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PubMed2003

Daptomycin dose-effect relationship against resistant gram-positive organisms.

Daptomycin exhibits in vitro bactericidal activity against clinically significant gram-positive bacteria. We employed pharmacodynamic modeling to determine a once-daily dosing regimen of daptomycin that correlates to pharmacodynamic endpoints for different resistant gram-positive clinical strains. An in vitro pharmacodynamic model with an initial inoculum of 6 log(10) CFU/ml was used to simulate daptomycin regimens ranging in dose from 0 to 9 mg/kg of body weight/day, with corresponding exposures reflecting free-daptomycin concentrations in serum. Bacterial density was profiled over 48 h for two methicillin-resistant Staphylococcus aureus (MRSA-67 and -R515), two glycopeptide intermediate-resistant S. aureus (GISA-992 and -147398), and two vancomycin-resistant Enterococcus faecium (VREF-12366 and -SF12047) strains. A sigmoid dose-response model was used to estimate the effective dose required to achieve 50% (ED(50)) and 80% (ED(80)) bacterial density reduction at 48 h. Daptomycin MICs for study isolates ranged from 0.125 to 4 micro g/ml. Model fitting resulted in an r(2) of >0.80 for all tested isolates. Control growths at 48 h ranged from 7.3 to 8.5 log(10) CFU/ml. Sigmoid relationships were not superimposable between categorical resistant species: ED(50) and ED(80) values were 1.9 and 3.1, 4.2 and 5.6, and 5.4 and 6.8 mg/kg for MRSA, GISA, and VREF isolates, respectively. Doses required to achieve ED(50) and ED(80) values correlated with MIC differences between tested organisms. Corresponding area under the concentration-time curve from 0 to 24 h/MIC exposure ratios demonstrated a wide range of ED(80) values among the tested isolates. Doses ranging between 3 and 7 mg/kg produced significant bactericidal activity (ED(80)) against these multidrug-resistant S. aureus and E. faecium isolates.

Animals↗
PubMed1997

Antimicrobial characteristics of quinupristin/dalfopristin (Synercid at 30:70 ratio) compared to alternative ratios for in vitro testing.

Quinupristin/dalfopristin is a new streptogramin combination that occurs at a natural ratio and formulation of 30:70. Rapid metabolism of the dalfopristin component to RP 12536 in vivo puts in question the validity of in vitro test of spectrum with the parent combination. In studies of quinupristin with both dalfopristin and RP 12536, a wide range of ratios (30:70, 50:50, 70:30) were tested by reference MIC and MBC tests. No significant potency differences were observed between combination ratios or metabolic components when testing 256 bacterial strains. Quinupristin/dalfopristin or quinupristin/RP 12536 remained active, by bactericidal action against many staphylococci and Streptococcus ssp. Enterococcus faecium strains were susceptible (MIC90, 2 micrograms/ml; static effect only) to the streptogramin, but E. faecalis, Pasteurella multocida, Pediococcus ssp., Haemophilus influenzae, and Bacteroides fragilis were generally less susceptible (MIC90, > or = 8 micrograms/ml). The log phase inoculum was preferred for MBC and kill-curve tests with this combination. The 30:70 ratio in vitro susceptibility test of quinupristin/dalfopristin as used to date, seems to predict the potency and spectrum of this streptogramin accurately and all clinically important in vivo ratios of the injectable form or its major metabolites. Quinupristin/dalfopristin should be further investigated for clinical use against emerging resistant Gram-positive infections, especially penicillin-resistant streptococci and glycopeptide-resistant E. faecium that exhibit susceptibility in this investigation.

Anti-Bacterial Agents↗
PubMed1992

Use of the E test to predict high-level resistance to aminoglycosides among enterococci.

The E test and the reference agar dilution methods were compared for detecting high-level aminoglycoside resistance (HLAR) among 71 selected clinical isolates, including 62 Enterococcus faecalis and 9 Enterococcus faecium isolates. High-level gentamicin resistance alone was found in 11% (5 E. faecalis and 3 E. faecium strains) and high-level streptomycin resistance was found in 42% (28 E. faecalis, 2 E. faecium strains) of the strains tested, and 31% of the strains demonstrated high-level resistance to both antimicrobial agents (21 E. faecalis and 1 E. faecium strains). The E test detected all HLAR populations, but the streptomycin strip may require recalibration to achieve absolute MIC comparisons with the reference value (twofold less) or the use of an alternative interpretive resistance breakpoint, e.g., > 1,000 micrograms/ml. By the E test, MIC results indicate that ampicillin, imipenem, penicillin, piperacillin, and vancomycin remain active against the HLAR E. faecalis isolates; however, these tested drugs were less effective on the HLAR E. faecium isolates (< 50%).

