The Aryl Hydrocarbon Receptor, Epigenetics and the Aging Process.

The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor, classically associated with the regulation of xenobiotic metabolism in response to environmental toxins. In recent years, transgenic rodent models have implicated AhR in aging and longevity. Moreover, several AhR ligands, such as resveratrol and quercetin, are compounds proven to extend the lifespan of model organisms. In this paper, we first review AhR biology with a focus on aging and highlight several AhR ligands with potential anti-aging properties. We outline how AhR-driven expression of xenobiotic metabolism genes into old age may be a key mechanism through which moderate induction of AhR elicits positive benefits on longevity and healthspan. Furthermore, via integration of publicly available datasets, we show that liver-specific AhR target genes are enriched among genes subject to epigenetic aging. Changes to epigenetic states can profoundly affect transcription factor binding and are a hallmark of the aging process. We suggest that the interplay between AhR and epigenetic aging should be the subject of future research and outline several key gaps in the current literature. Finally, we recommend that a broad range of non-toxic AhR ligands should be investigated for their potential to promote healthspan and longevity.

Evolving oxazolidinone resistance mechanisms in a worldwide collection of enterococcal clinical isolates: results from the SENTRY Antimicrobial Surveillance Program.

Objectives: This study evaluated the oxazolidinone resistance mechanisms among a global collection of enterococcal clinical isolates. The epidemiology of optrA-carrying isolates and the optrA genetic context were determined. Methods: Enterococcal isolates (26 648) from the SENTRY Antimicrobial Surveillance Program (2008-16) were identified by MALDI-TOF MS and MICs were determined by broth microdilution. Isolates with linezolid MICs of ≥4 mg/L were screened for resistance mechanisms. Isolates carrying optrA had their genome sequenced for genetic context and epidemiology information. Results: Thirty-six Enterococcus faecalis and 66 Enterococcus faecium had linezolid MICs of ≥4 mg/L (0.38% of surveillance enterococci). E. faecalis had a linezolid MIC range of 4-16 mg/L, while E. faecium displayed higher values (4-64 mg/L). Nine E. faecalis had G2576T mutations and optrA was detected in 26 (72.2%) isolates from the Asia-Pacific region, North America, Latin America and Europe; 3 isolates also produced Cfr [Thailand (1)] or Cfr(B) [Panama (2)]. All E. faecium isolates had G2576T alterations, while three isolates from the USA had concomitant presence of cfr(B). The optrA gene was plasmid- and chromosome-located in 22 and 3 E. faecalis, respectively. One isolate signalled hybridization on plasmid and chromosome. The genetic context of optrA varied. E. faecalis belonging to the same clonal complex were detected in distinct geographical regions. Also, genetically distinct isolates from Ireland had an identical optrA context, indicating plasmid dissemination. Conclusions: Alterations in 23S rRNA remained the main oxazolidinone resistance mechanism in E. faecium, while optrA prevailed in E. faecalis. These results demonstrate global dissemination of optrA and warrant surveillance for monitoring.

Clonal dissemination of two clusters of Acinetobacter baumannii producing OXA-23 or OXA-58 in Rome, Italy.

Thirty consecutive Acinetobacter baumannii isolates producing carbapenem-hydrolysing oxacillinases, OXA-23 or OXA-58, were recovered from patients hospitalized in Rome, Italy, between January and November 2007. Among these isolates, two clones not associated with the European clones I or II were observed. The oxacillinase-encoding genes were plasmid- or chromosome-borne. This study reports the dissemination of carbapenem-resistant A. baumannii belonging to two clones among several units in a single hospital and emphasizes the ability of A. baumannii to cause epidemic/endemic outbreaks and also to acquire various resistance genes circulating in the hospital environment.

Impact of drug-exposure intensity and duration of therapy on the emergence of Staphylococcus aureus resistance to a quinolone antimicrobial.

