Agents that increase the permeability of the outer membrane

The outer membrane of gram-negative bacteria provides the cell with an effective permeability barrier against external noxious agents, including antibiotics, but is itself a target for antibacterial agents such as polycations and chelators. Both groups of agents weaken the molecular interactions of the lipopolysaccharide constituent of the outer membrane. Various polycations are able, at least under certain conditions, to bind to the anionic sites of lipopolysaccharide. Many of these disorganize and cross the outer membrane and render it permeable to drugs which permeate the intact membrane very poorly. These polycations include polymyxins and their derivatives, protamine, polymers of basic amino acids, compound 48/80, insect cecropins, reptilian magainins, various cationic leukocyte peptides (defensins, bactenecins, bactericidal/permeability-increasing protein, and others), aminoglycosides, and many more. However, the cationic character is not the sole determinant required for the permeabilizing activity, and therefore some of the agents are much more effective permeabilizers than others. They are useful tools in studies in which the poor permeability of the outer membrane poses problems. Some of them undoubtedly have a role as natural antibiotic substances, and they or their derivatives might have some potential as pharmaceutical agents in antibacterial therapy as well. Also, chelators (such as EDTA, nitrilotriacetic acid, and sodium hexametaphosphate), which disintegrate the outer membrane by removing Mg2+ and Ca2+, are effective and valuable permeabilizers.

Agents that increase the permeability of the outer membrane

The outer membrane of gram-negative bacteria provides the cell with an effective permeability barrier against external noxious agents, including antibiotics, but is itself a target for antibacterial agents such as polycations and chelators. Both groups of agents weaken the molecular interactions of the lipopolysaccharide constituent of the outer membrane. Various polycations are able, at least under certain conditions, to bind to the anionic sites of lipopolysaccharide. Many of these disorganize and cross the outer membrane and render it permeable to drugs which permeate the intact membrane very poorly. These polycations include polymyxins and their derivatives, protamine, polymers of basic amino acids, compound 48/80, insect cecropins, reptilian magainins, various cationic leukocyte peptides (defensins, bactenecins, bactericidal/permeability-increasing protein, and others), aminoglycosides, and many more. However, the cationic character is not the sole determinant required for the permeabilizing activity, and therefore some of the agents are much more effective permeabilizers than others. They are useful tools in studies in which the poor permeability of the outer membrane poses problems. Some of them undoubtedly have a role as natural antibiotic substances, and they or their derivatives might have some potential as pharmaceutical agents in antibacterial therapy as well. Also, chelators (such as EDTA, nitrilotriacetic acid, and sodium hexametaphosphate), which disintegrate the outer membrane by removing Mg2+ and Ca2+, are effective and valuable permeabilizers.

Safety of probiotics that contain lactobacilli or bifidobacteria

Lactobacilli and bifidobacteria are extremely rare causes of infection in humans, as are probiotics based on these organisms. This lack of pathogenicity extends across all age groups and to immunocompromised individuals. Strains used for new probiotics should be chosen from the commensal flora of humans and should not carry intrinsic resistance to antibiotics that would prevent treatment of a rare probiotic infection. Vigilance regarding the detection of possible rare cases of infection due to probiotics should be maintained, and isolates should be sent to reference centers for molecular characterization and confirmation.

Postural Balance in a Random Sample of 7,979 Subjects Aged 30 Years and Over

BACKGROUND

Reliable normative data for force platform measurements of postural balance have not been available.

METHODS

Data on postural balance were collected from a representative nationwide sample of a Finnish population aged >or=30 years (n = 7,979). As part of a comprehensive health survey (Health 2000), postural balance was measured with the help of a force platform system in four test conditions: normal standing with eyes open and closed (both for 30 s), semi-tandem (20 s) and tandem stand with eyes open (20 s). In addition, balance abilities were also evaluated by a non-instrumented field test.

RESULTS

The main findings of this study indicated that the differences in balance between subjects belonging to different age categories were apparent already among young and middle-aged subjects. This is true, however, only for the more accurate force platform measurements, as the field test showed a clear ceiling effect up to 60 years of age. At higher ages both methods indicated a further, accelerating decline in balance function. In most cases, males tended to have more pronounced sway, as indicated by the speed and amplitude aspects of the movement of the center of pressure during the force platform registrations and these differences were larger in the older age groups. In contrast, in the field test a larger proportion of males were able to achieve the highest category (10 s in tandem stand) and the proportion of subjects unable to stand for a minimum of 10 s feet side by side was larger among females than males. These observations may partly be due to differences in the participation/acceptable performance in the different tests. In addition, the field test and force platform measurements may partially reflect different aspects of balance abilities.

