Novel approach to mapping of resistance mutations in whole genomes by using restriction enzyme modulation of transformation efficiency

Restriction enzyme modulation of transformation efficiencies (REMOTE) is a method that makes use of genome restriction maps and experimentally observed differences in transformation efficiencies of genomic DNA restriction digests to discover the location of mutations in genomes. The frequency with which digested genomic DNA from a resistant strain transforms a susceptible strain to resistance is primarily determined by the size of the fragment containing the resistance mutation and the distance of the mutation to the end of the fragment. The positions of restriction enzyme cleavage sites immediately flanking the resistance mutation define these parameters. The mapping procedure involves a process of elimination in which digests that transform with high frequency indicate that the restriction enzyme cleavage sites are relatively far away from the mutation, while digests that transform with low frequency indicate that the sites are close to the mutation. The transformation data are compared computationally to the genome restriction map to identify the regions that best fit the data. Transformations with PCR amplicons encompassing candidate regions identify the resistance locus and enable identification of the mutation. REMOTE was developed using Haemophilus influenzae strains with mutations in gyrA, gyrB, and rpsE that confer resistance to ciprofloxacin, novobiocin, and spectinomycin, respectively. We applied REMOTE to identify mutations that confer resistance to two novel antibacterial compounds. The resistance mutations were found in genes that can decrease the intracellular concentration of compounds: acrB, which encodes a subunit of the AcrAB-TolC efflux pump; and fadL, which encodes a long-chain fatty acid transporter.

Possible associations between Salmonella persistence in poultry houses and resistance to commonly used disinfectants and a putative role of mar

A putative link between Salmonella persistence in the agricultural sector and resistance to disinfectants has been sparsely investigated. Therefore, minimum inhibitory concentration (MIC) tests against five disinfectants commonly used in poultry premises (formaldehyde, glutaraldehyde/benzalkonium chloride compound, oxidising compound, tar oil phenol, iodophor) were performed on 286 Salmonella isolates, including 256 from Danish broiler houses, altogether representing nine serotypes. Six of these isolates were used for adaptation and de-adaptation studies involving the five disinfectants. Amongst 60 of these isolates selected for growth studies in cyclohexane (possibly associated with up-regulated efflux), only one isolate grew. From this isolate and the six isolates used in the adaptation and de-adaptation studies, mutants highly resistant to triclosan (a disinfectant linked with mar-type resistance) were selected. In addition, adaptation and de-adaptation studies with triclosan were performed. For the 286 isolates, the small variations in MICs could not be associated with Salmonella persistence in Danish broiler houses or previous use of relevant disinfectants. Adaptation and de-adaptation did not alter MICs to the five farm disinfectants. Compared to the parent isolates, MICs for the triclosan adapted and de-adapted isolates and the triclosan mutants were significantly increased to triclosan, but not to the five disinfectants. Moreover, most of the triclosan adapted and de-adapted isolates grew in cyclohexane. Thus, there was no correlation between triclosan and cyclohexane resistance on one hand and resistance to the five disinfectants on the other, suggesting that triclosan resistance is not linked with resistance to these disinfectants.

Farm disinfectants select for cyclohexane resistance, a marker of multiple antibiotic resistance, in Escherichia coli

AIMS

The aim of this study was to determine if three classes of farm disinfectants were able to select for ciprofloxacin or cyclohexane tolerant [indicative of a multiple antibiotic resistance (MAR) phenotype] Escherichia coli and if cyclohexane-tolerant E. coli could be isolated from farms.

METHODS AND RESULTS

Chicken slurry containing ca 1 : 99 ratio ciprofloxacin resistant : susceptible E. coli (10 different resistant strains examined) was treated for 24 h with each of the disinfectants and examined for survival of resistant : susceptible strains. Ciprofloxacin-sensitive (n=5) and -resistant (n=5) E. coli were grown with sublethal concentrations of the disinfectants and then plated to agar containing ciprofloxacin or overlaid with cyclohexane. Escherichia coli (n=389) isolated from farms were tested for cyclohexane tolerance. Minimum inhibitory concentrations (MIC) were determined against representative isolates and mutants. The disinfectants did not select for the ciprofloxacin-resistant E. coli in poultry slurry but following growth with each of the three disinfectants, higher numbers (P < or = 0.023) of cyclohexane-tolerant E. coli were isolated and these had a MAR phenotype. Of the 389 farm E. coli tested, only one was cyclohexane tolerant.