We have shown previously in animal model and in vitro systems that antimicrobial therapy intensity has a profound influence on subpopulations of resistant organisms. Little attention has been paid to the effect of therapy duration on resistant subpopulations. We examined the influence of therapy intensity (area under the concentration/time curve for 24 h:minimum inhibitory concentration [AUC24:MIC] ratio) and therapy duration on resistance emergence using an in vitro model of Staphylococcus aureus infection. AUC24:MIC ratios of>or=100 were necessary to kill a substantial portion of the total population. Importantly, we demonstrated that therapy duration is a critical parameter. As the duration increased beyond 5 days, the intensity needed to suppress the antibiotic-resistant subpopulations increased, even when the initial bacterial kill was>4 log10 (cfu/mL). These findings were prospectively validated in an independent experiment in which exposures were calculated from the results of fitting a large mathematical model to all data simultaneously. All of the prospectively determined predictions were fulfilled in this validation experiment.

blaVIM-2 and blaVIM-7 carbapenemase-producing Pseudomonas aeruginosa isolates detected in a tertiary care medical center in the United States: report from the MYSTIC program.

Two Pseudomonas aeruginosa strains resistant to beta-lactams, fluoroquinolones, aminoglycosides, tetracyclines, and carbapenems and susceptible only to polymyxin B (MIC

Antimicrobial activity of LB10827, a new orally administered cephalosporin, tested against Haemophilus influenzae, Moraxella catarrhalis, and Streptococcus pneumoniae.

A new orally administered cephalosporin, LB10827, was compared to 16 other antimicrobial agents tested against Streptococcus pneumoniae (520 strains), Haemophilus influenzae (302 strains) and Moraxella catarrhalis (188 strains) by reference broth microdilution methods. LB10827 (MIC90, 0.12 mg/L; highest MIC, 0.5 mg/L) was 8-16-fold more potent than cefdinir, cefpodoxime or cefuroxime when tested against S. pneumoniae. All Gram-negative strains were inhibited at

Bactericidal activity and synergy studies of BAL9141, a novel pyrrolidinone-3-ylidenemethyl cephem, tested against streptococci, enterococci and methicillin-resistant staphylococci.

BAL9141 has been reported to have inhibitory activity against methicillin-resistant Staphylococcus aureus (MRSA), many enterococci, and streptococci with various resistant patterns. BAL9141 potency was assessed by time-kill curves alone or with subinhibitory concentrations of gentamicin (MIC/4). BAL9141 exhibited bactericidal activity alone against all the streptococci and staphylococci. Among ampicillin-susceptible enterococci, BAL9141 was bactericidal against some strains, but no BAL9141 inhibition was observed of ampicillin-resistant Enterococcus faecium. The activity of BAL9141 with gentamicin was slightly enhanced (not synergy) or indifferent against staphylococci. BAL9141 demonstrated bactericidal action alone against Enterococcus faecalis and some E. faecium strains (-4.8 to -6.0 log10 CFU/mL), but static effects were also noted. Drug interactions with gentamicin showed early synergy (4-8 h) for all enterococci, and indifference or synergy at 24 h (no antagonism). BAL9141 (< or = 8 mg/L) showed promising bactericidal activity alone and synergy with gentamicin against some of the vancomycin-resistant enterococci tested.

Molecular epidemiology of extended-spectrum beta-lactamase-producing, fluoroquinolone-resistant isolates of Klebsiella pneumoniae in Taiwan.

Strains of extended-spectrum beta-lactamase-producing Klebsiella pneumoniae (ESBL-KP) have emerged worldwide. Concomitant ciprofloxacin resistance with ESBL production in K. pneumoniae isolates would severely restrict treatment options. Among 39 (18.5%) of 211 ESBL-KP isolates resistant to ciprofloxacin (MIC, >/=4 micro g/ml), 37 (95%) were high level resistant (MIC, >/=16 micro g/ml). These isolates were also cross resistant to the newer fluoroquinolones, including levofloxacin, gatifloxacin, gemifloxacin, and garenoxacin (BMS 284756). Sitafloxacin was most active against these ciprofloxacin-resistant ESBL-KP isolates with MICs for 67% of the isolates being

AZD2563, a new oxazolidinone: bactericidal activity and synergy studies combined with gentamicin or vancomycin against staphylococci and streptococcal strains.

