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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.cell.2007.03.004 Byline: Michael N. Alekshun (1), Stuart B. Levy (2) Abstract: Treatment of infections is compromised worldwide by the emergence of bacteria that are resistant to multiple antibiotics. Although classically attributed to chromosomal mutations, resistance is most commonly associated with extrachromosomal elements acquired from other bacteria in the environment. These include different types of mobile DNA segments, such as plasmids, transposons, and integrons. However, intrinsic mechanisms not commonly specified by mobile elements -- such as efflux pumps that expel multiple kinds of antibiotics -- are now recognized as major contributors to multidrug resistance in bacteria. Once established, multidrug-resistant organisms persist and spread worldwide, causing clinical failures in the treatment of infections and public health crises. Author Affiliation: (1) Schering-Plough Research Institute, 2015 Galloping Hill Road, Kenilworth, NJ 07033, USA (2) Center for Adaptation Genetics and Drug Resistance, Department of Molecular Biology & Microbiology and Department of Medicine, Tufts University School of Medicine, Boston, MA 02111, USA

Objectives Multidrug efflux pumps mediate resistance to antibiotics and other toxic compounds. We studied the role of AcrAB-TolC, the main efflux pump in Escherichia coli, in regulating gene expression. Methods Deletion mutants, an acrABp-lacZ fusion and reverse transcription–real-time quantitative PCR experiments were used to study the role of AcrAB-TolC and metabolism in regulating gene expression of the acrAB operon and its transcriptional regulators. Results Deletion of the acrB gene increased the expression of the acrAB operon. A similar induction of acrAB was found when acrA or tolC was deleted, and when the pump function was inhibited using phenylalanine-arginine-β-naphthylamide. The induction of acrAB in the ΔacrB strain was totally (AcrR or SoxS) or partially (SoxR or MarA) prevented when the genes for these acrAB regulators were also deleted. The expression of soxS and marA, but not of acrR, was increased in the ΔacrB strain, which also showed altered expression of many other genes related to different cellular processes, including motility. Deletion of the metabolic genes entA and entE (enterobactin biosysnthesis), glpX (gluconeogenesis), cysH (cysteine biosynthesis) and purA (purine biosynthesis) also prevented activation of the acrAB promoter in the ΔacrB strain. Addition of the enterobactin biosynthesis intermediate metabolite 2,3-dihydroxybenzoate induced the expression of acrAB. Conclusions These results together suggest a model in which the AcrAB-TolC pump effluxes cellular metabolites that are toxic and/or have a signalling role. If the pump is inactivated or inhibited, these metabolites would accumulate, inactivating AcrR and/or up-regulating soxS and marA expression, ultimately triggering the up-regulation of acrAB expression to restore homeostasis. [ABSTRACT FROM PUBLISHER]

Bacterial two-hybrid studies of randomly cloned Escherichia coli DNA identified a physical interaction between GyrA, subunit A of gyrase, and MarR, a repressor of the marRAB operon. GyrA-His immobilized on Ni-nitrilotriacetic acid (NiNTA) resin bound MarR, while MarR alone did not bind. GyrA interfered with MarR binding to marO, as detected by electrophoretic mobility assays. In a strain bearing the marRAB operon and a marO-lacZ reporter, overexpression of GyrA increased LacZ activity, indicating decreased repression of marO-lacZ by MarR. These results were confirmed by an increased survival of cells treated with quinolones and other antibiotics when GyrA was overexpressed. This work, like a previous study examining TktA (12), shows that unrelated proteins can regulate MarR activity. The findings reveal an unexpected regulatory function of GyrA in antibiotic resistance. [ABSTRACT FROM AUTHOR]

The Escherichia coli marRAB operon specifies two regulatory proteins, MarR (which represses) and MarA (which activates expression of the operon). The latter controls expression of multiple other chromosomal genes implicated in cell physiology, multiple drug resistance and virulence. Using randomly cloned E. coli DNA fragments in the bacterial adenylate cyclase two-hybrid system, we found that transketolase A (TktA) interacts with MarR. Purified (6H)-TktA immobilized on NiNTA resin-bound MarR. Overexpression or deletion of tktA showed that TktA interfered with MarR repression of the marRAB operon. Deletion of tktA increased antibiotic and oxidative stress susceptibilities, while its overexpression decreased them. Hydrogen peroxide induced tktA at 1 h treatment, while an increase in marRAB expression occurred only after 3 h exposure. This increase was dependent on the presence of tktA. Two MarR mutations which eliminated MarR binding to the marRAB operator and one which decreased dimerization of MarR had no effect on MarR interaction with TktA in the two-hybrid system. However, the interaction was disrupted by one of the three tested superrepressor mutant MarR proteins known to increase MarR binding to DNA. TktA inhibition of repression by MarR demonstrates a previously unrecognized level of control of the expression of marRAB operon. [ABSTRACT FROM AUTHOR]