CONCLUSIONS

It is possible that in a farm environment, E. coli could be exposed to similar concentrations of the disinfectants that are selected for MAR type organisms under these laboratory conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

Data from this study suggest that cyclohexane-resistant E. coli are not common on farms, but in view of the ease of isolating them in the laboratory with farm disinfectants, further investigations on farms are warranted.

Efflux-mediated antimicrobial resistance

Antibiotic resistance continues to plague antimicrobial chemotherapy of infectious disease. And while true biocide resistance is as yet unrealized, in vitro and in vivo episodes of reduced biocide susceptibility are common and the history of antibiotic resistance should not be ignored in the development and use of biocidal agents. Efflux mechanisms of resistance, both drug specific and multidrug, are important determinants of intrinsic and/or acquired resistance to these antimicrobials, with some accommodating both antibiotics and biocides. This latter raises the spectre (as yet generally unrealized) of biocide selection of multiple antibiotic-resistant organisms. Multidrug efflux mechanisms are broadly conserved in bacteria, are almost invariably chromosome-encoded and their expression in many instances results from mutations in regulatory genes. In contrast, drug-specific efflux mechanisms are generally encoded by plasmids and/or other mobile genetic elements (transposons, integrons) that carry additional resistance genes, and so their ready acquisition is compounded by their association with multidrug resistance. While there is some support for the latter efflux systems arising from efflux determinants of self-protection in antibiotic-producing Streptomyces spp. and, thus, intended as drug exporters, increasingly, chromosomal multidrug efflux determinants, at least in Gram-negative bacteria, appear not to be intended as drug exporters but as exporters with, perhaps, a variety of other roles in bacterial cells. Still, given the clinical significance of multidrug (and drug-specific) exporters, efflux must be considered in formulating strategies/approaches to treating drug-resistant infections, both in the development of new agents, for example, less impacted by efflux and in targeting efflux directly with efflux inhibitors.

The biocide triclosan selects Stenotrophomonas maltophilia mutants that overproduce the SmeDEF multidrug efflux pump

The possibility that triclosan selects Stenotrophomonas maltophilia mutants overexpressing the multidrug resistance pump SmeDEF is analyzed. Five out of 12 triclosan-selected mutants were less susceptible to antibiotics than the wild-type strain and overproduced SmeDEF. Results are discussed in relation to current debates on the potential selection of antibiotic-resistant bacteria by household biocides.

Induction of the mar operon by miscellaneous groceries

AIM

To investigate the potential of non-antibacterial consumer products to act as inducers of the multiple antibiotic resistance (mar) operon of Escherichia coli SPC105.

METHODS AND RESULTS

Wells were cut into chemically defined agar medium (CDM) contained within Petri dishes. Molten agar slurries were prepared by mixing known quantities of 35 consumer products with molten CDM and these were pipetted into each well. Plates were overlaid with molten CDM (5 ml), containing 40 microg ml(-1) X-gal and approx. 1000 CFU ml(-1) of an overnight culture of E. coli SPC105 containing a chromosomal marOII::lacZ fusion. After incubation (37 degrees C, 24 h), plates were examined for zones of growth inhibition and the presence of a blue coloration, indicative of mar (marOII::lacZ) induction. Of the 35 products tested (nine herbs and spices, 19 food and drinks and seven household products), 24 (69%) of the items produced inhibitory zones and 22 (63%) of the items induced mar expression. Apple puree was inhibitory but did not induce marOII::lacZ. Mustard, chilli and garlic were shown to be powerful inducers of marOII::lacZ. Overall six products were shown to be powerful marOII::lacZ inducers. None of these made hygiene claims.

CONCLUSIONS

In addition to induction by specific biocides and antibiotics, mar is induced by the exposure of bacteria to natural substances, many of which are common to a domiciliary setting.

SIGNIFICANCE AND IMPACT OF THE STUDY

Concern that the overuse of antibacterials within consumer products might select for mar-mediated resistance is shortsighted and fails to recognize the ubiquity of inducers in our environment.

