Increasing problems in the therapy of enterococcal infections

Early alert from the microbiology laboratory improves the outcome of elderly patients with Enterococcus spp. bloodstream infection: Results from a multicentre prospective study

OBJECTIVES

This study describes the clinical features and outcomes of patients with bloodstream infection (BSI) due to Enterococcus spp. and identified factors predictive of mortality.

METHODS

This analysis is part of a prospective multicentre observational study of consecutive hospitalised patients with BSI conducted from March 2012 to December 2012 in 31 internal medicine wards in Italy. Patients with enterococcal BSI were selected from the entire cohort. Patient characteristics, therapeutic interventions and outcome were reviewed. Cox regression analysis was performed to identify factors associated with in-hospital mortality. Hazard ratios (HRs) and 95% interval confidences (CIs) were calculated.

RESULTS

Among 533 patients with BSI, 41 (7.7%) had BSI by Enterococcus spp. (28 Enterococcus faecalis, 4 Enterococcus faecium and 3 each of Enterococcus avium, Enterococcus casseliflavus and Enterococcus gallinarum). Six BSIs (14.6%) were polymicrobial. Median (IQR) patient age was 73 (66-85.5) years. In-hospital mortality was 24.4%. Polymicrobial infection (HR = 9.100, 95% CI 1.295-63.949; P = 0.026), age (HR = 1.261, 95% CI 1.029-1.546; P = 0.025) and SOFA score (HR = 1.244, 95% CI 1.051-1.474; P = 0.011) were risk factors for in-hospital mortality. Conversely, receiving an alert from the microbiology laboratory before obtaining final antimicrobial susceptibility results was associated with survival (HR = 0.073, 95% CI 0.007-0.805; P = 0.033).

CONCLUSION

BSI due to Enterococcus spp. in elderly patients is associated with high mortality. Polymicrobial infection, age and SOFA score are factors associated with poor outcome. Conversely, early alert from the microbiology laboratory improves patient survival.

Antimicrobial resistance of enterococci in Turkey

Susceptibility to ampicillin, penicillin, vancomycin and teicoplanin, high-level resistance to aminoglycosides (gentamicin and streptomycin) and beta-lactamase production were investigated among 264 consecutive clinical enterococcal isolates in Turkey. Disc diffusion test was used to detect resistance to ampicillin, penicillin, vancomycin and teicoplanin. High-level resistance to aminoglycosides was determined both by standard agar screening and by disc diffusion methods. The values of minimum inhibitory concentration (MIC) of each isolate for ampicillin, vancomycin and teicoplanin were determined by the microbroth dilution technique. The isolates were found to consist of Enterococcus faecalis (78%), Enterococcus faecium (9%) and Enterococcus spp. (12%). In all strains, the penicillin and ampicillin resistance ratios were 27% and 26%, respectively. Enterococcus faecalis was more susceptible to penicillin and ampicillin than the other strains. None of the strains were resistant to glycopeptides. High-level aminoglycoside resistance was found in 16% E. faecalis and 88% E. faecium for gentamicin, and 35% and 44%, respectively, for streptomycin. There were no differences between the two methods used to determine the aminoglycoside resistance rates in the enterococcal isolates. No beta-lactamase-producing isolates were detected in either species. In conclusion, to determine the resistance of enterococci to the penicillin group of drugs by the disc diffusion method, both penicillin and ampicillin discs should be evaluated. In serious enterococcal infections, before starting combined therapy, high-level aminoglycoside resistance should be investigated.

Characterization of high-level aminoglycoside-resistant enterococci in Kuwait hospitals

This study investigated the distribution of genes for aminoglycoside-modifying enzymes (AME) and the genetic relatedness of high-level aminoglycoside-resistant enterococci isolated in Kuwait hospitals. A total of 117 enterococci, consisting of 109 Enterococcus faecalis, seven Enterococcus faecium, and one Enterococcus casseliflavus were studied. The MICs of gentamicin, kanamycin, amikacin, tobramycin, and streptomycin were determined by agar dilution and the genes encoding the AAC(6')- APH(2"), ANT(4'), APH(3'), APH (2")-Ib, APH (2")-Ic, APH (2")-Id, and ANT(6) enzymes were amplified by PCR. They were typed by pulsed-field gel electrophoresis (PFGE). Filter mating was used to transfer gentamicin resistance determinants. They were all resistant to kanamycin (MIC 2000 mg/L). Fifty-five isolates were resistant to gentamicin (MIC 500 mg/L), 72 were resistant to tobramycin (MIC 64 mg/L), 115 were resistant to amikacin (MIC 64 mg/L), and 97 were resistant to streptomycin (MIC 1000 mg/L). The aac(6')-Ie-aph(2")-Ia was detected in all isolates with gentamicin MIC 500 mg/L and in 15 isolates with gentamicin MIC 256 mg/L. The aph(3')-IIIa gene was detected in 101 isolates, whereas the ant(6')-Ia gene was detected in 85 of the 97 streptomycin-resistant isolates with MIC 1000 mg/L. The aac(6')-Ii gene was detected only in the seven E. faecium isolates. None of them contained ant(4')-Ia, aph(2")-Ib, aph(2")-Ic and aph(2")-Id. PFGE revealed heterogeneous patterns with no dominant clone. The results demonstrated that AME are common in aminoglycoside-resistant enterococci isolated in Kuwait. However, the absence of a dominant clone suggests that they acquired high-level aminoglycoside independently.

Antibiotic resistance of enterococci isolated at a teaching hospital in Kuwait

Enterococci isolated in a teaching hospital were studied for their resistance to different antibiotics. Minimum inhibitory concentrations to high-level aminoglycosides and glycopeptide antibiotics were determined by agar dilution and E-test methods respectively. Genes encoding aminoglycoside-modifying enzymes were detected by the polymerase chain reaction (PCR). 195 enterococci were isolated from urines (54.3%), wounds (16.4%), blood (10.2%), and miscellaneous sources (18.9%). They consisted of E. faecalis (88.7%), E. faecium (9.2%), E. casseliflavus (1.5%) and E. bovis (0.5%). None of the enterococci produced penicillinase but 3.5% of them were resistant to ampicillin. They were also resistant to high-level gentamicin (15.9%), kanamycin (22.0%), streptomycin (21.0%), tetracycline (65.1%), erythromycin (62.6%), ciprofloxacin (36.1%), chloramphenicol (26.1%), vancomycin (3.0%) and teicoplanin (2.0%). Most of the high-level aminoglycoside-resistant isolates contained genes coding the bifunctional aminoglycoside modifying enzymes AAC(6')-APH(2"), APH(3') and ANT(6') but not the ANT(4') enzyme. The results demonstrated a low prevalence of vancomycin resistance among Enterococci in this hospital.

