Nosocomial outbreak due to Enterococcus faecium highly resistant to vancomycin, penicillin, and gentamicin

Surveillance of intestinal colonization and of infection by vancomycin-resistant enterococci in hospitalized cancer patients

OBJECTIVE: To study epidemiologic features of and risk factors for intestinal colonization and infection by vancomycin-resistant enterococci (VRE) in cancer patients. METHODS: During a 41-month period, over 7600 fecal samples and all samples from sterile sites from hospitalized cancer patients were screened for VRE. Species were identified and isolates analyzed by pulsed-field gel electrophoresis (PFGE) of SmaI DNA restriction fragments. Antibiotic resistance was characterized by MIC determinations, and polymerase chain reaction for vanA, vanB, and vanC1 genes. Plasmid contents were analyzed before and after PstI and HindIII restriction, and by Southern hybridization with a vanA probe. Two case-control studies were performed to identify risk factors for colonization or infection by VRE, respectively. RESULTS: Eighty-two isolates were recovered from 81 patients. Most (72%) isolates were Enterococcus faecium VanA/vanA, with 37 different PFGE types, each of which was found in only one to four patients, except for type P1, which was found in 20 patients hospitalized over a 3-month period in the pediatric wards. Plasmid analysis suggested that only two types of plasmid were carrying gene vanA, as part of a transposon related to transposon Tn 1546 from reference strain E. faecium BM4147. Seventy-seven patients were colonized during the study period. Six of them became infected. Four patients were infected but not colonized. Only one patient died during the course of infection, but intestinal colonization persisted for months in the survivors. Case-control analysis revealed that cephalosporin treatment was a significant risk factor for colonization. No significant risk factor for infection was found in colonized patients. CONCLUSION: Colonization by VRE was mostly endemic and the colonized patients were not often infected. However, when clustered cases of colonization occurred, they were then associated with an increased rate of infection.

Selective medium for screening for vancomycin-resistant enterococci in faeces

Infections caused by vancomycin-resistant enterococci (VRE) are becoming increasingly prevalent throughout the world. Control measures include detection and isolation of carriers of VRE. A selective medium to detect faecal carriage of VRE is described. The medium has a high productivity ratio (90.4%) for VRE with VanA resistance phenotype, a moderate productivity ratio (79.2%) for VRE with VanB resistance phenotype, and a relatively low productivity ratio (65.5%) for VRE with VanC resistance phenotype. There was no breakthrough of vancomycin-susceptible enterococci. The medium selected the growth of all three types of VRE, which were used to spike faecal specimens. In a limited clinical trial, six faecal specimens of carriers and contacts were screened using the selective medium. Vancomycin-resistant enterococci (Enterococcus faecalis, VanA phenotype) were detected in four of the specimens. In all four specimens the growth of VRE was nearly pure and easily identifiable.

Antimicrobial-resistant pathogens in the 1990s

Streptococcus pneumoniae, Enterococcus faecalis, Enterococcus faecium, Staphylococcus aureus, and Klebsiella pneumoniae have become increasingly resistant to antimicrobial agents. This chapter reviews the epidemiology of this resistance, its detection in the laboratory, the mechanisms of resistance, and the options for therapy and infection control.

First documented isolation of vancomycin-resistant Enterococcus faecium in Sweden

In recent years enterococci, and Enterococcus faecium in particular, have emerged as important nosocomial pathogens. Of major concern is the increasing antimicrobial resistance to traditionally used agents such as ampicillin, gentamicin and vancomycin. We present a patient with prosthetic heart valves colonized with vancomycin-resistant E. faecium. This is the first reported isolation of vancomycin-resistant E. faecium in Sweden.