AZD2563, a novel oxazolidinone, was tested against 10 well characterized multiple-resistant strains of staphylococci and viridans group or beta-hemolytic streptococci using kill curve kinetic methods. Generally, AZD2563 demonstrated bacteriostatic action and modest concentration-dependent cidal activity against a minority of strains of both genera. When combined with gentamicin (MIC/4 concentration), rapid bactericidal action was observed against all streptococci tested, but not against the staphylococci. No enhanced activity was noted when AZD2563 was added to subinhibitory concentrations of vancomycin. Linezolid used as a control, showed the same characteristics, confirming that AZD2563 possesses activity comparable to other agents in the oxazolidinone class. AZD2563 remained active (MIC, < or = 1 microg/ml) against all 10 strains tested.

Emerging elevated mupirocin resistance rates among staphylococcal isolates in the SENTRY Antimicrobial Surveillance Program (2000): correlations of results from disk diffusion, Etest and reference dilution methods.

Staphylococci cause one-third of all serious invasive infections in the SENTRY Antimicrobial Surveillance Program including bacteremias and lower respiratory tract infections. Staphylococci are also commensals of the skin and nasal passages; therefore, topical agents active against these organisms are valuable in preventing infections or transfer of the organisms between patients and/or health care workers. Mupirocin is a potent topical anti-staphylococcal compound, but its effectiveness has been compromised by emerging resistance. In early 2000, the SENTRY Program detected 302 mupirocin-resistant isolates (131 Staphylococcus aureus, and 171 coagulase-negative staphylococci [CoNS]) from the United States (19/25 medical centers), Canada (4/5), Latin America (3/9) and Europe (7/18). One hundred sixty-eight mupirocin-resistant and 59 susceptible isolates were tested further by reference MIC, Etest (AB BIODISK, Solna, Sweden) and disk diffusion (5-microg) methods. Mupirocin resistance rates for blood stream infections varied by geographic area: for S. aureus from 1.9 to 5.6%, and for CoNS from 12.8 to 39.9%. Using elevated mupirocin MIC results, two resistant populations were noted: low-level resistance at 8-128 microg/mL and high-level resistance at > or = 1024 microg/mL. Acceptable correlation was observed between Etest and disk diffusion results (r = 0.84) without serious intermethod interpretive errors. High-level resistant isolates had heavy growth with no visible zone around the disk; low-level resistant isolates produced hazy zones of inhibition, and susceptible strains had clear zones of inhibition at > or = 17 mm. As mupirocin resistance can be plasmid-mediated, the prudent and appropriate use of this topical agent is important to minimize the ongoing development of resistance. Local surveillance for emerging mupirocin resistance appears warranted particularly in the United States and Canada, pragmatically using a disk diffusion test screening. Where more precise data are needed, the Etest is a very accurate method for distinguishing mupirocin low-level from high-level resistance patterns.

Antimicrobial activity of BMS 284756 (T-3811) against Neisseria gonorrhoeae tested by three methods.

The potency of BMS 284756, a novel des-F(6)-quinolone, was tested against 137 clinical isolates of Neisseria gonorrhoeae including 50 strains observed to be resistant to ciprofloxacin and other newer quinolones. The gonococci were tested using NCCLS methods (agar dilution, disk diffusion) and Etest. BMS 284756 potency versus N. gonorrhoeae was generally two- to four-fold greater than ciprofloxacin. Penicillin resistance in the absence of ciprofloxacin resistance did not affect BMS 284756 activity. However, elevated ciprofloxacin MICs were associated with higher BMS 284756 MIC results as follows (BMS 284756 MIC(50)/MIC range in mg/l): ciprofloxacin-susceptible strains (0.016 or 0.03/0.004-0.06), ciprofloxacin-intermediate strains (0.06 or 0.12/0.008-0.25) and ciprofloxacin-resistant strains (0.12 or 0.5/0.12-1). Etest MICs were routinely lower than those produced by the reference agar dilution method, but the correlation coefficient remained acceptable (r = 0.87). Similarly acceptable correlation was achieved with 5 microg disk zone diameters (r = 0.78), where all zones were > or = 28 mm (MIC < or = 1 mg/l). In conclusion, BMS 284756 was very active against N. gonorrhoeae (MIC(50) 0.03 mg/l overall) including ciprofloxacin-resistant strains and could be considered as a single-dose therapeutic option for gonorrhoea.

GAR-936 (9-t-butylglycylamido-minocycline) susceptibility test development for streptococci, Haemophilus influenzae and Neisseria gonorrhoeae: preliminary guidelines and interpretive criteria.

