Salmonella: Scientists Discover Drug-Resistant Strain of Bacteria

Aug. 3, 2011— -- Researchers are warning of the emergence of a new strain of salmonella that is highly resistant to Cipro, the main drug used to treat infections with the bacteria.

In some cases, samples were resistant to a suite of other drugs, including such antibiotics as amoxicillin, streptomycin, spectinomycin, gentamicin, sulfamethoxazole and tetracycline.

Nearly 500 cases were identified in several European countries during the period 2002 through 2008, according to Dr. François-Xavier Weill of the Pasteur Institute in Paris and colleagues.

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Reports of infection in Canada and contamination of imported foods in the U.S. suggest that the strain has also reached North America, Weill and colleagues reported online in the Journal of Infectious Diseases.

The resistant strain, dubbed CIPR for its resistance characteristics, formed an increasing proportion of all cases of infection with Salmonella enterica serotype Kentucky in France, England and Wales, and Denmark over the study period, Weill and colleagues reported.

The report comes as U.S. officials are reporting that an outbreak of salmonellosis, probably linked to eating ground turkey, has killed one person and sickened 76 others.

In that outbreak, the strain responsible is salmonella Heidelberg, which is more commonly associated with human illness than the Kentucky strain.

Weill and colleagues used surveillance data from the three European countries and from the CDC to track the rise of the CIPR strain, and found 489 resistant samples over the study period, rising from three cases in 2002 to 174 in 2008.

That number is probably an underestimate, they noted, owing to "limitations in the catchment area of these national surveillance systems."

The first CIPR cases were observed in 2002 in Denmark and France and in 2004 in England and Wales. Excluding the U.S., CIPR cases have formed between 35 percent and 40.2 percent of all salmonella Kentucky samples from 2002 to 2008.

The earliest infections appear to have been acquired mainly in Egypt between 2002 and 2005; since 2006 the infections have also been acquired in various parts of Africa and the Middle East.

But in about 10 percent of cases, patients did not report international travel, the researchers noted, suggesting that infections may have also occurred in Europe through consumption of imported foods or through secondary contaminations.

The CIPR strain has been isolated from chickens and turkeys from Ethiopia, Morocco, and Nigeria, Weill and colleagues noted, which may mean that poultry is an important infection route for this strain as well as for the Heidelberg strain involved in the current U.S. outbreak.

In an accompanying editorial, Craig Hedberg of the University of Minnesota School of Public Health in Minneapolis argued that differences in national surveillance systems limit the ability to monitor such outbreaks.

The researchers found that the percentage of Salmonella samples submitted from clinical laboratories to national health reference laboratories ranged from 65 percent in France to 9 percent in Denmark.

"Given the medical costs and public health impact associated with the spread of multi-drug-resistant organisms, the potential benefits of such a system should far outweigh its costs," he argued.