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Everyday inhibitions
Cross-talk
Everyday inhibitions Scientific journals are showing signs of loosening up, relaxing constraints that formerly held them to needlessly dour traditions. One indication is the occasional appearance of colloquial and even joky titles. “Closing in on Chlamydia and its intracellular bag of tricks”, “The roles of plasmids in phytopathogenic bacteria: mobile arsenals?”, and “Bacterial [Cu,Zn]-superoxide dismutase: phylogenetically distinct from the eukaryotic enzyme, and not so rare after all!” are three I have seen over the past year or two. Note that exclamation mark! Editors, it seems, now have feelings—of surprise, enthusiasm, and possibly pleasure. They are allowing authors to express them, and readers to experience them too. Moreover, everyday language is becoming permissible, as long as it is not slovenly or imprecise. So when I spotted the word “groceries” while browsing the literature recently, I was less dismayed than had this been a decade or more ago. But then I peered more closely. “Induction of the mar operon by miscellaneous groceries” said the paper (Rickard AH, et al. J Appl Microbiol 2004; 97: 1063). Groceries? An unlikely and inexact term, surely, to find in a learned journal? Yet on this occasion, it is bang-on (if you will permit the expression). Because what Peter Gilbert and his colleagues at the University of Manchester, UK, have shown is that some everyday groceries and domestic products can induce the mar operon, which is essential for many bacterial species to adopt a multiple antibiotic resistance phenotype. We have, they suggest, been so concerned with induction by specific antibiotics and biocides that we have overlooked a much more commonplace phenomenon. The Manchester researchers point out that homologues of the chromosomal mar operon have been reported in many organisms found in the domestic environment, including Escherichia coli, Salmonella enterica, and Enterobacter, Klebsiella, and Citrobacter species. Indeed this
is one factor that has triggered concerns about the widespread incorporation of antibacterial agents into kitchen products such as detergents, dish-cloths, and chopping boards. In theory, mutations within mar could lead to the selection of resistant strains. Gilbert and his co-workers decided to investigate. They cut wells in chemically defined medium in Petri dishes to screen a wide range of products to see if they induced the mar operon in E coli SPC105. Three groups of substances were tested. Herbs and spices included cinnamon, dill, paprika, fenugreek, and tarragon. Foods and drinks included cocoa, mayonnaise, Marmite, and mustard. Household products ranged from hair gel and bath foam to fabric conditioner and a dishwashing liquid marketed for its power to vanquish microorganisms. Of 35 products screened, 24 (69%) produced inhibitory zones, while 22 (63%) induced mar expression. Four substances (such as soya sauce) and aqueous extracts of tarragon induced the operon but did not affect growth. Conversely, others, including the dishwashing liquid, inhibited growth without inducing mar. The Manchester group point out that hyper-expression of mar has been associated with clinical observations of antibiotic and biocide resistance. Exposure to substances that both inhibit growth and induce mar, such as pine oil and quaternary ammonium compounds, will select for hyperexpressing populations. “If the classes of substrates and inducers were restricted to biocides and antibiotics, then clearly their use alone would be a major selection pressure towards resistance”, they write. “The work presented here, however, shows that seemingly innocuous everyday products may induce a response by bacteria that is identical to that exhibited by those treated with antimicrobials.” The authors also observe that their data, certainly those on common culinary and medicinal herbs, are hardly surprising. “All of these materials yield essential oils by distillation, and it is these extracts that are responsible for their applications.” The results of these studies do not necessarily refute the concerns of those microbiologists who have been campaigning against the indiscriminate deployment of antimicrobials in the kitchen. What they do indicate is that this is by no means the only scenario in which bacteria acquire resistance through the mar operon. What a pity, though, that the authors should conclude by highlighting the significance of substances “which are common in a domiciliary setting”. I believe they mean “in the home”.
