EVALUATION OF AIR CLEANER “Aero 600BM” BY DESINFINATOR LTD
FINAL REPORT OF MICROBIOLOGICAL EVALUATION
1. MATERIALS AND METHODS
Arrangements of tests
This evaluation has been performed in the laboratory of Jyväskylä Professional University, Dep. of Technology and Logistics, Rajakatu, Jyväskylä.
The first 35 tests (in the beginning of July) were intended in the optimization of testing equipment (Figure 1).
Following values of main
parameters were then chosen :
1. Air pressure for spraying of the microbial suspension from ”Spira” (est. 10% of the constant output pressure in the laboratory)
2. ATP concentrations (related to cell counts) of bacterial suspensions (200 +/-50 RLU)
3. Length of spraying period (3 min)
4. Length of sampling period (1 min)
5. Length of chamber cleaning by continuous flow of air between trials (min. 10 min)
The densities of bacteria in suspensions for aerosol generation
with ”Spira” were controlled with luminometric ATP Assay (BIOORBIT
1253 Luminometer by BIO-ORBIT Oy, Finland, and ATP
Biomass Kit HS by BIOTHEMA AB, Sweden).
Densities of fungal spores in suspensions were analyzed with
microscopical countings, respectively. Certain variation of densities
were needed for statistical purposes but ATP values of bacteria were
limited inside a range of tens to hundreds RLU units and count of
spores inside a range of tens per field (with 100* objective and 10*
ocular) in every case.
Figure 1. Schematic presentation of test equipment for the air cleaners.
All microbes (Table 1) were aerosolized into air cleaner during periods
of 3 minutes from suspensions in sterile 0.9% NaCl buffer solutions.
Average speed of air inflow into air cleaner during aerolization was 5
km/h. Air flow was stopped after aerolization and microbes were
immediately sampled on nutrient agar plates with 6-stage Andersen
sampler from the sampling chamber. Sampling periods were either 5
minutes (M. luteus) or 1 minute (other microorganisms). Plates were
then incubated for 1 day to 5 days, depending on the microbial species
involved, in +30oC.
Colonies from both total 6-stage set (bacteria and yeast) and from two
last stages (fungal spores) were calculated, and results were
transformed into units ”CFU/m3”.
A special care has been taken to avoid any bacterial rests of previous
tests in sampling chamber. The efficacy of cleaning measures was
confirmed by frequent control samplings (Andersen sampling and
contact plate analyses of the sampling after trials).
Test organisms
Test organisms were chosen with certain criteria. All bacteria have
environmental origin and are not real pathogens. Genus Bacillus
includes common airborne bacteria which are capable to produce very
tolerant cell forms called spores. Micrococcus is frequently found in air
sampling because it produces pigments which cover it against radiation
of sunshine. Escherichia is also a common bacterium, both in aquatic
environments and human colon, acting therefore as an indicator
organism of fecal pollution. Among fungi were Penicillium and
Saccharomyces chosen – first of them because its universal distribution as
an actively sporulating mould, the second one as an internationally
accepted yeast species for different types of testing.
Table 1. The test organisms used in the study.
| Test organism |
Type of organism |
Strain code1 |
Nutrient agar2 |
Incubation (d)
|
| Bacillus subtilis |
Gram-positive, aerobic, sporulating, rod-shaped bacterium |
E-97009T |
TYGA |
2 |
| Escherichia coli |
Gram-negative, facultatively anaerobic, rod-shaped bacterium |
ATCC 25922 |
TYGA |
1 |
| Micrococcus luteus |
Gram-positive, aerobic, pigmented, cocci-shaped bacterium |
E-93442T |
TYGA |
4 |
| Penicillium chrysogenum |
A common mould |
D-88381 |
MEA |
5 |
| Saccharomyces cerevisiae |
A common yeast |
B-62001 |
MEA |
2 |
1 Strain codes of culture collection by ATCC (E.coli) or by VTT (other organisms)
2 TYGA = Tryptone Yeast Extract Glucose Agar, MEA = Malt Extract Agar
Statistical methods
Referring the prerequisites set for Poisson-distributed colony count data,
statistically confirmed results were derived from samples with min. 30
colonies.
Reductions of microbial densities in air were calculated as follows:
Reduction (%) = 100 * (Cc – Ct)/Cc
Where Cc = cumulative colony count in ANDERSEN plate set when
treatment was OFF and Ct = cumulative colony count on ANDERSEN
plate set when treatment was ON.
Statistical significances of reductions were estimated by taking into
account one basic feature of Poisson distribution: average of repeats (C)
= variance of repeats. Confidence ranges were therefore estimated with
following equations:
C +/- √C gives confidence range of 66%
C +/- 2√C gives confidence range of 95%
Whenever colony counts reach the value of 30 in all tests, estimates of
reductions were also statistically more reliable because ”overlapping”
of confidence ranges of control and test results do not exist. Several
repeats of tests also helps to confirm reduction values by minimizing
the effect of random errors of the tests.
2. RESULTS
Reductions of microbial densities in air, treated with “Aero 600BM”, are
collected into following figures. Figure 2 shows percentual reductions of
every test organism, Figure 3 describes the microbial densities in air,
with and without UV and ionizator treatments.
Two clusters of reduction values are visible: one between 0% and 90%,
another near or even over 99%.
Reductions of test organisms after treatment with Aero 600BM
Number of tests per organism = 3
Figure 2. Percentual reductions of microbial densities with Aero 600BM.
|
EVALUATION OF Aero 600BM:
REDUCTIONS OF MICROBIAL DENSITIES IN AIR
B = Bacillus subtilis,
E = Escherichia coli,
M = Micrococcus luteus,
P = Penicillium chrysogenum,
S = Saccharomyces cerevisiae
diagonal lines = reductions 0%, 90% and 99%
|
Figure 3. Microbial densities of test organisms in air with/without
UV&ionizator treatments.
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