Agar↗
PubMedDate not supplied

Simple combined agar-strip test for detection of enterococcal susceptibility to ampicillin, moderate- or high-level gentamicin resistance and potential additive activity of ampicillin plus gentamicin.

A simple combined agar-strip test (CAST), involving filter paper strips charged with 20 micrograms of ampicillin or 40 micrograms of gentamicin, accurately detected high-level gentamicin resistance among 43 of 146 isolates of Enterococcus faecalis and additive activity of ampicillin plus gentamicin against 101 of 103 (98%) isolates of E. faecalis with moderate-level gentamicin resistance (MLGR). All 15 MLGR Enterococcus faecium isolates were moderately to highly resistant to ampicillin; 5 isolates with moderate resistance to ampicillin (minimal inhibitory concentrations = 16 micrograms/ml) were additively inhibited by ampicillin plus gentamicin, whereas the highly ampicillin-resistant E. faecium isolates yielded an indifferent effect with the CAST procedure.

Ampicillin↗
PubMed2004

Antimicrobial susceptibility of vancomycin-susceptible and -resistant enterococci isolated in Italy from raw meat products, farm animals, and human infections.

The susceptibility of vancomycin-resistant (VRE) and vancomycin-susceptible (VSE) enterococci to 10 antimicrobial agents was evaluated. The strains, belonging to different species, were isolated in Italy from raw meat products, farm animals, and human clinical infections in the years 1997-2000. High frequency of resistance to tetracycline and erythromycin was observed in all the groups of strains. On the contrary, chloramphenicol was the only drug that showed a relatively low rate of resistance in all the groups examined. In general, the resistance rates observed for VSE did not differ from those observed for VRE of the same species and origin. Some differences could be noticed among the different enterococcal species, with Enterococcus faecium strains being usually more resistant to beta-lactams, and Enterococcus faecalis strains more resistant to gentamicin. However, the strongest differences were observed when the strains were compared according to their source, the human isolates being usually more resistant than the isolates of animal origin. No significant difference was observed between isolates of swine and poultry origin. Among VRE E. faecium, multiple resistance was much more frequent among the human strains (90%) than among poultry (48.9%) and swine (26.5%) strains. These results show that in Italy VRE isolates from human clinical infections are usually more resistant than isolates from meat products and farm animals, and possess different antimicrobial resistance profiles.

Animals↗
PubMed2002

Prevalence of streptogramin resistance genes among Enterococcus isolates recovered from retail meats in the Greater Washington DC area.

The prevalence of streptogramin resistance genes in enterococci recovered from retail poultry in the Greater Washington DC area was examined. Forty-three chicken and 32 turkey retail samples were analysed. Thirty-one non-Enterococcus faecalis enterococcal strains were isolated that displayed MICs of quinupristin-dalfopristin and virginiamycin of > or = 4 mg/L. These included Enterococcus faecium (turkey n = 4, chicken n = 23), Enterococcus gallinarum (turkey n = 2, chicken n = 1) and Enterococcus hirae (chicken n = 1). The presence of streptogramin resistance genes was examined by PCR in all non-E. faecalis isolates. The vat(E) gene was detected in 10/23 chicken E. faecium and from 2/4 turkey E. faecium. No other streptogramin resistance genes were detected by PCR. In addition, erm(B) was detected in all the E. faecium and E. gallinarum found in turkeys and in 7/23 E. faecium found in chickens. The vat(E) gene was transferable by conjugation from only two of the 12 E. faecium isolates (one from chicken and one from turkey). This study suggests that there is a high prevalence of low-level streptogramin resistance among enterococci found in retail poultry and that other, yet to be identified, mechanisms operate in these isolates that confer streptogramin resistance in enterococci.

Animals↗
PubMed2006

Importance of the structure of vancomycin binding pocket in designing compounds active against vancomycin-resistant enterococci (VRE).

