A rapid survey of micro-organisms:

Micro-organisms may vary in size from 1 micrometer (1µ = 10-6 meter) to several hundreds of micrometers.

Types Size

• 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.

Micro-organism's needs

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:

Treated water:

water generally used in the workshop and biocid (1) added, to rinse work containers after cleaning them in order to destroy residual micro-organisms.

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.

Exemples:

• Mixture of chlorinated and non chlorinated isothiazolon compounds, pH 3.5 + / - 0.5
• Aqueous solution of ortho-phenylphenol potassium salts, pH > 13
• 10% solution derived from oxazin with sulphur and nitrogen heterocyclic compounds, pH 10-11
• Aliphatic compound with sulphur heterocyclic compounds, pH 3-5

(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

In ceramics:

1-In liquids:

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 storage.

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 pH ).

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 ceramics:

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.

Opportunistic infections

1-Definition:

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:

Examples:

1. Patients suffering from extensive burns
2. 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.

Examples:

• Leukemias
• Myelomas
• Aplastic anemia
• AIDS
• Gammapathies
• Systemic lupus erythematosus
• Etc.

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 defence mecanisms.

In addition, those who suffer from Cushing‘s syndrome (increased secretion of an endogenous corticosteroid, cortisol) have an increased susceptibility to infections.

References:

1. The Biological and Clinical Basis of Infectious Diseases, Shulman, Phair, Peterson & Warren, last edition.
2. Vademecum Clinique du Diagnostique et du Traitement, Fattorusso V. & Ritter O., last edition.

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