Mechanisms of resistance in Salmonella enterica adapted to erythromycin, benzalkonium chloride and triclosan

The potential for adaptive resistance of S. enterica serovar Enteritidis, Typhimurium and Virchow to increasing sub-lethal concentrations of erythromycin, benzalkonium chloride and triclosan was investigated to identify mechanisms underlying resistance. Permeability changes of the outer membrane, including LPS, cell surface charge, hydrophobicity and the presence of an active efflux in the adapted strain compared with the parent were studied. Examination of the outer membrane and LPS did not reveal any significant changes, although most of the pre-adapted strains were notably less hydrophobic than resistant strains. More than one type of active efflux was identified in all strains investigated, on the basis of restored sensitivity in the presence of the inhibitors reserpine and carbonyl cyanide 3-chlorophenylhydrazone (CCCP). Cell surface hydrophobicity and the presence of active efflux could contribute to the resistance of S. enterica to the antibacterial agents studied here.

Effectiveness of sodium benzoate as a freshwater low toxicity antifoulant when dispersed in solution and entrapped in silicone coatings

The traditional solution for preventing organisms from attaching to submerged surfaces is to apply antifouling coatings or biocides. Based on the varied defence mechanisms exhibited by biofilms, the antifoulant needs to prevent bacterial attachment during the early stages of biofilm formation. The potential of benzoic acid and sodium benzoate (NaB) as antifoulants for deterring freshwater bacterial attachment was evaluated with the antifoulants dispersed in solution or entrapped in silicone coatings. Effectiveness was based on the decrease in microbial attachment, limited toxicity, and minimum alteration of the properties of the coatings. The optimal NaB concentration when dispersed in solution, 700 mg l-1, resulted in a biofilm surface coverage of only 3.34% after four weeks. The model silicone, Sylgard 184, demonstrated a better overall performance than the commercial coating, RTV11. Sylgard 184 containing sodium benzoate had 41-52% less biofilm in comparison to the control Sylgard 184, whereas both the control and NaB-entrapped RTV11 coatings had significant biofilm coverage.

Bioactive berry compounds?novel tools against human pathogens

Berry fruits are rich sources of bioactive compounds, such as phenolics and organic acids, which have antimicrobial activities against human pathogens. Among different berries and berry phenolics, cranberry, cloudberry, raspberry, strawberry and bilberry especially possess clear antimicrobial effects against, e.g. Salmonella and Staphylococcus. Complex phenolic polymers, like ellagitannins, are strong antibacterial agents present in cloudberry and raspberry. Several mechanisms of action in the growth inhibition of bacteria are involved, such as destabilisation of cytoplasmic membrane, permeabilisation of plasma membrane, inhibition of extracellular microbial enzymes, direct actions on microbial metabolism and deprivation of the substrates required for microbial growth. Antimicrobial activity of berries may also be related to antiadherence of bacteria to epithelial cells, which is a prerequisite for colonisation and infection of many pathogens. Antimicrobial berry compounds may have important applications in the future as natural antimicrobial agents for food industry as well as for medicine. Some of the novel approaches are discussed.

Promiscuity in the geometry of electrostatic interactions between the Escherichia coli multidrug resistance transporter MdfA and cationic substrates

The Escherichia coli multidrug transporter MdfA contains a single membrane-embedded charged residue (Glu-26) that plays a critical role in the recognition of cationic substrates (Edgar, R., and Bibi, E. (1999) EMBO J. 18, 822-832). Using an inactive mutant (MdfA-E26T), we isolated a spontaneous second-site mutation (MdfA-E26T/V335E) that re-established the recognition of cationic drugs by the transporter. Only a negative charge at position 335 was able to restore the functioning of the inactive mutant MdfA-E26T. Intriguingly, the two genetically interacting residues are located at remote and distinct regions along the secondary structure of MdfA. Glu-26 is located in the periplasmic half of transmembrane helix 1, and as shown here, the complementing charge at position 335 resides within the cytoplasmic loop connecting transmembrane helices 10 and 11. The spatial relation between the two residues was investigated by cross-linking. A functional split version of MdfA devoid of cysteines was constructed and introduced with a cysteine pair at positions 26 and 335. Strikingly, the results indicate that residues 26 and 335 are spatially adjacent, suggesting that they both constitute parts of the multidrug recognition pocket of MdfA. The fact that electrostatic interactions are preserved with cationic substrates even if the critical acidic residue is placed on another face of the pocket reveals an additional dimension of promiscuity in multidrug recognition and transport.

