Conductance of partially disordered graphene: crossover from temperature-dependent to field-dependent variable-range hopping.

We report an analysis of low-temperature measurements of the conductance of partially disordered reduced graphene oxide, finding that the data follow a simple crossover scenario. At room temperature, the conductance is dominated by two-dimensional (2D) electric field-assisted, thermally driven (Pollak-Riess) variable-range hopping (VRH) through highly disordered regions. However, at lower temperatures T, we find a smooth crossover to follow the exp(-E0/E)(1/3) field-driven (Shklovskii) 2D VRH conductance behaviour when the electric field E exceeds a specific crossover value EC(T)(2D) = (EaE(1/3)0 /3)(3/4) determined by the scale factors E0 and Ea for the high-field and intermediate-field regimes respectively. Our crossover scenario also accounts well for experimental data reported by other authors for three-dimensional disordered carbon networks, suggesting wide applicability.

Dielectric versus magnetic pairing mechanisms in high-temperature cuprate superconductors investigated using Raman scattering.

We suggest, and demonstrate, a systematic approach to the study of cuprate superconductors, namely, progressive change of ion size in order to systematically alter the interaction strength and other key parameters. R(Ba,Sr)2Cu3Oy (R={La,…,Lu,Y}) is such a system where potentially obscuring structural changes are minimal. We thereby systematically alter both dielectric and magnetic properties. Dielectric fluctuation is characterized by ionic polarizability while magnetic fluctuation is characterized by exchange interactions measurable by Raman scattering. The range of transition temperatures is 70-107 K, and we find that these correlate only with the dielectric properties, a behavior which persists with external pressure. The ultimate significance may remain to be proven, but it highlights the role of dielectric screening in the cuprates and adds support to a previously proposed novel pairing mechanism involving exchange of quantized waves of electronic polarization.

Effect of chemical treatment on electrical conductivity, infrared absorption, and Raman spectra of single-walled carbon nanotubes.

We investigate the magnitude and temperature dependence of electrical conductivity, the optical and infrared absorption, and the Raman spectra of single-walled carbon nanotube (SWNT) bucky-paper after chemical treatment and determine the correlations between the changes in these properties. Ionic-acceptor doping of the SWNT bucky-paper (with SOCl(2), iodine, H(2)SO(3), etc.) causes an increase of electrical conductivity that correlates with an increase of the absorbance in the far-IR region and an increase in the frequency of Raman spectral lines. Conversely, treatment with other molecules (e.g., aniline, PyPhF(5), PhCH(2)Br, etc.) leads to a decrease in both conductivity and far-IR absorption. The temperature dependence of the conductivity gives a good indication of the presence of metallic charge carriers and is in agreement with the model of interrupted metallic conduction.

Effect of PGG-glucan on the rate of serious postoperative infection or death observed after high-risk gastrointestinal operations. Betafectin Gastrointestinal Study Group.

