Role of rifampin against Propionibacterium acnes biofilm in vitro and in an experimental foreign-body infection model

Propionibacterium acnes is an important cause of orthopedic-implant-associated infections, for which the optimal treatment has not yet been determined. We investigated the activity of rifampin, alone and in combination, against planktonic and biofilm P. acnes in vitro and in a foreign-body infection model. The MIC and the minimal bactericidal concentration (MBC) were 0.007 and 4 μg/ml for rifampin, 1 and 4 μg/ml for daptomycin, 1 and 8 μg/ml for vancomycin, 1 and 2 μg/ml for levofloxacin, 0.03 and 16 μg/ml for penicillin G, 0.125 and 512 μg/ml for clindamycin, and 0.25 and 32 μg/ml for ceftriaxone. The P. acnes minimal biofilm eradication concentration (MBEC) was 16 μg/ml for rifampin; 32 μg/ml for penicillin G; 64 μg/ml for daptomycin and ceftriaxone; and ≥128 μg/ml for levofloxacin, vancomycin, and clindamycin. In the animal model, implants were infected by injection of 10⁹ CFU P. acnes in cages. Antimicrobial activity on P. acnes was investigated in the cage fluid (planktonic form) and on explanted cages (biofilm form). The cure rates were 4% for daptomycin, 17% for vancomycin, 0% for levofloxacin, and 36% for rifampin. Rifampin cured 63% of the infected cages in combination with daptomycin, 46% with vancomycin, and 25% with levofloxacin. While all tested antimicrobials showed good activity against planktonic P. acnes, for eradication of biofilms, rifampin was needed. In combination with rifampin, daptomycin showed higher cure rates than with vancomycin in this foreign-body infection model.     

Daptomycin Pharmacokinetics in Adult Oncology Patients with Neutropenic Fever

Daptomycin is the first antibacterial agent of the cyclic lipopeptides with in vitro bactericidal activity against gram-positive organisms, including vancomycin-resistant enterococci, methicillin-resistant staphylococci, and glycopeptide-resistant Staphylococcus aureus. The pharmacokinetics of daptomycin were determined in 29 adult oncology patients with neutropenic fever. Serial blood samples were drawn at 0, 0.5, 1, 2, 4, 8, 12, and 24 h after the initial intravenous infusion of 6 mg/kg of body weight daptomycin. Daptomycin total and free plasma concentrations were determined by high-pressure liquid chromatography. Concentration-time data were analyzed by noncompartmental methods. The results (presented as means ± standard deviations and ranges, unless indicated otherwise) were as follows: the maximum concentration of drug in plasma (C_max) was 49.04 ± 12.42 μg/ml (range, 21.54 to 75.20 μg/ml), the 24-h plasma concentration was 6.48 ± 5.31 μg/ml (range, 1.48 to 29.26 μg/ml), the area under the concentration-time curve (AUC) from time zero to infinity was 521.37 ± 523.53 μg·h/ml (range, 164.64 to 3155.11 μg·h/ml), the volume of distribution at steady state was 0.18 ± 0.05 liters/kg (range, 0.13 to 0.36 liters/kg), the clearance was 15.04 ± 6.09 ml/h/kg (range, 1.90 to 34.76 ml/h/kg), the half-life was 11.34 ± 14.15 h (range, 5.17 to 83.92 h), the mean residence time was 15.67 ± 20.66 h (range, 7.00 to 121.73 h), and the median time to C_max was 0.6 h (range, 0.5 to 2.5 h). The fraction unbound in the plasma was 0.06 ± 0.02. All patients achieved C_max/MIC and AUC from time zero to 24 h (AUC_0-24)/MIC ratios for a bacteriostatic effect against Streptococcus pneumoniae. Twenty-seven patients (93%) achieved a C_max/MIC ratio for a bacteriostatic effect against S. aureus, and 28 patients (97%) achieved an AUC_0-24/MIC ratio for a bacteriostatic effect against S. aureus. Free plasma daptomycin concentrations were above the MIC for 50 to 100% of the dosing interval in 100% of patients for S. pneumoniae and 90% of patients for S. aureus. The median time to defervescence was 3 days from the start of daptomycin therapy. In summary, a 6-mg/kg intravenous infusion of daptomycin every 24 h was effective and well tolerated in neutropenic cancer patients.     

Antimicrobial Activity of Ceftaroline Tested against Staphylococci with Reduced Susceptibility to Linezolid,Daptomycin, or Vancomycin from U.S. Hospitals, 2008 to 2011

