by Edouard Bastarache
A rapid survey of micro-organisms:
Micro-organisms may vary in size from 1 micrometer
(1µ = 10-6 meter) to several hundreds of micrometers.
- Viruses 10 to 300 µ
- Bacteria 1 to 10 µ
Family of Fungi
- Yeasts 2 to 12 µ
- Fungi 2 µ to x cm.
- Molds 2 µ to x cm.
- Lichens 2 µ to x cm.
- Algae 1 µ to x cm.
- Protozoa 2 to 300 µ
Micro-organisms are present everywhere in our environment:
in air, water, on surfaces, and on individuals of all kinds. They
are invisible and relatively unperceived. Micro-organisms are very
numerous: 1 gram of earth may contain up to 25 billions micro-organisms
(4 times the population of our planet).
Conditions for the development of micro-organisms
in ceramics products are related to the presence of nutritive elements
under the influence of temperature, moisture and pH of the medium.
Under favorable conditions, putting together these various factors,
one estimates that the population of micro-organisms can double
every 20 minutes... Therefore starting from a few micro-organisms
placed in a favorable medium, a true contamination can occur in
less than one day. The bacterial growth curve comprises a phase
of logarithmic increase followed by a stationary phase, then by
a phase of decline when food is suddenly lacking.
Needs Bacteria Molds and yeasts Light no no Medium pH Alcaline
Acid Temperature 20 to 40 °C 20 to 35°C Nutrients Nitrogen, Hydrogene,
Carbon Nitrogen, Hydrogene, Carbon
Presence of oxygen O2, or inorganics: SOx, NOx O2
Which are the signs of a microbial invasion in
an aqueous product?
In general, one observes changes, in the color
of the surface, viscosity, value of pH accompanied by odors and
gaseous emissions as well as variations in the behavior of the product.
One can determine the level and type of contamination by using indicators
containing gelose which make it possible to grow micro-organisms
quickly (48 to 96 hours), to quantify and identify according to
appearance, bacteria, yeasts or mushrooms.
Hygiene of manufacturing:
The hygiene of manufacturing often takes place
at the beginning of a bacterial contamination, on this matter it
is necessary to take care of the following points:
water generally used in the workshop and biocid (1) added,
to rinse work containers after cleaning them in order to destroy
To introduce a biocide at the beginning of manufacturing:
The biocid must be introduced into the product to be protected at
the beginning of the preparation of the aqueous phase (product to
be protected + workshop water + biocid). This is for ensuring the
protection of the product, but also for avoiding putting out of
order its properties (mainly viscosity), because the biocid pH can
modify those considerably.
To protect liquid organic additives by a biocide: Liquid
additives containing organic matter must also be protected by a
biocid in order not to act as contamination vectors during their
introduction into the preparations (i.e. . Liquid glazes in which
aqueous glue added CMC is introduced. This preparation of glue must
be treated by a biocid when manufactured to allow its preservation).
To entirely clean up facilities: To use disinfectant added
workshop water (i.e. sodium hypochlorite or bleach(2), an
effective and rather economic product, little polluting) to clean
containers having stored a contaminated product.
To use disinfectants during cleaning
To avoid complex and difficult to clean piping(dead lines)
To keep pipes and containers empty and dry when not in use
Beware of dust.
(1) Biocid: anti-bacterial and anti-fungic substance for
preventive use. The aqueous medium necessary to the implementation
of the majority of ceramic products must be protected by biocids
chosen for their compatibility with these and introduced at the
beginning of the aqueous phase taking into account their pH.
- Mixture of chlorinated and non chlorinated isothiazolon compounds,
pH 3.5 + / - 0.5
- Aqueous solution of ortho-phenylphenol potassium salts, pH
- 10% solution derived from oxazin with sulphur and nitrogen
heterocyclic compounds, pH 10-11
- Aliphatic compound with sulphur heterocyclic compounds, pH
(2) Bleach: Note that bleach is an excellent disinfectant,
but its high pH and its short duration effect make it a temporary
cleaning material not very compatible, as a stable protective biocide,
with ceramic products
The majority of disorders seen in liquid glazes
are due to bacterial activity which strongly modifies viscosity
and produces odors.
These disorders generally occur with natural products
containing organic matters (e.g. clays), under the effect of heat
and minerals concentration (High density of liquid glazes). For
sure, if the glaze contains glue, it is even worse because the organic
matters of the adhesives are very appreciated nutrients by bacteria.
There are often two distinct phases in the deterioration
of viscosity in the event of bacterial attack:
- Fluidification due to the consumption of the
components of the adhesive(glue) used in the glaze.