Effects of adjunctive treatment with combined cytokines in a neutropenic mouse model of multidrug-resistant Enterococcus faecalis septicemia

STUDY OBJECTIVE

To examine whether the antienterococcal efficacy of a regimen of gentamicin plus vancomycin combined with granulocyte colony-stimulating factor (G-CSF) is enhanced by concurrent therapy with interferon-gamma (IFN-gamma).

SETTING

Hospital laboratory.

INTERVENTION

Mice rendered neutropenic by cyclophosphamide were intraperitoneally inoculated with a gentamicin- and vancomycin-resistant Enterococcus faecalis isolate.

MEASUREMENTS AND MAIN RESULTS

Infected animals were randomized into treatment groups that received G-CSF alone or in combination with various dosages of IFN-gamma. Additional groups of animals received vancomycin; G-CSF, G-CSF plus vancomycin, IFN-gamma, and G-CSF; or vancomycin with both cytokines. Addition of IFN-gamma to G-CSF regimen resulted in no significant change (p>0.05) in survival, compared with treatment with G-CSF alone. Also, the antienterococcal efficacy of antibiotic plus G-CSF was not modified by coadministration of IFN-gamma.

CONCLUSION

This study suggests that adjunctive application of combined cytokines may not be more beneficial than only G-CSF in combination with an antibiotic to treat multidrug-resistant enterococcal infection.

Attributable mortality rate and duration of hospital stay associated with enterococcal bacteremia

The mortality rate of patients with cases of enterococcal bacteremia is high, although it has often been related to the patients' underlying conditions rather than to the infection itself. To analyze the attributable prognosis of enterococcal bacteremia (assessed by its attributable mortality rate and duration of hospital stay), a prospective, matched case-control study was done. All adults with an episode of enterococcal bacteremia without endocarditis were included. A control patient was randomly selected for every case patient and matched by sex, age and hospital ward. Univariate and multivariate analyses were performed. A total of 122 pairs were included, and incidence of enterococcal bacteremia was 2.3 episodes/1000 discharges. Crude 30-day mortality rates for case patients and control patients were 23% and 17%, respectively (P=.29); thus, the estimated attributable mortality rate was 6% (95% confidence interval, -4% to 16%). The mean duration of hospital stay of case patients and control patients were 38 and 17 days, respectively (P<.001); thus, the estimated attributable duration of hospital stay was 21 days (95% CI, 7-32 days). Enterococcal bacteremia without endocarditis does not increase risk of death by itself but extends the duration of hospital stay of patients who develop it.

Outbreak of infections in a Greek university hospital involving a single clone of high-level aminoglycoside-resistant Enterococcus faecalis

Among 145 Enterococcus faecalis isolates recovered during a 15-month period (April 1997-June 1998) in AHEPA University Hospital, Thessaloniki, Greece, 94 (65%) exhibited high-level resistance to gentamicin or streptomycin and 61 (42%) to both aminoglycosides; 73% of the high-level aminoglycoside-resistant E. faecalis isolates belonged to a single clone carrying the gene aac(6')-Ie-aph(2")-Ia. These findings differ from those of other regions, where high-level aminoglycoside-resistance genes are dispersed into genetically unrelated strains.

Vancomycin-resistant enterococci

After they were first identified in the mid-1980s, vancomycin-resistant enterococci (VRE) spread rapidly and became a major problem in many institutions both in Europe and the United States. Since VRE have intrinsic resistance to most of the commonly used antibiotics and the ability to acquire resistance to most of the current available antibiotics, either by mutation or by receipt of foreign genetic material, they have a selective advantage over other microorganisms in the intestinal flora and pose a major therapeutic challenge. The possibility of transfer of vancomycin resistance genes to other gram-positive organisms raises significant concerns about the emergence of vancomycin-resistant Staphylococcus aureus. We review VRE, including their history, mechanisms of resistance, epidemiology, control measures, and treatment.

Antienterococcal antibiotics

The treatment of severe enterococcal infections based on the currently available antibacterial agents is difficult. The help of the microbiology laboratory for determining MICs, MBCs, and most effective synergistic combinations is crucial. There is a need for good prospective multicenter clinical trials to improve the prognosis of such infections by defining therapeutic strategies better. Such a requirement is highly suitable for the treatment of infections caused by enterococci exhibiting acquired resistance mechanisms to the available agents. The current clinical development of new compounds looks promising in these persistently life-threatening infections mostly occurring in deficient hosts.

Vancomycin-resistant enterococci

After they were first identified in the mid-1980s, vancomycin-resistant enterococci (VRE) spread rapidly and became a major problem in many institutions both in Europe and the United States. Since VRE have intrinsic resistance to most of the commonly used antibiotics and the ability to acquire resistance to most of the current available antibiotics, either by mutation or by receipt of foreign genetic material, they have a selective advantage over other microorganisms in the intestinal flora and pose a major therapeutic challenge. The possibility of transfer of vancomycin resistance genes to other gram-positive organisms raises significant concerns about the emergence of vancomycin-resistant Staphylococcus aureus. We review VRE, including their history, mechanisms of resistance, epidemiology, control measures, and treatment.

Pharmacokinetics of an everninomicin (SCH 27899) in mice, rats, rabbits, and cynomolgus monkeys following intravenous administration

The pharmacokinetics of SCH 27899, a novel oligosaccharide compound of the everninomicin class with excellent activity against gram-positive strains, was studied with mice, rats, rabbits, and cynomolgus monkeys following intravenous administration as SCH 27899-N-methylglucamine-hydroxypropyl beta-cyclodextrin. Concentrations of SCH 27899 in mouse serum, rat plasma, and rabbit serum were determined by a high-pressure liquid chromatography method on a poly(styrene-divinyl benzene) column, and those in monkey plasma were determined by a paired-ion chromatographic method. Plasma and serum concentrations of SCH 27899 exhibited a biexponential decline in all species following intravenous administration. The half-lives at beta phase were 3.0 to 7.9 h in mice, rats, and rabbits and 24 h in cynomolgus monkeys. There was a linear relationship between the area under the curve extrapolated to infinity [AUC(I)] in mice and dose. Rabbits also exhibited dose proportionality in AUC(I). However, in rats, increasing the dose from 3 to 60 mg/kg of body weight resulted in a 49-fold increase in AUC(I). When the species was changed from mouse to rat, rabbit, or cynomolgus monkey, AUC(I) increased, whereas clearance (CL) decreased. It was concluded that the pharmacokinetics of SCH 27899 in animals varied with species; CL was the highest in mice and rats, followed by rabbits and cynomolgus monkeys.

