A type of Salmonella enterica found originally in pigs can be transmitted to people when they eat pork tainted by the bacteria, say microbiologists this month in Applied and Environmental Microbiology. The sub-strain, known as 4,[5],12:i:–, has widened its reach in Europe over recent years, they add.

"The studies reported here support the observation that S. enterica serovar 4,[5],12:i:– is an emerging hazard for humans and that hazard is directly linked to the consumption of contaminated pork," write Elizabeth Hauser of the German National Reference Laboratory in Berlin and colleagues at Emerging Health Threats Forum.

S. enterica 4,[5],12:i:– was first seen in Europe during the 1990s in Spanish pigs and in recent years, it has been an increasing cause of gastroenteritis in people worldwide, the authors explain. It is now one of the top 10 Salmonella sub-strains found in pigs and people in several European countries and the US, and the strain's prevalence may still be under-reported due to its genetic diversity.

Until now, it has not been clear whether the S. enterica 4,[5],12:i:– bacteria that circulated in pigs and people are related to each other. So Dr Hauser and colleagues analysed the genetic make-up of 148 samples of the bacteria collected from live pigs, pork meat and people in Germany between 2006 and 2007. More than 50 of the bacterial isolates came from pigs, 30 from pork meat and the remaining 66 were collected from people suffering gastroenteritis.

They found that the bacterial samples from pigs, pork and people were closely related genetically, which suggests the sub-strain is transmitted along the food chain. Molecular tests revealed two main lineages of the bacteria circulating in Germany, known as phage type DT193 and DT120.

"It is essential that interventions are introduced at the farm level in order to limit human infections," say the authors.

The new bug is closely related to the Typhimurium sub-strain of S. enterica. Two years ago, European scientists reported the emergence of drug resistance in Salmonella typhimurium strains circulating on the continent. As part of their analysis, Dr Hauser and colleagues determined whether the 4,[5],12:i:– sub-strain carries antibiotic resistance genes too.

More than 80 per cent of the bacterial isolates, including those from both phage type DT193 and ST120, carried genes that make them resistant to four or more antimicrobials, they say. Most isolates were resistant to the drugs ampicillin, sulfamethoxazole, streptomycin and tetracycline, they add. However, these antibiotics are not typically used to treat Salmonella infections.

Reference

Hauser E., Tietze E., Helmuth R., Junker E., Blank K. and Prager R. 2010. Pork contaminated with Salmonella enterica serovar 4,[5],12:i:–, an emerging health risk for humans. Appl Environ Microbiol 2010, 76:4601–10. doi: 10.1128/AEM.02991-09.

Further Reading

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