By ; Microsearch Laboratories
www.micro-search.co.uk

1.0 Introduction

Matrix cleaning systems Ltd are in the business of providing technological solutions for the sanitisation of industrial and medical environments.  This report details the results and findings of laboratory trials relating to the performance of the SDV8000 and SDV4500 floor cleaning systems.  Both of these systems are intended for cleaning floor surfaces.

These devices consist of a mobile steam generation unit and waste collection unit to which a tube assembly is connected through which steam is delivered to a work head and by which a vacuum suction system removes treated debris from the working environment. Debris is generated during use and is collected in a waste vessel, which is in tended to be maintained in a sanitary state by the addition of a disinfectant agent.

Figure 1; The SDV8000 Steam generation unit

The objectives of the work reported here were as follows:

• To quantify the antimicrobial performance of each device against a range of medically significant organisms with respect to the cleaning of soiled surfaces.
• To assess the performance of a range of candidate antimicrobial substances with regard to the sanitisation of the debris collection vessel.
• To determine the existence and quantify the nature of any undesirable cross contamination events during operation.
• To describe and provide measurement of the temperature dynamics inside and below the work head treatment area during usage

2.0 Conditions; Floor Cleaning trials

Assessment of Test Surfaces and Debris reservoir

The test surface consisted of a 2-m2 sheet of stainless steel plate (6 mm thick) onto which 48 X 25 cm2 numbered quadrants had been etched.  This etched matrix established the sampling template for recovery of organisms.

Contamination of the test surface was achieved by the application of an organic matrix containing   suitable numbers microorganisms or spores. The organic matrix was manufactured with ¼ strength Ringers or Thigycollate solution (in the case of Clostridia) containing 3 % Albumin (Cohn fraction) and 2 % Lecithin. After addition of challenge culture the matrix was mixed and applied by roller to the test surface after which the system was allowed to dry for 24 hours at ambient temperature. In this manner a dry film of microbiologically contaminated debris was obtained on the test surface. All challenge organisms were applied in monoculture or as groups of types within the same genus.

At the end of a cyclic cleaning cycle sequentially involving all test organisms 150 ml of  the process liquor was recovered from the waste  chamber.  After creating a 1/10 dilution  ( in  Universal quenching agent )  and creating appropriate dilution series, the analysis of residual contamination was  determined as described above.

3.0 Recovery of organisms

Attempts to recover organisms from the test surface were conducted prior to and after treatments involving steam cleaning.

For each sampling effort 6 X 25 cm2   quadrants were designated by random number.  Each designated area was swabbed with a transport swab pre-moistened in either ¼ strength ringers or Thioglycollate medium (Clostridial recovery).

Charged swabs were vortexed (1 minute) in either ¼ strength ringers or Thioglycollate medium prior to the creation of a decimal dilution series.  The recovery effort proceeded by spiral plating (50 ul log) of the each member of the dilution series on an appropriate agar for the challenge organism.  Additionally   recovery from the 1 /10 test dilution of treated surfaces was achieved employing membrane filtration followed by whole membrane incubation on the appropriate agar and a non selective medium.  Standard incubation conditions applied. Confirmation of isolates was achieved by biochemical typing, serology and where appropriate by genomic analysis.

In the case of the Debris reservoir liquor, after creating a 1/10 dilution  (in Universal quenching agent) and creating appropriate dilution series, the analysis of residual contamination was determined as described above.

4.0 Measurement of operational characteristics

Temperature measurements were conducted on both the test surface and in the steam delivery environment of the cleaning head.

In the case of   surface measurements thermistors were arranged through holes cut in a section of test surface 1 meter long and 0.75 meter wide. These were arranged perpendicular to the line of motion to of the cleaning head at 50 cm intervals Thermal measurements were taking during reciprocating motion of the cleaning head over the test surface for a period of 1 minute.

In the case of the cleaning head, a thermistor was located at the geometric centre of the device and a further two thermistors were located at points where steam vented from the delivery tube.

Data was recovered by data logger at a sampling rate of 3 measurements per second.