Vancomycin, linezolid, and daptomycin are very active against staphylococci, but isolates with decreased susceptibility to these antimicrobial agents are isolated sporadically. A total of 19,350 Staphylococcus aureus isolates (51% methicillin resistant [MRSA]) and 3,270 coagulase-negative staphylococci (CoNS) were collected consecutively from 82 U.S. medical centers from January 2008 to December 2011 and tested for susceptibility against ceftaroline and comparator agents by the reference broth microdilution method. Among S. aureus strains, 14 isolates (0.07%) exhibited decreased susceptibility to linezolid (MIC, ≥8 μg/ml), 18 (0.09%) to daptomycin (MIC, ≥2 μg/ml), and 369 (1.9%) to vancomycin (MIC, ≥2 μg/ml; 368 isolates at 2 μg/ml and 1 at 4 μg/ml). Fifty-one (1.6%) CoNS were linezolid resistant (MIC, ≥8 μg/ml), and four (0.12%) were daptomycin nonsusceptible (MIC, ≥2 μg/ml). Ceftaroline was very active against S. aureus overall (MIC_50/90, 0.5/1 μg/ml; 98.5% susceptible), including MRSA (MIC_50/90, 0.5/1 μg/ml; 97.2% susceptible). All daptomycin-nonsusceptible and 85.7% of linezolid-resistant S. aureus isolates were susceptible to ceftaroline. Against S. aureus isolates with a vancomycin MIC of ≥2 μg/ml, 91.9, 96.2, and 98.9% were susceptible to ceftaroline, daptomycin, and linezolid, respectively. CoNS strains were susceptible to ceftaroline (MIC_50/90, 0.25/0.5 μg/ml; 99.1% inhibited at ≤1 μg/ml), including methicillin-resistant (MIC_50/90, 0.25/0.5 μg/ml), linezolid-resistant (MIC_50/90, 0.5/0.5 μg/ml), and daptomycin-nonsusceptible (4 isolates; MIC range, 0.03 to 0.12 μg/ml) strains. In conclusion, ceftaroline demonstrated potent in vitro activity against staphylococci with reduced susceptibility to linezolid, daptomycin, or vancomycin, and it may represent a valuable treatment option for infections caused by these multidrug-resistant staphylococci.     

Activities of Fosfomycin and Rifampin on Planktonic and Adherent Enterococcus faecalis Strains in an Experimental Foreign-Body Infection Model

Enterococcal implant-associated infections are difficult to treat because antibiotics generally lack activity against enterococcal biofilms. We investigated fosfomycin, rifampin, and their combinations against planktonic and adherent Enterococcus faecalis (ATCC 19433) in vitro and in a foreign-body infection model. The MIC/MBC_log values were 32/>512 μg/ml for fosfomycin, 4/>64 μg/ml for rifampin, 1/2 μg/ml for ampicillin, 2/>256 μg/ml for linezolid, 16/32 μg/ml for gentamicin, 1/>64 μg/ml for vancomycin, and 1/5 μg/ml for daptomycin. In time-kill studies, fosfomycin was bactericidal at 8× and 16× MIC, but regrowth of resistant strains occurred after 24 h. With the exception of gentamicin, no complete inhibition of growth-related heat production was observed with other antimicrobials on early (3 h) or mature (24 h) biofilms. In the animal model, fosfomycin alone or in combination with daptomycin reduced planktonic counts by ≈4 log₁₀ CFU/ml below the levels before treatment. Fosfomycin cleared planktonic bacteria from 74% of cage fluids (i.e., no growth in aspirated fluid) and eradicated biofilm bacteria from 43% of cages (i.e., no growth from removed cages). In combination with gentamicin, fosfomycin cleared 77% and cured 58% of cages; in combination with vancomycin, fosfomycin cleared 33% and cured 18% of cages; in combination with daptomycin, fosfomycin cleared 75% and cured 17% of cages. Rifampin showed no activity on planktonic or adherent E. faecalis, whereas in combination with daptomycin it cured 17% and with fosfomycin it cured 25% of cages. Emergence of fosfomycin resistance was not observed in vivo. In conclusion, fosfomycin showed activity against planktonic and adherent E. faecalis. Its role against enterococcal biofilms should be further investigated, especially in combination with rifampin and/or daptomycin treatment.     

A marked increase in gastric fluid volume during cardiopulmonary bypass

Major physiological stress occurs during cardiac surgery with cardiopulmonary bypass. This is related to hypothermia and artificial organ perfusion. Thus, serious gastrointestinal complications, particularly upper gastrointestinal bleeding, sometimes follow cardiac surgery. We have compared the antisecretory effects of a preanesthetic H₂ antagonist (roxatidine, cardiopulmonary bypass-H₂ group, n = 15) and a proton pump inhibitor (rabeprazole, cardiopulmonary bypass-PPI group, n = 15) in patients undergoing cardiac surgery with cardiopulmonary bypass, and also compared in patients undergoing a off-pump coronary artery bypass graft surgery (off-pump cardiopulmonary bypass-H₂ group, n = 15). Gastric pH (5.14 ± 0.61) and gastric fluid volume (13.2 ± 2.4 mL) at the end of surgery in off-pump cardiopulmonary bypass-H₂ groups was significantly lower and higher than those in both cardiopulmonary bypass-H₂ (6.25 ± 0.54, 51.3 ± 8.0 mL) and cardiopulmonary bypass-PPI (7.29 ± 0.13, 63.5 ± 14.8 mL) groups, respectively although those variables did not differ between groups after the induction of anesthesia. Plasma gastrin (142 ± 7 pg/mL) at the end of surgery and maximal blood lactate levels (1.50 ± 0.61 mM) in off-pump cardiopulmonary bypass-H₂ group were also significantly lower than those in both cardiopulmonary bypass-H₂ (455 ± 96 pg/mL, 3.97 ± 0.80 mM) and cardiopulmonary bypass-PPI (525 ± 27 pg/mL, 3.15 ± 0.44 mM) groups, respectively. In addition, there was a significant correlation between gastric fluid volume and maximal blood lactate (r = 0.596). In conclusion, cardiopulmonary bypass may cause an increase in gastric fluid volume which neither H₂ antagonist nor PPI suppresses. A significant correlation between gastric fluid volume and maximal blood lactate suggests that gastric fluid volume may predict degree of gastrointestinal tract hypoperfusion.     