Identification and biological evaluation of grapefruit oil components as potential novel efflux pump modulators in methicillin-resistant Staphylococcus aureus bacterial strains

Methicillin-resistant Staphylococcus aureus (MRSA) and MSSA strains were treated with: (a) grapefruit oil (GFO) components, isolated by chromatography and characterised by NMR and mass spectroscopy; (b) antimicrobial agents, or (c) a combination of both to evaluate (MIC determination) intrinsic antibacterial activity and to determine whether GFO components could modulate bacterial sensitivity to the anti-bacterial agents. Preliminary data suggested that the grapefruit component 4-[[(E)-5-(3,3-dimethyl-2-oxiranyl)-3-methyl-2-pentenyl]oxy]-7H-furo[3,2-g]chromen-7-one (2) enhances the susceptibility of test MRSA strains to agents, e.g., ethidium bromide and norfloxacin, to which these micro-organisms are normally resistant.

Epidemiologic background of hand hygiene and evaluation of the most important agents for scrubs and rubs

The etiology of nosocomial infections, the frequency of contaminated hands with the different nosocomial pathogens, and the role of health care workers' hands during outbreaks suggest that a hand hygiene preparation should at least have activity against bacteria, yeasts, and coated viruses. The importance of efficacy in choosing the right hand hygiene product is reflected in the new Centers for Disease Control and Prevention guideline on hand hygiene (J. M. Boyce and D. Pittet, Morb. Mortal. Wkly. Rep. 51:1-45, 2002). The best antimicrobial efficacy can be achieved with ethanol (60 to 85%), isopropanol (60 to 80%), and n-propanol (60 to 80%). The activity is broad and immediate. Ethanol at high concentrations (e.g., 95%) is the most effective treatment against naked viruses, whereas n-propanol seems to be more effective against the resident bacterial flora. The combination of alcohols may have a synergistic effect. The antimicrobial efficacy of chlorhexidine (2 to 4%) and triclosan (1 to 2%) is both lower and slower. Additionally, both agents have a risk of bacterial resistance, which is higher for chlorhexidine than triclosan. Their activity is often supported by the mechanical removal of pathogens during hand washing. Taking the antimicrobial efficacy and the mechanical removal together, they are still less effective than the alcohols. Plain soap and water has the lowest efficacy of all. In the new Centers for Disease Control and Prevention guideline, promotion of alcohol-based hand rubs containing various emollients instead of irritating soaps and detergents is one strategy to reduce skin damage, dryness, and irritation. Irritant contact dermatitis is highest with preparations containing 4% chlorhexidine gluconate, less frequent with nonantimicrobial soaps and preparations containing lower concentrations of chlorhexidine gluconate, and lowest with well-formulated alcohol-based hand rubs containing emollients and other skin conditioners. Too few published data from comparative trials are available to reliably rank triclosan. Personnel should be reminded that it is neither necessary nor recommended to routinely wash hands after each application of an alcohol-based hand rub. Long-lasting improvement of compliance with hand hygiene protocols can be successful if an effective and accessible alcohol-based hand rub with a proven dermal tolerance and an excellent user acceptability is supplied, accompanied by education of health care workers and promotion of the use of the product.

The AcrAB-TolC pump is involved in macrolide resistance but not in telithromycin efflux in Enterobacter aerogenes and Escherichia coli

The role of the AcrAB-TolC pump in macrolide and ketolide susceptibility in Escherichia coli and Enterobacter aerogenes was studied. Efflux pump inhibitor restored erythromycin, clarithromycin, and telithromycin susceptibilities to multidrug-resistant isolates. No modification of telithromycin accumulation was detected in E. aerogenes acrAB or tolC derivatives compared to that in the parental strain. Two independent efflux pumps, inhibited by phenylalanine arginine beta-naphthylamide, expel macrolides and telithromycin in E. aerogenes.