BACKGROUND: Postoperative infections remain common after high-risk gastrointestinal procedures. PGG-glucan (Betafectin; Alpha Beta Technology Inc, Worcester, Mass), derived from yeast cell walls, promotes phagocytosis and intracellular killing of bacterial pathogens by leukocytes, prevents infection in an animal model of wound infection, and acts synergistically with antibiotics to reduce mortality in rat peritonitis. HYPOTHESIS: We hypothesized that infectious complications in these patients might be reduced by the administration of a nonspecific immune-enhancing agent. DESIGN: Multicenter, prospective, randomized, double-blind, placebo-controlled trial of 1249 patients prospectively stratified into colorectal or noncolorectal strata. SETTING: Thirty-nine medical centers throughout the United States. PATIENTS: Aged 18 years or older, scheduled for gastrointestinal procedure lasting 2 to 8 hours, with 2 or more defined risk factors. INTERVENTIONS: PGG-glucan, 0.5 mg/kg or 1.0 mg/kg, or placebo once preoperatively and 3 times postoperatively. All patients received standardized antibiotic prophylaxis. MAIN OUTCOME MEASURES: Serious infection or death within 30 days. RESULTS: All randomized patients revealed no difference in serious infections and deaths in the treated groups compared with placebo groups (15% vs 14%, P>.90). In the prospectively defined noncolorectal stratum (n = 391), PGG-glucan administration was associated with a statistically significant relative reduction (39%) in serious infections and death (placebo, 46 [36%] of 129 vs either PGG-glucan group, 29 [21%] of 132 and 28 [22%] of 130, P<.02). PGG-glucan reduced postoperative infection or death in malnourished patients having noncolorectal procedures (31 [44%] of 70, placebo group; 16 [24%] of 68, 0.5-mg/kg PGG-glucan group; 12 [17%] of 72, 1.0-mg/kg PGG-glucan group; P<.001). Study drug was stopped owing to adverse effects more frequently for patients receiving PGG-glucan than placebo (2%, 4%, and 7% for the placebo group, 0.5-mg/kg PGG-glucan group, and 1.0-mg/kg PGG-glucan group, respectively, P<.003). CONCLUSION: Perioperative administration of PGG-glucan reduced serious postoperative infections or death by 39% after high-risk noncolorectal operations.

Synergism between poly-(1-6)-beta-D-glucopyranosyl-(1-3)-beta-D-glucopyranose glucan and cefazolin in prophylaxis of staphylococcal wound infection in a guinea pig model.

To determine whether the infection-preventing capability of the neutrophil-activating agent poly-(1-6)-beta-D-glucopyranosyl-(1-3)-beta-D-glucopyranose glucan (PGG-glucan) can be enhanced with antibiotic prophylaxis, we administered PGG-glucan and cefazolin, alone and in combination, to guinea pigs inoculated with isolates of staphylococci. Guinea pigs receiving both PGG-glucan and cefazolin had 50% infective doses that were 8- to 20-fold higher than those obtained with cefazolin alone and 100- to 200-fold higher than those obtained with PGG-glucan alone. PGG-glucan and cefazolin are synergistic in their ability to prevent staphylococcal wound infection.

Beta-lactamase production diminishes the prophylactic efficacy of ampicillin and cefazolin in a guinea pig model of Staphylococcus aureus wound infection.

Clinical trials in surgery suggest that some failures of antibiotic prophylaxis are related to the in vivo degradation of beta-lactams by Staphylococcus aureus beta-lactamase. To explore this issue further, isogeneic isolates of S. aureus differing only in whether they contained the structural gene for type A staphylococcal beta-lactamase were constructed and compared for their ability to establish an abscess in a guinea pig model. With ampicillin prophylaxis, the ID50 was 870 cfu for the beta-lactamase-negative isolate VK7114 and 240 cfu for the beta-lactamase-producing isolate VK7115 (P < .001). Similarly, the ID50 was greater for the beta-lactamase-negative isolate when cefazolin prophylaxis was administered (599 vs. 128 cfu, VK7114 and VK7115; P < .001). In the setting of prophylaxis with beta-lactamase-susceptible antibiotics, beta-lactamase contributes to the pathogenesis of S. aureus wound infections.

Prophylactic anti-infective activity of poly-[1-6]-beta-D-glucopyranosyl-[1-3]-beta-D-glucopryanose glucan in a guinea pig model of staphylococcal wound infection.