High Activity of Fosfomycin and Rifampin against Methicillin-Resistant Staphylococcus aureus Biofilm In Vitro and in an Experimental Foreign-Body Infection Model

Increasing antimicrobial resistance reduces treatment options for implant-associated infections caused by methicillin-resistant Staphylococcus aureus (MRSA). We evaluated the activity of fosfomycin alone and in combination with vancomycin, daptomycin, rifampin, and tigecycline against MRSA (ATCC 43300) in a foreign-body (implantable cage) infection model. The MICs of the individual agents were as follows: fosfomycin, 1 μg/ml; daptomycin, 0.125 μg/ml; vancomycin, 1 μg/ml; rifampin, 0.04 μg/ml; and tigecycline, 0.125 μg/ml. Microcalorimetry showed synergistic activity of fosfomycin and rifampin at subinhibitory concentrations against planktonic and biofilm MRSA. In time-kill curves, fosfomycin exhibited time-dependent activity against MRSA with a reduction of 2.5 log₁₀ CFU/ml at 128 × the MIC. In the animal model, planktonic bacteria in cage fluid were reduced by <1 log₁₀ CFU/ml with fosfomycin and tigecycline, 1.7 log₁₀ with daptomycin, 2.2 log₁₀ with fosfomycin-tigecycline and fosfomycin-vancomycin, 3.8 log₁₀ with fosfomycin-daptomycin, and >6.0 log₁₀ with daptomycin-rifampin and fosfomycin-rifampin. Daptomycin-rifampin cured 67% of cage-associated infections and fosfomycin-rifampin cured 83%, whereas all single drugs (fosfomycin, daptomycin, and tigecycline) and rifampin-free fosfomycin combinations showed no cure of MRSA cage-associated infections. No emergence of fosfomycin resistance was observed in animals; however, a 4-fold increase in fosfomycin MIC (from 2 to 16 μg/ml) occurred in the fosfomycin-vancomycin group. In summary, the highest eradication of MRSA cage-associated infections was achieved with fosfomycin in combination with rifampin (83%). Fosfomycin may be used in combination with rifampin against MRSA implant-associated infections, but it cannot replace rifampin as an antibiofilm agent.     

Daptomycin Concentrations in Valve Tissue and Vegetation in Patients with Bacterial Endocarditis

In a patient with mitral-aortic native-valve Streptococcus oralis endocarditis, daptomycin concentrations in aortic and mitral valves were 8.6 and 30.8 μg/g, respectively, and 26 μg/g in the mitral vegetation. In the case of porcine-aortic-valve Staphylococcus epidermidis endocarditis, the daptomycin concentrations were 53.1 μg/g in the valve and 18.1 μg/g in perivalvular tissues. Daptomycin achieved apparently adequate tissue concentrations. S. epidermidis was eradicated, whereas Streptococcus oralis persisted, and its daptomycin MIC displayed a 4-fold increase.     

In vitro activities of dalbavancin and nine comparator agents against anaerobic gram-positive species and corynebacteria

Dalbavancin is a novel semisynthetic glycopeptide with enhanced activity against gram-positive species. Its comparative in vitro activities and those of nine comparator agents, including daptomycin, vancomycin, linezolid, and quinupristin-dalfopristin, against 290 recent gram-positive clinical isolates strains, as determined by the NCCLS agar dilution method, were studied. The MICs of dalbavancin at which 90% of various isolates tested were inhibited were as follows: Actinomyces spp., 0.5 μg/ml; Clostridium clostridioforme, 8 μg/ml; C. difficile, 0.25 μg/ml; C. innocuum, 0.25 μg/ml; C. perfringens, 0.125 μg/ml; C. ramosum, 1 μg/ml; Eubacterium spp., 1 μg/ml; Lactobacillus spp., >32 μg/ml, Propionibacterium spp., 0.5 μg/ml; and Peptostreptococcus spp., 0.25 μg/ml. Dalbavancin was 1 to 3 dilutions more active than vancomycin against most strains. Dalbavancin exhibited excellent activity against gram-positive strains tested and warrants clinical evaluation.     

Characterization of High-Level Daptomycin Resistance in Viridans Group Streptococci Developed upon In Vitro Exposure to Daptomycin

Viridans group streptococci (VGS) are part of the normal flora that may cause bacteremia, often leading to endocarditis. We evaluated daptomycin against four clinical strains of VGS (MICs = 1 or 2 μg/ml) using an in vitro-simulated endocardial vegetation model, a simulated bacteremia model, and kill curves. Daptomycin exposure was simulated at 6 mg/kg of body weight and 8 mg/kg every 24 h for endocardial and bacteremia models. Total drug concentrations were used for analyses containing protein (albumin and pooled human serum), and free (unbound) drug concentrations (93% protein bound) were used for analyses not containing protein. Daptomycin MICs in the presence of protein were significantly higher than those in the absence of protein. Despite MICs below or at the susceptible breakpoint, all daptomycin regimens demonstrated limited kill in both pharmacodynamic models. A reduction of approximately 1 to 2 log₁₀ CFU was seen for all isolates and dosages except daptomycin at 6 mg/kg, which achieved a reduction of 2.7 log₁₀ CFU/g against one strain (Streptococcus gordonii 1649) in the endocardial model. Activity was similar in both pharmacodynamic models in the presence or absence of protein. Similar activity was noted in the kill curves over all multiples of the MIC. Regrowth by 24 h was seen even at 8× MIC. Postexposure daptomycin MICs for both pharmacodynamic models increased to >256 μg/ml for all isolates by 24 and 72 h. Despite susceptibility to daptomycin by standard MIC methods, these VGS developed high-level daptomycin resistance (HLDR) after a short duration following drug exposure not attributed to modification or inactivation of daptomycin. Further evaluation is warranted to determine the mechanism of resistance and clinical implications.     