The structural basis of substrate translocation by the Escherichia coli glycerol-3-phosphate transporter: a member of the major facilitator superfamily

The major facilitator superfamily represents the largest group of secondary active membrane transporters in the cell. The 3.3A resolution structure of a member of this protein superfamily, the glycerol-3-phosphate transporter from the Escherichia coli inner membrane, reveals two domains connected by a long central loop. These N- and C-terminal domains, each containing a six-helix bundle, are related by pseudo-twofold symmetry. A substrate translocation pore is located between the two domains and is open to the cytoplasm. Two arginines at the closed end of the pore comprise the substrate-binding site. Biochemical experiments show that, upon substrate binding, the protein adopts a more compact conformation. The crystal structure suggests that the transporter operates through a single binding site, alternating access mechanism via a rocker-switch type of movement of the N- and C-terminal domains. The structure and mechanism of the glycerol-3-phosphate transporter form a paradigm for other members of the major facilitator superfamily.

Detection and prevalence of active drug efflux mechanism in various multidrug-resistant Klebsiella pneumoniae strains from Turkey

The prevalence of active drug efflux pump and porin alterations was investigated in Turkish nosocomial strains of Klebsiella pneumoniae exhibiting a multidrug-resistant phenotype. MICs of various antibiotics, including quinolones, chloramphenicol, tetracycline, and beta-lactams, for those strains were determined either with or without the efflux pump inhibitor phenylalanine arginine beta-naphthylamide (PAbetaN). Thirty-nine percent of the strains exhibited a PAbetaN-modulated resistance for quinolones, chloramphenicol, and tetracycline. In these strains, a significant increase of chloramphenicol accumulation was gained in the presence of the efflux pump inhibitor PAbetaN or with the energy uncoupler carbonyl cyanide m-chlorophenylhydrazone. Moreover, high-level expression of the membrane fusion protein AcrA, which was immunodetected in most of those isolates, suggests that the AcrAB/TolC efflux machinery contributed to their antibiotic resistance. Studies of K. pneumoniae porins indicated that the majority of the strains, including extended-spectrum beta-lactamase producers and efflux-positive ones, presented an alteration in their sorbitol-sensitive porin (OmpK35) expression. This is the first report showing the prominent role of active drug efflux in the antibiotic resistance of nosocomial K. pneumoniae strains from Turkey.

Effect of triclosan or a phenolic farm disinfectant on the selection of antibiotic-resistant Salmonella enterica

OBJECTIVE

To determine the effect of growth of five strains of Salmonella enterica and their isogenic multiply antibiotic-resistant (MAR) derivatives with a phenolic farm disinfectant or triclosan (biocides) upon the frequency of mutation to resistance to antibiotics or cyclohexane.

METHODS

Strains were grown in broth with or without the biocides and then spread on to agar containing ampicillin, ciprofloxacin or tetracycline each at 4x MIC or agar overlaid with cyclohexane. Incubation was for 24 and 48 h and the frequency of mutation to resistance was calculated for strains with and without prior growth with the biocides. MICs were determined and the presence of mutations in the acrR and marR regions was determined by sequencing and the presence of mutations in gyrA by light-cycler analysis, for a selection of the mutants that arose.

RESULTS

The mean frequency of mutation to antibiotic or cyclohexane resistance was increased approximately 10- to 100-fold by prior growth with the phenolic disinfectant or triclosan. The increases were statistically significant for all antibiotics and cyclohexane following exposure to the phenolic disinfectant (P </= 0.013), and for ampicillin and cyclohexane following exposure to triclosan (P </= 0.009). Mutants inhibited by >1 mg/L ciprofloxacin arose only from strains that were MAR. Reduced susceptibility to ciprofloxacin (at 4x MIC for parent strains) alone was associated with mutations in gyrA. MAR mutants did not contain mutations in the acrR or marR region.

CONCLUSIONS

These data renew fears that the use of biocides may lead to an increased selective pressure towards antibiotic resistance.

Effects of quaternary-ammonium-based formulations on bacterial community dynamics and antimicrobial susceptibility