GAR-936, a new semisynthetic derivative of minocycline, has earlier shown promising activity against tetracycline-resistant pathogens, including Streptococcus pneumoniae. In this study, the activity of GAR-936 was tested against a total of 514 tetracycline-susceptible and -resistant strains of S. pneumoniae, beta-haemolytic streptococci, viridans group streptococci, Haemophilus influenzae and Neisseria gonorrhoeae. All strains of H. influenzae, were inhibited by < or =2 mg/l of GAR-936, with MIC(90)s for all streptococci and gonococci of < or =0.5 mg/l. Scattergrams of GAR-936 comparing MICs by broth microdilution testing and zone diameters using 30 microg disks, confirmed the proposed susceptibility criteria of < or 2 mg/l or > or =20 mm zone diameter. Clinical trial results should be correlated with these preliminary in vitro results to confirm and/or adjust these susceptibility interpretive criteria for GAR-936 when testing fastidious streptococci, H. influenzae and N. gonorrhoeae.

Accuracy of broth microdilution and E test methods for detecting chloramphenicol acetyl transferase mediated resistance in Streptococcus pneumoniae: Geographic variations in the prevalence of resistance in The SENTRY Antimicrobial Surveillance Program (1999).

High antimicrobial resistance rates in Streptococcus pneumoniae has caused a need for alternative therapies. Chloramphenicol is currently being reconsidered as an empiric treatment for respiratory tract infections particularly in developing countries. In this study, we assessed the ability of the reference broth microdilution and Etest (AB BIODISK, Solna, Sweden) methods to detect chloramphenicol resistance among pneumococci as compared to the chloramphenicol acetyltransferase (CAT) assay. In the 1999 SENTRY Antimicrobial Surveillance Program, 1671 S. pneumoniae strains from respiratory tract infections were collected from 49 participants located in the Americas and Europe. The rates of penicillin and macrolide non-susceptibility were 15.6-41.3 and 12.4-26.8%, respectively. All chloramphenicol-resistant strains were CAT assay positive (n = 154; 9.2% of isolates) with highest resistance rates in Europe (12.7%; range among sites, 0.0-38.5%) and the United States (10.6%; range, 0.0-25.6%). Etest MICs correlated with reference results and the current breakpoint for chloramphenicol resistance (> or = 8 microg/mL) remains valid for S. pneumoniae and Haemophilus influenzae (eight strains tested). CAT-mediated resistances dominate among chloramphenicol-resistant S. pneumoniae, and marked geographic variations in susceptibility were discovered.

Laboratory and field assessment of arsenic testing field kits in Bangladesh and West Bengal, India.

High concentrations of arsenic in ground waters in West Bengal and Bangladesh have become a major cause for concern in recent years. Given the enormity and the severity of the problem of arsenic poisoning, a task of evaluating the commercially available arsenic detection field kits for their capabilities was undertaken. In the light of the findings, generic specifications were recommended which could form the basis for indigenous manufacture of these kits in the arsenic affected countries. This article presents the results of the laboratory and field evaluation conducted in Bangladesh and West Bengal of five arsenic testing field kits. The salient features of the kits, their merits and limitations have been brought out. Based on the criteria of kit design, quality of chemicals used, colour comparator charts, detection range, time required for analysis, cost etc., a comparative ranking of the kits has been made to facilitate the choice of the kit to meet specific requirements.

Cataleptic effect of neurosteroid 3alpha-hydroxy-5alpha-pregnan-20-one in mice: modulation by serotonergic agents.