Daptomycin Activity against Uncommonly Isolated Streptococcal and Other Gram-Positive Species Groups

A total of 1,356 clinical isolates were tested against daptomycin by broth microdilution methods. Daptomycin was active against seven groups of viridans group streptococci (MIC₅₀ and MIC₉₀ values ranging from ≤0.06 and ≤0.06 μg/ml [Streptococcus bovis and Streptococcus dysgalactiae] to 0.5 and 1 μg/ml [Streptococcus mitis, Streptococcus oralis, and Streptococcus parasanguinis], respectively), beta-hemolytic streptococci serogroups C, F, and G (MIC₅₀ and MIC₉₀, ≤0.06 to 0.25 and 0.12 to 0.25 μg/ml, respectively), Corynebacterium spp. (MIC₅₀ and MIC₉₀, ≤0.06 and 0.12 μg/ml, respectively), and Micrococcus spp. (MIC₅₀ and MIC₉₀, ≤0.06 and 0.25 μg/ml, respectively). Listeria monocytogenes exhibited higher daptomycin MICs (MIC₅₀ and MIC₉₀, 2 and 4 μg/ml, respectively) than other tested organisms.     

Nine-Hospital Study Comparing Broth Microdilution and Etest Method Results for Vancomycin and Daptomycin against Methicillin-Resistant Staphylococcus aureus