Background. Much has been written recently about the potential hazards versus benefits of antibacterial (biocide)—containing soaps. The purpose of this systematic literature review was to assess the studies that have examined the efficacy of products containing triclosan, compared with that of plain soap, in the community setting, as well as to evaluate findings that address potential hazards of this use—namely, the emergence of antibiotic-resistant bacteria. Methods. The PubMed database was searched for English-language articles, using relevant keyword combinations for articles published between 1980 and 2006. Twenty-seven studies were eventually identified as being relevant to the review. Results. Soaps containing triclosan within the range of concentrations commonly used in the community setting (0.1%–0.45% wt/vol) were no more effective than plain soap at preventing infectious illness symptoms and reducing bacterial levels on the hands. Several laboratory studies demonstrated evidence of triclosan-adapted cross-resistance to antibiotics among different species of bacteria. Conclusions. The lack of an additional health benefit associated with the use of triclosan-containing consumer soaps over regular soap, coupled with laboratory data demonstrating a potential risk of selecting for drug resistance, warrants further evaluation by governmental regulators regarding antibacterial product claims and advertising. Further studies of this issue are encouraged. [ABSTRACT FROM AUTHOR]

We examined whether household use of antibacterial cleaning and hygiene products is an emerging risk factor for carriage of antimicrobial drug-resistant bacteria on hands of household members. Households (N = 224) were randomized to use of antibacterial or nonantibacterial cleaning and hygiene products for 1 year. Logistic regression was used to assess the influence of antibacterial product use in homes. Antibacterial product use did not lead to a significant increase in antimicrobial drug resistance after 1 year (odds ratio 1.33, 95% confidence interval 0.74-2.41), nor did it have an effect on bacterial susceptibility to triclosan. However, more extensive and longer term use of triclosan might provide a suitable environment for emergence of resistant species. Further research on this issue is needed. [ABSTRACT FROM AUTHOR]

Abstract: While previously recognized antibiotic-resistant bacteria continue to increase in frequency and numbers globally, new resistance problems have recently emerged which further complicate and impede treatment of critical infectious diseases. Vancomycin resistance among Staphylococcus aureus, extended spectrum β-lactamases among gram-negative pathogens, and fluoroquinolone resistance among already multidrug-resistant Escherichia coli and Neisseria gonorrheae are adding to the toll of resistance on patients suffering with infectious diseases. [Copyright &y& Elsevier]

Within Nepal, geographic, social, and economic barriers greatly limit access to allopathic health care. The country therefore offered the opportunity to evaluate the effect of antibiotic accessibility (as measured by allopathic medicine consumption) on antibiotic resistance in the normal intestinal flora. The aerobic gram-negative fecal flora of 33–34 healthy adults from each of 3 villages with different access to health care facilities in Kathmandu were examined for antibiotic susceptibility. The frequency of antibiotic resistance decreased significantly with increasing distance from Kathmandu and decreasing population density but did not reflect contact with health care providers or individual medicine consumption. The findings suggest that an individual's overall exposure to antibiotics and antibiotic-resistant bacteria (resulting from close proximity to other community members and to sources of accessible allopathic health care, such as in the vicinity of Kathmandu), has an equal or greater impact on an individual's carriage of antibiotic-resistant bacteria than does direct consumption of antibiotics. [ABSTRACT FROM AUTHOR]

MarR is a regulator of multiple antibiotic resistance in Escherichia coli. It is the prototypical member of the MarR family of regulatory proteins found in bacteria and archaea that play important roles in the development of antibiotic resistance, a global health problem. Here we describe the crystal structure of the MarR protein, determined at a resolution of 2.3 Å. This is the first reported crystal structure of a member of this newly-described protein family. The structure shows MarR as a dimer with each subunit containing a winged-helix DNA binding motif. [ABSTRACT FROM AUTHOR]

