Safe disinfection: wash and paint!
Man himself is the principal source of bacteria and viruses living in the indoor air. Sneezing and cough release up to 40 000 pathogen-containing droplets into the air.
There is no need to enlarge upon the importance of the necessary disinfection in living premises and workrooms, in medical and child-care institutions, at the food industry and agricultural facilities. However, a few words should be said concerning the quality of disinfection and the safety of the existing disinfectants.
It is well known that man himself is the principal source of bacteria and viruses living in the indoor air. Sneezing and cough release up to 40 000 pathogen-containing droplets into the air.
These droplets in still air settle on the various surfaces and become an epidemic hazard. The number of grippe and hepatitis epidemic instances has grown over the recent years in Russia. And what is still more dangerous, tuberculosis instances increased in number, especially in penitentiary establishments.
This hazard is aggravated by a very high immunity of tuberculosis mycobacteria (TMB) with respect to the physical and chemical external conditions. The stability of TMB with respect to the disinfectants exceeds that of almost all the fungi types and is inferior only to that of spores and mould.
Cattle farms and poultry farms are sources of enormous number of pathogenic microorganisms, which precipitate to the surface, but which can also be found in the air as high as 3 km above the farms. Salmonellosis, brucellosis, and other diseases are very dangerous both for people and animals. Food industry facilities provide favourable conditions for microorganism propagation. Mould fungi, yeast, and bacteria can be most often found there.
Microbe strains are constantly changing, adapting themselves to the traditional disinfectants.
Difficult sanitary and epidemiological conditions, environment degradation, and a real threat of terrorist attacks with biological weapons require development of new general-purpose disinfectants and safe technologies for application of such chemicals. Modern disinfectants should be able to suppress rapidly and reliably various types of pathogenic microflora.
Prolonged antimicrobial action is also required. The procedure of the chemicals’ application should be easy: the chemicals should have no specific odour, be stable in long-term storage and during transport, cause no equipment derangement and treated material degradation. And, above all, they should be absolutely safe for humans and animals in the treated premises.
One of the motives for searching for new disinfectants is the adaptability of microflora to the traditional disinfectants. And, last but not least, is the requirement of environmental friendliness of these chemicals (i.e. their complete biological degradability into neutral chemical components under normal environmental conditions).
Active chlorine-containing disinfectants are highly volatile and inhalation-toxic. Therefore application of these disinfectants is permitted only in the absence of patients, and the personnel should make use of individual protection equipment.
On the traditional disinfectants
Unfortunately, most of the disinfectants traditionally used both in Russia and in other countries do not meet the requirements discussed above either in the respect of efficiency, or safety, or environmental friendliness. Thus, e.g., chemicals containing active chlorine (chlorinated lime, chloramine, and hypochlorides) are highly efficient against most of the microorganisms (with the exception of spores).
However, they have a pungent smell, irritate skin and mucous tunics of eyes and respiratory tract, and being the principal source of dioxins they pose a danger for the environment. Due to the high volatility and inhalation toxicity of active chlorine-containing disinfectants, their application in medical institutions is permitted only in the absence of patients; the personnel should use their individual protection equipment.
Oxygen-containing compounds (hydrogen peroxide, formalin, etc.), though environment-friendly and having a wide range of antimicrobial activity, are characterised by low activity against most of the microorganisms. Note that all the chemicals emitting active chlorine or oxygen are strong oxidants and therefore discolour and damage the treated materials and cause corrosion of the metal parts of equipment. They cause chemical burns when coming in contact with skin; their low stability makes their storage and transport inconvenient.
Disinfectants based on cationic surfactants such as quaternary ammonium compounds and low-molecular guanidine-containing compounds (e.g. chlorhexidine bigluconate) are more stable and safe.
Oxygen containing and quaternary ammonium compounds are characterised by low efficiency towards a number of microorganisms.
These chemicals are not oxidants, and the mechanism of their antimicrobial activity is different. However, these disinfectants have also essential drawbacks, such as relatively low efficiency and selectivity of antimicrobial activity. A number of papers criticising the quaternary ammonium compounds (QACs) have been published recently.