Vancomycin and daptomycin MIC results for 1,800 randomly selected oxacillin (methicillin [meticillin])-resistant Staphylococcus aureus (MRSA) bloodstream isolates from nine U.S. hospitals (collected from 2002 to 2006) were determined by a reference broth microdilution (BMD) method using frozen-form panels with precise incremental dilutions and by the Etest technique. The Etest provided vancomycin and daptomycin MIC results that were consistently higher (0.5 to 1.5 log₂ dilution steps) than those provided by the reference BMD method. The dominant MRSA population (91.2% of MRSA isolates) would be categorized as vancomycin nonsusceptible by the MIC results from the Etest method if the susceptibility breakpoint was adjusted downward to ≤1 μg/ml, as suggested by clinical outcome studies.Vancomycin is still used extensively for the treatment of oxacillin (methicillin [meticillin])-resistant Staphylococcus aureus (MRSA) bacteremia, as well as other less serious MRSA infections. However, vancomycin treatment failure is not uncommon, even when the MRSA strains are fully susceptible to vancomycin according to the criterion (breakpoint MIC, ≤2 μg/ml) used by the Clinical and Laboratory Standards Institute (CLSI). A reduction in the efficacy of vancomycin against MRSA strains for which vancomycin MICs are elevated (to 1 to 2 μg/ml) has been widely reported, suggesting that modest elevations in MICs may explain some suboptimal clinical outcomes (10, 13).The vast majority of clinical laboratories use automated systems and a distinct minority use the disk diffusion method as the routine susceptibility testing technique. However, the disk diffusion method and some automated systems do not accurately detect vancomycin-intermediate S. aureus (7). In addition, there have been a growing number of reports showing discrepancies between in vitro susceptibility test results for vancomycin and clinical outcomes of MRSA infections treated with this glycopeptide (6, 11). Thus, many laboratories are being requested to assess exact MICs by reference or alternative methods, such as that of Etest (AB Biodisk, Solna, Sweden).Although daptomycin remains very active against S. aureus, an association between reduced susceptibility to vancomycin and reduced susceptibility to daptomycin has been reported by some investigators (1). S. aureus isolates classified as daptomycin nonsusceptible according to MICs (≥2 μg/ml) are still rare, and no definitive resistance mechanism has been identified. However, genetic mutations and increases in daptomycin MICs after prolonged vancomycin and/or daptomycin treatment of infections associated with septic arthritis, osteomyelitis, septic thrombophlebitis, and endocarditis, especially in the presence of intravenous catheters and other prosthetic devices, have been reported previously (1). Thus, microbiology laboratories may be required to perform proper daptomycin susceptibility testing. Since a daptomycin disk diffusion test has not been developed, daptomycin susceptibility has to be evaluated by reference methods (2, 3) or the Etest method. In the present study, we evaluated the correlation between vancomycin and daptomycin MICs obtained by the Etest technique and the CLSI reference broth microdilution (BMD) method.(This study was presented in part at the 48th Interscience Conference on Antimicrobial Agents and Chemotherapy-46th Infectious Diseases Society of America meeting, Washington, DC, 25 to 28 October 2008.)A total of 1,800 MRSA strains from nine hospitals, one in each of the U.S. census regions, were tested. Each medical center contributed 200 MRSA strains collected from patients with bloodstream infections from 2002 through 2006 (target, 40 strains per year per center). The participant centers were as follows: Tufts Medical Center, Boston, MA; New York Hospital Queens, New York, NY; Ochsner Clinic Foundation, New Orleans, LA; University of Colorado Denver, Aurora, CO; University of Nebraska Medical Center, Omaha, NE; University of Washington, Seattle, WA; University of Alabama at Birmingham, Birmingham, AL; Wayne State University, Detroit, MI; and the Medical University of South Carolina, Charleston, SC.MICs of daptomycin and vancomycin were determined by the reference BMD method (using frozen-form panels), with the appropriate medium variation (the addition of 50 mg/liter of calcium) for testing daptomycin (2). Thirty-six precise incremental dilutions of vancomycin between 64 and 0.06 μg/ml (64, 32, 16, 8, 4, 3, 2.5, 2, 1.875, 1.75, 1.625, 1.5, 1.375, 1.25, 1.125, 1, 0.938, 0.875, 0.813, 0.75, 0.688, 0.625, 0.563, 0.5, 0.469, 0.438, 0.406, 0.375, 0.344, 0.313, 0.281, 0.25, 0.188, 0.12, 0.094, and 0.06 μg/ml) were tested, and 20 dilutions of daptomycin between 16 and 0.06 μg/ml (16, 8, 4, 2, 1.5, 1, 0.875, 0.75, 0.625, 0.5, 0.438, 0.375, 0.313, 0.25, 0.219, 0.188, 0.156, 0.12, 0.094, and 0.06 μg/ml) were tested. Isolates were also evaluated by Etest for susceptibilities to daptomycin and vancomycin according to the recommendations of the Etest manufacturer (AB Biodisk). To compare the results obtained with the BMD method and those obtained with the Etest technique, BMD results were rounded up to the next dilution provided for the Etest method. Resistance to oxacillin was confirmed by the reference BMD method (dilution range tested, 0.5 to 4 μg/ml) and cefoxitin susceptibilities tested by disk diffusion (2, 3). Quality control strains S. aureus ATCC 25923 and Enterococcus faecalis ATCC 29212 were evaluated concurrently with every set of tests.MICs of vancomycin obtained by the Etest method were consistently higher (+0.5 to 1.5 log₂ dilutions) than those obtained by the BMD method (Fig. ​(Fig.1a).1a). For strains from all centers combined, the overall vancomycin MIC mode determined by the BMD method was 0.75 μg/ml (corresponding to 75.3% of values, including those rounded up from measured 0.563-, 0.625-, and 0.688-μg/ml MICs) and 96.9% of strains exhibited vancomycin MIC results of ≤1 μg/ml. In contrast, when tested by the Etest, MICs for 58.3 and 32.1% of MRSA strains were 1.5 and 2 μg/ml, respectively (Fig. ​(Fig.1a1a).Open in a separate windowFIG. 1.Scattergrams showing the correlations between vancomycin (a) and daptomycin (b) MICs obtained by the BMD method and the Etest. Solid lines indicate CLSI susceptibility breakpoints, and broken lines indicate complete agreement between results from the two methods.For all strains except one, the Etest yielded higher vancomycin MICs than the reference method. Among 1,628 strains for which the Etest MIC was 1.5 μg/ml (1,050 strains) or 2 μg/ml (578 strains), only 44 (2.7%) had BMD MIC results of >1 μg/ml. Furthermore, among 13 strains considered to be nonsusceptible (intermediate) to vancomycin (MIC, 3 or 4 μg/ml) according to the Etest results, only 1 had a vancomycin MIC result of >2 μg/ml by the reference method, demonstrating a positive predictive value of only 7.7%.Etest MICs of daptomycin were also slightly elevated (+0.5 to 1 log₂ dilution) compared to BMD MICs (Fig. ​(Fig.1b).1b). When tested by the BMD method, the daptomycin MIC mode was 0.19 μg/ml (corresponding to 55.4% of values, including MICs of 0.156 and 0.188 μg/ml) and 92.9% of strains exhibited daptomycin MIC results of ≤0.25 μg/ml. In contrast, when tested by the Etest, the MIC mode was 0.38 μg/ml (corresponding to 37.2% of values), which is 1 doubling dilution higher than that obtained by the BMD method. Among nine strains considered to be daptomycin nonsusceptible according to the Etest results, only two had a MIC result of >1 μg/ml when tested by the reference BMD method, demonstrating a positive predictive value of 22.2% (Fig. ​(Fig.1b1b).Although the emergence of vancomycin-intermediate S. aureus strains and that of vancomycin-resistant S. aureus strains are reasons for concern, these organisms still are extremely rare (12). Nevertheless, a number of studies have demonstrated increased clinical failure with MRSA isolates for which vancomycin MICs are increased (>1 μg/ml) but still within the CLSI-defined susceptibility range (≤2 μg/ml) (3, 11, 13). In addition, there are reports of the increase of vancomycin MICs over time (designated “MIC creep”) at individual institutions, although this trend has not been validated by large, multi-institutional studies (14). Thus, it is becoming clear to physicians that an “S” result for vancomycin is not sufficient to appropriately guide therapy and that the clinical laboratory should provide accurate and reliable MICs.Since most clinical laboratories use automated systems to perform susceptibility testing and these systems do not provide a precise vancomycin MIC, many laboratories are using alternative methods for testing vancomycin in selected cases (6). The Etest method is an attractive option for alternative vancomycin testing since it is easy to perform and cost-effective for testing only one drug-bug combination. However, the results of the present study clearly show that the Etest provides vancomycin and daptomycin MIC results consistently higher (by 0.5 to 1.5 log₂ dilutions) than those provided by precisely performed reference BMD tests. Furthermore, the fact that the higher vancomycin MIC results provided by the Etest appear to be more reliable in predicting vancomycin treatment responses (6) indicates that the vancomycin susceptibility breakpoint should be reevaluated.The susceptibility testing method used may have a large impact on physician decisions for vancomycin and daptomycin treatment of MRSA infections. According to the information presented here, the dominant MRSA population (91.2% of strains) would be categorized as vancomycin nonsusceptible by the Etest method if the susceptibility breakpoint was adjusted to ≤1 μg/ml, as suggested by some published clinical outcome studies on recognizing isolates for which vancomycin MICs are 2 μg/ml (4, 5, 8-10, 14). Daptomycin MICs were also affected by the method used, but to a lesser degree (MICs were found to be 0.5 to 1 dilution step higher by the Etest method than by the reference method, with 0.4% false-nonsusceptible results), and may also suffer from the perception of declining daptomycin potency.     