The neurosteroid 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP) induced catalepsy in mice is modified by dopaminergic, adenosinergic and GABAergic agents. In light of serotonergic agents being implicated in antipsychotic-induced catalepsy and their ability to increase brain neurosteroid content, the present study was undertaken to investigate the effect of various 5-HT agents on catalepsy induced by 3alpha,5alpha-THP in mice. Pretreatment with selective serotonin reuptake inhibitor, fluoxetine (5 mg/kg, i.p.), 5-HT releaser, fenfluramine (10 mg/kg, i.p.), 5-HT(1A) receptor agonist, 8-OH-DPAT (0.3 mg/kg, s.c.), 5-HT1B/1C receptor agonist, TFMPP (3 mg/kg, i.p.), 5-HT2A/1C receptor agonist, DOI (1.5 mg/kg, s.c.) and 5-HT3 agonist, 2-methylserotonin (5 mg/kg, i.p.) potentiated the catalepsy induced by exogenous administration of 3alpha,5alpha-THP. Furthermore, FGIN 1-27, an MDR agonist that increases endogenous content of 3alpha,5alpha-THP although per se failed to exhibit any cataleptic effect but enhanced the cataleptic response in combination with these serotonergic agents. The potentiating action of 5-HT1A, 5-HT2A/1C or 5-HT3 receptor agonist on 3alpha,5alpha-THP induced catalepsy was not blocked by prior administration of sub-effective dose (1 mg/kg, s.c.) of their respective receptor antagonists pindolol, ritanserin or ondansetron or by pretreatment with serotonergic neurotoxin 5,7-DHT (100 microg/mouse, i.c.v.). However this effect of different serotonergic agents was antagonized by the GABA(A) receptor antagonist, bicuculline (1 mg/kg, i.p.) or the 3alpha-hydroxysteroid oxidoreductase enzyme inhibitor, indomethacin (5 mg/kg, i.p.). The 5-HT agents enhance neurosteroid-induced catalepsy by increasing GABAergic tone, likely as a consequence of increased brain content of 3alpha,5alpha-THP.

In vitro activity of ceftiofur tested against clinical isolates of Escherichia coli and Klebsiella pneumoniae including extended spectrum beta-lactamase producing strains.

In vitro activity of ceftiofur, a cephalosporin used in veterinary practice was compared using ceftriaxone-resistant (producing extended spectrum beta-lactamase (ESBL)) and -susceptible clinical isolates of Esherichia coli and Klebsiella pneumoniae. The ceftriaxone-susceptible isolates exhibited a lower range of ceftiofur MICs (MIC50, 0.5 mg/l, MIC90 1.0 mg/l). Those isolates known to produce an ESBL were also resistant to ceftiofur (MIC50, > or = 32 mg/l). The latter isolates were also less susceptible to other comparator drugs (cefquinome, gentamicin and trimethoprim/sulphamethoxazole) in contrast to the ceftriaxone-susceptible strains. The clinical isolates showed high correlation between ceftriaxone and ceftiofur MICs (y = 2.6 + 0.89x, r = 0.95). Using the current ceftiofur susceptible breakpoint (< or = 2 mg/l) used for veterinary practice (respiratory tract pathogens), the ESBL-producing strains of E. coli and K. pneumoniae could be accurately separated from susceptible strains. This ceftiofur breakpoint MIC corresponds to the National Committee for Clinical Laboratory Standards ESBL screening concentration for ceftriaxone set at < or = 1 mg/l = negative for ESBL production. Ceftiofur was also observed to be very active in vitro against ampicillin-resistant, non-ESBL producing enteric isolates. This new cephem appears to be very potent against the tested Enterobacteriaceae and of potential wide clinical veterinary utility.

Antimicrobial activity of advanced-spectrum fluoroquinolones tested against more than 2000 contemporary bacterial isolates of species causing community-acquired respiratory tract infections in the United States (1999).

In vitro activity of four newer fluoroquinolones (clinafloxacin, gemifloxacin, moxifloxacin, sitafloxacin) and an equal number control drugs in the same class (ciprofloxacin, grepafloxacin, levofloxacin, trovafloxacin) was determined by reference dilution tests against 2156 recent United States clinical isolates of Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. All the fluoroquinolones demonstrated excellent in vitro activity against these pathogens. Streptococcus pneumoniae isolates were fully susceptible to clinafloxacin, sitafloxacin, and gemifloxacin at 0.5 microg/ml, and over 98% of sampled strains had MICs of

Anti-gonococcal activity of gemifloxacin against fluoroquinolone-resistant strains and a comparison of agar dilution and Etest methods.