The judicious use of perioperative antibiotic prophylaxis reduces the infectious complications of surgery. However, increased bacterial resistance within hospitals may make antibiotic prophylaxis less effective in the future and alternative strategies are needed. New immunomodulatory agents might prevent wound infections by stimulation of the host immune system. To test this hypothesis, we administered poly-[1-6]-beta-D-glucopyranosyl- [1-3] -beta-D-glucopyranose glucan (PGG glucan), which enhances neutrophil microbicidal activity, intravenously to guinea pigs in doses ranging from 0.015 to 4 mg/kg of body weight on the day before, on the day of, and on the day after intermuscular inoculation with methicillin-resistant strains of Staphylococcus aureus and Staphylococcus epidermidis. Abscesses were identified at 72 h, and median infective doses (ID50) and statistical significance were determined by logistic regression. Guinea pigs receiving PGG glucan and inoculated with methicillin-resistant S. aureus and S. epidermidis exhibited ID50 of as much as 2.5- and 60-fold higher, respectively, than those of control guinea pigs not receiving PGG glucan. Maximal protection was observed with a dose of 1 mg of PGG glucan per kg, and efficacy was reduced at higher as well as at lower PGG glucan doses. Furthermore, a single dose of PGG glucan given 24 h following bacterial inoculation was found to be effective in preventing infection. We conclude that PGG glucan reduces the risk of staphylococcal abscess formation. Neutrophil-activating agents are a novel means of prophylaxis against surgical infection and may be less likely than antibiotics to be affected adversely by the increasing antibiotic resistance of nosocomial pathogens.

Association of borderline oxacillin-susceptible strains of Staphylococcus aureus with surgical wound infections.

Staphylococcus aureus isolates which produce type A staphylococcal beta-lactamase have been associated with wound infections complicating the use of cefazolin prophylaxis in surgery. To further evaluate this finding, 215 wound isolates from 14 cities in the United States were characterized by antimicrobial susceptibility and beta-lactamase type and correlated with the preoperative prophylactic regimen. Borderline-susceptible S. aureus isolates of phage group 5 (BSSA-5), which produce large amounts of type A beta-lactamase and exhibit borderline susceptibility to oxacillin, comprised a greater percentage of the 120 wound isolates associated with cefazolin prophylaxis than they did of the 95 isolates associated with other prophylactic regimens (25% versus 12.6%, respectively; P < 0.05). In contrast, methicillin-resistant S. aureus isolates were distributed evenly between the two groups (8.3% versus 11.6%, respectively). In vitro assays demonstrated that cefazolin was hydrolyzed faster by BSSA-5 strains than by other beta-lactamase-producing, methicillin-susceptible strains (1.54 versus 0.50 microg/min/10(8) CFU, respectively; P < 0.0001). These data demonstrate that BSSA-5 strains are a distinct subpopulation of methicillin-susceptible S. aureus which frequently cause deep surgical wound infections. Cefazolin use in prophylaxis is a risk factor for BSSA-5 infection.

Purpura fulminans in pneumococcal sepsis: case report and review.

Purpura fulminans is classically defined by ecchymotic skin lesions, fever, and hypotension. The majority of cases occur in association with bacterial sepsis, and disseminated intravascular coagulation (DIC) is usually present. Prompted by our experience with a patient with pneumococcal sepsis and purpura fulminans in whom hypotension was never observed, we evaluated the important parameters of sepsis in reports of this syndrome. 42 additional cases of pneumococcal bacteremia and purpura fulminans were identified. Hypotension was present in only 51%. Although DIC was present in 85% of patients, hypofibrinogenemia was documented in only 26%. By contrast, both hypotension and hypofibrinogenemia are present in the vast majority of patients described with purpura fulminans in association with meningococcal sepsis. These data confirm that hypotension is not a necessary feature of the syndrome of purpura fulminans associated with pneumococcal sepsis and suggest further that qualitative or quantitative differences exist in the DIC cascade of pneumococcal vs meningococcal sepsis.

Comparative prophylactic efficacies of ciprofloxacin, ofloxacin, cefazolin, and vancomycin in experimental model of staphylococcal wound infection.