In vitro activity of TD-1792, a multivalent glycopeptide-cephalosporin antibiotic, against 377 strains of anaerobic bacteria and 34 strains of Corynebacterium species

TD-1792 is a multivalent glycopeptide-cephalosporin heterodimer antibiotic with potent activity against Gram-positive bacteria. We tested TD-1792 against 377 anaerobes and 34 strains of Corynebacterium species. Against nearly all Gram-positive strains, TD-1792 had an MIC₉₀ of 0.25 μg/ml and was typically 3 to 7 dilutions more active than vancomycin and daptomycin.     

Telavancin In Vitro Activity against a Collection of Methicillin-Resistant Staphylococcus aureus Isolates,Including Resistant Subsets,from the United States

Telavancin had MIC₅₀, MIC₉₀, and MIC₁₀₀ values of 0.03, 0.06, and 0.12 μg/ml, respectively, against methicillin-susceptible Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), and non-multidrug-resistant (non-MDR) and MDR subsets. MRSA with elevated MIC values for vancomycin (2 to 4 μg/ml) or daptomycin (1 to 2 μg/ml) had telavancin MIC₅₀ (0.06 μg/ml) values 2-fold higher than those of isolates with lower MIC results (MIC₅₀, 0.03 μg/ml). However, telavancin had MIC₉₀ and MIC₁₀₀ results of 0.06 and 0.12 μg/ml (100% susceptible), respectively, regardless of the MRSA subset.     

Efficacy of vancomycin and daptomycin against Staphylococcus aureus isolates collected over 29 years

We investigated vancomycin and daptomycin efficacy for Staphylococcus aureus isolates at our institution by testing 221 methicillin-sensitive and 299 methicillin-resistant isolates recovered from serious infections between 1979 and 2007 using a microdilution method. The MIC₉₀'s for vancomycin remained constant at 2 μg/mL for methicillin-resistant S. aureus (MRSA) and methicillin-sensitive S. aureus (MSSA). For MSSA, the geometric mean vancomycin MICs remained at 1.1 μg/mL but varied from 1.1 to 1.7 for MRSA. Tolerance to vancomycin was seen in 6.5% of MRSA and 10.5% of MSSA. Daptomycin MIC₉₀'s remained at ≤1 μg/mL, and the daptomycin concentration at which 90% of the strains were killed (MBC₉₀) remained at 2 μg/ml. Over 29 years, no trend was detected in vancomycin or daptomycin susceptibilities. Daptomycin had excellent inhibitory and bactericidal activities against all strains throughout the years. Although vancomycin's inhibitory activity was consistent over time, vancomycin-tolerant strains whose presence was not predicted by their MIC were found.     

Oritavancin Activity against Staphylococcus aureus Causing Invasive Infections in U.S. and European Hospitals: a 5-Year International Surveillance Program

In this study, oritavancin had modal MIC, MIC₅₀, and MIC₉₀ values of 0.03, 0.03, and 0.06 μg/ml, respectively, against Staphylococcus aureus. Similar results (MIC_50/90, 0.03/0.06 μg/ml) were observed against methicillin-resistant and -susceptible isolates and those demonstrating multidrug-resistant (MDR) and non-MDR phenotypes. When oritavancin (MIC_50/90, 0.06/0.12 mg/ml) was tested against S. aureus with elevated MIC values for daptomycin (i.e., 1 to 4 mg/ml) and vancomycin (i.e., 2 mg/ml), it showed MIC results 2-fold higher than those for the more susceptible vancomycin or daptomycin counterparts (MIC_50/90, 0.03/0.06 mg/ml), yet it inhibited these isolates at ≤0.25 mg/ml.     

Evaluation of the Novel Combination of High-Dose Daptomycin plus Trimethoprim-Sulfamethoxazole against Daptomycin-Nonsusceptible Methicillin-Resistant Staphylococcus aureus Using an In Vitro Pharmacokinetic/Pharmacodynamic Model of Simulated Endocardial Vegetations

