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Biomedical subjects

S B Levy

Publications and source records attributed to S B Levy.

At least 19 recordsLinked to original sources
PubMed2003

Role of AcrR and ramA in fluoroquinolone resistance in clinical Klebsiella pneumoniae isolates from Singapore.

The MICs of ciprofloxacin for 33 clinical isolates of K. pneumoniae resistant to extended-spectrum cephalosporins from three hospitals in Singapore ranged from 0.25 to >128 microg/ml. Nineteen of the isolates were fluoroquinolone resistant according to the NCCLS guidelines. Strains for which the ciprofloxacin MIC was >or=0.5 microg/ml harbored a mutation in DNA gyrase A (Ser83-->Tyr, Leu, or IIe), and some had a secondary Asp87-->Asn mutation. Isolates for which the MIC was 16 microg/ml possessed an additional alteration in ParC (Ser80-->IIe, Trp, or Arg). Tolerance of the organic solvent cyclohexane was observed in 10 of the 19 fluoroquinolone-resistant strains; 3 of these were also pentane tolerant. Five of the 10 organic solvent-tolerant isolates overexpressed AcrA and also showed deletions within the acrR gene. Complementation of the mutated acrR gene with the wild-type gene decreased AcrA levels and produced a two- to fourfold reduction in the fluoroquinolone MICs. None of the organic solvent-tolerant clinical isolates overexpressed another efflux-related gene, acrE. While marA and soxS were not overexpressed, another marA homologue, ramA, was overexpressed in 3 of 10 organic solvent-tolerant isolates. These findings indicate that multiple target and nontarget gene changes contribute to fluoroquinolone resistance in K. pneumoniae. Besides AcrR mutations, ramA overexpression (but not marA or soxS overexpression) was related to increased AcrAB efflux pump expression in this collection of isolates.

Anti-Infective Agents↗
PubMed2002

Active efflux, a common mechanism for biocide and antibiotic resistance.

Energy-driven drug efflux systems are increasingly recognized as mechanisms of antibiotic resistance. Chromosomally located or acquired by bacteria, they can either be activated by environmental signals or by a mutation in a regulatory gene. Two major categories exist: those systems energized by proton motive force and those dependent on ATP. The pumps may have limited or broad substrates, the so-called multiple drug resistance pumps, which themselves form a number of related families. The multiple antibiotic resistance (mar) locus and mar regulon in Escherichia coli and other members of the Enterobacteriaceae is a paradigm for a generalized response locus leading to increased expression of efflux pumps. One such pump, the AcrAB pump extrudes biocides such as triclosan, chlorhexidine and quaternary ammonium compounds as well as multiple antibiotics. In Pseudomonas aeruginosa, a number of multidrug efflux pumps export a broad range of substrates. Since bacteria expressing these pumps thwart the efficacy of both kinds of therapeutic agents which control infectious diseases -- biocides which prevent transmission of infectious disease agents and antibiotics which treat and cure infectious diseases -- they are of particular concern. The prudent use of antibiotics and biocides will guard against the selection and propagation of drug-resistant mutants and preserve the efficacy of these valuable anti-infective agents.

Anti-Bacterial Agents↗
PubMed2002

Active efflux, a common mechanism for biocide and antibiotic resistance.

Energy-driven drug efflux systems are increasingly recognized as mechanisms of antibiotic resistance. Chromosomally located or acquired by bacteria, they can either be activated by environmental signals or by a mutation in a regulatory gene. Two major categories exist: those systems energized by proton motive force and those dependent on ATP. The pumps may have limited or broad substrates, the so-called multiple drug resistance pumps, which themselves form a number of related families. The multiple antibiotic resistance (mar) locus and mar regulon in Escherichia coli and other members of the Enterobacteriaceae is a paradigm for a generalized response locus leading to increased expression of efflux pumps. One such pump, the AcrAB pump extrudes biocides such as triclosan, chlorhexidine and quaternary ammonium compounds as well as multiple antibiotics. In Pseudomonas aeruginosa, a number of multidrug efflux pumps export a broad range of substrates. Since bacteria expressing these pumps thwart the efficacy of both kinds of therapeutic agents which control infectious diseases--biocides which prevent transmission of infectious disease agents and antibiotics which treat and cure infectious diseases--they are of particular concern. The prudent use of antibiotics and biocides will guard against the selection and propagation of drug-resistant mutants and preserve the efficacy of these valuable anti-infective agents.