In vitro activity of RP 59500 (quinupristin/dalfopristin) and ramoplanin against vancomycin-resistant Enterococcus faecium

Vancomycin-resistant Enterococcus faecium (VREF) collected between July 1991 and February 1994 were tested in vitro against RP 59500 and ramoplanin using agar dilution and standard macro broth dilution procedures. Colony counts were determined at 0, 4, and 24 h. RP 59500 had an MIC range of < or = 0.5-8 micrograms/ml with an MIC90 of 2 micrograms/ml and a MBC range of < or = 0.5-16 micrograms/ml with an MBC90 of 16 micrograms/ml. Ramoplanin had an MIC range of < or = 0.125-1 microgram/ml with an MBC range of < or = 0.125-4 micrograms/ml. The MIC90 for ramoplanin was 1 microgram/ml and the MBC90 was 4 micrograms/ml for the tested isolates. Against these isolates of E. faecium, RP 59500 was bactericidal at 8x MIC, a potentially achievable level using a high drug dosage. Ramoplanin was bactericidal at 2x MIC.

Association of alterations in ParC and GyrA proteins with resistance of clinical isolates of Enterococcus faecium to nine different fluoroquinolones

The parC and gyrA genes of 73 ciprofloxacin-resistant and 6 ciprofloxacin-susceptible Enterococcus faecium clinical isolates were partly sequenced. Alterations in ParC and GyrA, possibly in combination with other resistance mechanisms, severely restricted the in vitro activities of the nine quinolones tested. For all isolates, clinafloxacin and sitafloxacin showed the best activities.

Influence of adjunctive interferon-gamma on treatment of gentamicin- and vancomycin-resistant Enterococcus faecalis infection in mice

Increasing antibiotic resistance and the development of multidrug-resistance in the enterococci has complicated the treatment of serious enterococcal infections. It has been demonstrated in vitro that interferon-gamma (IFN-gamma) significantly augments the activities of gentamicin and vancomycin against Enterococcus faecalis resistant to these antibiotics. The present study was aimed at determining whether this beneficial effect of IFN-gamma on antienterococcal antibiotic activity can be validated in vivo. Following intraperitoneal inoculation in mice with a gentamicin- and vancomycin-resistant E. faecalis clinical isolate, the animals received IFN-gamma, antibiotic or a combination of both agents, subcutaneously, at determined dosing regimens. Treatment with IFN-gamma alone significantly improved survival of infected animals in a dose-dependent manner. High dose IFN-gamma was not beneficial and the level of enterococcal infectious burden influenced the effectiveness of the cytokine. The addition of IFN-gamma to therapy with gentamicin or vancomycin, or a combination of both antibiotics was associated with a marked increase in survival of infected non-neutropenic mice compared to treatments with the agents alone. However, the same treatments made in infected neutropenic mice did not show an enhancement effect by IFN-gamma after a combination therapy with antibiotics. In a study to examine pharmacokinetic interactions, concurrent administration with IFN-gamma significantly modified the disposition of gentamicin but not that of vancomycin. The results of this study suggest that the use of IFN-gamma in combination with vancomycin or gentamicin is a new treatment option that might improve the outcome of therapy of multidrug-resistant E. faecalis infections.

Simple and sensitive high-performance liquid chromatographic method for the determination of an everninomycin, SCH 27899, in rat plasma

A simple and sensitive high-performance liquid chromatographic (HPLC) method was developed for the determination of SCH 27899, an everninomycin antibiotic, in rat plasma. The method involved plasma protein precipitation with acetonitrile, followed by reversed-phase HPLC analysis using a polymeric column and a mobile phase containing acetonitrile and ammonium phosphate, pH 7.8. The linear relationship between detector response and concentration was demonstrated with a correlation coefficient of larger than 0.996 at concentrations ranging from 0.2 to 100 microg/ml. The results showed that the HPLC method was accurate (bias < or = 6%) and precise (coefficient of variation, C.V. < or = 6%). The limit of quantitation was 0.2 microg/ml with a C.V. of 2.6% and bias of 5%. SCH 27899 was stable in rat plasma at -20 degrees C for at least 40 days. The HPLC method has been utilized for the determination of SCH 27899 in plasma samples from rats following single intravenous administration (3 mg/kg).

Comparison of direct plating and broth enrichment culture for the detection of intestinal colonization by glycopeptide-resistant enterococci among hospitalized patients

The results of prevalence studies on glycopeptide-resistant enterococci (GRE) in the intestine may be influenced by the detection methods applied. In most studies different media, different concentrations of antibiotics, and different methods are used, and these differences result in differences in recovery rates. In this cross-sectional study on the carrier state of GRE among patients at the University Hospital Antwerp, Antwerp, Belgium, performed on 21 May 1996, direct plating and broth enrichment were compared by using the same media. Stool samples (n = 213) or rectal swabs (n = 122) were plated directly on Enterococcosel agar (bioMérieux) and after enrichment in Enterococcosel broth. The prevalence of GRE was 12.8%. Direct plating recovered 53.4% of the GRE isolates, and broth enrichment recovered an additional 46.5% of them; in the latter test the isolates were thus present at less than 10(3) CFU per g of feces. The prevalence of GRE among dialysis patients was higher than among the other patients, but the difference was not significant (P = 0.06), possibly as a result of the small numbers of dialysis patients examined. The GRE species isolated included 19 E. gallinarum (44.2%), 13 E. faecium (30.2%), 6 E. faecalis (13.9%), and 5 E. casseliflavus (11.6%) isolates. All E. faecalis and E. faecium strains isolated carried the vanA gene, and E. gallinarum and E. casseliflavus carried the vanC1 and vanC2 gene, respectively. The majority of isolates were polyclonal. Our data indicate that the rate of detection of GRE from both stool samples and rectal swabs is significantly increased with enrichment cultures.

