High level of antibiotic resistance in bacteria that cause food poisoning

More than 40% of bacteria found in chicken on sale in Switzerland is resistant to at least one antibiotic, says research published this week in BMC Public Health. The findings could have implications for treating food poisoning.

The bacteria, Campylobacter, causes between 5 and 14 percent of all diarrhoeal illness worldwide. The most common sources of infection are inadequately cooked meat, particularly poultry, unpasteurised milk and contaminated drinking water. The illness normally clears up after a week, without treatment. But small children and people with a weakened immune system often take antibiotics to prevent the infection from spreading to the bloodstream – and causing life threatening septicaemia.

Researchers from the Swiss Federal Veterinary Office collected raw poultry meat samples from 122 retail outlets across Switzerland and Liechtenstein, and tested their antibiotic resistance. From 415 meat samples, they isolated 91 strains of Campylobacter, 59% of which were sensitive to all the antibiotics tested.

19 strains (22%) were resistant to one antibiotic, 9 strains (10%) to two antibiotics, and 8 strains (9%) were resistant to at least three antibiotics. Two strains were resistant to five antibiotics. One of these showed resistance to ciprofloxacin, tetracycline and erythromycin – the most important antibiotics for treating Campylobacter infection in humans.

Meat was more likely to be infected with Campylobacter if it was kept chilled, rather than frozen. However, the storage conditions did not affect the frequency of antibiotic resistance in the bacteria.

Although the frequency of antibiotic resistance in Switzerland may seem high, meat produced in the country was, in fact, less likely to be infected with antibiotic resistant Campylobacter than meat produced elsewhere. Juerg Danuser commented: “The level of antibiotic resistance in Campylobacter depends on the amount of antibiotics that the chickens received. Maybe in Switzerland antibiotics were used less, so there is less resistance”

Initially, the researchers thought that poultry was more likely to be infected with antibiotic resistant bacteria if it was raised using conventional indoor farming methods rather than in an animal-friendly way. However, the majority of meat produced in an animal friendly way came from Switzerland, and this skewed the results. The researchers therefore concluded that only the country of origin and not the farming methods were likely to influence the level of antibiotic resistance in the bacteria.

Juerg Danuser discussed this: “It’s possible that chickens raised in an animal-friendly way are more healthy, so they need less treatment with antibiotics and so their Campylobacter are less resistant to antibiotics. But the other side of the story is that these chickens go outside more often, so they are in more contact with wild birds, which is the reservoir of Campylobacter.”

These findings are of concern for Swiss consumers, but, as mentioned above, the picture for other countries is even bleaker. The researchers wrote: “The high prevalence of Campylobacter in raw poultry meat samples found in this study agrees with data from other studies.” In the USA, 90% of Campylobacter strains isolated from poultry meat had resistance to at least one, and 45% to at least two antibiotics.

Worries over antibiotic resistant bacteria led the EU to ban the use of four antibiotics as growth promoters in chickens, in 1999. The US Food and Drugs administration (FDA) followed their lead in late 2000, by banning the use of a particular class of antibiotics called fluorquinolones in poultry farming.

Food poisoning caused by eating Campylobacter infected poultry is on the increase. In Switzerland, 1 in 1,086 people suffer from Campylobacter infection every year; the number is approximately ten times higher in the US.

This press release is based on the following article:

Risk factors for antibiotic resistance in Campylobacter spp. isolated from raw poultry meat in Switzerland
Ursula Ledergeber, Gertraud Regula, Roger Stephan, Juerg Danuser, Beatrice Bissig and Katharina D.C Stark
BMC Public Health 2003, 3:39
To be published 9 December 2003