Methicillin-resistant coagulase-negative staphylococcal osteomyelitis and its relationship to broad-spectrum oral antibiosis in a predominantly diabetic population

Awareness of the virulence of coagulase-negative Staphylococci, previously regarded as saprophytes with minimal pathogenicity, has steadily increased. Eighty-seven individual patients diagnosed with acute osteomyelitis, as confirmed by microbiologic and pathologic analysis, were included in this study. Of these patients, 82% (71/87) were known to have diabetes mellitus. The prevalence of coagulase negative Staphylococcus was 40% (35/87) in deep bone cultures, 63% (22/35) of which were methicillin resistant. When the coagulase negative Staphylococcus group was assessed for prior long-term (> 2 week) oral antibiotic treatment with ciprofloxacin, it was found that 54% (12/22) of the methicillin-resistant coagulase-negative Staphylococcal infected patients had received such treatment, compared with 15% (2/13) of patients with methicillin-sensitive coagulase-negative Staphylococcal osteomyelitis (p < 0.034). When the group was analyzed for prior long-term antibiotic treatment with amoxicillin/clavulanate, 23% (5/22) of the methicillin-resistant patients had received oral amoxicillin/clavulanate, compared with 23% (3/13) of patients with methicillin-sensitive coagulase-negative Staphylococcal osteomyelitis (p > 0.05). Prevalence of polymicrobial infections, which constituted 29% (25/87) of all individual patients, was also analyzed. Of those patients with coagulase-negative isolates, 29% (10/35) were polymicrobial (p > 0.05). The results from this study suggest that infections of bone caused by coagulase-negative Staphylococci are associated with a high prevalence of methicillin resistance. This study also raises the question of whether injudicious prolonged use of ciprofloxacin may, in fact, promote proliferation of resistant organism strains.

Identification of chromosomal mobile element conferring high-level vancomycin resistance in Enterococcus faecium

A clinical isolate of Enterococcus faecium that contains a chromosomally encoded vanA gene cluster, Tn1546::IS1251, transferred vancomycin resistance to the plasmid-free strain Enterococcus faecalis JH2-2 during filter matings. Hybridization of a vanHAXY probe to SmaI restriction-digested genomic DNA separated by pulsed-field gel electrophoresis showed that the vanA gene cluster was located on a 40-kb fragment in the original donor strain and on fragments of different sizes (150 to 450 kb) in the transconjugants. No hybridization to vanA gene cluster probes was obtained with plasmid DNA preparations from the donor or transconjugants. These results suggested that in each case, the van genes had integrated into the recipient chromosome. The transconjugants in turn could act as donors of vancomycin resistance, and resistance was transferable to a Rec- recipient. The results of restriction analyses and DNA hybridizations of genomic DNA from the donor and transconjugants were consistent with the transfer of a mobile element that includes the 12.3-kb Tn1546::IS1251 gene cluster and at least 13 kb of additional DNA. This element has been tentatively designated Tn5482. DNA sequence analysis of a fragment predicted to contain the left end of Tn5482 revealed two insertion sequence-like elements: IS1216V and an apparently truncated IS3-like element. Restriction mapping and DNA hybridization patterns of the van gene clusters of three additional clinical isolates from New York City showed an element similar to Tn5482. Transfer of Tn5482 and related elements may be involved in dissemination of vancomycin resistance.

Activities of the semisynthetic glycopeptide LY191145 against vancomycin-resistant enterococci and other gram-positive bacteria

LY191145 is the prototype of a series of compounds with activities against vancomycin-resistant enterococci derived by modification of the glycopeptide antibiotic LY264826. LY191145 had MICs for vancomycin- and teicoplanin-resistant enterococci of < or = 4 micrograms/ml for 50% of isolates and < or = 16 micrograms/ml for 90% of isolates. Its MICs for vancomycin-resistant, teicoplanin-susceptible enterococci were 1 to 8 micrograms/ml. LY191145 retains the potent activities of its parent compound against staphylococci and streptococci. In vivo studies in a mouse infection model confirmed these activities. This compound indicates the potential of semisynthetic glycopeptides as agents against antibiotic-resistant gram-positive bacteria.