Survey of antibiotic resistance among enterococci in North Rhine-Westphalia, Germany

A surveillance study on antibiotic resistance of enterococcal isolates (n = 730) was carried out in North Rhine-Westphalia, Germany, in 1997. Resistance rates to ampicillin (7.4%), high-level gentamicin (15.0%), high-level streptomycin (27.9%), ciprofloxacin (37.9%), vancomycin (1.5%), and teicoplanin (1.5%) were determined. All vancomycin-resistant enterococci (VRE) carried the vanA gene. SmaI and ApaI macrorestriction patterns indicated an intra- and interhospital spread of VRE.

Clinical and molecular epidemiology of hospital Enterococcus faecalis isolates in eastern France

OBJECTIVE: To report on the occurrence of Enterococcus faecalis hospital isolates obtained during 1 year in hospitals in the Franche-Comté region of France. METHODS: Clinical isolates of E. faecalis of different antibiotic susceptibility phenotypes from hospitalized patients were characterized by pulsed-field gel electrophoresis. Patients with positive cultures were investigated by three case-control studies to identify risk factors for colonization/infection. RESULTS: The crude incidence of colonization/infection was 2.37%, and 4-day and 7-day colonization rates after admission were 10.0% and 6.36%, respectively. The rates of high-level resistance to kanamycin (HLKR) and to gentamicin (HLGR) were 47.1% and 7.1%, respectively. No isolate was resistant to glycopeptides or produced beta-lactamase. The 209 hospital isolates obtained during the study yielded 98 major DNA patterns, of which two were major epidemic patterns including HLKR isolates. No single factor was significantly associated with colonization/infection by HLKR isolates. The length of hospitalization before isolation was associated with colonization by HLGR isolates. CONCLUSIONS: The isolation frequency of E. faecalis strains with acquired resistance to aminoglycoside antibiotics, and the wide dissemination of resistant strains with characteristics that allow them to persist and spread, argue for further large prospective surveys of clinical isolates of E. faecalis in hospitals.

Interferon-gamma effects on activities of gentamicin and vancomycin against Enterococcus faecalis resistant to the drugs: an in vitro study with human neutrophils

The emergence of multidrug-resistant enterococci presents a major therapeutic challenge since there is currently no clearly effective antimicrobial therapy for these infections. The combinatorial effects of interferon-gamma (IFN-gamma) with gentamicin and/or vancomycin against a clinical isolate of drug-resistant Enterococcus faecalis, were evaluated in an in vitro system with human neutrophils. Following inoculation of cultures of human neutrophils with the organism, treatments were initiated immediately after the infection and the number of viable bacteria was determined at 12, 18 and 24 h. Antibiotics were applied at concentrations close to their clinically achievable serum trough and peak levels. Treatment with IFN-gamma alone induced a maximal growth inhibition of up to 40% at a concentration of 100 U/ml. Addition of the cytokine to either therapeutic trough or peak concentrations of gentamicin and vancomycin, or a combination of both antimicrobials, was associated with a significant (P < 0.01) enhancement of anti-enterococcal activity compared with the effects of the agents alone. Investigation of a potential underlying mechanism of anti-enterococcal action of IFN-gamma reveals that it is, most probably, largely due to an activated secretion of the microbicidal reactive oxygen intermediates by neutrophils. The results of this study show that there is a possibility that IFN-gamma could be a useful adjunct in the treatment of multidrug-resistant E. faecalis.

Activity of HMR 3647 compared to those of six compounds against 235 strains of Enterococcus faecalis

Agar dilution was used to test the activities of HMR 3647, erythromycin A, azithromycin, clarithromycin, roxithromycin, clindamycin, and quinupristin-dalfopristin against 235 strains of Enterococcus faecalis. HMR 3647 was the most active compound (MICs at which 50 and 90% of the isolates are inhibited [MIC50 and MIC90, respectively] of 0.06 and 4.0 microg/ml, respectively). The MIC50 and MIC90 (with the MIC50 given first and the MIC90 given second; both in micrograms per milliliter) for other compounds were as follows: 4.0 and >32.0 for erythromycin A, 16.0 and >32.0 for azithromycin, 2.0 and >32 for clarithromycin, 32.0 and >32.0 for roxithromycin, 32.0 and >32.0 for clindamycin, and 8.0 and 16.0 for quinupristin-dalfopristin. All compounds were only bacteriostatic.

Susceptibility patterns of Enterococcus spp. isolated in Poland during 1996

Susceptibility of Enterococcus spp. isolated from various clinical specimens to different antimicrobial agents was evaluated. Of the 346 enterococcal isolates obtained from four regional Polish hospitals during 6 months of 1996, 261 (75.4%) were identified as Enterococcus faecalis, 75 (21.7%) as Enterococcus faecium and ten (2.9%) as other enterococcal species. High-level resistance to gentamicin was expressed by 33.4% of E. faecalis and 86.5% of E. faecium strains and corresponding streptomycin resistance by 43.9 and 82.4%, respectively. Over 80% of E. faecium isolates were resistant to ampicillin. None of the isolates was resistant to teicoplanin, however 7.9% of E. fecalis and 1.4% of E. faecium strains were moderately susceptible to vancomycin.

Antimicrobial mixtures used by tissue banks for harvested skin: comparative in vitro activity

The activities of antimicrobial combinations from three geographically diverse skin/tissue banks used in the processing of skin/ tissue were compared using bacteria and yeast isolated from burn patients. All formulations showed 90% or more effectiveness against bacteria generally susceptible to antibiotics but were less effective (60-80%) when tested against bacteria resistant to specific antimicrobials. Anti-yeast activity was present when an appropriate antifungal agent was included in the combination. All formulations were stable for at least six weeks. Results of this study raise certain questions about the use of these antimicrobial combinations in contemporary skin/tissue banking and point the way toward areas for future study.

Characterization of glycopeptide-resistant enterococci from a Swiss hospital

Between August 1994 and September 1996, 28 glycopeptide-resistant enterococci (GRE) were isolated from 8 infected patients and 11 intestinal carriers hospitalized at the University Hospital of Geneva. Identification to the species was made by both phenotypic (API 20 STREP and Rapid ID 32 STREP systems, and Vitek Gram Positive Identification Card) and genotypic methods using a multiplex PCR assay developed also for the determination of the genotype of glycopeptide resistance (vanA, vanB, vanC1, and vanC2-C3 genes). Fifteen isolates were identified as Enterococcus faecium, 8 as E. gallinarum, 4 as E. faecalis, and 1 as E. hirae. All of the phenotypic identification methods failed to differentiate some isolates of E. gallinarum from E. faecium, or vice versa. Both vanA (n = 18) and vanB (n = 4) glycopeptide resistance genotypes were found. For the first time, the vanB determinant was found in two isolates of E. gallinarum. Two patients were colonized by two different species containing the vanA gene and one by two different species containing the vanB gene. All vanA isolates were highly resistant to both vancomycin and teicoplanin except for three isolates which were susceptible to teicoplanin. Molecular typing by pulsed-field gel electrophoresis showed identical or similar patterns among E. faecium isolates with the vanA gene in five patients for whom the epidemiological link could not be always elucidated. This study emphasizes the necessity of utilizing both phenotypic and genotypic methods to characterize GRE.