Daptomycin-nonsusceptible (DNS) Staphylococcus aureus is found in difficult-to-treat infections, and the optimal therapy is unknown. We investigated the activity of high-dose (HD) daptomycin plus trimethoprim-sulfamethoxazole de-escalated to HD daptomycin or trimethoprim-sulfamethoxazole against 4 clinical DNS methicillin-resistant S. aureus (MRSA) isolates in an in vitro pharmacokinetic/pharmacodynamic model of simulated endocardial vegetations (10⁹ CFU/g). Simulated regimens included HD daptomycin at 10 mg/kg/day for 14 days, trimethoprim-sulfamethoxazole at 160/800 mg every 12 h for 14 days, HD daptomycin plus trimethoprim-sulfamethoxazole for 14 days, and the combination for 7 days de-escalated to HD daptomycin for 7 days and de-escalated to trimethoprim-sulfamethoxazole for 7 days. Differences in CFU/g (at 168 and 336 h) were evaluated by analysis of variance (ANOVA) with a Tukey''s post hoc test. Daptomycin MICs were 4 μg/ml (SA H9749-1, vancomycin-intermediate Staphylococcus aureus; R6212, heteroresistant vancomycin-intermediate Staphylococcus aureus) and 2 μg/ml (R5599 and R5563). Trimethoprim-sulfamethoxazole MICs were ≤0.06/1.19 μg/ml. HD daptomycin plus trimethoprim-sulfamethoxazole displayed rapid bactericidal activity against SA H9749-1 (at 7 h) and R6212 (at 6 h) and bactericidal activity against R5599 (at 72 h) and R5563 (at 36 h). A ≥8 log₁₀ CFU/g decrease was observed with HD daptomycin plus trimethoprim-sulfamethoxazole against all strains (at 48 to 144 h), which was maintained with de-escalation to HD daptomycin or trimethoprim-sulfamethoxazole at 336 h. The combination for 14 days and the combination for 7 days de-escalated to HD daptomycin or trimethoprim-sulfamethoxazole was significantly better than daptomycin monotherapy (P < 0.05) and trimethoprim-sulfamethoxazole monotherapy (P < 0.05) at 168 and 336 h. Combination therapy followed by de-escalation offers a novel bactericidal therapeutic alternative for high-inoculum, serious DNS MRSA infections.     

In Vitro Pharmacodynamics of Human Simulated Exposures of Telavancin against Methicillin-Susceptible and -Resistant Staphylococcus aureus with and without Prior Vancomycin Exposure

Telavancin is a lipoglycopeptide with potent activity against methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA). The activity of telavancin against MRSA and MSSA after prior vancomycin exposure was studied in an in vitro pharmacodynamic model. Two clinical MRSA and two MSSA isolates, all with vancomycin MICs of 2 μg/ml, were subjected to humanized free drug exposures of vancomycin at 1 g every 12 h (q12h) for 96 h, telavancin at 750 mg q24h for 96 h, and vancomycin at 1 g q12h for 72 h followed by telavancin at 750 mg q24h for 48 h (120 h total). The microbiological responses were measured by changes from 0 h in log₁₀ CFU/ml at the end of experiments and area under the bacterial killing and regrowth curves over 96 h (AUBC₀₋₉₆). The control isolates grew to 8.8 ± 0.3 log₁₀ CFU/ml. Initially, all regimens caused −4.5 ± 0.9 reductions in log₁₀ CFU/ml by 48 h followed by slight regrowth over the following 48 to 72 h. After 96 h, vancomycin and telavancin achieved −3.7 ± 0.9 and −3.8 ± 0.8 log₁₀ CFU/ml changes from baseline, respectively (P = 0.74). Sequential exposure to telavancin after vancomycin did not result in additional CFU reductions or increases, with ultimate log₁₀ CFU/ml reductions of −4.3 ± 1.1 at 96 h and −4.2 ± 1.3 at 120 h (P > 0.05 for all comparisons at 96 h). The AUBC_0–96 was significantly smaller for the regimen of telavancin for 96 h than for the regimens of vancomycin for 96 h and vancomycin followed by telavancin (P ≤ 0.04). No resistance was observed throughout the experiment. Against these MRSA and MSSA isolates with vancomycin MICs of 2 μg/ml, telavancin was comparable with vancomycin and its activity was unaffected by prior vancomycin exposure.     

Effect of Renin-Angiotensin System Blockade on Insulin Resistance and Inflammatory Parameters in Patients With Impaired Glucose Tolerance

OBJECTIVE

The study investigated the effect of angiotensin receptor blockers (ARB) on glucose homeostasis and inflammatory parameters in patients with impaired glucose tolerance (IGT).

RESEARCH DESIGN AND METHODS

We prospectively studied the insulin sensitivity index (ISI) and homeostasis model assessment–insulin resistance (HOMA-IR) in 13 obese males with IGT and in 13 matched control subjects with normal glucose tolerance (NGT) during hyperglycemic testing over 90 min. Adiponectin, retinol-binding protein 4 (RBP4), and high-sensitive C-reactive protein (hsCRP) were analyzed. Measurements were performed at baseline and after a 4-week treatment with 160 mg/day valsartan. The results of the IGT and NGT groups were compared.

RESULTS

At baseline, HOMA-IR (IGT 4.1 ± 3 vs. NGT 2.3 ± 1.0, P < 0.01), hsCRP (IGT 3.9 ± 1.9 vs. NGT 1.8 ± 1 mg/l, P < 0.05), and RBP4 (IGT 27.1 ± 2.1 vs. NGT 24.0 ± 2.0 ng/ml, P < 0.05) were significantly higher, whereas ISI (IGT 1.5 ± 0.9 vs. NGT 1.8 ± 1.2, P < 0.05) and plasma adiponectin (IGT 3.2 ± 0.9, NGT 5.2 ± 2.4 μg/ml, P < 0.05) were significantly lower in the IGT group compared with the NGT group. Under ARB, there was an increase in both groups of adiponectin (IGT 4.1 ± 1.9 μg/ml, NGT 6.3 ± 2.9 μg/ml, P < 0.05) and an increase in ISI (IGT 1.5 ± 0.9 to 2.3 ± 1 μg/ml, NGT 1.8 ± 1 to 2.5 ± 2 μg/ml, P < 0.05). HOMA-IR (4.1 ± 3 to 2.6 ± 2; P < 0.01), hsCRP (3.9 ± 1.9 to 1.8 ± 1 mg/l, P < 0.05), and RBP4 (27.1 ± 2.1 to 22.1 ± 1.8 ng/ml, P < 0.01) decreased significantly in the IGT group.