Anti-Bacterial Agents↗
PubMed2001

Carriage of antibiotic-resistant fecal bacteria in Nepal reflects proximity to Kathmandu.

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.

Adolescent↗
PubMed2001

Antibiotic resistance: consequences of inaction.

Bacterial resistance presents therapeutic dilemmas to clinicians worldwide. The warnings were there long ago, but too few people heeded them. Thus an emerging problem has grown to a crisis. Resistance is an ecological phenomenon stemming from the response of bacteria to the widespread use of antibiotics and their presence in the environment. While determining the consequences of inaction on the present and future public health, we must work to remedy the lack of action in the past. By improving antibiotic use and decreasing resistance gene frequency at the local levels, we can move towards reversing the resistance problem globally.

Animals↗
PubMed2001

Antimicrobial resistance: a plan of action for community practice.

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.

Anti-Bacterial Agents↗
PubMed2001

The crystal structure of MarR, a regulator of multiple antibiotic resistance, at 2.3 A resolution.

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 A. 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.

Amino Acid Motifs↗
PubMed2001

A soxRS-constitutive mutation contributing to antibiotic resistance in a clinical isolate of Salmonella enterica (Serovar typhimurium).

The soxRS regulon is activated by redox-cycling drugs such as paraquat and by nitric oxide. The >15 genes of this system provide resistance to both oxidants and multiple antibiotics. An association between clinical quinolone resistance and elevated expression of the soxRS regulon has been observed in Escherichia coli, but this association has not been explored for other enteropathogenic bacteria. Here we describe a soxRS-constitutive mutation in a clinical strain of Salmonella enterica (serovar Typhimurium) that arose with the development of resistance to quinolones during treatment. The elevated quinolone resistance in this strain derived from a point mutation in the soxR gene and could be suppressed in trans by multicopy wild-type soxRS. Multiple-antibiotic resistance was also transferred to a laboratory strain of S. enterica by introducing the cloned mutant soxR gene from the clinical strain. The results show that constitutive expression of soxRS can contribute to antibiotic resistance in clinically relevant S. enterica.

Anti-Bacterial Agents↗
PubMed2001

Mdt(A), a new efflux protein conferring multiple antibiotic resistance in Lactococcus lactis and Escherichia coli.

The mdt(A) gene, previously designated mef214, from Lactococcus lactis subsp. lactis plasmid pK214 encodes a protein [Mdt(A) (multiple drug transporter)] with 12 putative transmembrane segments (TMS) that contain typical motifs conserved among the efflux proteins of the major facilitator superfamily. However, it also has two C-motifs (conserved in the fifth TMS of the antiporters) and a putative ATP-binding site. Expression of the cloned mdt(A) gene decreased susceptibility to macrolides, lincosamides, streptogramins, and tetracyclines in L. lactis and Escherichia coli, but not in Enterococcus faecalis or in Staphylococcus aureus. Glucose-dependent efflux of erythromycin and tetracycline was demonstrated in L. lactis and in E. coli.

Amino Acid Sequence↗
PubMed2001

Genetic characterization of highly fluoroquinolone-resistant clinical Escherichia coli strains from China: role of acrR mutations.