Activities and time-kill studies of selected penicillins, beta-lactamase inhibitor combinations, and glycopeptides against Enterococcus faecalis

The activities of piperacillin, piperacillin-tazobactam, ticarcillin, ticarcillin-clavulanate, ampicillin, ampicillin-sulbactam, vancomycin, and teicoplanin were tested against 212 Enterococcus faecalis strains (9 beta-lactamase producers) by standard agar dilution MIC testing (10[4] CFU/spot). The MICs at which 50 and 90% of the isolates were inhibited (MIC50s and MIC90s, respectively) were as follows (microg/ml): piperacillin, 4 and 8; piperacillin-tazobactam, 4 and 8; ticarcillin, 64 and 128; ticarcillin-clavulanate, 64 and 128; ampicillin, 2 and 2; ampicillin-sulbactam, 1 and 2; vancomycin, 1 and 4; and teicoplanin, 0.5 and 1. Agar dilution MIC testing of the nine beta-lactamase-positive strains with an inoculum of 10(6) CFU/spot revealed higher beta-lactam MICs (piperacillin, 64 to >256 microg/ml; ticarcillin, 128 to >256 microg/ml; and ampicillin, 16 to 128 microg/ml); however, MICs with the addition of inhibitors were similar to those obtained with the lower inoculum. Time-kill studies of 15 strains showed that piperacillin-tazobactam was bactericidal (99.9% killing) for 14 strains after 24 h at four times the MIC, with 90% killing of all 15 strains at two times the MIC. After 12 and 6 h, 90% killing of 14 and 13 strains, respectively, was found at two times the MIC. Ampicillin gave 99.9% killing of 14 beta-lactamase-negative strains after 24 h at eight times the MIC, with 90% killing of all 15 strains at two times the MIC. After 12 and 6 h, 90% killing of 14 and 13 strains, respectively, was found at two times the MIC. Killing by ticarcillin-clavulanate was slower than that observed for piperacillin-tazobactam, relative to the MIC. For the one beta-lactamase-producing strain tested by time-kill analysis with a higher inoculum, addition of the three inhibitors (including sulbactam) to each of the beta-lactams resulted in bactericidal activity at 24 h at two times the MIC. For an enzyme-negative strain, addition of inhibitors did not influence kinetics. Kinetics of vancomycin and teicoplanin were significantly slower than those of the beta-lactams, with bactericidal activity against 6 strains after 24 h at eight times the MIC, with 90% killing of 12 and 14 strains, respectively, at four times the MIC. Slower-kill kinetics by both glycopeptides were observed at earlier periods.

Successful single-dose teicoplanin prophylaxis against experimental streptococcal, enterococcal, and staphylococcal aortic valve endocarditis

Teicoplanin is a glycopeptide antibiotic that is administered both intramuscularly and intravenously. It has a prolonged half-life and a less toxic profile in comparison to those of vancomycin. The efficacy of a single dose of teicoplanin (18 mg/kg of body weight given intramuscularly) for the prevention of endocarditis due to Streptococcus oralis, Enterococcus faecium, and methicillin-resistant Staphylococcus aureus (MRSA) was evaluated after applying the rabbit model. Vancomycin at a single dose of 30 mg/kg given intravenously was used as the comparative agent for the prevention of endocarditis due to MRSA and E. faecium, while ampicillin at a single dose of 40 mg/kg given intravenously was used as the comparative agent for the prevention of endocarditis due to S. oralis. Rabbits in the teicoplanin group were infected at 1 h postdosing with approximately 10(7) CFU of each strain. Rabbits in the other groups were infected at 0.5 h postdosing with approximately 10(7) CFU of S. oralis (ampicillin group) or E. faecium and MRSA (vancomycin group). All rabbits were sacrificed 5 days later. Teicoplanin and vancomycin protected the animals challenged with E. faecium by 87.5 and 50%, respectively, and protected the animals challenged with MRSA by 100 and 92%, respectively. Teicoplanin and ampicillin protected the animals challenged with S. oralis by 100 and 77%, respectively. Prevention of endocarditis by teicoplanin was likely to be due to a prolonged inhibition of bacterial growth by the sustained supra-MICs. It is concluded that teicoplanin is very effective in preventing experimental streptococcal, enterococcal, and staphylococcal endocarditis and may be an attractive alternative antibiotic in patients allergic to beta-lactams, especially in the outpatient setting.

Neonatal bacteremia due to high level aminoglycoside resistant (HLAR) enterococci

A study was conducted to determine the drug resistance pattern of enterococci isolated from cases of neonatal bacteremia. A total of 41 strains of enterococci were isolated of which 35 (85.4%) were Enterococcus faecalis and 6 (14.6%) were Enterococcus faecium. A total of 3 (8.6%) strains of E. faecalis and 2 (33.3%) E. faecium strains showed high level aminoglycoside resistance (HLAR). None of the enterococci tested were vancomycin resistant. Drug resistance was more common among E. faecium strains. All clinically significant isolates of enterococci should be tested for their antibiotic sensitivity pattern including HLAR, and for treatment, antibiotics are selected based on in vitro antibiotic sensitivity test results.

