Biomedical subjects
Publications and source records attributed to G M Eliopoulos.
The in vitro activities of GAR-936, the 9-t-butylglycylamido derivative of minocycline, were compared with those of doxycycline, minocycline, and tetracycline against 527 gram-positive clinical isolates. GAR-936 inhibited all strains, including those resistant to other tetracyclines, at concentrations of </=2 microg/ml, except two strains of JK diphtheroids for which the MIC was 4 microg/ml.
The highly conserved central loop of domain V of 23S RNA (nucleotides 2042 to 2628; Escherichia coli numbering) is implicated in peptidyltransferase activity and represents one of the target sites for macrolide, lincosamide, and streptogramin B antibiotics. DNA encoding domain V (590 bp) of several species of Enterococcus was amplified by PCR. Twenty enterococcal isolates were tested, including Enterococcus faecium (six isolates), Enterococcus faecalis, Enterococcus avium, Enterococcus durans, Enterococcus gallinarum, Enterococcus casseliflavus (two isolates of each), and Enterococcus raffinosus, Enterococcus mundtii, Enterococcus malodoratus, and Enterococcus hirae (one isolate of each). For all isolates, species identification by biochemical testing was corroborated by 16S rRNA gene sequencing. The sequence of domain V of the 23S rRNA gene from E. faecium and E. faecalis differed from those of all other enterococci. The domain V sequences of E. durans and E. hirae were identical. This was also true for E. gallinarum and E. casseliflavus. E. avium differed from E. casseliflavus by 23 bases, from E. durans by 16 bases, and from E. malodoratus by 2 bases. E. avium differed from E. raffinosus by one base. Despite the fact that domain V is considered to be highly conserved, substantial differences were identified between several enterococcal species.
VanD-mediated glycopeptide resistance has been reported for an isolate of Enterococcus faecium, BM4339. Three clinical isolates of vancomycin-resistant E. faecium collected from 3 patients during a 6-week period in 1993 had agar dilution MICs of vancomycin and teicoplanin of 128 and 4 microg/mL, respectively. Polymerase chain reaction (PCR) using degenerate primers complementary to genes encoding d-Ala-d-X ligases yielded a 630-bp product that was similar to the published partial sequence of vanD. By use of inverse PCR, vanD, vanHD, and two partial flanking open-reading frames were sequenced. The deduced amino acid sequence of VanD showed 67% identity with VanA and VanB. vanD appeared to be located on the chromosome and was not transferable to other enterococci. The 3 isolates were indistinguishable by pulsed-field gel electrophoresis and differed from BM4339. No other isolates carrying vanD were found in a subset of 875 recent US isolates of vancomycin-resistant enterococci.
OBJECTIVE: To define the epidemiology of broad-spectrum cephalosporin-resistant gram-negative bacilli in intensive care units (ICUs) during a nonoutbreak period, including the prevalence, the risk factors for colonization, the frequency of acquisition, and the rate of infection. DESIGN: Prospective cohort study. SETTING: Tertiary care hospital. PATIENTS: Consecutive patients admitted to two surgical ICUs. MAIN OUTCOME MEASUREMENTS: Serial patient surveillance cultures screened for ceftazidime (CAZ) resistance, antibiotic and hospital exposure, and infections. RESULTS: Of the 333 patients enrolled, 60 (18%) were colonized with CAZ-resistant gram-negative bacilli (CAZ-RGN) at admission. Clinical cultures detected CAZ-RGN in only 5% (3/60) of these patients. By using logistic regression, CAZ-RGN colonization was associated with duration of exposure to cefazolin (odds ratio, 10.3; p < or = .006) and to broad-spectrum cephalosporins/penicillins (odds ratio, 2; p < or = .03), Acute Physiology and Chronic Health Evaluation III score (odds ratio, 1.2; p < or = .008), and previous hospitalization (odds ratio, 3.1; p < or = .006). Of the 100 patients who remained in the surgical ICU for > or = 3 days, 26% acquired a CAZ-RGN. Of the 14 infections caused by CAZ-RGN, 11 (79%) were attributable to the same species present in surveillance cultures at admission to the surgical ICU. CONCLUSIONS: Colonization with CAZ-RGN was common and was usually not recognized by clinical cultures. Most patients colonized or infected with CAZ-RGN had positive surveillance cultures at the time of admission to the surgical ICU, suggesting that acquisition frequently occurred in other wards and institutions. Patients exposed to first-generation cephalosporins, as well as broad-spectrum cephalosporins/penicillins, were at high risk of colonization with CAZ-RGN. Empirical treatment of nosocomial gram-negative infections with broad-spectrum cephalosporins, especially in the critically ill patient, should be reconsidered.
