Since 2011, the level of resistant ESBL bacteria has increased in broiler meat imported into Denmark and Danish produced broiler meat still contains ESBL bacteria. In addition, campylobacter bacteria originating from broiler meat contains high levels of resistance to antimicrobial agents that are particularly crucial for treatment of life-threatening infections in humans. This appears from the 2012 DANMAP report prepared by the National Food Institute, Technical University of Denmark and Statens Serum Institut.
ESBL bacteria are one of the fastest emerging resistance problems worldwide. ESBL bacteria are resistant to the broad-spectrum antimicrobial agents cephalosporins which are often used for treating life-threatening infections in humans.
The 2012 DANMAP report shows that almost two thirds of the samples of imported broiler meat and more than one third of Danish broiler meat contain ESBL bacteria. This is significantly more than in previous years for imported broiler meat. As regards Danish broiler meat the findings are at the same level as for 2011.
International collaboration is necessary
The use of cephalosporins for broilers is considered the primary reason for the development of ESBL resistance. But cephalosporins have not been used in Danish broiler production in the past ten years and, thus, cannot explain the development of ESBL in Denmark.
However, findings of ESBL bacteria in Danish broilers may be due to spread from imported parent animals, which are imported from few producers to the entire Europe, and which have been treated with cephalosporins before being imported.
“As long as ESBL bacteria enter Denmark via imported parent animals it is difficult to get rid of ESBL bacteria. Therefore, international solutions and interventions are necessary to limit spreading and survival in the herds”, says Yvonne Agersø, senior researcher at the National Food Institute, Technical University of Denmark.
Resistance to other important antimicrobial agents
Broiler meat also contains other bacteria which are resistant to the so-called critically important antimicrobial agents, antimicrobial agents which are used for treating life-threatening infections in humans.
Broiler meat is the cause of around one third of all infections with campylobacter. In 2012, 29% of the campylobacter bacteria found in Danish broilers were resistant to fluoroquinolones, which are critically important antimicrobial agents. This is the highest level since 2007. However, the occurrence in imported broiler meat is significantly higher, 46%. In general, imported broiler meat has a significantly higher level of resistant bacteria than Danish broiler meat.
“Broiler meat is one of the major sources of campylobacter infections in humans whereas we yet don’t know how big a proportion of human infections are caused by ESBL bacteria originating from meat”, says Yvonne Agersø.
The investigations indicate that bacteria resistant to critically important antimicrobial agents occur more frequently in both Danish and imported broiler meat than in beef and pork meat.
“There is a need for putting international focus on resistance to critically important antimicrobial agents in broilers. Nationally, it is important to consider initiatives in the broiler production to reduce the occurrence of resistant bacteria in broiler meat”, adds Yvonne Agersø.
ESBL bacteria
When bacteria are exposed to antimicrobial agents they protect themselves by developing resistance, enabling them to survive. Resistant bacteria have changed their gene pool – their genes. Researchers find the same types of ESBL genes in bacteria in both humans and meat.
By using broad-spectrum antimicrobial agents, especially cephalosporins, the bacteria become resistant to this particular antibiotic type. What’s special about cephalosporin resistance is that the bacteria become resistant to almost all ordinary types of penicillin as well.
The enzymes which cause cephalosporin resistance are called ESBL (extended spectrum beta-lactamase or cephalosporinase). Cephalosporin-resistant bacteria, e.g. E.coli, Salmonella and Klebsiella, are called ESBL-producing bacteria or just ESBL bacteria.
The occurrence of ESBL E. coli bacteria in Danish broiler meat was at the same level in 2012 (36%) as in 2011 (44%), whereas the occurrence in imported broiler meat was significantly higher in 2012 (61%) than in 2011 (48%).
Campylobacter
Campylobacter is a disease-causing bacterium, which may be transferred from animals to humans. If resistance is developed in these bacteria in livestock production, this resistance may be transferred to humans via food. In certain cases this may result in failure in disease treatment.
Campylobacter jejuni is the most common campylobacter type in broiler meat. Seen in a European context, the resistance occurrence in Campylobacter jejuni from Danish chickens kept for meat production and broiler meat as well as Campylobacter coli from pigs is among the lowest in Europe.
Critically important antimicrobial agents
The World Health Organization, WHO, has identified a number of different types of antimicrobial agents as critically important, which means they are considered the only antibiotic or one of few which can be used for treating serious infections in humans.
Cephalosporins and fluoroqinolones are among the critically important antimicrobial agents. It is important to reduce animals’ consumption of cephalosporins and fluoroquinolones to avoid the development of resistant bacteria which may be transferred to humans.
DANMAP 2012
The findings appear in 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 the National Food Institute, the National Veterinary Institute (both institutes are under the Technical University of Denmark) and Statens Serum Institut. The DANMAP report is prepared by the National Food Institute and Statens Serum Institut.
The DANMAP report is available as a PDF file on www.danmap.org.