Paper on biocide incomplete growth inhibition *potentiating toxin production* in stachybotrys chartarum

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What doesn't kill it, makes it stronger!

Not a good omen for the biocide-users.

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Applied and Environmental Microbiology, July 2003, p. 3751-3757, Vol. 69, No. 7

0099-2240/03/$08.00+0 DOI: 10.1128/AEM.69.7.3751-3757.2003

Copyright © 2003, American Society for Microbiology. .

Effect of Plasterboard Composition on Stachybotrys chartarum Growth

and Biological Activity of Spores

Timo Murtoniemi,* Aino Nevalainen, and Maija-Riitta Hirvonen

National Public Health Institute, Department of Environmental Health,

Kuopio, Finland

Received 26 September 2002/ Accepted 7 April 2003

ABSTRACT

The effects of plasterboard composition on the growth and sporulation

of Stachybotrys chartarum as well as on the inflammatory potential of

the spores were studied. S. chartarum was grown on 13 modified

plasterboards under saturated humidity conditions. The biomass was

estimated by measuring the ergosterol content of the S. chartarum

culture while the spore-induced cytotoxicity and production of nitric

oxide (NO), tumor necrosis factor alpha (TNF-{alpha}), and

interleukin-6 in mouse macrophages was used to illustrate the

bioactivity of spores. The ergosterol content of S. chartarum

correlated with the number of spores collected from plasterboards. The

growth and sporulation decreased compared to that of the reference

board in those cases where (i) the liner was treated with biocide,

(ii) starch was removed from the plasterboard, or (iii)

desulfurization gypsum was used in the core. Spores collected from all

the plasterboards were toxic to the macrophages. The biocide added to

the core did not reduce the growth; in fact, the spores collected from

that board evoked the highest cytotoxicity. The conventional additives

used in the core had inhibitory effects on growth. Recycled

plasterboards used in the core and the board lacking the starch

triggered spore-induced TNF-{alpha} production in macrophages. In

summary, this study shows that the growth of a strain of S. chartarum

on plasterboard and the subsequent bioactivity of spores were affected

by minor changes to the composition of the core or liners, but it

could not be totally prevented without resorting to the use of

biocides. However, incomplete prevention of microbial growth by

biocides even increased the cytotoxic potential of the spores.

INTRODUCTION

Plasterboard is a commonly used building material, since it has many

favorable technical characteristics. It is composed of two paper

liners sandwiching a core, containing gypsum, starch, and some

additives. In the good practice of building design, construction, and

maintenance, the structures should remain dry. However, in cases of

moisture damage, the materials may be in contact with water for

prolonged times. In such conditions, plasterboard may provide suitable

nutritional conditions to permit the growth of microbes. The fungus

Stachybotrys has been especially shown to occur often on moist and

contaminated plasterboard (15). It has been suggested that the paper

liner of plasterboard favors Stachybotrys chartarum growth because of

its strong cellulolytic capacity (3, 10, 23). Our group has recently

shown that S. chartarum growth on plasterboards is due not only to the

liners but also to the core material, which plays an essential role

(20). The growth of S. chartarum is often associated with adverse

health effects in the occupants of buildings with mold problems (7,

14, 16). S. chartarum can produce several biologically potent

mycotoxins such as trichothecenes (11, 21, 22, 23, 34), which are

carried along with spores (24, 25, 27, 33). Our group has demonstrated

that microorganisms, when grown on wetted plasterboards, can produce

bioactive compounds capable of inducing a dose-dependent production of

major inflammatory mediators such as nitric oxide (NO), tumor necrosis

factor alpha (TNF-{alpha}), and interleukin-6 (IL-6) and capable of

evoking cell death in mammalian cells (19).

In order to identify the critical components of plasterboard which can

affect microbial growth with subsequent production of bioactive

compounds, we grew S. chartarum on plasterboards of different

compositions. The ergosterol content of S. chartarum culture on

plasterboards was used to quantify the fungal biomass while

spore-induced cytotoxicity and production of NO, TNF-{alpha}, and IL-6

in mouse macrophages were used to assess the bioactivity of spores.

MATERIALS AND METHODS

Plasterboards.

The plasterboards used in this study were prepared in cooperation with

plasterboard...

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See

http://aem.asm.org/cgi/reprint/69/7/3751