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Naughty but nice
Cross-talk
Naughty but nice Smoked salmon, with its polycyclic hydrocarbons, is just one of many delicious foods with potentially harmful constituents. We reassure ourselves, however, that the carcinogens are present in such vanishingly tiny concentrations that they pose only the remotest of risks. And when we do eat dangerously—flirting with scombroid toxins in elderly mackerel or with microbiological hazards in suspect seafood—we tell ourselves that we do not do these things very often. Now, we may need to add Turkish olives and other naturally fermented foods to our catalogue of delicacies that we should treat with suspicion. That is the implication of some work carried out recently by Sine Özmen Toğay at Hacettepe University in Ankara with colleagues there and at other centres in Turkey. The constituents in this case are enterococci, whose associations with food have usually been seen as largely positive. I remember last year enjoying some especially succulent San Simon cheese, which—like many other cheeses—owes its taste to enterococcal activities. Over the past decade, it has become clear that the proteolytic and lipolytic enzymes of enterococci greatly enhance the flavour of many foods, from cheeses to sausages. A voluminous literature now exists on the roles of these organisms as both starter cultures and probiotics. However, some enterococci, particularly specific strains of Enterococcus faecium and Enterococcus faecalis, also produce virulence factors. These include cytolysins, hyaluronidase, gelatinase, serine protease, and aggregation substance. Several recent reports have also confirmed the widespread presence of antibiotic-resistant enterococci in foodstuffs. Can this resistance be transferred to pathogenic strains? Indeed, can enterococcal pathogens be transmitted through food? The reason why Sine Özmen Toğay and co-workers were anxious to study enterococci in their country’s olives, cheeses, and sausages was because the organisms are resistant to low pH (and high temperatures). Although some have been implicated in meat spoilage, and although their presence can betray poor hygiene during food processing, the pathogenic potential of enterococci in naturally fermented Turkish foods has not been thoroughly investigated. The team began by collecting 20 samples of white cheese, 20 samples of olives, and ten samples of sausages from domestic markets and local producers in several different parts of the country. They then used the polymerase chain reaction to test for the presence of virulence genes (agg2, gelE, cylM, cylB, cylA, espfs, espfm, efaAfs, efaAfm, cpd, cop, ccf, and cad) and the resistance genes vanA and vanB. Antibiotic resistance was assessed by a disc diffusion method.
820
The outcome, reported in the Journal of Applied Microbiology (2010; 109: 1084–92), is disquieting rather than alarming. Most of the isolates proved positive for virulence genes and were resistant to some antibiotics. One of the E faecalis strains from cheese carried the vanA gene and was moderately resistant to vancomycin. And many isolates contained large plasmids that might harbour acquired antibiotic resistance. “The findings of this study suggest that food origin strains of E faecium and E faecalis may be potential risk factors for consumer health in terms of virulence genes and antibiotic resistance”, the authors write. They urge the importance of further studies not only on virulence gene expression and the possibility of gene transfer to other bacteria in food but also on the selection of appropriate enterococcal starter, probiotic, and co-cultures in the food industry. The Turkish group cites a previous report of 29 E faecium strains, isolated from probiotic products that were resistant to kanamycin, tetracyclines, benzylpenicillin, and vancomycin. Another study identified two E faecalis strains carrying multiple virulence determinants and showed that starter strains acquired virulence determinants from pathogenic strains. Both of these reports, together with the Turkish results, indicate the need for continuous attention to be paid to the selection of probiotic strains free of transferable antibiotic resistance. These cautions may, of course, also apply to similar fermented foods from other countries. For that reason alone, I will continue to enjoy olives and cheese as part of the excellent Turkish cuisine.
Bernard Dixon 130 Cornwall Road, Ruislip Manor, Middlesex, HA4 6AW, UK [email protected]
www.thelancet.com/infection Vol 10 December 2010
Naughty but nice Smoked salmon, with its polycyclic hydrocarbons, is just one of many delicious foods with potentially harmful constituents. We reassure ourselves, however, that the carcinogens are present in such vanishingly tiny concentrations that they pose only the remotest of risks. And when we do eat dangerously—flirting with scombroid toxins in elderly mackerel or with microbiological hazards in suspect seafood—we tell ourselves that we do not do these things very often. Now, we may need to add Turkish olives and other naturally fermented foods to our catalogue of delicacies that we should treat with suspicion. That is the implication of some work carried out recently by Sine Özmen Toğay at Hacettepe University in Ankara with colleagues there and at other centres in Turkey. The constituents in this case are enterococci, whose associations with food have usually been seen as largely positive. I remember last year enjoying some especially succulent San Simon cheese, which—like many other cheeses—owes its taste to enterococcal activities. Over the past decade, it has become clear that the proteolytic and lipolytic enzymes of enterococci greatly enhance the flavour of many foods, from cheeses to sausages. A voluminous literature now exists on the roles of these organisms as both starter cultures and probiotics. However, some enterococci, particularly specific strains of Enterococcus faecium and Enterococcus faecalis, also produce virulence factors. These include cytolysins, hyaluronidase, gelatinase, serine protease, and aggregation substance. Several recent reports have also confirmed the widespread presence of antibiotic-resistant enterococci in foodstuffs. Can this resistance be transferred to pathogenic strains? Indeed, can enterococcal pathogens be transmitted through food? The reason why Sine Özmen Toğay and co-workers were anxious to study enterococci in their country’s olives, cheeses, and sausages was because the organisms are resistant to low pH (and high temperatures). Although some have been implicated in meat spoilage, and although their presence can betray poor hygiene during food processing, the pathogenic potential of enterococci in naturally fermented Turkish foods has not been thoroughly investigated. The team began by collecting 20 samples of white cheese, 20 samples of olives, and ten samples of sausages from domestic markets and local producers in several different parts of the country. They then used the polymerase chain reaction to test for the presence of virulence genes (agg2, gelE, cylM, cylB, cylA, espfs, espfm, efaAfs, efaAfm, cpd, cop, ccf, and cad) and the resistance genes vanA and vanB. Antibiotic resistance was assessed by a disc diffusion method.
820
The outcome, reported in the Journal of Applied Microbiology (2010; 109: 1084–92), is disquieting rather than alarming. Most of the isolates proved positive for virulence genes and were resistant to some antibiotics. One of the E faecalis strains from cheese carried the vanA gene and was moderately resistant to vancomycin. And many isolates contained large plasmids that might harbour acquired antibiotic resistance. “The findings of this study suggest that food origin strains of E faecium and E faecalis may be potential risk factors for consumer health in terms of virulence genes and antibiotic resistance”, the authors write. They urge the importance of further studies not only on virulence gene expression and the possibility of gene transfer to other bacteria in food but also on the selection of appropriate enterococcal starter, probiotic, and co-cultures in the food industry. The Turkish group cites a previous report of 29 E faecium strains, isolated from probiotic products that were resistant to kanamycin, tetracyclines, benzylpenicillin, and vancomycin. Another study identified two E faecalis strains carrying multiple virulence determinants and showed that starter strains acquired virulence determinants from pathogenic strains. Both of these reports, together with the Turkish results, indicate the need for continuous attention to be paid to the selection of probiotic strains free of transferable antibiotic resistance. These cautions may, of course, also apply to similar fermented foods from other countries. For that reason alone, I will continue to enjoy olives and cheese as part of the excellent Turkish cuisine.
Bernard Dixon 130 Cornwall Road, Ruislip Manor, Middlesex, HA4 6AW, UK [email protected]
www.thelancet.com/infection Vol 10 December 2010