In this manner we able to measure the exit temperature of steam from the delivery tube and that of the internal environment of the cleaning head.

Measurement of the thermal dynamics of steam treated surfaces was conducted as a separate trial from the challenge work and the performance with and without vacuum on is reported

5.0   Form of Use of the Matrix Steam Cleaning  devices

In all trials the machine under evaluation was charged with tap water. The device was powered up and allowed to stabilise until the steam ready indicator actuated. All trials surface challenge trials were commenced with an empty, sanitised debris bucket charged with either 100 mls of 10 % solution of Aqualin ECO F or dry but containing   4 X 20 gram Sodium dichloroisocyanurate tablets.

Trials were conducted on challenged surfaces both with vacuum in operation.

For any one test organism, a total of four contaminated surfaces were examined.  Each surface was cleansed with the steam device according to the manufacturers instructions and each replicate was performed by the same operator.   In practise the surface was treated until it was visually clean  which  on average   accounted    60 seconds treatment under these conditions.

6.0 Test organisms

All organisms employed in this work were obtained as clinical or industrial isolates.  During the trial working cultures were maintained on non selective agar slopes under appropriate conditions of storage.  

Spore stocks of the Clostridium difficle strains were generated by recovery of the sediment from exponential liquid cultures which had been shocked with 96 % Ethanol for 50 minutes

Microbial suspensions intended for challenge work were prepared by recovery of cell mass from mid exponential liquid cultures after centrifugation.  Cells pellets were washed and re-suspended in Ringers solution prior to adjustment to the desired cell density by Nephalometry.

7.0 Environmental monitoring

During the treatment of contaminated surfaces air monitoring was conducted on agar surfaces employing an impaction device at a sample rate of 100 litres/atmosphere per minute. Additionally open agar plates were radiated around the axes treatment area commencing at 0.1 metres from the periphery of the treatment area   and then at intervals 0.25, 0.5, 0.75 and 1 metre.  These test were performed to detect any environmental cross contamination due to steam-generated aerosols during steam/vacuum operation

8.0 Results

During the treatment of contaminated surfaces air monitoring was conducted on agar surfaces

Table 1

Mean thermal performance in the deliver head data of the SDV8000 device and SDV4500 device during standard use.

Table 2

Mean thermal performance of a stainless track during standard use of the SDV8000 and SDV4500 device during standard use with and without vacuum on.

Table 3

Performance of the SDV8000 in the decontamination of challenged stainless steel surfaces by the application of steam and vacuum processing

Table 4

Performance of the SDV4500 in the decontamination of challenged stainless steel surfaces by the application of steam and vacuum processing

Table 5

Microbiological status of the   contents of the  debris reservoir  after 13 sequential cleaning  cycles  of the  test environment involving  each test culture

Table 6

Microbiological status of the peritreatment environment during treatments with the SDV8000 and SDV4500 devices.

9.0 Discussion

In this trial we have examined two steam cleaning devices , manufactured by Matrix Cleaning Systems Ltd under laboratory conditions. These trials were conducted in “dirty” conditions where the challenge  organisms were present in high numbers and the matrix was presented as a dry  film on a stainless steel surface.

The goals of the trial included assessment of  environmental reduction of the microbiological challenge together with an understanding of the  thermodynamics  involved. Additionally we sought to gain some understanding of  the impact of operating each device upon the environment peripheral to the cleaning area

Cleaning systems based on steam generation  appear to work  by  the creation of  constantly replaced pressurised  cloud of hot saturated water vapour under a cleaning head.  As a general model the impingement of this  vapour  and direct steam impact on to surfaces  together with the physical action of the head brushes serve to solubilise organic and microbiological materials. 

With earlier generations of steam cleaning devices it was anticipated that the model proposed  above would provide a regime capable of  satisfactory levels of  antimicrobial  sanitisation.  However, common criticisms of devices not offering the vacuum option involved  the possible generation  of microbiologically contaminated aerosols and sub lethal thermal dosing of organism.  Our data suggests that under the conditions of trial no measurable, pressure generated  cross contamination of surfaces outside the treatment area were occurred . ( Table 6). We did record low levels of  atmospheric recovery of  Aspergillus niger  however this organism  is know to be present in the normal atmosphere of the test environment.

