Study finds high levels of ESBL bacteria in Danish chicken meat

Nearly half of the samples from chicken meat imported into Denmark contain ESBL bacteria and for the first time the level is almost as high in Danish chicken meat. By contrast, the occurrence in Danish pigs has decreased significantly since farmers stopped using cephalosporins for pigs. This appears from the Danish surveillance report, DANMAP, for 2011. ESBL bacteria are resistant to antimicrobial agents that are essential for treatment of severe infections in humans.

ESBL bacteria are among the most rapidly increasing global resistance problems. ESBL bacteria are resistant to the broad-spectrum antimicrobial agents, cephalosporins, that are widely used for treating life-threatening infections in humans.

The annual DANMAP report from 2011 shows that almost every other sample from both imported and Danish chicken meat contains ESBL bacteria. It is significantly more than found earlier in Danish chicken meat. In 2010, almost every tenth sample from Danish chicken meat was positive.

"The high occurrence of resistance to cephalosporins in chicken meat is alarming because there is a risk that bacteria are transferred from chicken meat to humans", says Yvonne Agersø, Senior Researcher, the National Food Institute, Technical University of Denmark.
 
There is a need for more studies to determine the proportion of human infections with ESBL derived from animals.

Highly undesirable resistance
Consumption of cephalosporins is thought to be the main reason for the development of ESBL resistance. However, cephalosporins have not been used in the Danish chicken production for the past decade and thus cannot explain the increase in ESBL bacteria in the Danish chicken meat.

The discovery of ESBL bacteria in Danish chicken can be due to spread from parent animals imported from a few manufacturers that export to all of Europe, animals which prior to export have been treated with cephalosporins. In recent years an increase in the use of broad-spectrum penicillins in Danish chicken production have occurred, which may also have contributed to the increase in the occurrence of ESBL bacteria. Generally, the use of antimicrobial agents in chicken production is low.

"As long as ESBL bacteria enter Denmark via imported parent animals, it will be difficult to combat them. We must therefore pursue international solutions and initiatives that can limit the spread and the survival of ESBL bacteria in the herds. Detection of bacteria in chicken meat shows that the bacteria survive the slaughter process", says Yvonne Agersø.

Significant decrease in the occurrence of ESBL in Danish pigs
In 2010, Danish agriculture introduced a voluntary ban on the use of broad-spectrum cephalosporins for pigs, resulting in the consumption for pigs being very close to zero for the past two years.

The voluntary ban on the use of cephalosporins has had a positive impact on the occurrence of ESBL in both herds and pigs at slaughter. In the 78 pig herds examined, no ESBL bacteria were found, while 3.6% of the pigs examined at slaughter contained ESBL bacteria. The figures are significantly lower than in 2010 where 11% of pig herds and pigs at slaughter contained ESBL bacteria.
 
"The voluntary ban on the use of cephalosporins in pig production seems to have effectively reduced the occurrence of ESBL bacteria in pigs. It is therefore important to uphold it", says Yvonne Agersø.

FACTS
ESBL bacteria When bacteria are exposed to antimicrobial agents, they protect themselves by developing resistance in order to survive. The resistant bacteria have changed their hereditary material - their genes. Researchers find the same types of ESBL genes in bacteria in both humans and meat.
 
Due to the use of broad-spectrum antimicrobial agents, in particular cephalosporins, the bacteria become resistant to this type of antimicrobial agent. What is special about cephalosporin-resistance is that the bacteria also become resistant to almost all ordinary types of penicillin.
 
The enzymes responsible for cephalosporin resistance are called ESBL (Extended-Spectrum Beta-Lactamases or cephalosporinases). Cephalosporin-resistant bacteria, such as E. coli, Salmonella and Klebsiella are thus called ESBL-producing bacteria or just ESBL-bacteria.
 
The occurrence of ESBL coli bacteria in Danish chicken meat increased from 8.6% in 2010 to 44% 2011 while the occurrence in imported chicken meat was 50% in 2010 and 48% in 2011.
 
Resistance to critically important antimicrobial agents
The World Health Organization has identified a number of different types of antimicrobial agents as critically important. An antimicrobial agent is considered critically important if it is the only compound, or one of limited available therapy, to treat serious human disease. Cephalosporins are among the most critically important antimicrobial agents. It is important to minimise the use of cephalosporins in animals to prevent the development of resistant bacteria that are transmittable to humans.