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Photo: Centers for Disease Control and Prevention

Effect of disinfectants on bacteria developing resistance

Food safety Health and diseases

Thursday 16 Jan 14

Biocides, e.g. disinfectants, are used to fight disease-causing bacteria in hospitals and in the food industry, as well as to fight pests and fungi. A PhD project at the National Food Institute, Technical University of Denmark, has investigated whether the use of biocides may contribute to bacteria developing resistance towards antimicrobial agents, either by increasing the spread of resistant genes or by mutating.

Biocides are largely used to fight and control health-damaging bacteria in e.g. hospitals and food industry in order to achieve a satisfactory hygiene level. Knowledge about possible unwanted side-effects, which the use of biocides may cause, is relatively limited.

In her PhD thesis work at the National Food Institute, Maria Amalie Seier-Petersen investigated whether commonly used biocide compounds may affect the development and spread of antimicrobial resistance in bacteria and whether biocide resistance occurs in bacteria which, potentially, are harmfulhuman health.

Bacteria from pig farming were investigated

The project investigated, amongst others, whether different biocides may result in bacteria developing resistance to antibiotics by increasing the spread of resistance genes between bacteria The project also investigated whether biocides can stress staphylococci bacteria so that they mutate and develop resistance to antibiotics. Furthermore, MRSA bacteria from pig farming were examined for their sensibility towards biocides commonly used as disinfectants in pig production.

It turned out that MRSA bacteria’s sensibility towards the biocides tested was not reduced. However, data from the PhD thesis indicate that certain biocides have the potential to contribute to development and spread of antibiotic resistance in bacteria. In order to determine the potential risk of resistance development when using different biocides to fight bacteria further research and data collection are necessary.

Read the entire PhD thesis: Development of bacterial resistance to biocides and antimicrobial agents as a consequence of biocide usage (pdf).

Read more about the National Food Institute’s work in the field of antimicrobial resistance and consumption of antimicrobial agents.

Facts about MRSA

MRSA bacteria

MRSA is short for Methicillin-Resistant Staphylococcus aureus.

When bacteria are exposed to antimicrobial agents, they protect themselves by developing resistance. They do so by altering their DNA - either through mutation or by transferring resistance genes between bacteria. It is therefore important to only use antimicrobial agents as required to prevent overuse.

Staphylococci are bacteria found in humans, animals and in our surrounding environment. Staphylococcus aureus is part of the normal nasal and skin flora in approx. 50% of the population. Staphylococcus aureus can cause a wide range of infections ranging from superficial wounds and abscesses to serious infections such as Osteitis and Endocarditis. In hospitals, Staphylococcus aureus is the most frequent cause of post-surgery infections.

In 2012, MRSA was identified in 1,556 people. This represents an increase of 20% on 2011, when 1,292 people were infected. Only 67 people were infected at hospitals, which is at the same level as in 2011 (58 cases). Community-acquired MRSA was identified in 726 people compared to 596 in 2011 (an increase of 22%), and cases of pig-type MRSA (CC398) rose by 41% from 164 in 2011 to 232 in 2012. Of those infected with pig-type MRSA, 92 (40%) had an infection when the diagnosis was made, compared to 62 (38%) in 2011.

The incidence of MRSA in humans in Denmark is still low compared to many other countries in Europe.

Animal and meat production in Denmark

A large majority of the meat products produced in Denmark come from pigs. In 2012, Denmark produced a total of 29,047,000 pigs, corresponding to 1,902 million kg of pork, along with 111,080,000 broiler chickens, corresponding to 168 million kg of chicken meat, and 539,000 cattle, corresponding to 138 million kg of beef. In addition, there were 580,000 dairy cattle in Denmark, producing 4,928 million kg of milk.

Meat was examined for MRSA in the period 2009–11, but this was not done in 2012. The risk of meat constituting a source of MRSA infection in humans is still considered to be very small.

New MRSA guidelines in 2012

The second edition of the Danish Health and Medicines Authority’s guidelines on MRSA was published in November 2012. These are national guidelines for people employed in the healthcare and social services sectors and are designed to prevent the spread of MRSA both within and outside hospitals. The revised guidelines include contact with pigs as a risk factor. In addition, the follow-up of otherwise healthy carriers of MRSA has been tightened up so as to restrict the spread of MRSA. The Danish Health and Medicines Authority now recommends that the entire household is checked after treatment to identify any cases in which treatment has not been successful and which may therefore constitute a continued risk of infection.

DANMAP 2012

The figures are from the 2012 DANMAP report—the 17th time this report has been published. Each year, the DANMAP report accounts for the use of antimicrobial agents and the occurrence of antimicrobial resistance in animals, food and humans. The organisations behind DANMAP are National Food Institute, National Veterinary Institute, both at the Technical University of Denmark and Statens Serum Institut. The DANMAP report is prepared by National Food Institute and Statens Serum Institut

The DANMAP report is available in PDF format at www.danmap.org.