The grounds for criticism are relatively low efficiency against gram-negative bacteria, neutrality towards tuberculosis pathogens, picornoviruses, pseudomonades, and mucoid staphylococcus strains. Due to the low activity of QACs against gram-negative bacteria, especially pseudomonades, such bacteria even sometimes contaminate the working solutions of these disinfectants.
Such occurrences were described in the literature and happen quite often. Thus disinfection can have hazardous consequences and lead to the infection propagation in medical institutions. Apart from the natural stability of various microorganisms with respect to the QACs, some pathogens rapidly develop immunity to these disinfectants.
Application of PAGs for disinfecting is especially appealing because they have a unique combination of properties. These are the following: wide range of biocidal activity towards microorganism, low toxicity towards macroorganisms (humans and animals), environment-friendliness, and convenient physical forms for various applications.
Chlorhexidine bigluconate is widely applied outside Russia. However, there are data confirming low activity of this disinfectant against tuberculosis mycobacteria, some of the gram-negative bacteria, yeasts, dermatophytes, and especially against Pseudomonas aeruginosa.
Viruses are immune to chlorhexidine bigluconate as well as to QACs. Another essential drawback of this disinfectant is that people with high skin sensitivity develop allergic reactions to this agent. Besides, this chemical is not produced in Russia and its availability for Russian commodity producers is limited due to its high cost.
Thus creation of new disinfectants becomes increasingly urgent. New biocide chemicals having enhanced features should be developed so as to meet the requirements of environmental and medical safety.
New concept: “PAG”
Disinfectants based on polymeric biocides called polyalkylene guanidines developed by the Institute of Ecotechnologies are very perspective in many respects. The new family of chemicals includes water-soluble disinfectants Biopag and Phosphopag, organosoluble chemical Septopag, and also a series of biocidal paints with a general name Biokrapag.
Application of PAGs for disinfection is especially attractive because they combine a number of remarkable properties. These are the following: wide range of biocidal activity against microorganisms, low toxicity for macroorganisms (men and animals), environmental friendliness, and physical properties making their application convenient and easy. Further we discuss the properties of PAGs in more detail.
Stability of PAG-based disinfectants and their long-term antimicrobial activity is the unique feature, which is due to the polymeric structure of these chemicals and their ability to form an impalpable film on the surface of the treated objects.
Efficiency and long-term activity. PAGs exhibit a wide range of antimicrobial activity against gram-positive and gram-negative bacteria (including tuberculosis mycobacteria), viruses, fungi of the Candidae family, dermatophytes, moulds, etc. PAGs also have deodorising properties. They belong to the limited family of biocides that are active against both aerobic and anaerobic microflora.
PAGs are effective against most pathogenic microorganisms that cause suppurative, respiratory, intestinal, venereal etc. diseases of humans. They also suppress many pathogens causing animal diseases (salmonellosis, listeriosis, brucellosis, tuberculosis, etc.), have fungicidal, insecticidal, pesticidal, and algaecidal properties.
Many specialised research institutions performed studies of biocidal activity and toxicity of PAGs: Scientific Research Disinfectology Institute of the Public Health Ministry of Russian Federation (PHM RF), N.F.Gamalei Research Institute for Microbiology and Epidemiology, Institute of Medical and Biological Problems, Moscow state university for Applied Biotechnology, Central Research Institute for tuberculosis of Russian Academy of Medical Science, Institute for Physiotherapy of the PHM RF, Biophysics research institute of the PHM RF (branch No.5), etc.
A large number of disinfectants are offered in the market nowadays. Let us see, however, what features should modern efficient disinfectants have?
These studies have shown that the antimicrobial activity of PAGs is as high as that of the best Russian- and foreign-made disinfectants, including QACs and chlorhexidine. In some respects (e.g., activity against pyocyanic infection, tuberculosis mycobacteria, viruses, legionellas) PAGs are even better than the latter.
Unique property of PAG-based disinfectants is their stability and long-term antimicrobial activity. This is due to the polymeric structure of the chemicals and their ability to form a thin biocidal film on the surface of the treated objects. The antimicrobial activity of PAGs can last as long as eighteen months (but not less than several months), whereas the activity of traditional volatile disinfectants lasts several hours (up to several days at best).