The genetic basis for fluoroquinolone resistance was examined in 30 high-level fluoroquinolone-resistant Escherichia coli clinical isolates from Beijing, China. Each strain also demonstrated resistance to a variety of other antibiotics. PCR sequence analysis of the quinolone resistance-determining region of the topoisomerase genes (gyrA/B, parC) revealed three to five mutations known to be associated with fluoroquinolone resistance. Western blot analysis failed to demonstrate overexpression of MarA, and Northern blot analysis did not detect overexpression of soxS RNA in any of the clinical strains. The AcrA protein of the AcrAB multidrug efflux pump was overexpressed in 19 of 30 strains of E. coli tested, and all 19 strains were tolerant to organic solvents. PCR amplification of the complete acrR (regulator/repressor) gene of eight isolates revealed amino acid changes in four isolates, a 9-bp deletion in another, and a 22-bp duplication in a sixth strain. Complementation with a plasmid-borne wild-type acrR gene reduced the level of AcrA in the mutants and partially restored antibiotic susceptibility 1.5- to 6-fold. This study shows that mutations in acrR are an additional genetic basis for fluoroquinolone resistance.

Anti-Infective Agents↗
PubMed2001

The adnA transcriptional factor affects persistence and spread of Pseudomonas fluorescens under natural field conditions.

A soil plot was inoculated with a mixture of Pseudomonas fluorescens Pf0-2, the wild type, and Pf0-5a, a Tn5 insertion mutant in adnA, at 7.84 log CFU/g of soil. Over a period of 231 days, culturable populations of both strains were measured at selected times below and away from the point of inoculation. Pf0-5a did not spread as fast and attained significantly lower populations than Pf0-2. At sample depths below the inoculation site, the adnA mutant showed a significant decrease in CFU/g of soil as compared to Pf0-2. Pf0-2 was first detected at the 1.5-cm annular site at 3 days after inoculation, whereas Pf0-5a required 7 days to travel the same distance. At this distance, the wild-type strain could be detected at a 21.5- to 25-cm depth, whereas Pf0-5a could be detected only as deep as 15.5 to 18 cm. At 4.5 cm from the site of inoculation and in soil fractions corresponding to 13 to 18 cm, Pf0-2 was the only strain detected. These results suggest that the transcription factor AdnA provides a fitness advantage in P. fluorescens, allowing it to spread and survive in soil under field conditions.

Bacterial Proteins↗
PubMed2001

Antibacterial household products: cause for concern.

The recent entry of products containing antibacterial agents into healthy households has escalated from a few dozen products in the mid-1990s to more than 700 today. Antibacterial products were developed and have been successfully used to prevent transmission of disease-causing microorganisms among patients, particularly in hospitals. They are now being added to products used in healthy households, even though an added health benefit has not been demonstrated. Scientists are concerned that the antibacterial agents will select bacteria resistant to them and cross-resistant to antibiotics. Moreover, if they alter a person's microflora, they may negatively affect the normal maturation of the T helper cell response of the immune system to commensal flora antigens; this change could lead to a greater chance of allergies in children. As with antibiotics, prudent use of these products is urged. Their designated purpose is to protect vulnerable patients.

Anti-Infective Agents, Local↗
PubMed2000

Evidence for interactions between helices 5 and 8 and a role for the interdomain loop in tetracycline resistance mediated by hybrid Tet proteins.

An interdomain hybrid Tet protein consisting of a class C alpha domain and a class B beta domain (Tet(C/B)) lacks detectable efflux ability and provides only minimal levels of resistance to tetracycline (Tc) (3 microg/ml) compared with intact class B (256 microg/ml) and class C (64 microg/ml). Twenty-one independently isolated mutants of the Tet(C/B) protein with increased Tc resistance were generated by random chemical mutagenesis. Nine mutants with a Glu substitution for Gly-152 in helix 5 of the class C alpha domain produced a resistance of 48 microg/ml, whereas another 9 with an Asp replacement of Gly-247 in helix 8 of the class B beta domain mediated resistance at 32 microg/ml. The third type of mutation, found in 3 mutants expressing 24 microg/ml resistance, was a S202F replacement in the putative interdomain cytoplasmic loop of Tet(C/B). The latter underscores a previously unappreciated function of the interdomain cytoplasmic loop. All three types of Tet(C/B) mutant proteins were expressed in amounts comparable with that of the original protein and demonstrated restored energy-dependent efflux of tetracycline. Site-directed mutational analysis demonstrated that a Gly-247 to Asn mutation could also facilitate Tc resistance by the Tet(C/B) hybrid, and a negatively charged side chain at position 152 was required for Tet(C/B) activity. These mutations appear to promote the necessary functional interactions between the interclass domains that do not occur in the Tet(C/B) hybrid protein and suggest a direct association between helix 5 and helix 8 in the function of Tet efflux proteins.