Vancomycin-resistant enterococci colonizing the intestinal tracts of hospitalized patients

A point prevalence culture survey was carried out to investigate the prevalence of fecal carriage of vancomycin-resistant enterococci (VRE) among patients admitted to an 800-bed general hospital where no VRE had been isolated previously. Twenty-two of 636 patients (3.5%) were found to be VRE carriers. Eighteen strains were identified as Enterococcus faecium, three were identified as Enterococcus gallinarum, and one was identified as Enterococcus faecalis. The susceptibilities of the enterococci to ampicillin, vancomycin, and teicoplanin were determined by the disk diffusion and the agar dilution methods. High-level resistance (HLR) to gentamicin and streptomycin was determined by the agar screening method. Eighteen strains (82%) were highly resistant to vancomycin, and four strains (18%) were moderately resistant to vancomycin. Five strains were susceptible to teicoplanin (23%; MICs, < or = 8 micrograms/ml). Only one strain (4.5%, E. faecium) showed HLR to gentamicin, and six strains (27%) showed HLR to streptomycin (one E. faecalis and five E. faecium strains). All 18 E. faecium and 1 E. faecalis strain carried the vanA gene, and 3 E. gallinarum strains carried the vanC gene. An epidemiological investigation revealed several risk factors for VRE colonization: hospitalization and duration of stay in the hematology department and prior vancomycin treatment. The study demonstrates that the patient's gastrointestinal tract is a possible reservoir for VRE, even in hospitals where VRE infections have not yet been observed. Therefore, we conclude that infection control precautions and restriction of glycopeptide usage may be key issues in limiting the emergence and spread of nosocomial VRE infections.

Current perspectives on glycopeptide resistance

In the last 5 years, clinical isolates of gram-positive bacteria with intrinsic or acquired resistance to glycopeptide antibiotics have been encountered increasingly. In many of these isolates, resistance arises from an alteration of the antibiotic target site, with the terminal D-alanyl-D-alanine moiety of peptidoglycan precursors being replaced by groups that do not bind glycopeptides. Although the criteria for defining resistance have been revised frequently, the reliable detection of low-level glycopeptide resistance remains problematic and is influenced by the method chosen. Glycopeptide-resistant enterococci have emerged as a particular problem in hospitals, where in addition to sporadic cases, clusters of infections with evidence of interpatient spread have occurred. Studies using molecular typing methods have implicated colonization of patients, staff carriage, and environmental contamination in the dissemination of these bacteria. Choice of antimicrobial therapy for infections caused by glycopeptide-resistant bacteria may be complicated by resistance to other antibiotics. Severe therapeutic difficulties are being encountered among patients infected with enterococci, with some infections being untreatable with currently available antibiotics.

Synergistic effect of amoxicillin and cefotaxime against Enterococcus faecalis

The antibacterial efficacy of the combination of amoxicillin and cefotaxime was assessed against 50 clinical strains of Enterococcus faecalis. For 48 of 50 strains, the MIC of amoxicillin that inhibited 50% of isolates tested decreased from 0.5 microgram/ml (range, 0.25 to 1 microgram/ml) to 0.06 microgram/ml (range, 0.01 to 0.25 microgram/ml) in the presence of only 4 micrograms of cefotaxime per ml. Alternatively, the MIC of cefotaxime that inhibited 50% of isolates tested decreased from 256 micrograms/ml (range, 8 to 512 micrograms/ml) to 1 micrograms/ml (range, 0.5 to 16 micrograms/ml) in the presence of only 0.06 microgram of amoxicillin per ml. For JH2-2, a reference strain of E. faecalis, the MICs of amoxicillin, cefotaxime, and amoxicillin in the presence of cefotaxime (4 micrograms/ml) were 0.5, 512, and 0.06 microgram/ml, respectively. By using a penicillin-binding protein (PBP) competition assay, it was shown that with cefotaxime, 50% saturation of PBPs 2 and 3 was obtained at very low concentrations (< 1 microgram/ml), while 50% saturation of PBPs 1, 4, and 5 was obtained with > or = 128 micrograms/ml. With amoxicillin, 50% saturation of PBPs 4 and 5 was obtained at 0.12 and 0.5 microgram/ml, respectively. Therefore, the partial saturation of PBPs 4 and 5 by amoxicillin combined with the total saturation of PBPs 2 and 3 by cefotaxime could be responsible for the observed synergy between these two compounds.