Gemifloxacin is a novel quinolone with excellent activity against Gram-positive and some Gram-negative pathogens. Its activity was tested against 150 Neisseria gonorrhoeae strains, including 50 ciprofloxacin-resistant isolates, using reference agar dilution and Etest methods. Gemifloxacin was found to be highly potent against ciprofloxacin-susceptible strains (MIC(90) 0.008 mg/L), but was 16-fold less potent against ciprofloxacin-resistant gonococci. The order of quinolone potency against these fluoroquinolone-resistant mutants was: gemifloxacin (MIC(90) 0.12 mg/L) > trovafloxacin (0.25 mg/L) > moxifloxacin = grepafloxacin (0.5 mg/L) > ciprofloxacin (1 mg/L). Etest and reference agar dilution MIC results showed excellent correlation (r = 0.96) and >98% of MICs were within +/-1 log(2) dilution step (essential agreement). The excellent potency of gemifloxacin indicates its potential for the treatment of infections with quinolone-resistant N. gonorrhoeae.

Evaluation of the in vitro antimicrobial activity of cefepime compared to other broad-spectrum beta-lactams tested against recent clinical isolates from 10 Chinese hospitals. Chinese Antimicrobial Resistance Study Group.

A surveillance study was initiated in China in 1998 in which 10 medical centers participated. The susceptibility profiles of 996 commonly occurring pathogens belonging to 10 different species groups were tested by the Etest (AB BIODISK, Solna, Sweden) against six broad-spectrum beta-lactam antimicrobial agents (cefepime, ceftazidime, ceftriaxone, imipenem, cefoperazone/sulbactam and piperacillin or oxacillin). Quality control was closely monitored and cefepime- and/or imipenem-resistant Enterobacteriaceae were referred to the reference laboratory (University of Iowa College of Medicine, Iowa City, IA) for confirmation. The isolates of Citrobacter spp. and Enterobacter spp. were generally inhibited by imipenem (100% susceptible) and cefepime (89-94%), but were more resistant to the other drugs tested (< or = 74% susceptible). The indole-positive Proteus spp. and Serratia spp. isolates were > 94% susceptible to all tested beta-lactams except piperacillin. Organisms capable of producing extended spectrum beta-lactamases (ESBLs), which included Klebsiella spp. and Escherichia coli, were most susceptible to imipenem (100%) and cefepime (> 90%). Among the non-enteric Gram-negative bacilli, all drugs were marginally active against Pseudomonas aeruginosa (MIC90s, 32-> 256 ug/mL) and the Acinetobacter spp. were rather resistant to all the compounds, except imipenem (96% susceptible). All strains of Staphylococcus spp. were susceptible to the tested antimicrobials except for ceftazidime, which had a low potency (MIC90, 12-16 micrograms/mL) against Chinese isolates with MICs that fell into the intermediate category. Cefepime, the fourth-generation cephalosporin, showed a very broad spectrum of activity against Gram-negative pathogens as well as oxacillin-susceptible Staphylococcus spp. that was comparable with imipenem (widest spectrum) and superior to the other tested beta-lactams overall. Continued monitoring of clinical strains in China seems necessary to guide chemotherapy.

Comparative activity of clinafloxacin and nine other compounds tested against 2000 contemporary clinical isolates from patients in United States hospitals.

The in vitro activity of clinafloxacin (formerly CI-960, AM-1091, PD-127391) was compared with other fluoroquinolones, cephalosporins, gentamicin, vancomycin, imipenem, piperacillin/tazobactam, clindamycin, and metronidazole against 2000 recent clinical strains from a large number of hospitals in the United States. Overall, clinafloxacin was the most active compound tested. Against Pseudomonas aeruginosa, clinafloxacin and ciprofloxacin demonstrated comparable activity (88% and 80% susceptible, respectively), and were four- to 16-fold more potent than levofloxacin (MIC90, 16 micrograms/ml) or trovafloxacin (MIC90, 32 micrograms/ml). Among anaerobic bacteria, clinafloxacin (MIC50s, 0.25-0.5 microgram/ml) and trovafloxacin (MIC50s, 0.5-2.0 micrograms/ml) were the most active quinolones, whereas metronidazole, imipenem and piperacillin/tazobactam were the most potent comparators. Clinafloxacin demonstrated sustained activity when compared to several available peer drugs against contemporary clinical isolates. The clinafloxacin spectrum against the 15 important pathogens monitored ranged from nil or 4.0% (vancomycin-resistant enterococci) to 100.0% (four different species) susceptible with an average percent susceptibility of 94.0%. This degree of potency and spectrum for clinafloxacin provides a wide potential for use against many species with established resistance to other anti-microbial classes.