations on cooling in laboratory autoclaves.

SUMMARY The performance of autoclaves in 27 laboratories, operated in accordance with the normal routine of local practice, has been monitored using thermometric equipment. Sterilising performance was unsatisfactory on 10 of 62 occasions, and cooling was inadequate on 52 of 60 occasions.As part of the general concern over safety standards, laboratories in the Public Health Laboratory Service (PHLS) were encouraged to obtain thermometric equipment to monitor the performance of their autoclaves. This provided an opportunity to discover whether, when the autoclaves were operated in accordance with the normal practices in use in those laboratories at the time of acquisition of the equipment, sterilising performance was satisfactory and cooling of the loads was adequate to allow the autoclaves to be opened safely. The results of a survey of these aspects of autoclaving practice in 27 laboratories are reported here. Survey material LABORATORIES AND AUTOCLAVESIn all, 46 downward-displacement autoclaves in 27 laboratories were tested. Twenty-four of the autoclaves were vertical and cylindrical, and 22 were horizontal. Some were the responsibility of the PHLS Board, some of Area Health Authorities and, in one case, of a university department.Twenty-three of the laboratories were engaged, to a varying extent, in clinical microbiology and four were reference laboratories in special microbiology. MethodTests were made when the autoclaves were loaded, operated, and unloaded in their normal manner according to local custom and practice. Most temperature measurements were made with copper/ constantan thermocouples (02 mm diameter) insulated with polytetrafluoroethylene (PTFE) but unsheathed. Usually these could be led into the autoclave chamber between the door and the seal. They were inserted at those points in the load where experience had shown that performance was likely to be unsatisfactory as regards either sterilising or subsequent cooling. For example, when testing the processing of discarded cultures, a thermocouple was placed inside one of the cultures making up the load, and this was placed at the centre and about one-third of the way up the discard container. Similarly, when observing cooling times, thermocouples were placed in the largest units of volume making up the load since it was in these that cooling was likely to be most prolonged.Thermocouple signals were recorded on a suitable instrument; these were checked at intervals against a mercury-in-glass thermometer which had been certified by the National Physical Laboratory.Not surprisingly, the choice of sterilising temperatures or times among the laboratories was not uniform, thus making comparison difficult. Furthermore, distinction has to be drawn between the treatment given to discarded cultures and other materials that have to be sterilised to make them safe, and that accorded to culture media which require to be heated to the minimum temperature and for the time which experience will have shown 418

Section: Coolingmentioning

confidence: 71%

Autoclaving practice in microbiology laboratories: report of a survey. The Public Health Laboratory Service Subcommittee on laboratory autoclaves.

1978

“…Cooling is quicker if the medium is distributed in several small containers rather than in one large one. Everall and Morris (1975) autoclaved blood agar base in large and small containers under the same conditions. Colonies of Streptococcus pyogenes and Streptococcus pneumoniae were smaller when grown on medium from the large container which took a longer time to cool down; viable counts were similar on both batches of medium.…”

Section: Resultsmentioning

confidence: 99%

A comparison of brain heart infusion blood agar sterilized by filtration and heat on the growth of Neisseria gonorrhoeae.

Seth¹,

Wilkinson²

1976

SYNOPSISThe growth of Neisseria gonorrhoeae on brain heart infusion blood agar in which the base was sterilized by filtration has been compared with growth on the same medium sterilized by heat. Colonies were larger on the unheated medium, and autoclaving at 11 5°C or 121°C for 15 minutes was accompanied by a progressive decrease in colony size. Viable counts on the three media showed no difference in end points. Colonies on the unheated medium were usually large enough to be easily recognizable after overnight incubation.The routine medium used for -the isolation of Neisseria gonorrhoeae in this laboratory is brain heart infusion agar with 10% horse blood and vancomycin, 3 ,tg/ml, and colistin, 7 5 tg/ml. This usually gives a good growth of gonococci with colonies about 1-2 mm in diameter after incubation for 48 hours in 10% CO2, but over a period it was noticed that the colonies were extremely small, which made identification difficult. Enquiries suggested that the basal medium might have been left in the autoclave for an unduly long time. This led to an examination of the effect of the temperature of sterilization and sterilization by filtration on the colony size and density of growth of gonococci. Material and methodsBRAIN HEART INFUSION AGAR (OXOID CM 375) Of the dehydrated medium, 14-1 g was suspended in 267 ml of distilled water and left at room temperature for 30 minutes. This basal medium was autoclaved at 121°C for 15 minutes, cooled to 48°C, and 30 ml horse blood (Oxoid SR 50) and 3 mil of mixed antibiotic solution containing equal parts of vancomycin 0-06% and colistin 0.15% were added to give final concentrations of vancomycin, 3 ,ug/ml, and colistin, 7-5 ,ug/ml. After thorough mixing plates were poured. This medium is designated BH 121/15.

“…Attention has been drawn in the past to the lack of adequate instrumentation on many laboratory autoclaves and to the operator being forced to rely almost solely on his previous experience in the judging of cooling times (Everall and Morris, 1975). Equally, most laboratory autoclaves at present in use tell the operator little or nothing of the temperatures in the load which he is attempting to sterilise; although some loads, because of their shape and nature (for example, tissue culture tubes), may present particular problems of heat penetration of which he is quite unaware.…”

Section: Discussionmentioning

confidence: 99%

Sterilisation in the laboratory autoclave using direct air displacement by steam.

Everall¹,

Morris²,

Yarnell³

1978

Self Cite

SUMMARY A device using a steam injection funnel is described by means of which air can be driven quickly and surely from an autoclave load. It is simple and inexpensive, necessitates no changes in the working routine of a microbiology laboratory, and does not interfere with the operation of the autoclave in its normal mode.While it is accepted that air must be removed from the chamber of a laboratory autoclave and from the interstices of its load if sterilization is to be attained, the means of achieving this with certainty are usually not so well understood. For a variety of reasons the method of air removal so effective in a porous load autoclave is not suitable, and reliance is usually placed on downward displacement of the heavier air by the lighter steam. When the load consists of material for discard, contained in, say, a stainless steel bucket, sterilisation will depend on the production of sufficient turbulence in the steam in the chamber to dispel the air from the bucket. Without such turbulence it is hard to see why the heavier air should ever be displaced, so that much thought has been given to maximising turbulence by varying the position of the chamber steam inlet and the shape and size of the baffle plate; by removing the baffle plate (Scruton, M.W., personalcommunication 1975); bycareful selection of thediscardcontainers; andeven by providing them with holes permitting the more easy escape of the air (Gillespie and Gibbons, 1975