Quaternary ammonium compounds (QACs) are widely used as adjuncts to hygiene in domestic cleaning products. Current concern that the increased use of such biocides in consumer products might contribute to the emergence of antibiotic resistance has led us to examine the effects of a QAC-containing domestic cleaning fluid on the population dynamics and antimicrobial susceptibility of domestic sink drain biofilm communities. QAC susceptibilities of numerically dominant, culturable drain bacteria (15 genera, 17 species) were determined in vitro before and after repeated QAC exposure (14 passages). A fully characterized drain microcosm was then exposed to short-term (12 days) and long-term (3 months) dosing with a QAC-containing domestic detergent (QD). QAC exposure of isolated cultures caused both increases (three species) and circa twofold decreases (six species) in QAC susceptibility. The susceptibility of Ralstonia sp. was considerably decreased following 14 consecutive QAC passages. Control drain microcosm biofilms maintained dynamic stability, as evidenced by culture and denaturing gradient gel electrophoresis (DGGE) analysis. Bacterial population densities were largely unaffected during short-term exposure to use levels of QD, although 50% QD caused circa 10-fold viability reductions. DGGE analysis supported these observations; identified the major microcosm genera as Pseudomonas, Pseudoalteromonas, Erwinia, and Enterobacter, and showed that aeromonads increased in abundance under 10 to 50% QD. Long-term exposure of the microcosms to QD did not significantly alter the pattern of antimicrobial susceptibility. These data demonstrate the recalcitrance of domestic drain biofilms toward QAC and that although repeated QAC exposure of drain isolates in pure culture results in susceptibility change in some test bacteria, such changes do not necessarily occur within complex communities.

Adaptive resistance to biocides in Salmonella enterica and Escherichia coli O157 and cross-resistance to antimicrobial agents

The mechanisms by which bacteria resist killing by antibiotics and biocides are still poorly defined, although repeated exposure to sublethal concentrations of antibacterial agents undoubtedly contributes to their development. This study aimed both to investigate the potential of Salmonella enterica and Escherichia coli O157 for adaptive resistance to commonly used biocides and to determine any cross-resistance to antibiotics. Strains were repeatedly passaged in media containing increasing concentrations of a biocide or antibiotic until adaptive resistance was obtained. A wide panel of antimicrobial agents was then screened by using the adapted strain to determine cross-resistance, if any. Adaptive resistance was readily achieved for both S. enterica and E. coli O157. Cross-resistance in adaptively resistant S. enterica varied with the serotype; Salmonella enterica serovar Enteritidis expressed cross-resistance to chloramphenicol, whereas Salmonella enterica serovar Typhimurium expressed cross-resistance to chlorhexidine. Benzalkonium chloride-resistant Salmonella enterica serovar Virchow showed elevated resistance to chlorhexidine; however, chlorhexidine-resistant Salmonella serovar Virchow did not demonstrate reciprocal cross-resistance to benzalkonium chloride, suggesting specific rather than generic resistance mechanisms. E. coli O157 strains acquired high levels of resistance to triclosan after only two sublethal exposures and, when adapted, repeatedly demonstrated decreased susceptibilities to various antimicrobial agents, including chloramphenicol, erythromycin, imipenem, tetracycline, and trimethoprim, as well as to a number of biocides. These observations raise concern over the indiscriminate and often inappropriate use of biocides, especially triclosan, in situations where they are unnecessary, whereby they may contribute to the development of microbial resistance mechanisms.

Determinants of substrate recognition by the Escherichia coli multidrug transporter MdfA identified on both sides of the membrane

The Escherichia coli multidrug transporter MdfA contains a membrane-embedded charged residue (Glu-26) that was shown to play an important role in substrate recognition. To identify additional determinants of multidrug recognition we isolated 58 intragenic second-site mutations that restored the function of inactive MdfA E26X mutants. In addition, two single-site mutations that enhanced the activity of wild-type MdfA were identified. Most of the mutations were found in two regions, the cytoplasmic half of transmembrane segments (TMs) 4, 5, and 6 (cluster 1) and the periplasmic half of TM 1 and 2 (cluster 2). The identified residues were mutated to cysteines in the background of a functional cysteine-less MdfA, and substrate protection against alkylation was analyzed. The results support the suggestion that the two clusters are involved in substrate recognition. Using inverted membrane vesicles we observed that a proton electrochemical gradient (Deltamicro(H(+)), inside positive and acidic) enhanced the substrate-protective effect in the cytoplasmic region, whereas it largely reduced this effect in the periplasmic side of MdfA. Therefore, we propose that substrates interact with two sites in MdfA, one in the cytoplasmic leaflet of the membrane and the other in the periplasmic leaflet. Theoretically, these domains could constitute a large part of the multidrug pathway through MdfA.