Development of fluoroquinolone resistance in Enterococcus faecalis and role of mutations in the DNA gyrase gyrA gene

We have analyzed the development of fluoroquinolone resistance between 1986 and 1993 among clinical isolates of Enterococcus faecalis from a French hospital. One hundred randomly selected isolates per year were screened for resistance to ciprofloxacin (MIC > 2 micrograms/ml) and for high-level resistance to gentamicin (MIC > 1,000 micrograms/ml). The percentages of ciprofloxacin-resistant strains for these years were as follows: 1986, 0; 1987, 1; 1988 to 1989, 2; 1990, 6; 1991, 16; 1992, 24; and 1993, 14. Eighty-three percent of the ciprofloxacin-resistant isolates were coresistant to high levels of gentamicin. Forty-eight high-level gentamicin-resistant E. faecalis strains, which were resistant (24 strains) or susceptible (24 strains) to ciprofloxacin, were examined by pulsed-field gel electrophoresis (PFGE) of SmaI-digested total DNA. Numerous PFGE types were observed among the ciprofloxacin-susceptible isolates, whereas one type was largely predominant among the ciprofloxacin-resistant strains, which suggests that the increase in fluoroquinolone resistance was due to the spread of a single clone. A 241-bp fragment of gyrA, corresponding to the quinolone resistance-determining region, was amplified and sequenced for seven ciprofloxacin-resistant isolates. Six strains had high levels of resistance (MICs, 32 to 64 micrograms/ml) and had a mutation at position 83 (Escherichia coli coordinates) from Ser to Arg (three strains) or to Ile (two strains) or at position 87 from Glu to Gly (one strain), whereas the low-level-resistant isolate (MIC, 8 micrograms/ml) had no mutations.

Epidemiology of an outbreak due to glycopeptide-resistant Enterococcus faecium on a leukaemia unit

The clinical and molecular epidemiology of two clusters of colonization and infection of patients by glycopeptide-resistant enterococci (GRE) on a leukaemia and bone marrow transplantation unit was studied over a two-and-a half-year period. Thirty-five patients became colonized, of whom six developed clinical infections. Of the 53 isolates of GRE, 49 were Enterococcus faecium, multiply-resistant to vancomycin and ampicillin. DNA fingerprinting of 48 E. faecium isolates by pulsed-field gel electrophoresis identified six DNA types. One strain of VanB phenotype E. faecium predominated during the initial outbreak, and an unrelated strain of the VanA phenotype was present in a second cluster. Environmental and patient isolates of E. faecium were indistinguishable by DNA typing. The VanA phenotype enterococci probably arose by transfer from the renal ward at a nearby hospital, and a patient with persistent diarrhoea may have contributed to contamination and cross-infection. GRE may cause significant infections in immunocompromised patients, and are readily transmitted between them. GRE were controlled, but not eradicated on the unit; infection control measures included improved environmental cleaning and modification of antibiotic use. In order to control GRE, it is necessary to educate healthcare workers and implement the traditional, effective values of good personal hygiene and environmental cleanliness.

Survey of enterococcal susceptibility patterns in Belgium

A national surveillance study was performed in order to identify the enterococci causing important infections, to determine their susceptibilities to first-choice agents for treatment, and to characterize the phenotypes and genotypes of the glycopeptide-resistant strains. A total of 472 isolates were collected between 15 January and 15 April 1993. The ability of the API rapid ID 32 STREP gallery to identify enterococci was evaluated. The majority of the Belgian enterococci were identified as E. faecalis (89.4%). E. faecium and other enterococci were present in small percentages only (9.1 and 1.5%, respectively). The API rapid ID 32 STREP system identified 88.6% of the strains with an excellent or very good identification score. For the majority of the strains with uncertain identification scores, the results of a single test only were aberrant. Only 2.3% of the strains remained unidentified. High-level aminoglycoside resistance was widespread in E. faecalis (streptomycin, 50.8%; gentamicin, 8.7%), and the emergence of ciprofloxacin resistance was found to be associated with aminoglycoside resistance. E. faecium is generally more resistant to a wide range of antibiotics, but glycopeptide-resistant strains (1.5%) have not yet become widespread.

The emergent needs for basic research, education, and surveillance of antimicrobial resistance. Problems facing the report from the American Society for Microbiology Task Force on Antibiotic Resistance

The American Society for Microbiology (ASM) convened a task force to study the current prevelance of antibiotic resistance and the problems associated with it. The task force produced a series of recommendations centered around three key elements: (a) education of the physician and the public; (b) encouragement of more basic research directed to the development of new antimicrobials and vaccines; and (c) the setting-up of a national surveillance system to both confirm and monitor the extent of the problem. Since the publication of this report in 1995, progress has been slow. No "consortium-style" funding has been set aside and any initiatives, such as the first steps in an education program by the ASM, are still in their planning phases. The spirit of cooperation and trust needed to deal with this problem appears to be lacking.

Two investigational glycylcyclines, DMG-DMDOT and DMG-MINO. Antimicrobial activity studies against gram-positive species

DMG-DMDOT (CL-331,002 OR CL-331,928) and DMG-MINO (CL-329,998 or CL-344,677) are two new semisynthetic tetracyclines called glycylcyclines, with a broad spectrum of activity and includes Enterobacteriaceae, Gram-positive cocci, JK diphtheroids, and Bacillus cereus. Potent activity was demonstrated against all Streptococcus spp. strains [minimum inhibitory concentrations] (MIC90S) 0.06-0.25 micrograms/ml) and staphylococci (oxacillin susceptible ans resistant; MIC90S 0.12-2 micrograms/ml). Both glycylcyclines (MIC90, 0.06 micrograms/ml) were more potent than minocycline (MIC90 8 micrograms/ml) against Enterococcus faecium, many of which were vancomycin resistant (116 strains). Organisms with minocycline MICs at > or = 8 micrograms/ml (Staphylococcus aureus, enterococci, beta-hemolytic streptococci, and pneumococci) had glycylcycline MIC results ranging from 0.06 to 0.5 micrograms/ml (e.g., apparent use against existing tetracycline-resistance phenotypes). Drugs in this class appear promising for therapy of infections caused by Gram-positive species now testing resistant to contemporary antimicrobial agents, and further development of compounds in this class is encouraged.

Preliminary interpretive criteria for disk diffusion susceptibility testing of SCH 27899, a compound in the everninomicin class of antimicrobial agents

As antimicrobial resistance among Gram-positive species becomes more common, alternative agents need to be developed for the therapy of serious infections. SCH 27899 is a compound from the everninomicin class of antimicrobial agents that possesses a potent Gram-positive spectrum. We evaluated three disk concentrations (0.25, 1, and 5 micrograms) of three SCH 27899 formulations including SCH 27899 base (SCHB), N-methylglucamine SCH 27899 (NMG-SCH), and NMG-SCH complexed with hydroxypropyl beta-cyclodextrin. Disk zone diameters were correlated with minimum inhibitory concentration for 209 aerobic, nonfastidious Gram-positive strains and selected Gram-negative bacilli to develop disk diffusion interpretive criteria. No significant differences in activity were noted among the three SCH 27899 preparations. Of the three disk concentrations, the correlation coefficient was greatest (r = 0.88) for the 5-micrograms SCHB disk test. For a tentative break point of < or = 2 micrograms SCHB/ml, preliminary disk interpretive criteria were: susceptible at > or = 12 mm, intermediate at 10-11 mm, and resistant at < or = 9 mm (absolute categorical agreement, 99.5%). Zones were small secondary to drug solubility and diffusion limitations. Using these criteria for the SCHB 5-micrograms disks, nearly all of the tested Gram-positive organisms were susceptible including methicillin-resistant staphylococci and vancomycin-resistant enterococci.