- Flocculation or thickening due to the acid dejections
of bacteria following the consumption of the organic elements of
glazes. It is then necessary to rectify this situation by correcting
the parameters of viscosity by adding adhesive or deflocculant in
the glaze containers.
2) In porous moulds:
The storage and maintenance of porous resin moulds
for casting under high pressure require an anti-bacterial and anti-fungic
action. The mould capillary network is rather large (10 to 20 µ)
and clay fines penetrate into it. Bacterial activity, in the mould
layer impregnated with fines, leads to the filling of the pores
not easily curable by chemical action(When this filling is on the
surface, the mechanical action of a high-pressure water spray makes
it possible to cure this problem). The best solution consists in
permanently having an anti-bacterial and anti-fungic preventive
action during the startup of the mould, for its cleaning and its
The role of biocides:
Biocides are products with anti-bacterial and anti-fungic
action. They are products for preventive action, generally used
at very low doses (high cost, toxicity) and their action on the
rheology of liquid glazes is not to be neglected (due to the biocide
The most current biocides are introduced at the
beginning of the preparation, in the mixing water at a rate of 0,05%
to 0,50% by weight.
In ceramics, biocides which are bactericide-fungicide
with broad spectrum activity, containing sulphureous aliphatic and
heterocyclic compounds of low toxicity, are often used.
Careful, in too low doses, these products will
not have the expected effect and will give a false sense of security
because they can under certain conditions favour a selective adaptation
on the part of the micro-organisms. In too large doses, they will
be too expensive, their toxic effects will be enhanced, and risks
of pollution are possible.
Some french companies specialized in the use of biocides in
- THOR S.A.R.L
- 325, rue des Balmes
- 38150 Salaise-sur-Sanne - FRANCE
- tel : 04.74.11.20.00
- fax : 04.74.29.65.35
- Givaudan Lavirotte
- 56, rue Paul Cazeneuve
- 69008 Lyon - FRANCE
- tel : 04.78.61.55.42
- fax : 04.78.61.55.94
- ZSCHIMMER & SCHWARZ - FRANCE
- 10, rue Saint-Marc
- 75002 Paris - FRANCE
- tel : 01.42.33.10.33
- fax : 01.40.26.23.81
- LAMBERT-RIVIERE S.A.
- 17, avenue Louison Bobet
- Val de Fontenay
- 94132 Fontenay-sous-bois
- tel : 01.49.74.80.80
- fax : 01.49.74.81.11
The vast majority of micro-organisms in nature
are saprophytes, i.e. that in the majority of situations they do
not cause infections unless there are particular host conditions
we have described further: they are the opportunistic infections.
Infections among patients whose defence mechanisms
are weakened, and that make individuals particularly susceptible
to infections. These infections are due to micro-organisms usually
which are not very pathogenic.
Defence mechanisms, physiological, immunological
can be disturbed, or a breach
made in them, by a disease, a traumatism, or by
procedures or products used for diagnostic or therapeutic goals.
Following are a few exemples.
2 - Antibiotics and host defence mechanisms reduction.
A treatment by antibiotics modifies the normal
flora of the skin, mucous membranes, digestive tract, and can lead
to colonization of these organs by new micro-organisms.
This colonization is inoffensive if it is not followed
by superinfection (invasion by indigenous germs, or micro-organisms
from the environment).
Predisposing factors are:
- Extremes of life
- Chronic infections
- Debilitating diseases
- Use of excessive amounts of antibiotics
- Use of broad spectrum antibiotics
3 - Modifications of anatomical barriers:
- Patients suffering from extensive burns
- Patients having undergone therapeutic or diagnostic procedures.
The normal anatomical barriers of these patients
are broken and they can not fight infections any more.
4 - Disturbances of cellular or humoral defence mechanisms:
Neoplastic and immunodeficiency diseases.
Treatments by radiotherap; Intensive immunosuppressive therapy, etc.
- Aplastic anemia
- Systemic lupus erythematosus
5 - Cytotoxic drugs:
Opportunist infections are then due to a severe
leucopenia (lowering of white blood cells).
6 - Corticosteroids:
Their systemic use disturbs many aspects of host
In addition, those who suffer from Cushing‘s syndrome
(increased secretion of an endogenous corticosteroid, cortisol)
have an increased susceptibility to infections.
Many thanks to Smart.Conseil
and Edouard Bastarache M .D. (Occupational & Environmental
Medicine), author of Substitutions
for Raw Ceramic Materials for the use of this article.
- The Biological and Clinical Basis of Infectious
Diseases, Shulman, Phair, Peterson & Warren, last edition.
- Vademecum Clinique du Diagnostique et du Traitement,
Fattorusso V. & Ritter O., last edition.