Biocide use and antibiotic resistance: the relevance of laboratory findings to clinical and environmental situations

Antibiotics are used as chemotherapeutic drugs, and biocides are used as antiseptics, disinfectants, and preservatives. Several factors affect biocidal activity, notably concentration, period of contact, pH, temperature, the presence of interfering material, and the types, numbers, location, and condition of microorganisms. Bacterial cells as part of natural or artificial (laboratory) biofilm communities are much less susceptible than planktonic cells to antibiotics and biocides. Assessment of biocidal activity by bactericidal testing is more relevant than by determination of minimum inhibitory concentrations. Biocides and antibiotics may show some similarities in their mechanisms of action and common mechanisms of bacterial insusceptibility may apply, but there are also major differences. In the laboratory, bacteria can become less susceptible to some biocides. Decreased resistance may be stable or unstable and may be accompanied by a low-level increase in antibiotic resistance. Laboratory studies are useful for examining stress responses and basic mechanisms of action and of bacterial insusceptibility to antibacterial agents. Translation of such findings to the clinical and environmental situations to provide evidence of a possible relation between biocide use and clinical antibiotic resistance is difficult and should be viewed with caution.

Microbial shifts after subgingival debridement and formation of bacterial resistance when combined with local or systemic antimicrobials

Antibiotics have played a major role in the improvement of life expectancy in the last 50 years and have led many to believe that bacterial infections were about to vanish as a disease entity of any importance. Emerging problems resulting from a widespread use of antibiotics have modified the general perception of the capabilities of antimicrobial agents. Over the years, bacteria have become increasingly resistant to formerly potent antimicrobial agents, including some antiseptics. The use of antimicrobials may also disturb the delicate ecological equilibrium of the body, allowing the proliferation of resistant bacteria or non-bacterial micro-organisms. This shift may initiate new infections that are worse than the ones originally treated. No antimicrobial drug is absolutely non-toxic and the use of an agent carries accompanying risks. This paper discusses the development and occurrence of antimicrobial resistance in the subgingival flora towards antiseptics and local or systemic antibiotics and is focussed on the question: how can the outcome of periodontal therapy with/without antimicrobials be improved?

Structure and mechanism of the glycerol-3-phosphate transporter from Escherichia coli

The major facilitator superfamily represents the largest group of secondary membrane transporters in the cell. Here we report the 3.3 angstrom resolution structure of a member of this superfamily, GlpT, which transports glycerol-3-phosphate into the cytoplasm and inorganic phosphate into the periplasm. The amino- and carboxyl-terminal halves of the protein exhibit a pseudo two-fold symmetry. Closed off to the periplasm, a centrally located substrate-translocation pore contains two arginines at its closed end, which comprise the substrate-binding site. Upon substrate binding, the protein adopts a more compact conformation. We propose that GlpT operates by a single-binding site, alternating-access mechanism through a rocker-switch type of movement.

Genetic strategies for antibacterial drug discovery

The availability of genome sequences is revolutionizing the field of microbiology. Genetic methods are being modified to facilitate rapid analysis at a genome-wide level and are blossoming for human pathogens that were previously considered intractable. This revolution coincided with a growing concern about the emergence of microbial drug resistance, compelling the pharmaceutical industry to search for new antimicrobial agents. The availability of the new technologies, combined with many genetic strategies, has changed the way that researchers approach antibacterial drug discovery.

Potential impact of increased use of biocides in consumer products on prevalence of antibiotic resistance

There has recently been much controversy surrounding the increased use of antibacterial substances in a wide range of consumer products and the possibility that, as with antibiotics, indiscriminate use of biocides might contribute to the overall pattern of susceptibility in the general environment and in the clinic. Such speculation, based on the isolation of resistant mutants from in vitro monoculture experiments, is not reflected by an emergence of biocide-resistant strains in vivo. This review provides a broad coverage of the biocide and resistance literature and evaluates the potential risks, perceived from such laboratory monoculture experiments, against evidence gathered over 50 years of field studies. An explanation for the continued effectiveness of broad-spectrum biocidal agents against the decline in efficacy of therapeutic agents is provided based on the fitness costs of resistance and the ubiquity of naturally occurring substances that possess antibacterial effect. While we conclude from this review of the literature that the incorporation of antibacterial agents into a widening sphere of personal products has had little or no impact on the patterns of microbial susceptibility observed in the environment, the associated risks remain finite. The use of such products should therefore be associated with a clear demonstration of added value either to consumer health or to the product life. Hygienic products should therefore be targeted to applications for which the risks have been established.