Effects of Biocides on antibiotic resistance

2. What are the main uses of biocides?

• 2.1 What are the main applications for biocides in health care?
• 2.2 In which consumer products are biocides used?
• 2.3 How are biocides used in the food industry?
• 2.4 How are biocides used in animal husbandry and in products of animal origin?
• 2.5 How are biocides used in water treatment and industrial applications?

2.1 What are the main applications for biocides in health care?

The proper use of biocides is crucial in preventing and controlling the spread of infectious diseases in hospitals and other health facilities. Biocides are used to decontaminate the skin of patients and health professionals, any surfaces that could harbour bacteria, and any instruments in contact with patients. Biocides are also used as antiseptics to treat infections in mucous membranes and damaged skin.

Disinfectants are classified as low, medium or high-level disinfectants, depending on how many types of micro-organisms they kill. High-level disinfectants that are applied for long periods of time can inactivate all micro-organisms and are called chemical sterilants.

Table 3: Biocides approved by US-FDA for health care settings, or registered by the US-EPA

The level of disinfection in medical facilities usually depends on the degree of infection risk involved:

1. Surgical instruments, needles, catheters and any other devices that enter the patient’s tissues must be sterile. The best way to achieve this is to use steam under pressure but instruments that cannot be heated need to be treated with chemical sterilants instead.
2. The risk of infection from devices that come into contact with mucous membranes or damaged skin, such as endoscopes and tubes used in anaesthesia, is not as high but these should still be sterilized to provide the widest margin of safety.
3. Stethoscopes, bedpans, blood-pressure cuffs and similar devices pose little risk of transmitting infections and can be treated with low-level disinfectants. Biocides are used to disinfect these as well as surfaces that are near patients such as floors, walls, tables, bedrails and screens.

There is evidence that surfaces can act as a source of contamination and may contribute to the spread of infections such as MRSA and Clostridium difficile. However, the routine use of biocides to treat these surfaces is controversial. Antimicrobial wipes are increasingly common in hospitals but their inappropriate use, for instance cleaning several surfaces with the same wipe, can cause problems. There are new products such as shower curtains and trolleys that incorporate biocides in their surfaces. In some health facilities they have reintroduced the use of metals for surfaces that are touched frequently hoping to reduce the spread of infections, but it is difficult to evaluate precisely if these have had any effects.

Biocides are also used to kill or reduce the numbers of harmful micro-organisms on the skin of patients and medical staff. The most common method of disinfecting the hands of medical staff is the use of alcohol-based hand-rubs because they are easy to use and effective. In addition to alcohols, common disinfectants and antiseptics include quaternary ammonium compounds and triclosan, and some preparations combine several substances. More...

Table 4: Commonly used skin disinfectants and antiseptics

2.2 In which consumer products are biocides used?

Many consumer products contain biocides but the major sources of exposure in homes are the regular use of cosmetics and wipes, cleaning products, some toothpastes, laundry detergents, pet disinfectants and general disinfectants.

Biocides are added to cosmetics and personal care products to prevent micro-organisms from growing on them. In the EU, the use of 57 different chemicals is allowed for this purpose. Besides these chemicals, cosmetics often contain other non-regulated antimicrobials.

Many of the substances that are added to household products to improve their properties also kill bacteria. This is for instance the case of surfactants that are included in detergents to decrease the surface tension of water enabling the detergent to better penetrate and loosen dirt. Cleaning products and laundry detergents contain preservatives and disinfectants but the use of these substances in household products is not regulated. Surfaces coated with biocides have been developed recently. These biocide-treated surfaces include several active ingredients such as triclosan and metallic ions.

The biocide triclosan is used in consumer products and textiles, notably in cosmetics, toothpastes and products for dental hygiene, and in deodorants, but also in cleaning products, paints, plastic products and in clothes to avoid unpleasant odours produced by decomposition of sweat. More...

2.3 How are biocides used in the food industry?

Biocides are widely used in the food industry as disinfectants and food preservatives.

They treat production plants, processing areas and food containers to control the microbial growth in food and drinks. They are also commonly used to disinfect equipment, containers, surfaces or pipes associated with the production, transport and storage of food or drink, including drinking water. In the EU, the use of disinfectants in the food-processing industry and in the treatment of drinking water is regulated.

Drinking water is treated with biocides to eliminate any harmful micro-organisms at the water works and in the distribution system to ensure that the water that reaches the consumer is fit to drink. For the last century, chlorine has been added to the water before it enters the waterworks for treatment. Ozone and chlorine-dioxide are now more commonly used for that purpose to avoid the creation of unwanted by-products. In some countries, disinfection in the distribution system is always performed with chlorine or chloramines.

Biocides are added as preservatives to foodstuffs to prolong their shelf-life by protecting them against deterioration caused by micro-organisms. They are considered as food additives and their use in the EU is regulated. More...

2.4 How are biocides used in animal husbandry and in products of animal origin?

Proper cleaning and disinfection play a vital role in protecting food animals from diseases that they could pass on to humans. Although the use of biocides in breeding and raising livestock is regulated in each Member State, there are no exact data on the amounts of biocides used. It appears that each farm only uses few types of disinfectants and the same brand may be used for extended periods of time.

Biocides have four main uses in animal husbandry:

• Cleaning and disinfecting farm buildings, particularly between batches of animals as well as decontaminating ponds and equipment in fish farming.
• Creating barriers against bacteria, such as foot dips outside animal houses, and disinfecting vehicles and materials during outbreaks of infectious diseases.
• Preventing infections through direct application to animal skin, for instance to clean the udders of animals used for milk production
• Preserving specific products such as eggs or semen.

Table 5: Major biocides used in veterinary medicine and animal husbandry

Moreover, biocides are used to protect animal feed from deterioration by micro-organisms. They are considered as food additives and they are not allowed without a safety assessment.

Chemicals used in animal production could leave residues in milk, meat or eggs. Therefore, before antimicrobials are allowed, they are tested to see if they are safe. This includes an assessment of the possible effects of these residues on the bacteria that naturally live in the human gut.

Biocides can be used to kill bacteria on the surface of animal products such as poultry and other carcasses. This practice is not authorized in the EU so far. More...

2.5 How are biocides used in water treatment and industrial applications?

Biocides are used in industry and in the treatment of drinking water and wastewater, but the quantities involved are not known.

Many wastewater treatment plants, especially those near the sea, include a final step of disinfection with chlorine. However, this practice is being increasingly questioned because the by-products are toxic to sea animals and because it can lead to false-negative tests, where water samples appear clean but in fact contain viruses and other micro-organisms that survive chlorine and may cause outbreaks that can affect swimmers or consumers of sea-food.

Disinfectants are intensively used in cooling towers since some harmful bacteria such as Legionella might otherwise thrive in the warm water and be spread through air by tiny water droplets (aerosols) released by the cooling tower. After use, these biocides may reach the environment either as aerosols or in the wastewater.

Biocides are increasingly added to building materials, antimicrobial surfaces and other products, to stop them becoming encrusted with moulds or other micro-organisms; but the quantities used are unknown. Some of these surfaces release small amounts of biocide progressively into the environment and this could kill certain types of bacteria in the immediate vicinity, leaving only resistant-bacteria. Therefore, biocide aerosols could have a role in emerging resistance of bacteria to biocides or antibiotics, but this point has not yet been investigated. More...