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Activity of Biostatic Agents on the
Microbial Colonization in
Particle Filter
Department of Comparative Morphology and Biochemistry,
University of Camerino, Italy
EKASTU Safety GmbH, Stuttgart, Germany
Introduction
It is well known that atmospheric air acts as a carrier responsible for the non uniform distribution
of the airborne microbial cells and/or sporal forms, the concentration of which is subject to strong
variations according to the habitat to man. The need to control the particulate has lead to new
attention towards the media types and techniques for the filtration and depollution of the air
especially where the absence of polluting particles and micro organisms are required. Recent
researches have demonstrated that some micro organisms, particularly certain fungi, are capable of
colonizing substrates in situ. The efficacy of particle filters in retaining particles, including micro
organisms, has been well studied and other studies prove that filter matrix can represent a feeding
source for bacteria and fungi and it can become a colonization site. Moreover, the
organic/inorganic material settled on the panel after air filtration contributes to the microbial
growth, that inevitably leads to a loss of filter efficacy and to a probable filter deterioration (bio
oration) with the eventual release of micro organisms, both vegetative and spiral forms and the
probable emission of Volatile Organic Compounds (VOCs) produced by the microbial metabolism
on the downstream site.
The aim of this study was to verify the real microbial colonization of test strains on microfiber
glass-acrylic filter media, both before and after a significant utilization time. We then tested some
antimicrobial agents added to the filters, which are able to reduce the microbial colonization, in
order to preserve the efficiency, so excluding them as potential risk agents for the air quality.
Materials and Methods
Studied Filters
Untreated Filter
Filter
used
new
BIOSTOP Filter
Microbial Growth on
Filter
50 l of each test microbial
strain spread on the sections
( 9 mm). Incubation at
25°C, humidity of 90%
Filter Integrity
Verification
-Sections (  48 mm ) spread with
50 l of a mixed culture.
Incubation at 25°C, humidity of
90%
-20 l/min air flow aspiration for 5
min through used sections and
count of released colonies
Microbial Growth on Filter Samples
TEST
ATCC*
Strains
Bacteria
B. subtilis
E. faecalis
E. coli
M. luteus
P. aeruginosa
P. aeruginosa
Salmonella sp
S. aureus
S. aureus
S. bovis
BIOSTOP Filter
Untreated Filter
unused
used
unused
used
6833
29212
11775
49732
27853
90207
29890
25923
6538P
48147
+
++
+
+
+
-
++
+
++
++
++
+
+
+
++
-
-
+
+
+
16404
10663
14053
10291
18803
20369
++
+
+
+
+++
+
+
+
+
++
+
+
+
+
+
Fungi
A. niger
B. capitatus
C. albicans
C. albicans
C. laurentii
Penicillium sp.
*
+
++
+++

ATCC American Type Culture Collection, Rockville, MD, USA
no Colony
< 5 Colonies
> 5 <20 Colonies
> 20 <80 Colonies
Untreated filters showed a growth of microbial strains both in new filters and
more abundantly, in used ones. BIOSTOP Filters treated with antimicrobial
gave only a slight evidence of fungal colonization.
Release Curves of Bacteria and Fungi from BIOSTOP
and Untreated Filter at Different Incubation Times
Numbers of Colonies
Bacteria + Fungi
18
16
14
12
10
8
6
4
2
0
Untreated Filter
BIOSTOP Filter
0
7
17
27
37
47
57
67
77
87 100
Incubation time in Days

Untreated filters showed a growth of microbial strains both in new filters and,
more abundantly, in used ones. BIOSTOP Filters treated antimicrobial gave only
a slight evidence of fungal colonization.
Test Micro Organisms Yielded on Filter
Sections
BIOSTOP Filter
used
new
Untreated Filter
Bioporation Testing Apparatus
20 l/min air flow
Untreated
Filter after 27
Days of
Incubation
BIOSTOP
Filter after
27 Days of
Incubation
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