The in vivo effectiveness of oxazolidinones eperezolid (U-100592) and linezolid (U-100766) against one strain each of Enterococcus faecalis and vancomycin-resistant Enterococcus faecium was examined in a rat model of intra-abdominal abscess. MICs of both drugs were 2 microg/ml for each strain. At doses of 25 mg/kg of body weight twice daily intravenously or orally, linezolid produced small but statistically significant reductions in abscess bacterial density for E. faecalis. The reduction in viable cells observed would not likely be clinically relevant. Eperezolid was ineffective at this dose. At a dosage of 100 mg/kg/day, linezolid treatment led to an approximately 100-fold reduction in viable cells per gram of abscess. Against E. faecium infections, intravenous eperezolid and oral linezolid were effective, reducing densities approximately 2 log(10) CFU/g. Both oxazolidinones demonstrated activity against enterococci in this model. However, results were modest with the dosing regimens employed.
Pseudomonas aeruginosa is a leading cause of nosocomial infections. The risk of emergence of antibiotic resistance may vary with different antibiotic treatments. To compare the risks of emergence of resistance associated with four antipseudomonal agents, ciprofloxacin, ceftazidime, imipenem, and piperacillin, we conducted a cohort study, assessing relative risks for emergence of resistant P. aeruginosa in patients treated with any of these drugs. A total of 271 patients (followed for 3,810 days) with infections due to P. aeruginosa were treated with the study agents. Resistance emerged in 28 patients (10.2%). Adjusted hazard ratios for the emergence of resistance were as follows: ceftazidime, 0.7 (P = 0.4); ciprofloxacin, 0.8 (P = 0.6); imipenem, 2.8 (P = 0.02); and piperacillin, 1.7 (P = 0.3). Hazard ratios for emergence of resistance to each individual agent associated with treatment with the same agent were as follows: ceftazidime, 0.8 (P = 0.7); ciprofloxacin, 9.2 (P = 0.04); imipenem, 44 (P = 0.001); and piperacillin, 5.2 (P = 0.01). We concluded that there were evident differences among antibiotics in the likelihood that their use would allow emergence of resistance in P. aeruginosa. Ceftazidime was associated with the lowest risk, and imipenem had the highest risk.
Several newer fluoroquinolones, which have been recently introduced or are under investigation, display substantially greater potency against gram-positive organisms than the older generation agents of this class. Nevertheless, for problem organisms including methicillin-resistant strains of Staphylococcus aureus and many Enterococcus faecium, concentrations of newer antimicrobials required to inhibit 90% of organisms in the collections studied remain above those that are projected to be achievable with clinical use. Nevertheless, enhanced potency of several newer quinolones may result in a favourable pharmacodynamic profile leading to improved outcomes against gram-positive infections and possibly to the delayed or diminished emergence of resistance to these agents.
The in vitro antibacterial activity of BAY 12-8039, a novel 8-methoxy-quinolone, was compared with those of other quinolones, amoxicillin/clavulanate, cefuroxime and erythromycin against species commonly implicated in respiratory tract infections as well as viridans group streptococci. The new compound was highly active against methicillin-susceptible staphylococci (MIC90 0.125 microgram/ml), penicillin-susceptible and penicillin-resistant pneumococci (MIC90 0.5 and MIC50 0.25 microgram/ml, respectively), penicillin-susceptible and penicillin-resistant viridans group streptococci (MIC90 0.5 and 0.25 microgram/ml, respectively), group A streptococci (MIC90 0.25 microgram/ml), M. catarrhalis (MIC90 0.125 microgram/ml) and H. influenzae (MIC90 0.063 microgram/ml), irrespective of beta-lactamase production. It was, however, less active against methicillin-resistant staphylococci (MIC50 and MIC90, 2 and 4 micrograms/ml, respectively). The new compound demonstrated bactericidal activity at concentrations 2, 4, 8 times the MIC against representative isolates of the above collection. At a concentration of eight times the MIC, the frequency of spontaneous resistance ranged from 2.5 x 10(-7) to < 4 x 10(-8). These results suggested that BAY 12-8039 would be a promising agent for the eradication of respiratory tract pathogens and that clinical trials assessing its efficacy for the management of infections caused by these organisms are warranted.