16-Membered meta, para-cyclophanes mimicking the vancomycin binding pocket (D-O-E ring) are designed and synthesized. The structural features of these biaryl ether containing macrocycles are: a) the deletion of the carboxyl group of vancomycin's central amino acid (amino acid D); b) the elongation of the N-terminal; c) the presence of lipidated aminoglucose at the D-ring. Cycloetherification by way of an intramolecular nucleophilic aromatic substitution reaction (S(N)Ar) is used as a key step for the construction of the macrocycle. Minimum inhibitory concentrations for all of the derivatives are measured using a standard microdilution assay. Compounds 2a-2c and 3a-3c displayed weak activities against resistant strain Enterococcus faecalis L560 and were inactive against Enterococcus faecium resistant strain L2215.

Anti-Bacterial Agents↗
PubMed2000

Antimicrobial susceptibilities of enterococci isolated from faeces of broiler and layer chickens.

Enterococci were isolated from faecal droppings of chickens in broiler and layer farms and the susceptibilities to nine therapeutic antimicrobial agents and six growth-promoting antibiotics were determined by the agar dilution method. Resistance to therapeutic antimicrobial agents such as ampicillin, clindamycin, erythromycin, streptomycin, tetracycline or tylosin was more frequent in enterococcal isolates from broiler farms than in those from layer farms. Resistance to ofloxacin was rare, occurring in only one (0.7%) of the Enterococcus faecium isolates from broiler farms. Resistance to growth-promoting antibiotics such as avilamycin, salinomycin and virginiamycin was common among isolates from broiler farms. Of the E. faecium isolates from broiler farms, 12.4% were resistant to avilamycin and 27.4% were resistant to virginiamycin. Resistance to salinomycin was detected in all enterococcal species, ranging from 12.4% of E. faecium isolates to 50% of E. hirae isolates.

Animal Husbandry↗
PubMed2006

Intravenous linezolid administered orally: a novel desensitization strategy.

A 41-year-old woman with a history of myasthenia gravis was admitted to a local hospital because of severe muscle weakness, ptosis, shortness of breath, nausea and vomiting, and fever. Blood cultures revealed Enterococcus faecium resistant to several antimicrobial agents. The organism had minimum inhibitory concentrations above 16 microg/ml for vancomycin and above 2 microg/ml for quinupristin-dalfopristin. In the absence of therapeutic alternatives, treatment with linezolid was required (minimum inhibitory concentration 1.5 microg/ml). The first dose of linezolid resulted in a hypersensitivity reaction consistent with an immunoglobulin E-mediated response requiring medical intervention. Because of a lack of intravenous access and because of limited availability of the oral suspension from the manufacturer, a desensitization protocol was implemented in which the intravenous formulation of linezolid was given orally. The patient was successfully desensitized by using an escalating, 14-dose procedure. We believe this is the first case in the English language literature to describe successful desensitization with the oral administration of intravenous linezolid in a patient with E. faecium bacteremia who was allergic to oxazolidinone.

Acetamides↗
PubMed2006

PFGE analysis of enterococci isolates from recreational and drinking water in Greece.

Biotyping and DNA fingerprinting by pulsed-field gel electrophoresis were applied to a collection of enterococci recovered from recreational and drinking water, in order to identify possible genetic relationships. Clinical strains of hospital origin were compared to the environmental isolates. A total of 104 enterococci were isolated from 128 recreational water (94 marine and 34 river water) and 470 drinking water supplies (440 municipal and 30 natural spring water samples). Sixty-two isolates were characterised as Enterococcus faecium recovered from all sources, 32 E. faecalis (from all sources), 4 E. durans (from marine, river and municipal water), 4 E. gallinarum (from marine water) and 2 E. avium (from marine and municipal water). Biotypes, determined with API20Strep, among E. faecium were correlated with certain environmental sources, while antibiotypes, determined with Etest, did not reveal any relationship to the sample origin. Even though genetic diversity was observed among the studied strains, common clonal types were also identified in different sources, suggesting a possible common origin of the enterococci. Cluster analysis revealed a genetic relationship between certain environmental E. faecium and clinical strains.

Bacterial Typing Techniques↗
PubMed1993

Epidemiologic analysis and genotypic characterization of a nosocomial outbreak of vancomycin-resistant enterococci.

