Seasonal variation in basal metabolic rates among the Yakut (Sakha) of Northeastern Siberia.

OBJECTIVES: Previous research has shown that indigenous circumpolar populations have elevated basal metabolic rates (BMRs), yet few studies have explored whether metabolic rates increase during the winter. This study addresses this gap by examining seasonal variation in BMR and its associations with thyroid function and lifestyle factors among the Yakut (Sakha) of Siberia. METHODS: Anthropometric dimensions, BMR, and thyroid hormone levels (free triiodothyronine [fT3], free thyroxine [fT4], thyroid-stimulating hormone [TSH]) were measured on two occasions (July/August, 2009 and January 2011) on a sample of 94 Yakut (Sakha) adults (35 men, 59 women) from the rural village of Berdygestiakh, Sakha Republic, Russia. RESULTS: Seasonal changes in BMR varied by age. Younger Yakut adults (19-49 years) showed significant elevations in winter-time BMR of 6% (P < 0.05), whereas older individuals (≥50 years) showed modest declines (2%; n.s.). Both younger and older Yakut men and women showed increased respiratory quotients during the winter. FT3 and fT4 levels significantly declined during the winter in both younger and older Yakut men and women (P < 0.05). Lifestyle factors were significant predictors of BMR variation, particularly among older men and women. CONCLUSIONS: Among the Yakut, increased wintertime BMR was observed among younger but not older adults, whereas all adults showed sharp reductions in free thyroid hormone levels during the winter. Among men, greater participation in subsistence activities was associated with increased BMRs and greater fat oxidation. Among women, variation in food use had the strongest impact on metabolic function.

In vitro and in vivo antibacterial activities of omadacycline, a novel aminomethylcycline.

Omadacycline is the first intravenous and oral 9-aminomethylcycline in clinical development for use against multiple infectious diseases including acute bacterial skin and skin structure infections (ABSSSI), community-acquired bacterial pneumonia (CABP), and urinary tract infections (UTI). The comparative in vitro activity of omadacycline was determined against a broad panel of Gram-positive clinical isolates, including methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE), Lancefield groups A and B beta-hemolytic streptococci, penicillin-resistant Streptococcus pneumoniae (PRSP), and Haemophilus influenzae (H. influenzae). The omadacycline MIC90s for MRSA, VRE, and beta-hemolytic streptococci were 1.0 µg/ml, 0.25 µg/ml, and 0.5 µg/ml, respectively, and the omadacycline MIC90s for PRSP and H. influenzae were 0.25 µg/ml and 2.0 µg/ml, respectively. Omadacycline was active against organisms demonstrating the two major mechanisms of resistance, ribosomal protection and active tetracycline efflux. In vivo efficacy of omadacycline was demonstrated using an intraperitoneal infection model in mice. A single intravenous dose of omadacycline exhibited efficacy against Streptococcus pneumoniae, Escherichia coli, and Staphylococcus aureus, including tet(M) and tet(K) efflux-containing strains and MRSA strains. The 50% effective doses (ED50s) for Streptococcus pneumoniae obtained ranged from 0.45 mg/kg to 3.39 mg/kg, the ED50s for Staphylococcus aureus obtained ranged from 0.30 mg/kg to 1.74 mg/kg, and the ED50 for Escherichia coli was 2.02 mg/kg. These results demonstrate potent in vivo efficacy including activity against strains containing common resistance determinants. Omadacycline demonstrated in vitro activity against a broad range of Gram-positive and select Gram-negative pathogens, including resistance determinant-containing strains, and this activity translated to potent efficacy in vivo.

Commensals upon us.

A battle to control and curtail bacterial infectious diseases is being waged in our hospitals and communities through antibiotic therapies and vaccines targeting specific species. But what effects do these interventions have on the epidemiology of infections caused by the organisms that are part of our natural microbial flora? Gram-positive and gram-negative bacteria appear as new disease agents from among commensal flora. These include vancomycin resistant enterococci (VRE), community-associated methicillin resistant Staphylococcus aureus (CA-MRSA), non-vaccine invasive serotypes of Streptococcus pneumoniae, new strains of non-type b Haemophilus influenzae and multi-drug resistant Escherichia coli. These examples illustrate how clinical improvements and widespread use and misuse of antibiotics have pushed evolution, allowing normally non-pathogenic strains to become infectious disease threats to human health.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

The quarternary molecular architecture of TetA, a secondary tetracycline transporter from Escherichia coli.

TetA, a tetracycline cation/proton antiporter, was expressed in Escherichia coli with a C-terminal tag of six histidines, solubilized in dodecyl maltoside and purified in a single step using Ni2+ affinity chromatography. Two-dimensional crystals were obtained after reconstitution of purified protein with lipids. Electron microscopy of negatively stained crystals revealed a trigonal symmetry, from which we infer that this secondary transporter has a trimeric structure. An overall molecular envelope can be described by a triangle of side approximately 100 A enclosing a central stain-filled depression. These dimensions are consistent with those obtained from projection views of single, isolated TetA particles that also display a trimeric architecture, confirming that the threefold symmetry is not simply a consequence of crystal-packing interactions. These data represent the first direct view of the quarternary arrangement of any antibiotic efflux pump. They are fully consistent with biochemical data on TetA, which indicate that it functions as a multimer and that the monomer consists of two domains, one of which plays the major part in oligomerization interactions.

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.

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.

Antibiotic and antiseptic resistance: impact on public health.

More and more we are moving patients from hospitals to homes for continued treatment. Vancomycin and triclosan were used for 30 years before any resistance emerged, because their applications were strictly limited. Today, after greatly increased use, resistance to both antibiotics and antibacterials has appeared. Of importance there are genetic links between resistance to antibiotics and to antibacterials. Health professionals and the public need to be educated about the rational use of drugs that affect the microbial world. The Alliance for the Prudent Use of Antibiotics, an international organization established in 1981 with members in more than 100 countries, has adopted education as its prime mission. Via its web site (www.apua.org) and linked information on reservoirs of antibiotic resistance (ROAR) among nonpathogenic bacteria, it reaches both providers and consumers. The message is simple: bacteria are needed for our survival. The vast majority of bacteria perform important functions that are crucial for our lives. Prudent use of both antibiotics and antibacterials must be championed to achieve and maintain the balanced microbial environment in which we have entered and evolved.