Control of infection with multiple antibiotic resistant bacteria in a hospital renal unit: the value of plasmid characterization

An outbreak of infections due to multiple antibiotic-resistant bacteria took place over a period of approximately 18 months in a renal unit. Strains of Escherichia coli, Enterobacter aerogenes, Klebsiella pneumoniae, Citrobacter spp. and Pseudomonas spp. were involved, and a variety of antibiotic resistances was encountered. Closely related plasmids encoding resistance to aztreonam, ceftazidime and piperacillin, possibly derived from an archetypal plasmid of 105 kb were found in the majority of isolates examined. After limiting the use of aztreonam the incidence of new patient isolates of multiple-resistant organisms was greatly reduced. This study demonstrated how molecular studies can contribute to the control of an outbreak situation in a hospital unit by providing an impetus to reduce the use of specific antibiotics.

Treatment of experimental endocarditis due to erythromycin-susceptible or -resistant methicillin-resistant Staphylococcus aureus with RP 59500

RP 59500 is a new injectable streptogramin composed of two synergistic components (quinupristin and dalfopristin) which are active against erythromycin-susceptible and -resistant gram-positive pathogens. The present experiments compared the therapeutic efficacy of RP 59500 with that of vancomycin against experimental endocarditis due to either of two erythromycin-susceptible or two constitutively erythromycin-resistant isolates of methicillin-resistant Staphylococcus aureus. RP 59500 had low MICs for the four test organisms as well as for 24 additional isolates (the MIC at which 90% of the isolates were inhibited was < 1 mg/liter) which were mostly inducibly (47%) or constitutively (39%) erythromycin resistant. Aortic endocarditis in rats was produced with catheter-induced vegetations. Three-day therapy was initiated 12 h after infection, and the drugs were delivered via a computerized pump, which permitted the mimicking of the drug kinetics produced in human serum by twice-daily intravenous injections of 7 mg of RP 59500 per kg of body weight or 1 g of vancomycin. Both antibiotics reduced vegetation bacterial titers to below detection levels in ca. 70% of animals infected with the erythromycin-susceptible isolates (P < 0.05 compared with titers in controls). Vancomycin was also effective against the constitutively resistant strains, but RP 59500 failed against these isolates. Further experiments proved that RP 59500 failures were related to the very short life span of dalfopristin in serum (< or = 2 h, compared with > or = 6 h for quinupristin), since successful treatment was restored by artificially prolonging the dalfopristin levels for 6 h. Thus, RP 59500 is a promising alternative to vancomycin against methicillin-resistant S. aureus infections, provided that pharmacokinetic parameters are adjusted to afford prolonged levels of both of its constituents in serum. This observation is also relevant to humans, in whom the life span of dalfopristin in serum is also shorter than that of quinupristin.