We are reporting on a nosocomial outbreak of 213 cases of vancomycin-resistant enterococcus infection involving 2,812 enterococcal isolates from patients over a period of 36 months. In 1990, the Enterococcus faecium vancomycin susceptibility rate was found to be 85.7% (36 of 42 cases), and an incidence of 10.9% (42 of 383) was noted. The 1991 data showed E. faecium with a vancomycin susceptibility rate of 61.8% (110 of 178) and an incidence of 26.0% (178 of 684). Subsequently, in 1992, the incidence of E. faecium increased to 34.0% (599 of 1,745), with a decreased vancomycin susceptibility rate of 25.8% (155 of 599). The E. faecalis vancomycin susceptibility rate remained near 97% (1,768 of 1,823) over the 36-month period. Of 115 vancomycin-resistant enterococcus (VRE) clinical isolates identified by the MicroScan MIC Combo-6 panels (Baxter Healthcare, Sacramento, Calif.), the agar dilution method indicated the resistance rate to be 92.3% (106 of 115) (high level), 3.5% (4 of 115) midlevel, and 3.5% (4 of 115) (low level). Genotypic characterization of 32 different VRE isolates by field-inversion gel electrophoresis demonstrated 19 dissimilar restriction endonuclease patterns, with 9 patterns associated with VRE quinolone resistance. Statistical analysis of case-control data for 32 patients with VRE infections indicated a positive association with intrabdominal surgical procedures (odds ratio, 24.12), multidrug therapy (odds ratio, 37.80), preexposure to vancomycin (odds ratio, 20.21), and death (odds ratio, 17.50).

Case-Control Studies↗
PubMed2002

Analysis of the conjugal transfer system of the pheromone-independent highly transferable Enterococcus plasmid pMG1: identification of a tra gene (traA) up-regulated during conjugation.

pMG1 (65.1 kbp) is a pheromone-independent Enterococcus faecium conjugative plasmid conferring gentamicin resistance. pMG1 is able to transfer to enterococci at a high frequency in broth mating experiments, and it does not respond to the sex pheromones which are involved in the high-frequency transfer system of some conjugative plasmids in Enterococcus faecalis. To analyze regulation of tra gene expression in pMG1, transcripts of pMG1 were examined during conjugation. RNA samples were prepared from mating mixtures 20, 40, 80, and 160 min after initiation of mating and were subsequently analyzed by Northern hybridization by using a variety of pMG1 DNA fragments as probes. One transcript of gene 71ORF2 increased to the maximal level 20 min after the start of mating. The level of this transcript decreased after 40 min of mating to the same level as the level in the control donor culture. The increase was not observed in cultures of the donor cells or recipient cells. These findings suggested that the increase was a conjugation-specific event. The 71ORF2 gene of pMG1 was disrupted by using the suicide vector pMG226 carrying an erythromycin resistance gene that is expressed in enterococci. The transfer frequencies of mutant plasmid pMG229, which had a disrupted 71ORF2 gene in pMG1, and the parent plasmid pMG1 were 1.6 x 10(-7) and 1.1 x 10(-3) per donor cell, respectively, in broth mating experiments, and the transfer frequencies of pMG229 and pMG1 were 2.7 x 10(-3) and 8.5 x 10(-2) per donor cell, respectively, in filter mating experiments. This indicated that the transfer frequency of plasmid pMG229 was reduced during broth mating and was not altered during filter mating. 71ORF2, which is designated traA, is a gene involved in the tra gene system for conjugation, and the product of this gene is associated with the formation or stabilization of mating aggregates during broth mating.

Base Sequence↗
PubMedDate not supplied

In vitro susceptibilities of enterococcal blood culture isolates from the Hamburg area to ten antibiotics.

Treatment of enterococcal infections is often difficult because of intrinsic and acquired resistance to a variety of antimicrobial agents. Between January 1993 and May 1997, enterococci were isolated from blood cultures of 117 patients at the Institute of Medical Microbiology and Immunology, University Hospital Eppendorf, Hamburg, Germany. Eightynine (76%) isolates were phenotypically identified as Enterococcus faecalis, and 24 (21%) as Enterococcus faecium. All E. faecalis isolates, but only 17% of the E. faecium isolates were susceptible to ampicillin. Two E. faecium isolates (8%) but no E. faecalis were vancomycin resistant (vanA genotype). Quinupristin/dalfopristin shows a high degree of susceptiblity of E. faecium (79%) and may be suitable for the therapy of infections caused by glycopeptide-resistant E. faecium strains.

Aged↗
PubMed2003

In vitro activity of daptomycin against vancomycin-resistant enterococci of various Van types and comparison of susceptibility testing methods.