Toxicity and hazard. Thanks to their polymeric structure, PAGs have lower toxicity than their closest analogue among the low-molecular compounds, namely, chlorhexidine bigluconate, to tell nothing about other highly toxic chemicals used as disinfectants. According to the classification over the acute toxicity parameter, PAGs belong to the 3rd class of moderately toxic compounds for oral exposure, and to the 4th class of low-hazard compounds for skin exposure.
Their fumes are also low-hazard in case of respiratory intake; they do not irritate mucous tunics. These chemicals in concentration recommended for disinfection cause neither allergy, nor sensibilising effect, they do not accumulate in the organism, and do not produce long-term effects.
Water solutions of PAGs do not irritate skin; on the opposite, they facilitate healing of scratches and fissures. Already 5 minutes after applying PAG solution to hand skin (which was previously specially infected with pathogens) only single microorganisms remain active. This effect lasts at least 5 hours.
Environmental safety of PAGs is one of the most important advantages favouring their wide application.
The grounds for the safety of PAGs are as following. They do not contain heavy metals, active chlorine or other hazardous chemicals.
Physical properties and solubility. PAGs are thermally stable (up to ca. 200°C) colourless and odourless solids well soluble in water. Disinfectants Biopag-D and Phosphopag-D based on these chemicals are produced both in solid form and in concentrated (20%) solutions. Working solutions (0.05 - 5 %) are prepared by dilution of the concentrated solution.
The chemicals and their solutions are very stable, they retain their biocidal activity during a long-term storage (test storage period was 15 years for solid biocides, and 1 year for working solutions).
The Institute of Ecotechnologies has developed a technique for application of PAGs as biocidal additives to ordinary paints (nitrocellulose, and pentaphthalic enamels, water emulsion and oil paints). Biocidal paints of the Biokrapag series can ensure long-term (at least 1 year) antiseptic properties of the treated surfaces.
Organosoluble disinfectant Septopag has its additional advantages: it forms a waterproof biocide coating. This is due to the chemical bond between the biocide molecules and the film-forming varnish that prevents the biocide from being washed off from the varnish coating by the water condensed on the walls in moist rooms. This also allows washing the surfaces with detergents. The activity term of such coatings is at least 18 months, so that no additional disinfection is necessary during this period. This saves both disinfectants and labour inputs.
Application of the disinfectants. Water-soluble disinfectants Biopag-D and Phosphopag-D can be used for disinfection of indoor surfaces, linen, furniture (without upholstery), equipment surfaces, sanitary equipment, nursing utensils, household equipment, and single-use medical equipment (before disposal).
These chemicals are efficient against pathogens of bacterial (including tuberculosis), viral, fungal (candidoses and dermatophytes) aetiology. They can be applied in medical, rehabilitation, and child-care institutions, at public facilities, and in public catering establishments.
Organosoluble disinfectant Septopag as well as biocidal paints of the Biokrapag series can be used for antimicrobial coating of walls in medical and rehabilitation institutions, at public facilities, as well as in penitentiary establishments, evacuation centres and other crowded places. These biocides are effective for prophylactics of infectious diseases of bacterial (including tuberculosis) aetiology, candidoses, and also for mould prevention.
Biokrapag paints have a wide colour spectrum, good physical and mechanical characteristics and stability of the paint coating in different climates (at least 4 years in normal climate, 2 years in tropical climate).
This qualifies them for application in construction and maintenance of living premises and industrial facilities. Septopag forms a transparent coating that does not change the appearance of the treated surface. It can be applied over oil paint, wood, brickwork, concrete, and plastic for antimicrobial protection and mould prevention during the term between the regular repairs.
This is especially important in case of high humidity indoors, as well as outdoors under the direct action of atmospheric precipitates.
Being low-toxic compounds, Biopag-D and Phosphopag-D can be applied in the presence of people, e.g. in medical institutions for the maintenance and final disinfection of surfaces, sanitary and nursing equipment, linen, and medical tools.
These disinfectants are indispensable for cleaning in medical, rehabilitation, and childcare institutions, and also for prophylactic disinfection of premises, equipment, linen, and utensils in public catering facilities. Biopag-D and Phosphopag-D can be also successfully used in household, food industry, food carriers, public facilities, and transport.
Leading research associate
of the Institute of Ecotechnologies.