Bernard Dixon 130 Cornwall Road, Ruislip Manor, Middlesex HA4 6AW, UK
6
http://infection.thelancet.com Vol 5 January 2005
Everyday inhibitions Scientific journals are showing signs of loosening up, relaxing constraints that formerly held them to needlessly dour traditions. One indication is the occasional appearance of colloquial and even joky titles. “Closing in on Chlamydia and its intracellular bag of tricks”, “The roles of plasmids in phytopathogenic bacteria: mobile arsenals?”, and “Bacterial [Cu,Zn]-superoxide dismutase: phylogenetically distinct from the eukaryotic enzyme, and not so rare after all!” are three I have seen over the past year or two. Note that exclamation mark! Editors, it seems, now have feelings—of surprise, enthusiasm, and possibly pleasure. They are allowing authors to express them, and readers to experience them too. Moreover, everyday language is becoming permissible, as long as it is not slovenly or imprecise. So when I spotted the word “groceries” while browsing the literature recently, I was less dismayed than had this been a decade or more ago. But then I peered more closely. “Induction of the mar operon by miscellaneous groceries” said the paper (Rickard AH, et al. J Appl Microbiol 2004; 97: 1063). Groceries? An unlikely and inexact term, surely, to find in a learned journal? Yet on this occasion, it is bang-on (if you will permit the expression). Because what Peter Gilbert and his colleagues at the University of Manchester, UK, have shown is that some everyday groceries and domestic products can induce the mar operon, which is essential for many bacterial species to adopt a multiple antibiotic resistance phenotype. We have, they suggest, been so concerned with induction by specific antibiotics and biocides that we have overlooked a much more commonplace phenomenon. The Manchester researchers point out that homologues of the chromosomal mar operon have been reported in many organisms found in the domestic environment, including Escherichia coli, Salmonella enterica, and Enterobacter, Klebsiella, and Citrobacter species. Indeed this
is one factor that has triggered concerns about the widespread incorporation of antibacterial agents into kitchen products such as detergents, dish-cloths, and chopping boards. In theory, mutations within mar could lead to the selection of resistant strains. Gilbert and his co-workers decided to investigate. They cut wells in chemically defined medium in Petri dishes to screen a wide range of products to see if they induced the mar operon in E coli SPC105. Three groups of substances were tested. Herbs and spices included cinnamon, dill, paprika, fenugreek, and tarragon. Foods and drinks included cocoa, mayonnaise, Marmite, and mustard. Household products ranged from hair gel and bath foam to fabric conditioner and a dishwashing liquid marketed for its power to vanquish microorganisms. Of 35 products screened, 24 (69%) produced inhibitory zones, while 22 (63%) induced mar expression. Four substances (such as soya sauce) and aqueous extracts of tarragon induced the operon but did not affect growth. Conversely, others, including the dishwashing liquid, inhibited growth without inducing mar. The Manchester group point out that hyper-expression of mar has been associated with clinical observations of antibiotic and biocide resistance. Exposure to substances that both inhibit growth and induce mar, such as pine oil and quaternary ammonium compounds, will select for hyperexpressing populations. “If the classes of substrates and inducers were restricted to biocides and antibiotics, then clearly their use alone would be a major selection pressure towards resistance”, they write. “The work presented here, however, shows that seemingly innocuous everyday products may induce a response by bacteria that is identical to that exhibited by those treated with antimicrobials.” The authors also observe that their data, certainly those on common culinary and medicinal herbs, are hardly surprising. “All of these materials yield essential oils by distillation, and it is these extracts that are responsible for their applications.” The results of these studies do not necessarily refute the concerns of those microbiologists who have been campaigning against the indiscriminate deployment of antimicrobials in the kitchen. What they do indicate is that this is by no means the only scenario in which bacteria acquire resistance through the mar operon. What a pity, though, that the authors should conclude by highlighting the significance of substances “which are common in a domiciliary setting”. I believe they mean “in the home”.
Bernard Dixon 130 Cornwall Road, Ruislip Manor, Middlesex HA4 6AW, UK
6
http://infection.thelancet.com Vol 5 January 2005