Ability of commercial and reference antimicrobial susceptibility testing methods to detect vancomycin resistance in enterococci

We evaluated the abilities of 10 commercially available antimicrobial susceptibility testing methods and four reference methods (agar dilution, broth microdilution, disk diffusion, and the agar screen plate) to classify enterococci correctly as vancomycin susceptible or resistant using 50 well-characterized strains of enterococci. There was a high level of agreement of category classification data obtained with broth-based systems (Sceptor, MicroMedia, Pasco, and Sensititre), agar dilution, and an antibiotic gradient method (E test) with data obtained by reference broth microdilution; no very major or major errors were seen, and minor errors were < or = 6%. Increased minor error rates were observed with disk diffusion (12%), Alamar (16%), Uniscept (16%), and conventional (overnight) MicroScan panels (16%). The errors were primarily with Enterococcus casseliflavus strains and organisms containing the vanB vancomycin resistance gene. Very major error rates of 10.3 and 20.7% were observed with Vitek and MicroScan Rapid (MS/Rapid) systems, respectively; however, only the MS/Rapid system produced major errors (13.3%). On repeat testing of discrepant isolates, the very major error rate with the Vitek system dropped to 3.4%, while the very major error rate with the MS/Rapid system increased to 27.6%; major errors with the MS/Rapid system were not resolved. Many of the commercial systems had only 4 dilutions of vancomycin, which resulted in up to 84% of values being off scale (e.g., Uniscept). Of the methods tested, most conventional broth- and agar-based methods proved to be highly accurate when incubation was done for a full 24 h, although several of the tests had high minor error rates. Automated systems continued to demonstrate problems in detecting low-level resistance.

Reducing the spread of antimicrobial-resistant microorganisms. Control of vancomycin-resistant enterococci

Strategies to reduce the spread of hospital-acquired microorganisms resistant to multiple antimicrobial agents are discussed. Because hospitals have experienced a rapid increase in the incidence of infection and colonization with vancomycin-resistant enterococci (VRE) in the past 5 years, the Hospital Infection Control Practices Advisory Committee of the Centers for Disease Control and Prevention has issued recommendations for preventing the spread of vancomycin resistance. Controlling VRE dissemination in pediatric patients requires prompt detection of VRE by microbiology laboratories, education of staff and families about VRE, use of infection control measures to prevent person-to-person VRE transmission, and prudent vancomycin use.

The emergence of Enterococcus faecium resistant to glycopeptides and other standard agents--a preliminary report

We describe the emergence of vancomycin-resistant (VmR) Enterococcus faecium on a liver unit. Over a 22 month period, 110 patients acquired VmR E. faecium. Ribotyping identified 116 patient isolates. Five ribotypes accounted for 78% of patient isolates, the maximum number of patient isolates of a single ribotype was 37, and five clusters of four ribotypes were found. Seven patients acquired more than one ribotype. Environmental sampling yielded VmR E. faecium of the same ribotype as concurrent patient isolates. Clinical specimens from 38 liver transplant patients yielded VmR E. faecium and these were compared to 29 who acquired vancomycin-sensitive (VmS) E. faecium. Logistic regression analysis indicated that duration of admission was the only independent risk factor for acquisition of VmR E. faecium.

Antibacterial activity of 7-aminocholesterol, a new sterol

A new sterol, 7-aminocholesterol, which inhibits growth of Saccharomyces cerevisiae, also displayed antibiotic activity against Gram-positive bacteria. The 50% growth inhibitory concentration against strains of Listeria innocua, L. monocytogenes, Staphylococcus aureus, Enterococcus hirae and Bacillus cereus was 3 microM.