Antibiotic resistance was once confined primarily to hospitals but is becoming increasingly prevalent in family practice settings, making daily therapeutic decisions more challenging. Recent reports of pediatric deaths and illnesses in communities in the United States have raised concerns about the implications and future of antibiotic resistance. Because 20 percent to 50 percent of antibiotic prescriptions in community settings are believed to be unnecessary, primary care physicians must adjust their prescribing behaviors to ensure that the crisis does not worsen. Clinicians should not accommodate patient demands for unnecessary antibiotics and should take steps to educate patients about the prudent use of these drugs. Prescriptions for targeted-spectrum antibiotics, when appropriate, can help preserve the normal susceptible flora. Antimicrobials intended for the treatment of bacterial infections should not be used to manage viral illnesses. Local resistance trends may be used to guide prescribing decisions. [ABSTRACT FROM AUTHOR]

Reports on the generation and characterization of MarR superrepressor mutants in Escherichia coli. Bacterial strains, plasmids, and genetic techniques; Assay of repressor activity by Beta-galactosidase; Selection of MarR superrrepressors.

Opinion. Argues efforts at all levels of drug discovery and use are needed to control and reverse the problem of drug resistance. Awareness and acknowledgment of problem's reality; Shorter treatment schedules for certain diseases; Epidemiological spread of resistance genes and their host bacteria; Individual as gatekeeper for antibiotic use; Supporting research in molecular and genetic basis of resistance.

The article correct the results in a study that previously appeared in the 2007 issue of the magazine regarding the physical interaction of the enzyme Transketolase A (TktA) with the MarR, finding that it depresses the Escherichia coli marRAB multiple antibiotic resistance operon. It cites that further laboratory work failed to confirm the interaction of the TktA gene with the MarR. It indicates that the original conclusions may have resulted from an unexplained variability of LacZ activity.

MarA, a transcriptional regulator in Escherichia coli, affects functions such as multiple-antibiotic resistance (Mar) and virulence. Usually an activator, MarA is a repressor of hdeAB and other acid resistance genes. We found that, in wild-type cells grown in LB medium at pH 7.0 or pH 5.5, repression of hdeAB by MarA occurred only in stationary phase and was reduced in the absence of H-NS and GadE, the main regulators of hdeAB. Moreover, repression of hdeAB by MarA was greater in the absence of GadX or Lrp in exponential phase at pH 7.0 and in the absence of GadW or RpoS in stationary phase at pH 5.5. In turn, MarA enhanced repression of hdeAB by H-NS and hindered activation by GadE in stationary phase and also reduced the activity of GadX, GadW, RpoS, and Lrp on hdeAB under some conditions. As a result of its direct and indirect effects, overexpression of MarA prevented most of the induction of hdeAB expression as cells entered stationary phase and made the cells sevenfold more sensitive to acid challenge at pH 2.5. These findings show that repression of hdeAB by MarA depends on pH, growth phase, and other regulators of hdeAB and is associated with reduced resistance to acid conditions. [ABSTRACT FROM AUTHOR]

In this article, the authors discuss the society's failure to recognize the potential benefits of antibiotics development. They state that antibiotic discovery and development has almost stop due to the continued underestimation of the implications of antibiotic resistance of bacteria. They also add that a halt in antibiotic development is putting an end to an important infection-control measure.

A spontaneous mutant (M113) of Escherichia coli AG100 with an unstable multiple antibiotic resistance (Mar) phenotype was isolated in the presence of tetracycline. Two mutations were found: an insertion in the promoter of lon (lon3::IS186) that occurred first and a subsequent large tandem duplication, dupIS186, bearing the genes acrAB and extending from the lon3::IS186 to another IS186 present 149 kb away from lon. The decreased amount of Lon protease increased the amount of MarA by stabilization of the basal quantities of MarA produced, which in turn increased the amount of multidrug effux pump AcrAB-TolC. However, in a mutant carrying only a lon mutation, the overproduced pump mediated little, if any, increased multidrug resistance, indicating that the Lon protease was required for the function of the pump. This requirement was only partial since resistance was mediated when amounts of AcrAB in a lon mutant were further increased by a second mutation. In M113, amplification of acrAB on the duplication led to increased amounts of AcrAB and multidrug resistance. Spontaneous gene duplication represents a new mechanism for mediating multidrug resistance in E. coli through AcrAB-TolC. [ABSTRACT FROM AUTHOR]