The increasing prevalence of vancomycin-resistant enterococcal (VRE) infections and the limited number of antimicrobial agents for their treatment emphasize a need for new, more effective agents. In this study, the in vitro activity of daptomycin was determined against a collection of 156 VRE from seven different institutions. Van types were characterized by PCR, and pulsed-field gel electrophoresis was performed to exclude isolates with >85% relatedness by dendrogram. Included were 126 Enterococcus faecium (109 vanA, 17 vanB) isolates, 5 Enterococcus faecalis (3 vanA, 2 vanB) isolates, 2 Enterococcus avium (vanA) isolates, 1 Enterococcus durans (vanA) isolate, 10 Enterococcus gallinarum (vanC1) isolates, and 12 Enterococcus casseliflavus (vanC2) isolates. MICs of daptomycin and five additional agents were determined by the NCCLS broth microdilution method with Mueller-Hinton (MH) broth containing supplemental calcium. MICs were also determined using two investigational E-test strip formulations, and disk diffusion testing was performed by the standard NCCLS method. The MIC of daptomycin at which 50% of the isolates tested were inhibited for this isolate collection was 4 microg/ml, and the MIC at which 90% of the isolates tested were inhibited was 8 microg/ml. Two isolates of vanA E. faecium were resistant to linezolid, and one isolate was resistant to quinupristin-dalfopristin. MICs of daptomycin determined by the E test with and without added calcium varied by 8- to 16-fold, and disk diffusion zones varied by 3 to 6 mm according to the calcium content of the commercial MH agar lots used in the study. This study has shown daptomycin to have good activity against a diverse collection of contemporary VRE isolates. However, improved standardization of the calcium content of MH agar will be important for reliable testing of daptomycin by clinical laboratories using either the E test or disk diffusion methods.

Anti-Bacterial Agents↗
PubMed2005

Antimicrobial agents for treatment of serious infections caused by resistant Staphylococcus aureus and enterococci.

As clinicians increasingly contend with infections due to staphylococci or enterococci resistant to, or failing treatment with, traditional antimicrobial agents, understanding the potential roles of older as well as more recently introduced antimicrobial agents becomes important. Older agents, such as clindamycin and trimethoprim-sulfamethoxazole, have been used to treat infections due to community-acquired methicillin-resistant Staphylococcus aureus. Among the licensed agents, quinupristin-dalfopristin, linezolid, daptomycin, and tigecycline are active in vitro against most strains of methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium, but these agents differ in their approved clinical indications. New agents currently under investigation may further expand treatment options.

Anti-Bacterial Agents↗
PubMed1997

Active efflux of antimicrobial agents in wild-type strains of enterococci.

Enterococci are intrinsically resistant to numerous antimicrobial agents. We examined the energy-dependent efflux of radiolabeled drugs from four reference strains of Enterococcus faecalis and a strain of Enterococcus faecium and found that most strains pumped out norfloxacin and chloramphenicol. Efflux of tetracycline was detected only in certain strains.

Anti-Bacterial Agents↗
PubMed2006

[Genotypes of aminoglycoside-modifying enzyme and clinical study of high-level gentamycin resistant enterococcus].

OBJECTIVE: To determine the antibiotics resistance, aminoglycoside-modifying enzymes and homology of high-level gentamycin resistant enterococcus in clinical specimens. METHODS: The high-level gentamicin resistant (HLGR) isolates were screened by the agar method and the resistance of 14 antimicrobial agents was determined by K-B method. The aminoglycoside-modifying enzyme genes were detected by polymerase chain reaction (PCR). Pulsed-field gel electrophoresis (PFGE) was used to analyze the homology of HLGR isolates. RESULTS: The ratio of HLGR was 64.2% (68/106). Among the HLGR,there were no isolates resistant to linezolid, vancomycin and tecoplanin, and Enterococcus faecium was more resistant to beta-lactam antibiotics and quinolone than Enterococcus faecalis. The positive rate of aac(6')-Ie-aph(2')-Ia was 92.6% and 3 isolates had the resistance gene mostly similar to aph(2')-Id. And among 51 HLGR isolates from the hospitalized patients, PFGE grouped 17 E. faecalis isolates into 4 clusters (A-D), and 33 E. faecium isolates into 8 clusters (A-H) with A cluster as predominant. CONCLUSION: HLGR has become the important antibiotic resistance bacteria which results in nosocomial infection; and aac(6')-Ie-aph(2')-Ia is the main aminoglycoside-modifying enzyme gene which causes HLGR.

Drug Resistance, Bacterial↗