The comparative in-vitro activity of HMR 3647, a new ketolide antibiotic, was investigated against 492 clinical isolates of gram-positive bacteria, including multiply resistant strains, by an agar-dilution technique. All streptococci tested were inhibited by the new ketolide at concentrations < or = 0.5 mg/L. HMR 3647 was more potent than erythromycin against staphylococci. For enterococci the new compound yielded an MIC90 of 8 mg/L. Erysipelothrix spp., Pediococcus spp., Leuconostoc spp., Lactobacillus spp., JK diphtheroids and Listeria monocytogenes were also susceptible to the new ketolide.
In the course of clinical studies with the investigational streptogramin antimicrobial dalfopristin-quinupristin, isolates of vancomycin-resistant Enterococcus faecium were referred to our laboratory from across the United States. Seventy-two percent of the strains were of the VanA type, phenotypically and genotypically, while 28% were of the VanB type. High-level resistance to streptomycin or gentamicin was observed in 86 and 81%, respectively, of the VanA strains but in only 69 and 66%, respectively, of the VanB strains. These enterococci were resistant to ampicillin (MIC for 50% of the isolates tested [MIC50] and MIC90, 128 and 256 microg/ml, respectively) and to the other approved agents tested, with the exception of chloramphenicol (MIC90, 8 microg/ml) and novobiocin (MIC90, 1 microg/ml). Considering all of the isolates submitted, dalfopristin-quinupristin inhibited 86.4% of them at concentrations of < or = 1 microg/ml and 95.1% of them at < or = 2 microg/ml. However, for the data set comprised of only the first isolate submitted for each patient, 94.3% of the strains were inhibited at concentrations of < or = 1 microg/ml and 98.9% were inhibited at concentrations of < or = 2 microg/ml. Multiple drug resistance was very common among these isolates of vancomycin-resistant E. faecium, while dalfopristin-quinupristin inhibited the majority at concentrations that are likely to be clinically relevant.
The in vitro activities of 13 antimicrobial agents against 30 strains of Legionella spp. were determined. Rifapentine, rifampin, and clarithromycin were the most potent agents (MICs at which 90% of isolates are inhibited [MIC90s], < or = 0.008 microgram/ml). The ketolide HMR 3647 and the fluoroquinolones levofloxacin and BAY 12-8039 (MIC90s, 0.03 to 0.06 microgram/ml) were more active than erythromycin A or roxithromycin. The MIC90s of dalfopristin-quinupristin and linezolid were 0.5 and 8 micrograms/ml, respectively. Based on class characteristics and in vitro activities, several of these agents may have potential roles in the treatment of Legionella infections.
Trimethoprim-sulfamethoxazole has been used to treat various respiratory tract infections. Nevertheless, for many patients, intolerance of the sulfonamide component precludes use of this combination. This study examined the activity of trimethoprim alone in comparison to that of trimethoprim-sulfamethoxazole and other antimicrobials against bacterial species implicated in respiratory tract infections. For Haemophilus influenzae, minimal inhibitory concentrations of trimethoprim were equal to or one dilution greater than those of trimethoprim-sulfamethoxazole, with 56 of 58 strains inhibited by the former at < or = 0.25 microgram/ml. All oxacillin-susceptible Staphylococcus aureus and 96.7% of Streptococcus pyogenes were inhibited by trimethoprim < or = 2 micrograms/ml. In contrast, only 50% of Streptococcus pneumoniae were inhibited by this concentration of trimethoprim, whereas 93.3% were susceptible to the combination at < or = 2/38 micrograms/ml. All oxacillin-resistant S. aureus and all Moraxella catarrhalis were resistant to trimethoprim, although many of the former and all of the latter were susceptible to trimethoprim-sulfamethoxazole.
Vancomycin-resistant enterococci have spread widely throughout the United States. Mechanisms of glycopeptide resistance are understood to a significant extent. These organisms are associated with considerable morbidity. Treatment options are limited, and control of their spread requires considerable effort and results in increased costs.