Resistance of Enterococcus faecium to neutrophil-mediated phagocytosis

During a previous study of the opsonic requirements for neutrophil (polymorphonuclear leukocyte [PMN])-mediated killing of enterococci, we identified two strains of Enterococcus faecium (TX0015 and TX0016) that were resistant to PMN-mediated killing. To better define the mechanism of this resistance, we examined phagocytosis with a fluorescence assay and found that TX0016 was completely resistant to phagocytosis by PMNs; this finding was confirmed by electron microscopy. Examination of multiple strains of enterococci revealed that all 20 strains of Enterococcus faecalis tested were readily phagocytosed (mean, 18 intracellular organisms per PMN; range, 7 to 28). In contrast, only 13 (50%) of 26 strains of E. faecium tested were susceptible to phagocytosis (> or = 7 organisms per PMN); the other 13 strains showed < or = 3 organisms per PMN. Enterococcus casseliflavus ATCC 25788 and one strain of Enterococcus hirae were also resistant to phagocytosis, while two strains of Enterococcus durans, Enterococcus mundtii ATCC 43186, and one strain each of Enterococcus raffinosus and Enterococcus solitarius were readily phagocytosed. Exposure of E. faecium TX0016 to sodium periodate, but not to the protease trypsin or pronase or to phospholipase C, eliminated resistance to phagocytosis. Sialic acid, a common periodate-sensitive structure used by microorganisms to resist opsonization, could not be demonstrated in E. faecium TX0016 by the thiobarbituric acid method, nor was phagocytosis of TX0016 altered by neuraminidase treatment. This study suggests that there is a difference in susceptibility to phagocytosis by PMNs between different species of enterococci and that a carbohydrate-containing moiety which is not sialic acid may be involved in the resistance of E. faecium TX0016 to phagocytosis.

Risk factors for acquiring ampicillin-resistant enterococci and clinical outcomes at a Canadian tertiary-care hospital

The number of ampicillin-resistant enterococci (ARE) was noted to be increased at our teaching hospital. To determine the risk factors for acquiring this organism and to compare clinical outcomes, over a 5-month period 38 patients infected or colonized with ARE were compared with 76 patients, infected or colonized with ampicillin-susceptible enterococci (ASE). Risk factors included nosocomial acquisition, duration of hospitalization, admission to a medical service, prior antimicrobial therapy, and combination therapy for at least 7 days. The mortality rate of patients infected or colonized with ARE was higher than that of patients infected or colonized with ASE (34 versus 14%; P = 0.03), but most deaths did not appear to be related to enterococcal infection. Over a 2-year period, 16 patients with ARE bacteremia were also compared with 23 patients with ASE bacteremia. The risk factors associated with ARE bacteremia also included nosocomial acquisition, duration of hospitalization, and prior antimicrobial therapy. The mortality of patients with ARE bacteremia was also higher than that of patients with ASE bacteremia (81 versus 30%; P = 0.003), with most deaths being due to the underlying disease or a complication of it. Typing of ARE isolates by pulsed-field gel electrophoresis showed that two genotypes predominated in our institution. A prolonged hospital stay, exposure to multiple antimicrobial agents, and perhaps nosocomial transmission are important factors in acquiring ARE. The presence of ARE may also be a marker for poor outcome.

An old antibiotic for a new multiple-resistant Enterococcus faecium?

Enterococci have become an important cause of nosocomial infections and may demonstrate high-level resistance to multiple antibiotics. We present the case of a 68-year-old man with a history of small cell lung cancer, who developed bacteremia due to a strain of Enterococcus faecium. The isolate was resistant to multiple antibiotics including vancomycin, ampicillin, aminoglycosides, quinolones, and macrolides. The patient was successfully treated with doxycycline and removal of an infected central venous catheter.

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.

Activity of clinafloxacin against multidrug-resistant Enterococcus faecium

Enterococci resistant to ampicillin, vancomycin, and/or aminoglycosides are a growing clinical problem. We studied the in vitro activity of the new fluoroquinolone clinafloxacin (PD 127,391) against 15 clinical isolates of multidrug-resistant Enterococcus faecium. In kill-kinetic studies, clinafloxacin (1 microgram/ml) was bactericidal against 7 of 12 susceptible isolates, although substantial regrowth occurred in 4 isolates at 48 h. The addition of ampicillin (20 micrograms/ml) resulted in bactericidal activity in all 12 isolates, and no regrowth was seen. For three isolates resistant to clinafloxacin, effective killing was not observed at these concentrations of antibiotics. Clinafloxacin with ampicillin shows promising activity against many of these multiply resistant enterococci.