CONCLUSION

The results of the present study provide normative values for force platform balance tests at an age of 30 years and above. Deterioration in balance function clearly starts at relatively young ages and further accelerates from at about 60 years upwards. Due to systematic differences between males and females, separate normative values for both sexes are needed. Due to marked ceiling effects the field test can only be recommended for older individuals, aged >/=60. On the other hand, force platform registrations in the more demanding tests (semi-tandem and tandem stands) suffer from floor effects in the oldest age groups.

Sensitization of Gram-negative bacteria to antibiotics and complement by a nontoxic oligopeptide

A major virulence factor of bacteria that cause generalized infections is their resistance to the lytic action of the complement cascade, an important defence mechanism of the host. Invasive Gram-negative enteric bacteria, which cause about one-third of all bacteraemic infections, are completely resistant to lysis by complement, even in the presence of hyperimmune serum. The same bacteria are also resistant to many antibiotics that are effective therapeutic agents against other bacteria, as the outermost surface layer (the outer membrane) of the bacteria functions as a permeability barrier. Here we show that it is possible to sensitize such bacteria to both complement and antibiotics by using an agent that binds to the outer membrane. This agent is a nontoxic derivative of polymyxin which by itself has no bactericidal action.

Polycations as outer membrane-disorganizing agents

The outer membrane-disorganizing effect of a short (10-min) treatment with polycationic agents was studied with smooth Salmonella typhimurium used as a test organism. The polycationic agents were the protamine salmine, a lysine polymer with 20 lysine residues (lysine20), and the deacylated polymyxin B derivative polymyxin B nonapeptide. Two different types of outer membrane-disorganizing were found. Protamine and lysine20 released 20 to 30% of the lipopolysaccharide from the outer membrane and sensitized the bacteria to the anionic detergent sodium dodecyl sulfate but did not (under these conditions) make the bacteria permeable to the hydrophobic probes fusidic acid and actinomycin D. In contrast, polymyxin B nonapeptide did not release lipopolysaccharide or sensitize the bacteria to sodium dodecyl sulfate but made the outer membrane permeable to the hydrophobic probes. None of the agents was bactericidal under the conditions used or caused any leakage of periplasmic beta-lactamase. Polymyxin B was used as a reference and showed characteristic outer membrane-disorganizing action. In thin-section electron microscopy, polymyxin B nonapeptide caused the appearance of long, narrow, finger-like projections on the outer membrane. Protamine and lysine20 caused a distinctly wrinkled appearance of the outer membrane but no projections.

Polycations sensitize enteric bacteria to antibiotics

Polymyxin B nonapeptide, a polymyxin B derivative which lacks the fatty acyl part and the bactericidal activity of polymyxin, was shown to sensitize smooth encapsulated Escherichia coli (O18:K1) and smooth Salmonella typhimurium to hydrophobic antibiotics (novobiocin, fusidic acid, erythromycin, clindamycin, nafcillin, and cloxacillin). The polymyxin B nonapeptide-treated bacteria were as sensitive to these antibiotics as are deep rough mutants. A lysine polymer with 20 lysine residues (lysine 20) had a largely similar effect. Larger lysine polymers and the protamine salmine were bactericidal but, at sublethal concentrations, sensitized the strains to the antibiotics mentioned above, whereas lysine4, streptomycin, cytochrome c, lysozyme, and the polyamines cadaverine, spermidine, and spermine had neither bactericidal nor sensitizing activity.