CONCLUSIONS

Insulin sensitivity and associated inflammatory factors improve under ARB in IGT patients.Insulin resistance has a causal role in type 2 diabetes, a crucial risk factor for cardiovascular and renal disease (1). Impaired glucose tolerance (IGT) represents an intermediate state of abnormal glucose regulation between normal glucose homeostasis and manifest diabetes. IGT is defined as elevated 2-h plasma glucose concentration >140 and <200 mg/dl after a 75-g oral glucose load in an oral glucose tolerance test (2). A combination of β-cell dysfunction and insulin resistance with decreased insulin sensitivity or responsiveness to the metabolic action of insulin plays a pathogenetic role. Insulin resistance is common in subjects with visceral adiposity, hypertension, hyperglycemia, and dyslipidemia. Patients with metabolic syndrome have a high risk of developing frank diabetes (3).Adiponectin is a fat-derived hormone specifically produced and secreted by adipocytes. This adipocytokine is considered an important modulator of insulin sensitivity in patients with IGT (4,5). Adiponectin levels decrease in the obese, which may be a contributing factor to insulin resistance. Anti-inflammatory properties also have been attributed to adiponectin. This is indicated by serum concentrations of adiponectin, which are inversely associated with inflammatory markers such as C-reactive protein (CRP). Retinol-binding protein 4 (RBP4) is another adipocyte-secreted molecule and is elevated in serum before development of overt diabetes (6).The interaction of these different metabolic and inflammatory parameters in IGT has not been fully clarified. Our study investigates insulin sensitivity and associated risk factors focusing on obese subjects with IGT. We tested the effect of a short-term 4-week angiotensin receptor blocker (ARB) treatment on glucose disposal and inflammatory markers in subjects with IGT.     

Release of daptomycin from polymethylmethacrylate beads in a continuous flow chamber

Because daptomycin is active against Gram-positive cocci, it may be useful in the treatment and prevention of bone and joint infections when incorporated into polymethylmethacrylate (PMMA). The release kinetics of daptomycin from PMMA were studied in a continuous flow chamber designed to simulate in vivo conditions. Three-millimeter beads containing 2.5%, 7.5%, and 15.0% daptomycin (weight daptomycin per weight PMMA) were individually placed in a chamber with 1 mL Krebs Ringer buffer flowing at 1 mL/hour. The majority of daptomycin was released in the first 24 hours. The mean peak concentrations were 13.4, 62.3, and 146.7 μg/mL; the mean AUC_0–∞ were 30, 272, and 1204 h × μg/mL; and the mean percentages of daptomycin released were 6%, 18%, and 42% for the beads containing 2.5%, 7.5%, and 15.0% daptomycin, respectively. Daptomycin is released from PMMA in a continuous flow chamber at a rate similar to that previously determined by our laboratory for vancomycin.     

In Vitro Pharmacodynamics of Human Simulated Exposures of Ceftaroline and Daptomycin against MRSA,hVISA, and VISA with and without Prior Vancomycin Exposure

The effects of prior vancomycin exposure on ceftaroline and daptomycin therapy against methicillin-resistant Staphylococcus aureus (MRSA) have not been widely studied. Humanized free-drug exposures of vancomycin at 1 g every 12 h (q12h), ceftaroline at 600 mg q12h, and daptomycin at 10 mg/kg of body weight q24h were simulated in a 96-h in vitro pharmacodynamic model against three MRSA isolates, including one heteroresistant vancomycin-intermediate S. aureus (hVISA) isolate and one VISA isolate. A total of five regimens were tested: vancomycin, ceftaroline, and daptomycin alone for the entire 96 h, and then sequential therapy with vancomycin for 48 h followed by ceftaroline or daptomycin for 48 h. Microbiological responses were measured by the changes in log₁₀ CFU during 96 h from baseline. Control isolates grew to 9.16 ± 0.32, 9.13 ± 0.14, and 8.69 ± 0.28 log₁₀ CFU for MRSA, hVISA, and VISA, respectively. Vancomycin initially achieved ≥3 log₁₀ CFU reductions against the MRSA and hVISA isolates, followed by regrowth beginning at 48 h; minimal activity was observed against VISA. The change in 96-h log₁₀ CFU was largest for sequential therapy with vancomycin followed by ceftaroline (−5.22 ± 1.2, P = 0.010 versus ceftaroline) and for sequential therapy with vancomycin followed by ceftaroline (−3.60 ± 0.6, P = 0.037 versus daptomycin), compared with daptomycin (−2.24 ± 1.0), vancomycin (−1.40 ± 1.8), and sequential therapy with vancomycin followed by daptomycin (−1.32 ± 1.0, P > 0.5 for the last three regimens). Prior exposure of vancomycin at 1 g q12h reduced the initial microbiological response of daptomycin, particularly for hVISA and VISA isolates, but did not affect the response of ceftaroline. In the scenario of poor vancomycin response for high-inoculum MRSA infection, a ceftaroline-containing regimen may be preferred.