We believe there is strong evidence to suggest that  the introduction of  the vacuum feature  in the Matrix  devices  strategically overcomes the  limitations of similar surface sanitising devices which  rely solely on steam doses.

Our results indicated  the range of operational vent temperatures achieved, by the two Matrix devices studied,  range between  99.3 ‘ C and 99.7 ‘c.  These latter data correspond to the generation  of core vapour temperatures ranging from 96.2 ’C to 98.2 ‘C. Although we were unable to measure dwell time  of microbiological debris in the vapour cloud  nor assess any protective effect due to lecithin present, it is not unreasonable , assuming a dwell time of 0.1 seconds or greater, to  postulate that any vegetative cells ( other than those of extreme thermoduric organisms or some bacterial spores) present within the cloud would be inactivated with a high degree of efficiency. 

During  the generation  of the steam and vacuum  effect  we have  recorded treatment surface temperature maxima  of circa 80 ‘c  under   standard conditions of use  with the temperature minimally falling to circa 62 ‘C   within 5 seconds after the  dosage head  had  passed any single measurement point.  Overall we assessed the time of dosing any of single surface treatment point  at a temperature above 72’C  to be  minimally  circa  11 seconds and  circa  6 seconds  for temperatures at or above 80’c. Again  conditions likely  afford Pasteurisation of  non thermoduric vegetative cells  and bacterial spores.

Considering the observed thermal performance data,  we postulated that surface treatment trials would be successful in the removal of  all vegetative microbial forms ( and fungal spores)  employed as challenge organisms during these trials. Our data ( tables 3 & 4)  confirms this prediction  where in a greater  than  99.999  % removal of all vegetative cells  was repeatedly recorded at the treatment surface. However  it is commonly accepted that the spores of Clostridium difficle  under optimum conditons of treatment require exposure to  conditions of  80’C  for a period  10 minutes  to achieve satisfactory levels of log reduction. Our data suggests that  > 99.999 spore removal was achieved by each device even though  neither device under standard conditions of use would deliver a thermal treatment equivalent to 80’c  for 10 minutes. 

With respect to the performance observed . in the  environmental removal of Clostridium difficle spores  we suggest  that, not withholding any degree of thermal lethality, the contribution of the nebulisation of  spores by the effects of steam vapour,  coupled with that of vacuum removal into  a sanitising solution , is a distinguishing key operational characteristic of the Matrix devices evaluated  during this trial.

These observations are corroborated  by  the work conducted on the  microbiological status of the debris bath ( Table 5)  where in our data clearly shows survival  and the development of  populations of some challenge organisms ( including Clostridium difficle) ) in the debris reservoir in the absence of an effective biocide.  Relatedly  our data  suggests that both antimicrobial agents studied were capable of satisfactorily  maintaining an acceptable level of sanitation in the debris reservoir.

10.0 Conclusions

Within the conditions and constraints of this laboratory trial both the SDV8000 and the SDV4500 have met the criteria assigned  for successful performance.

In these trials both devices consistently achieved  a visually clean post treatment surface with > 99.999 % removal of all challenge organisms under dirty conditions.  All test data indicated that the antimicrobial treatments  applied  to the debris reservoir  achieved satisfactory performance

These objectives were achieved with no measurable level of   microbiological contamination
of peritreatment surfaces  or  the immediate atmosphere.

The data obtained  robustly supports the  premise that steam cleaning combined with  vacuum removal is an effective technology.

On the basis of the results reported we are pleased to recommend both  devices  as candidates for  floor cleaning  solutions in both  the medical and  industrial environment.

It anticipated that equivalent levels of  performance will be obtained in imminent Clinical and Industrial trials which will afford the opportunity for  cross laboratory verification and further understanding of this cleaning strategy.

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                      D.O’Connor  B.Sc. Ci.Biol M.I.F.S.T.