Activity of two novel fluoroquinolones (DU-6859a and DV-7751a) tested against glycopeptide-resistant enterococcal isolates

Two novel fluoroquinolones, DU-6859a and DV-7751a, were compared with three peer compounds (ciprofloxacin, levofloxacin, and ofloxacin) by testing 150 strains of enterococci that were resistant to vancomycin. Standardized methods recommended by the National Committee for Clinical Laboratory Standards were used for all minimum inhibitory concentration tests, and DU-6859a was additionally tested by the standardized disk diffusion procedure (5-mu g disks). The rank order of the fluoroquinolone spectrums against these Enterococcus spp. isolates was DU-6859a (71.3% of strains inhibited at < or = 2 mu g/ml) > DV-7751a (38.7%) > levofloxacin (33.3%) > ofloxacin (32.0%) > ciprofloxacin (3.3%). Using previously proposed break point zone diameters of > or = 16 mm (susceptible) and < or = 12 mm (resistant), the DU-6859a disk diffusion tests for these glycopeptide-resistant organisms were without false-susceptible or false-resistant error (81.3% absolute agreement). These results indicate that among the investigational and currently marketed fluoroquinolones, DU-6859a appears to have the greatest potential value in the therapy of Enterococcus spp. strains that are resistant to the glycopeptides and many other therapeutic agents.

In vitro interactions between different beta-lactam antibiotics and fosfomycin against bloodstream isolates of enterococci

The effects of 16 different beta-lactam-fosfomycin combinations against 50 bloodstream enterococci were compared by a disk diffusion technique. Cefotaxime exhibited the best interaction. By checkerboard studies, the cefotaxime-fosfomycin combination provided a synergistic bacteriostatic effect against 45 of the 50 isolates (MIC of cefotaxime at which 90% of the isolates were inhibited, >2,048 micrograms/ml; MIC of fosfomycin at which 90% of the isolates were inhibited, 128 micrograms/ml; mean of fractional inhibitory concentration indexes, 0.195). By killing curves, cefotaxime (at 64 micrograms/ml) combined with fosfomycin (at > or = 64 micrograms/ml) was bactericidal against 6 of 10 strains tested.

Antimicrobial Activity of SCH 27899, Oligosaccharide Member of the Everninomycin Class with a Wide Gram-Positive Spectrum

The in vitro antimicrobial activity of SCH 27899 (everninomycin), a novel oligosaccharide compound of the everninomycin class, was compared with vancomycin, chloramphenicol, clinafloxacin, teicoplanin and doxycycline against 428 clinical strains of bacteria. Everninomycin base exhibited the greatest antimicrobial activity compared to other formulations against all strains tested (MIC90: 0.25 microg/ml) followed by clinafloxacin and teicoplanin (MIC90: 0.5 microg/ml), vancomycin (MIC90: 2 microg/ml), and doxycycline (MIC90: 16 microg/ml). Everninomycin demonstrated the best activity against Streptococcus spp. (serogroups A, B, C, F, G) and Streptococcus pneumoniae, and lower activity against coagulase-negative staphylococci (MIC90: 0.5 microg/ml). All enterococci had an everninomycin MIC of 0.5 microg/ml or less. Everninomycin had no measurable antimicrobial activity against gram-negative aerobic organisms except Flavobacterium meningosepticum (MIC50: 2 microg/ml). Some everninomycin activity was observed against Clostridium spp., Peptostreptococcus spp., and the Prevotella bivius-disiens group. Everninomycin showed excellent activity (MIC90: 0.25 microg/ml) against the fluoroquinolone-resistant strains and all gram-positive strains resistant to vancomycin (MICs less-than-or-equal 4 microg/ml). The MBC/MIC ratios and killing curve data suggest that everninomycin is not uniformly or rapidly bactericidal. These in vitro data indicate that everninomycin could be useful against emerging gram-positive strains resistant to other contemporary antimicrobials.

Vancomycin

Vancomycin is a nontoxic glycopeptide antibiotic most often used to treat serious gram-positive infections, C. difficile diarrhea/colitis, and endocarditis and hemodialysis shunt prophylaxis. Vancomycin should not be added to drug regimens for gram-positive coverage, and the empiric use of vancomycin should be discouraged to avoid the emergence of VRE. Vancomycin serum levels are no longer necessary or cost effective in most patients because vancomycin is not nephrotoxic.

National survey of the in vitro spectrum of piperacillin-tazobactam tested against more than 40,000 aerobic clinical isolates from 236 medical centers

Hospital microbiology laboratories from 41 states participated in a bacterial antimicrobial susceptibility study comparing in vitro results generated by the standardized disk diffusion method. Over 41,000 freshly isolated aerobic and facultative strains, representing all specimen types (except stools and urines), were tested for their susceptibility to piperacillin-tazobactam and 21 other antimicrobial agents. Enterococcus spp. was the second or third most common isolate from intraabdominal, gynecologic, and cutaneous infections, confirming its growing importance as a nosocomial pathogen. Escherichia coli was the most frequent isolate overall, despite the exclusion of urinary tract specimens from the study. Pseudomonas aeruginosa was the second most prevalent species, ranking first in frequency of recovery from lower-respiratory-tract specimens. Piperacillin-tazobactam was the most active beta-lactamase inhibitor combination tested against Gram-negative bacteria. Its activity against Gram-positive bacteria and Haemophilus influenzae was similar to that of ampicillin-sulbactam (95-97% susceptible). Imipenem and piperacillin-tazobactam displayed similar spectrums of activity against Gram-positive organisms and Haemophilus influenzae. Against Enterobacteriaceae, piperacillin-tazobactam and ceftazidime exhibited similarly wide spectrums of activity, but with some gaps, particularly among Enterobacter spp. and Citrobacter freundii. In this large-scale in vitro study, piperacillin-tazobactam and imipenem displayed the widest antimicrobial spectrums, inhibiting > 90% of all isolates tested.