Recent shifts in the species and antibiotic resistance patterns of bacteria causing nosocomial infections present new challenges for providing effective prophylaxis in surgery. Traditional regimens lack activity against methicillin-resistant staphylococci and many gram-negative species causing nosocomial infections. The new fluoroquinolones exhibit in vitro activity against many emerging surgical wound pathogens. To determine the potential of this class of antimicrobial agents for use in surgery, we compared the prophylactic efficacies of ciprofloxacin and ofloxacin with those of cefazolin and vancomycin in a guinea pig model of abscess formation. Four Staphylococcus aureus strains, one Staphylococcus epidermidis strain, and one Staphylococcus haemolyticus strain were evaluated. Vancomycin was the most effective prophylactic agent, exhibiting in vivo activity against all strains which was superior or equivalent to those of all other agents tested. Cefazolin was the least effective agent and surpassed the two quinolones in prophylactic efficacy against only one organism, a quinolone- and methicillin-resistant strain of S. aureus. The two quinolones provided excellent protection against infection with all but the quinolone-resistant isolate. The in vivo emergence of quinolone resistance among quinolone-susceptible isolates was not detected. The methicillin-resistant, quinolone-susceptible S. epidermidis and S. haemolyticus isolates were extremely susceptible to prophylaxis, exhibiting 50% infective doses above 4 x 10(6) CFU for seven of the eight antibiotic-strain combinations. We conclude that ciprofloxacin and ofloxacin may be effective antistaphylococcal agents in surgery. The role of these agents remains to be defined, and the definition should include consideration of an adverse effect upon antibiotic resistance patterns of organisms causing nosocomial infections.

Cefamandole versus cefazolin in vascular surgical wound infection prophylaxis: cost-effectiveness and risk factors.

PURPOSE: Recent studies of perioperative antimicrobial prophylaxis have indicated an improved efficacy of beta-lactamase-stable cephalosporins compared with cefazolin, the most commonly used prophylactic agent. Previous studies in our institution have revealed a superiority of cefamandole to cefazolin in patients undergoing heart surgery, although there was no difference between cefazolin and cefuroxime in patients undergoing peripheral vascular surgery. This study was therefore designed to compare cefamandole with cefazolin in wound infection prophylaxis in clean vascular surgery. METHODS: The study was conducted from August 1990 through May 1992 and consisted of 893 patients with aortic or infrainguinal arterial procedures randomized to receive either cefamandole or cefazolin. RESULTS: The difference in infection rates associated with cefamandole versus cefazolin prophylaxis (3.2% vs 1.9%, respectively) was not significant (p = 0.42). A cost savings of approximately $95,000 per year at our institution favors the continued use of cefazolin over cefamandole. Risk factor analysis was carried out for preoperative and postoperative events that might have predisposed to infection. Only preoperative use of aspirin and the postoperative finding of a lymphocele correlated with a higher infection rate. CONCLUSIONS: Cefazolin continues to be the most cost-effective antibiotic for prophylaxis in clean vascular surgical procedures.

Comparative prophylactic efficacy of cefazolin and vancomycin in a guinea pig model of Staphylococcus aureus wound infection.

The increasing prevalence of methicillin-resistant Staphylococcus aureus as a wound pathogen in some institutions has prompted the use of vancomycin for surgical prophylaxis, although clinical data comparing vancomycin and cephalosporins are not available. A guinea pig model was used to compare the efficacy of vancomycin and cefazolin in preventing intermuscular abscess formation by 7 S. aureus strains. Both antibiotics were administered to achieve peak serum levels at the time of bacterial inoculation, and each remained > 1 micrograms/mL for a comparable duration. Vancomycin provided equivalent protection from infection by 1 methicillin-susceptible strain and significantly better protection against 4 methicillin-susceptible and both methicillin-resistant S. aureus strains. For most strains, the bacterial inoculum with a 50% probability of causing an abscess was 2 to 4 log10-fold higher with vancomycin than cefazolin prophylaxis. Prophylaxis with vancomycin is superior to cefazolin in preventing intermuscular infection by methicillin-susceptible and -resistant S. aureus.

Efficacy of prophylaxis with beta-lactams and beta-lactam-beta-lactamase inhibitor combinations against wound infection by methicillin-resistant and borderline-susceptible Staphylococcus aureus in a guinea pig model.