Outbreak of vancomycin-, ampicillin-, and aminoglycoside-resistant Enterococcus faecium bacteremia in an adult oncology unit

An outbreak of bacteremia caused by Enterococcus faecium with high-level resistance to vancomycin (MIC of > or = 256 micrograms/ml), ampicillin (MIC of > or = 64 micrograms/ml), and gentamicin or streptomycin (MIC of > or = 2,000 micrograms/ml) occurred in an adult oncology unit from June 1991 to May 1992. Active surveillance for the presence of this organism in stool or perianal cultures was begun in September 1991. Between June 1991 and May 1992, seven patients with bacteremia and 22 noninfected carriers of the organism in stool were identified. The vanA gene, tested for by PCR and gene probe, was present in all isolates evaluated. All bacteremic patients also had resistant E. faecium present in a stool or perianal culture; the stool isolates tested were closely related to the respective blood isolates as determined by pulsed-field gel electrophoresis. Antibiotic regimens using high-dose ampicillin and an aminoglycoside were ineffective with four patients. Five patients (71%) had multiple positive blood cultures; four of these patients died. Following a multiple logistic regression analysis, it was found that bacteremic patients received a significantly greater number of total antibiotic days compared with noninfected stool carriers (P = 0.019). The emergence of E. faecium with high-level resistance to vancomycin, ampicillin, and aminoglycosides underscores the importance of performing susceptibility testing on all clinically significant isolates. In the neutropenic adult oncology patient, bacteremia with this organism is of probable gastrointestinal origin, is often persistent, and is refractory to treatment with ampicillin in combination with an aminoglycoside. Prolonged use of antibiotics may predispose patients with gastrointestinal colonization to develop bacteremia.

Outbreak of multidrug-resistant Enterococcus faecium with transferable vanB class vancomycin resistance

Enterococcus faecium strains resistant to ampicillin, high levels of gentamicin, and vancomycin but susceptible to teicoplanin (vanB class vancomycin resistance) were recovered from 37 patients during an outbreak involving a 250-bed university-affiliated hospital. Three isolates with vancomycin MICs ranging from 8 to 256 micrograms/ml all hybridized with a vanB probe. Restriction endonuclease analysis of chromosomal and plasmid DNA suggested that all isolates tested were derived from a single clone. Vancomycin resistance was shown to be transferable. Risk factors for acquiring the epidemic strain included proximity to another case patient (P, 0.0005) and exposure to a nurse who cared for another case patient (P, 0.007). Contamination of the environment by the epidemic strain occurred significantly more often when case patients had diarrhea (P, 0.001). Placing patients in private rooms and requiring the use of gowns as well as gloves by personnel controlled the outbreak. These findings suggest that multidrug-resistant E. faecium strains with transferable vanB class vancomycin resistance will emerge as important nosocomial pathogens. Because extensive environmental contamination may occur when affected patients develop diarrhea, barrier precautions, including the use of both gowns and gloves, should be implemented as soon as these pathogens are encountered.

Comparative in vitro activity of DU-6859a, a new fluoroquinolone agent, against gram-positive cocci

The in vitro activity of DU-6859a (DU), a new fluoroquinolone agent, was evaluated against 233 gram-positive cocci and was compared with those of ciprofloxacin, vancomycin, nafcillin, and ampicillin. The MICs of DU for 90% of the staphylococci tested were < or = 0.06 microgram/ml. All of the groups A and B and viridans group streptococci were inhibited by < or = 0.125 microgram of DU per ml, which was 32-fold more active than ciprofloxacin. On the basis of MICs for 90% of the strains tested, DU was 32- and 16-fold more active than ciprofloxacin against Enterococcus faecalis and Enterococcus faecium, respectively. The bactericidal activity of DU was demonstrated by time-kill techniques against all ciprofloxacin-susceptible enterococci. DU shows promise for the treatment of infections with gram-positive cocci and warrants further evaluation by in vitro and in vivo studies.