The Australian researchers discovered that only two per cent of the locally acquired Campylobacter isolates were resistant to the antibiotic ciprofloxacin, a type of fluoroquinolone used to treat patients infected with the pathogen. Countries that allow fluoroquinolone use in animals may have a drug resistance prevalence of up to 29 per cent, the scientists stated in an article in the 15 May issue of Clinical Infectious Diseases.
Consumer concern over the use of antibiotics as growth promoters for food animals has led to bans in some countries. The drugs are used at low doses in animal feeds as a means of lowering the percentage of fat and gaining a higher protein content in the meat. Antibiotic growth-promoters also help control zoonotic pathogens such as Salmonella, Campylobacter, Escherichia coli and enterococci.
The study adds to research showing that antibiotic use in food animals can lead to drug-resistant strains eventually infecting humans.
On 1 January this year, the EU banned the feeding of all antibiotics and related drugs to livestock for growth promotion purposes. The new policy follows a 1998 ban on the feeding of antibiotics that are valuable in human medicine to livestock for growth promotion. Now, no antibiotics can be used in European livestock for growth promotion purposes.
Campylobacter jejuni is a leading bacterial cause of foodborne illness in industrialised countries. Poultry products are a major source of the pathogen. Drug resistance can make Campylobacter infections difficult for physicians to treat, and can result in longer bouts of diarrhea and a higher risk of serious or even fatal illness. Bacterial resistance to drugs is generally attributed to inappropriate prescribing or the overuse of antibiotics.
"There are different causes that lead to bacterial antibiotic resistance, and use of antibiotics in food animals is only one of the multiple causes," said lead author Leanne Unicomb, an epidemiologist with OzFoodNet and Australia National University. "However, the evidence indicates that the use of fluoroquinolones in food animals in other countries has increased the risk of resistance in [Campylobacter] isolates infecting humans."
The Australian government prohibits the use of fluoroquinolone in food-producing animals, including poultry. The policy puts it in a relatively unique position, since its animal and food production levels are comparable to those of other industrialised nations, but it has avoided using the antibiotics that have been standard in the other countries' food animal production.
To evaluate whether the country's restrictive antibiotic policy has affected bacterial drug resistance, Australian researchers examined Campylobacter jejuni samples collected from 585 patients in five Australian states. None of the patients had received fluoroquinolone treatment within the month prior to becoming ill.
Among locally acquired infections, an average of only two per cent were resistant to ciprofloxacin. About 55 per cent of the samples also exhibited resistance to sulfisoxazole, 46 per cent to ampicillin, roxithromycin (38 per cent), tetracycline (seven per cent), nalidixic acid (six per cent), chloramphenicol (three per cent), pererythromycin (three per cent), gentamicin (two per cent), and kanamycin (0.2 per cent).
Other industrialized nations have also restricted antimicrobial use in animals. Sweden prohibited the use of fluoroquinolones for food animals in 1986. Norway has never licensed their use in food animals.
Both countries have reported low trends --similar to Australia's -- in fluoroquinolone-resistant Campylobacter infecting humans, the researchers stated.
The US Food and Drug Administration proposed banning fluoroquinolones in poultry in 2000, but one drugmaker fought the ban until it was finally enacted in September 2005.
High rates of antibiotic resistance in South and East Europe are higher than in northern Europe because the regions have high rates of antibiotic use, according to a study published last year in The Lancet.
Another study released last year by researchers from the Johns Hopkins Bloomberg School of Public Health indicated that the poultry industry's use of antibiotics promotes resistance among the foodborne bacteria that infect humans, including the bacterium Campylobacter.
The study, published in Environmental Health Perspectives, also provided evidence suggesting that chickens raised without antibiotics are less likely to carry antibiotic-resistant strains of Campylobacter. The data also showed that antibiotic-resistant Campylobacter can persist in poultry populations and products long after producers stop using the drugs.
The incidence of reported Campylobacter infection cases in Australia was 116.5 cases per 100,000 persons in 2003. About 277,000 cases Campylobacter infection are estimated to occur annually.
In Europe and the United States, increasing proportions of patients are infected with strains of Campylobacter species exhibiting antimicrobial resistance, particularly resistance to fluoroquinolones.
Antimicrobial resistance may also add to the burden of disease, research shows. Fluoroquinolone-resistant organisms have been reported to be associated with more-severe disease, including diarrhea of a longer duration and an increased likelihood of invasive disease and death.
The rising incidence of fluoroquinolone resistance has been attributed to the use of fluoroquinolones in food-producing animals and has been reflected in the high prevalence of ciprofloxacin-resistant animal Campylobacter samples found in animals in those countries, the researchers stated.