Although some beta-lactams and beta-lactam-beta-lactamase inhibitor combinations exhibit activity against methicillin-resistant Staphylococcus aureus, there remains the concern that therapeutic failures may result from the selection of resistant subpopulations. The prophylactic use of these antibiotics in clean surgery, however, may prove adequate since wound infections arise from the inoculation of small numbers of bacteria. In this clinical setting, heterogeneity in the phenotypic expression of beta-lactam resistance may facilitate antibiotic efficacy. Similarly, beta-lactamase-mediated resistance in S. aureus is dependent on inoculum size, and it may be possible to prevent infection from small inocula with relatively labile beta-lactams. To test this hypothesis, antibiotics were administered to guinea pigs as prophylaxis against infection by two methicillin-resistant strains and one borderline-susceptible strain. Following prophylaxis with sulbactam or placebo, inoculation of only a dozen or fewer bacteria had a 50% probability of creating an abscess (50% infective dose [ID50]). The efficacy of ampicillin was similar to that of cefazolin, exhibiting moderate activity against the borderline-susceptible strain (ID50s, greater than 300 bacteria) and minimal activity against the methicillin-resistant strains (ID50s, fewer than 100 bacteria). Coadministration of sulbactam with ampicillin or cefazolin yielded better results than the beta-lactam alone for five of six strain-beta-lactam combinations, including an 80-fold increase in the efficacy of ampicillin-sulbactam compared with that of ampicillin for one methicillin-resistant strain (ID50s, 2,017 and 25 bacteria, respectively). Prophylaxis with beta-lactams, especially beta-lactam-beta-lactamase inhibitor combinations, reduces the risk of wound infection by beta-lactam-resistant S. aureus.

Evaluation of new anti-infective drugs for surgical prophylaxis. Infectious Diseases Society of America and the Food and Drug Administration.

It has been established by substantial research that antimicrobial prophylaxis for various surgical procedures can reduce the risk of postoperative morbidity and mortality. When the incidence of infectious complications is high, the reduction with prophylaxis is most dramatic. However, even for many "clean" procedures (vascular procedures, total joint replacement), the small reduction in potentially calamitous complications justifies the use of prophylaxis. Many issues of detail remain unanswered: timing and duration of administration of antimicrobial drug; type of drug; use of topical anti-infective agents as ancillary measures; and choices for high-risk individuals and others ordinarily excluded from clinical trials. An approach to the conduct of clinical trials of anti-infective drugs for surgical prophylaxis is provided. Both general guidelines and specific recommendations for total hip replacement, colorectal operations, appendectomy, and transurethral resection of the prostate are included.

Low-inoculum model of surgical wound infection.

A model of surgical wound infection that uses low inocula of bacteria and closely simulates clinical infection involved inoculating suspensions of Staphylococcus aureus and dextran microbeads into intermuscular sites on the dorsum of guinea pigs, harvesting lesions at 72-96 h, identifying as a positive end point lesions yielding staphylococci on subculture, and using logistic regression for data analysis. Prophylaxis was placebo, ampicillin, or cefazolin, and three representative strains of S. aureus were used. A highly significant correlation (P less than .001) was observed between inoculum sizes and infection rates. Without antimicrobial prophylaxis, ID50 for each strain was less than 10 organisms; with antimicrobials, ID50 was significantly higher. Differences in the virulence of strains and in the efficacy of the antimicrobial regimens also were observed. The model should prove useful for understanding mechanisms of virulence among pathogenic bacteria and for elucidating subtle but important differences in efficacy among antibiotics used in prophylaxis.

Cefuroxime versus cefazolin as prophylaxis in vascular surgery.