Emerging multiply resistant enterococci among clinical isolates. II. Validation of the etest to recognize glycopeptide-resistant strains

Accurate, quantitative susceptibility testing of the enterococci for glycopeptide (vancomycin and teicoplanin) activity has become very important to guide chemotherapy as a result of emerging resistance. Reference dilution tests using broth and agar are generally difficult to perform, or in some commercial forms have demonstrated interpretive error. An alternative method, the Etest has promise as a system with qualitative and quantitative accuracy. Nearly 2000 enterococci from 97 laboratories in the United States were tested using broth microdilution, disk diffusion, and Etest methods. The Etest quantitative accuracy (+/- 1 log2 dilution) compared to the broth microdilution minimum inhibitory concentration was 90.1% (teicoplanin) to 94.1% (vancomycin). The qualitative interpretive accuracy of the Etest ranged from 98.7% for vancomycin to 99.9% for teicoplanin (no false-susceptible errors). All three tests were in remarkable agreement, with < or = 0.8% maximal discord by interpretive category. The Etest appears to be an excellent alternative to reference and standardized methods for producing quantitative activity measurements of glycopeptide susceptibility or resistance.

Emerging multiply resistant enterococci among clinical isolates. I. Prevalence data from 97 medical center surveillance study in the United States. Enterococcus Study Group

To assess the evolving problem of therapeutic drug resistances among enterococci, we organized a comprehensive national (United States) surveillance trial using 99 recruited microbiology laboratories in 48 of the 49 contiguous states or districts. All but two sites completed the protocol that generated information from nearly 2000 enterococci, usually isolated from blood cultures. All strains were speciated by the same method (API 20S) and were susceptibility tested by three methods (broth microdilution, disk diffusion, and Etest) against ampicillin, penicillin, vancomycin, teicoplanin, gentamicin, and streptomycin. Strains resistant to a glycopeptide or penicillin, or possessing high-level aminoglycoside resistance were referred to the monitor's laboratory for validation and additional susceptibility testing against other alternative antimicrobial agents. The most common species were Enterococcus faecalis and Enterococcus faecium. However, antimicrobial resistance occurred most often among the E. faecium isolates. Twenty-three percent of participant centers (22 sites) reported 87 vancomycin-resistant isolates, which accounts for 4.4% of the isolates evaluated. A recent audit (March 1994) of the laboratories not reporting vancomycin resistance during the study interval (October-December 1992) revealed that 61% of sites have now recognized these strains, a threefold increase in 12-15 months. Teicoplanin remained active against 28% (Van B phenotype) of vancomycin-resistant enterococci (10 E. faecalis, 13 E. faecium, and one Enterococcus spp.). Ampicillin-resistant beta-lactamase-positive strains were found only at one medical center (two strains, 0.2% of referred or validated strains); however, ampicillin-resistant strains represented 12% of all enterococcal, but nearly 60% of E. faecium strains.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis by PCR and direct DNA sequencing of gyrA mutations associated with fluoroquinolone resistance in Enterococcus faecalis

A region of gyrA, the gene encoding subunit A of DNA gyrase, that is known to be associated with resistance was amplified and sequenced from 16 Enterococcus faecalis and Enterococcus faecium isolates. Six ciprofloxacin-resistant clinical isolates (MICs of ciprofloxacin, 32 to 64 micrograms/ml) and one multistep resistant laboratory mutant of E. faecalis (MIC of ciprofloxacin, 128 micrograms/ml) contained a change from serine to arginine or to isoleucine at codon 83 or a change from glutamic acid to lysine or to glycine at codon 87 (Escherichia coli GyrA coordinates); these changes have been associated with fluoroquinolone resistance in other species. No difference in the region studied was found in two ciprofloxacin-resistant E. faecium isolates (MICs, 32 micrograms/ml) or in four laboratory derived, spontaneous ciprofloxacin-resistant mutants of E. faecalis (MICs, 8 to 16 micrograms/ml), suggesting that other mechanisms may be responsible for fluoroquinolone resistance in some enterococci.

Molecular epidemiology of gastric colonization by Enterococcus faecalis in a surgical intensive care unit

We applied restriction endonuclease analysis of genomic DNA using pulsed field gel electrophoresis (PFGE) to study gastric colonization with Enterococcus faecalis among patients hospitalized in the surgical intensive care unit (SICU). Isolates were obtained by culturing prospectively the gastric contents of 140 patients in the SICU. In addition, cultures of respiratory specimens were obtained daily and cultures of blood, normally sterile body fluids, wounds, and urine were obtained when indicated clinically. A total of 177 isolates were obtained from 45 patients. Concentrations of E. faecalis in gastric fluid ranged from 1 x 10(2) colony forming units (CFU)/ml to greater than 5 x 10(7) CFU/ml (mean 8.0 x 10(6) CFU/ml). Overall, 33 different DNA types were identified by PEGE. In examining strain variation among isolates obtained from multiple anatomic sites over time, we found that the same DNA type was recovered from gastric aspirates, sputum, and wounds in a given patient and that these strains were carried over time. In general, given individuals were colonized with their own unique DNA type; however, one DNA type (type C) was shared by 11 different patients, and seven DNA types were shared by two individuals each. These results demonstrate the potential importance of gastric colonization as a reservoir for nosocomial strains of E. faecalis in an SICU setting.

In vitro activities of two glycylcyclines against gram-positive bacteria

The glycylcyclines designated CL 329,998 and CL 331,002 are N,N-dimethylglycylamido derivatives of minocycline and 6-demethyl-6-deoxytetracycline, respectively. In vitro activities of these two antimicrobial agents were compared with those of tetracycline, minocycline, and seven other antimicrobial agents against 412 gram-positive organisms. Both new drugs were significantly more active than minocycline against methicillin-resistant Staphylococcus aureus (MICs for 90% of isolates tested, 0.25 and 0.5 microgram/ml versus 4 micrograms/ml). CL 329,998 inhibited all streptococci, lactobacilli, and Leuconostoc spp. at concentrations of < or = 0.5 microgram/ml, with CL 331,002 slightly less active against some species. All enterococci, including minocycline-resistant and multidrug-resistant isolates, were inhibited at < or = 0.5- and < or = 1.0-microgram/ml concentrations of the new drugs, respectively. Only bacteriostatic activity was evident by time-kill curves. The two glycylcyclines demonstrated activities in vitro that were superior to those of minocycline against several gram-positive bacterial species, and at relatively low concentrations, they inhibited isolates resistant to both tetracycline and minocycline.