RP 59500, a mixture of two semisynthetic streptogramin antibiotics (quinupristin and dalfopristin), is one of a few investigational agents currently in clinical trials with inhibitory activity against multiple-drug-resistant strains of Enterococcus faecium. We evaluated the bactericidal activity of this antimicrobial against 30 recent clinical isolates of vancomycin-resistant E. faecium, including 23 erythromycin-resistant (MIC, >256 microg/ml) and 7 erythromycin-intermediate (MIC, 2 to 4 microg/ml) strains. All isolates were inhibited by RP 59500 at 0.25 to 1.0 microg/ml. The bactericidal activity of RP 59500 was markedly influenced by the erythromycin susceptibility of the strains and by several technical factors, such as inoculum growth phase and time of incubation of counting plates. As determined by time-kill methods, RP 59500 at a concentration of 2 or 8 microg/ml failed to kill erythromycin-resistant organisms under any conditions. Bactericidal activity was observed against all seven erythromycin-intermediate isolates when log-phase inocula were used and the cells were counted after 48 h of incubation (mean reductions in viable bacteria for RP 59500 at concentrations of 2 and 8 microg/ml, 3.45 and 3.50 log10 CFU/ml, respectively), but killing was diminished when the plates were examined at 72 h (mean killing, 3.06 and 2.95 log10, CFU/ml, respectively). No bactericidal activity was observed when stationary-phase cultures were used. On the basis of these data, we expect that bactericidal activity of RP 59500 against the multiple-drug-resistant E. faecium strains currently encountered would be distinctly uncommon.
The in vivo activities of piperacillin-tazobactam and cefepime were compared with those of ticarcillin-clavulanate, ceftazidime, cefotaxime, and imipenem in a rat model of intra-abdominal abscess with a strain of Klebsiella pneumoniae elaborating an extended-spectrum beta-lactamase (TEM-26). With the exception of ceftazidime, all of the antimicrobial agents significantly reduced bacterial counts within abscesses at the end of therapy compared with those in untreated controls. Residual viable cell counts (mean +/- standard deviation in log10 CFU/gram) were as follows: control, 8.76 +/- 0.97; ceftazidime, 8.00 +/- 0.76; piperacillin-tazobactam, 3.87 +/- 1.72; ticarcillin-clavulanate, 3.74 +/- 1.34; cefepime, 3.15 +/- 1.19; cefotaxime, 2.61 +/- 0.77; imipenem, 2.41 +/- 0.93. Imipenem was more effective than either of the inhibitor combinations (P < 0.05). Cefotaxime was unexpectedly effective given its poor in vivo activity against this organism in our earlier studies, which used a different dose and total duration of therapy (L. B. Rice, J. D. C. Yao, K. Klimm, G. M. Eliopoulos, and R. C. Moellering, Jr., Antimicrob. Agents Chemother. 35:1243-1244, 1991). These observations suggest that the effectiveness of cephalosporins in the treatment of experimental infections caused by extended-spectrum beta-lactamase-producing K. pneumoniae may be highly dependent on dosing regimens, even for a specific organism and site of infection.
The comparative in vitro activity of RU 64004 (also known as HMR 3004), a new ketolide antibiotic, was tested by agar dilution against approximately 500 gram-positive organisms, including multiply resistant enterococci, streptococci, and staphylococci. All streptococci were inhibited by < or = 1 microg of RU 64004 per ml. The ketolide was more potent than other macrolides against erythromycin A-susceptible staphylococci and was generally more potent than clindamycin against erythromycin A-resistant strains susceptible to this agent. Clindamycin-resistant staphylococci (MIC, > 128 microg/ml) proved resistant to the ketolide, but some erythromycin A- and clindamycin-resistant enterococci remained susceptible to RU 64004.
The in vitro activity of levofloxacin against 506 Gram-positive bacteria was compared with those of D(-)-ofloxacin, ofloxacin, ciprofloxacin, and sparfloxacin. Levofloxacin was generally twice as active as ofloxacin against these organisms (range, 0-3 twofold dilutions). Sparfloxacin appeared to have the greatest activity overall, but for several groups of organisms minimum inhibitory concentrations (MIC90s) of this compound were within one twofold dilution of those of levofloxacin. Resistance to levofloxacin (MIC > or = 8 micrograms/ml) was not encountered among streptococcal species, was rare in methicillin-susceptible staphylococci (1.7%), and was infrequent in vancomycin-susceptible Enterococcus faecalis and Enterococcus faecium (8.7%). Resistance was more common among vancomycin-resistant enterococci and methicillin-resistant staphylococci.
The comparative in vitro activities of two new oxazolidinone antimicrobial agents, U-100592 and U-100766, against 180 isolates of enterococci representing several resistance profiles were examined by using an agar dilution technique. The two oxazolidinones inhibited all isolates, including strains resistant to vancomycin, ampicillin, and minocycline, at concentrations between 1 and 4 micrograms/ml.