Although cefazolin prophylaxis has proven efficacy in vascular surgery, Staphylococcus aureus wound infections are still an important postoperative complication. In cardiac surgery, cefazolin's susceptibility to hydrolysis by staphylococcal beta-lactamase has been proposed to account for some prophylaxis failures. To determine whether the incidence of vascular wound infections can be reduced by administering a more beta-lactamase-stable cephalosporin, we undertook a prospective, randomized trial of cefuroxime versus cefazolin. Cefuroxime was administered as a 1.5 gm dose before operation and 750 mg every 3 hours during operation. Cefazolin was given as 1 gm before operation and 500 mg every 4 hours during operation. Both agents were continued every 6 hours after operation for 24 hours. Deep wound infections developed in seven of 272 (2.6%) cefuroxime and three of 287 (1.0%) cefazolin recipients (p = 0.2). Staphylococcus aureus wound infections occurred in five cefuroxime versus two cefazolin recipients. In vitro evaluation of six of the study isolates plus an additional eight S. aureus strains from vascular wound infections showed greater susceptibility of the strains to cefazolin than cefuroxime (median minimal inhibitory concentrations of 0.5 and 2.0 micrograms/ml, respectively, p less than 0.05). Furthermore, despite its more frequent intraoperative redosing, cefuroxime exhibited lower trough serum concentrations than cefazolin. Among cefuroxime recipients, infection-associated procedures were significantly longer than infection-free procedures (p less than 0.05), suggesting that low tissue antibiotic concentrations may have contributed to the pathogenesis of these infections. In contrast, the length of the procedure was not a risk factor for infection among cefazolin recipients.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlation of in-vitro parameters of antimicrobial activity with prophylactic efficacy in an intradermal model of Staphylococcus aureus infection.

Cephalosporins differ in their ability to prevent staphylococcal wound infection. Although the reasons for the observed differences are not fully understood, the susceptibility of cephalosporins to hydrolysis by staphylococcal beta-lactamase has been correlated with failures of prophylaxis. To investigate the effect of beta-lactamase stability and other in-vitro parameters of the bacterial-antimicrobial interaction on the efficacy of antimicrobial prophylaxis, two beta-lactamase-stable agents, cefuroxime and cefmetazole were compared to cefazolin and cefamandole in an in-vivo model of intradermal infection employing four strains of Staphylococcus aureus. Following intraperitoneal administration of a single dose of cephalosporin or placebo, guinea pigs were inoculated at multiple intradermal sites with 2 x 10(7) cfu of a strain of staphylococcus. For three strains, the area of induration at 24 h following inoculation was significantly smaller in guinea pigs receiving prophylaxis with cephalosporins versus placebo; no cephalosporin was effective against the fourth strain. Differences were also noted among the cephalosporins; prophylaxis with cefuroxime and cefmetazole resulted in smaller lesions than seen in animals given cefazolin or cefamandole. Poor correlation was noted between results of the in-vivo model and in-vitro determinants of the bacterial-antimicrobial interaction which were MIC values, time-kill curves, and the rates of beta-lactamase-mediated cephalosporin hydrolysis by the different strains. The model demonstrated unexplained failures of prophylaxis and unexpected differences in efficacy of various cephalosporins as has been described before. This study highlights the need for an improved animal model of surgical antimicrobial prophylaxis and the identification of in-vitro determinants that predict in-vivo prophylactic efficacy more accurately.

Perioperative antimicrobial prophylaxis in middle Tennessee, 1989-1990.

The patterns of use of perioperative antimicrobial prophylaxis were assessed in a randomly selected sample of short-stay hospitals in middle Tennessee. Overall, 438 procedures (48%) were associated with antimicrobial prophylaxis. Prophylaxis was more common in hospitals with more than 400 beds than in smaller hospitals. Moreover, prophylactic antibiotics were given more often for procedures with a proven indication for prophylaxis than for those without a proven indication (60% vs. 41%, P less than .05); this relationship remained constant regardless of hospital size (common odds ratio, 2.09). However, prophylaxis for procedures with a proven indication was more likely to be given in teaching hospitals than in nonteaching hospitals (odds ratios, 5.41 vs. 1.94). The duration of prophylaxis was less than 2 days for 89% of procedures. A wide variety of agents were used. This study suggests that while improvements have been made over the past decade in decisions about the duration of prophylaxis, considerable variation remains in the selection of the procedures in which such treatment is administered and of the antimicrobial agents used.