Amino Acid Sequence↗
PubMed2000

Modern approaches to photoprotection.

UV light reacts with skin to produce undesirable changes, including photoaging and skin cancer. Sunscreen strategies are useful for protection against UV-B and short-wave UV-A, but complete protection against long-wave UV-A has not been achieved. Because UV-A is especially efficient at generating reactive oxygen species, it is being recognized increasingly as an important cause of photoaging and skin cancer.

Antioxidants↗
PubMed2000

Tanning preparations.

Increasing consumer awareness as to the hazards of UV light should fuel ongoing interest in self-tanning products. As a result of the benign toxicologic profile of DHA, products containing DHA represent a safe alternative to UV-induced tanning. The results obtained with these products depend on the final formulation, the individual application technique, and the consumer's complexion type. Greater experience in formulation combined with increasing sophistication on the part of the consumer should lead to continuing growth in interest and satisfaction with the use of DHA-containing sunless or self-tanning products. Individuals need to be informed that these products do not offer significant protection against UV-B. If formulated with standard sunscreens, consumers should be cautioned that the duration of UV protection is more short-lived than the color change.

Dermatologic Agents↗
PubMed2000

Mutational analysis of MarR, the negative regulator of marRAB expression in Escherichia coli, suggests the presence of two regions required for DNA binding.

MarR, the negative regulator of the Escherichia coli multiple antibiotic resistance (marRAB) operon, is a member of a newly recognized family of regulatory proteins. The amino acid sequences of these proteins do not display any apparent homologies to the DNA binding domains of prokaryotic transcription regulators and a DNA binding motif for any one of the MarR homologues is currently unknown. In order to define regions of MarR required for DNA binding, mutant repressors, selected based on their ability to interfere with (negatively complement) the activity of wild-type MarR, were isolated. As determined using gel mobility shift assays, 13 out of 14 negative complementing mutants tested were unable to bind DNA in vitro. Three negative complementing alleles presumably specify truncated repressors and one of these proteins, a 120 residue MarR, can bind DNA in vitro. Most of the negative complementing mutations were clustered within two areas of MarR with features related to a helix-turn-helix DNA binding motif. These regions are presumed to be required for the DNA binding activity of the repressor.

Amino Acid Motifs↗
PubMed2000

'Intergenic' blr gene in Escherichia coli encodes a 41-residue membrane protein affecting intrinsic susceptibility to certain inhibitors of peptidoglycan synthesis.

In the annotation of genomic sequences, small open reading frames (ORFs) are often neglected, particularly if they have no homology to other ORFs or proteins. A mini-TnphoA insertion in a 602 bp 'intergenic' region of the Escherichia coli chromosome at genomic nucleotide 1702674 gave rise to a membrane-bound PhoA fusion protein and a two- to fourfold increase in the intrinsic susceptibility to a wide spectrum of beta-lactam antibiotics without affecting beta-lactamase activity or susceptibility to tetracycline, chloramphenicol, gentamicin or quinolones. Susceptibility was also increased to cycloserine and bacitracin, but not to fosfomycin or valinomycin; these drugs, like beta-lactams, inhibit peptidoglycan synthesis, although by different mechanisms. A clone bearing only 358 bp of this 'blr' region restored resistance to the parental level. Two amber mutations in the clone prevented such restoration and were counteracted by an amber suppressor, proving that the active species is a protein. The Blr protein has 41 amino acids, with a single predicted transmembrane helix, but no clear homology to any other protein. A transcriptional start exists 39 bp upstream from the translational start. The membrane location of Blr suggests that it may be part of an efflux pump or involved in murein metabolism. The results indicate that genes for other very small functional proteins may lie within 'intergenic' regions.

Alkaline Phosphatase↗