BRCT domain-containing protein TopBP1 functions in DNA replication and damage response

Topoisomerase IIbeta-binding protein (TopBP1), a human protein with eight BRCT domains, is similar to Saccharomyces cerevisiae Dpb11 and Schizosaccharomyces pombe Cut5 checkpoint proteins and closely related to Drosophila Mus101. We show that human TopBP1 is required for DNA replication and that it interacts with DNA polymerase epsilon. In S phase TopBP1 colocalizes with Brca1 to foci that do not represent sites of ongoing DNA replication. Inhibition of DNA synthesis leads to relocalization of TopBP1 together with Brca1 to replication forks, suggesting a role in rescue of stalled forks. DNA damage induces formation of distinct TopBP1 foci that colocalize with Brca1 in S phase, but not in G(1) phase. We also show that TopBP1 interacts with the checkpoint protein hRad9. Thus, these results implicate TopBP1 in replication and checkpoint functions.

Lipopolysaccharides of polymyxin B-resistant mutants of Escherichia coli are extensively substituted by 2-aminoethyl pyrophosphate and contain aminoarabinose in lipid A

Lipopolysaccharides (LPS) of two polymyxin-resistant (pmr) mutants and the corresponding parent strain of Escherichia coli were chemically analysed for composition and subjected to 31P-NMR (nuclear magnetic resonance) for assessment of phosphate substitution. Whereas the saccharide portions, fatty acids, and phosphate contents were similar in wild-type and pmr LPS, the latter contained two- to threefold higher amounts of 2-aminoethanol. The pmr LPS also contained 4-amino-4-deoxy-L-arabinopyranose (L-Arap4N), which is normally not a component of E. coli LPS. This aminopentose has been assigned to be linked to the 4'-phosphate of lipid A. Comparative 31P-NMR analysis of the de-O-acylated LPS of the wild-type and pmr strains revealed that phosphate groups of the pmr LPS were mainly (71-79%) diphosphate diesters, which accounted for only 20% in the wild-type LPS. Diphosphate monoesters were virtually nonexistent in the pmr LPS, whereas they accounted for 42% of all phosphates in wild-type LPS. In the lipid A of the pmr strains, the 4'-phosphate was to a significant degree (35%) substituted by L-Arap4N, whereas in the wild-type LPS the L-ArapN was absent. In the pmr lipid A, 2-aminoethanol was completely substituting the glycosidic pyrophosphate but not the glycosidic monophosphate, forming a diphosphate diester linkage at this position in 40% of lipid A molecules. In the wild-type LPS the glycosidic position of lipid A carried mostly unsubstituted monophosphate and pyrophosphate. Thus the polymyxin resistance was shown to be associated, along with the esterification of the lipid A 4'-monophosphate by aminoarabinose, with extensive esterification of diphosphates in LPS by 2-aminoethanol.

Group of peptides that act synergistically with hydrophobic antibiotics against gram-negative enteric bacteria

A synthetic peptide, KFFKFFKFFK [corrected], consisting of cationic lysine residues and hydrophobic phenylalanine residues was found to sensitize gram-negative bacteria to hydrophobic and amphipathic antibiotics. At a concentration of 3 micrograms/ml, it decreased the MIC of rifampin for smooth, encapsulated Escherichia coli by a factor of 300. Other susceptible bacterial species included Enterobacter cloacae, Klebsiella pneumoniae, and Salmonella typhimurium, but Pseudomonas aeruginosa was resistant. Similar results were obtained with another synthetic peptide, IKFLKFLKFLK [corrected]. The fractional inhibitory concentration indices for the synergism of these peptides with rifampin, erythromycin, fusidic acid, and novobiocin were very close to those determined for the previously characterized potent outer-membrane-disorganizing agents polymyxin B nonapeptide and deacylpolymyxin B. KFFKFFKFFK [corrected] had direct activity against the gram-positive organism Micrococcus strain ML36, was strongly hemolytic, and was as active on polymyxin-resistant E. coli mutants as on their parent. These three attributes made KFFKFFKFFK [corrected] different from polymyxin derivatives and similar to cationic detergents, such as cetylpyridinium chloride. However, whereas the MIC of cetylpyridinium chloride for E. coli is low (0.5 to 4 micrograms/ml), that of KFFKFFKFFK [corrected] is much higher (30 to 100 micrograms/ml). Other groups of synthetic peptides studied included polymyxin-like peptides with an intrachain disulfide bridge. Their synergism with antibiotics was less marked. Still other peptides, including KEKEKEKEKE and KKKKKKFLFL, lacked any synergism with the probe antibiotics.

Effects of a 6-month exercise program on patients with multiple sclerosis: a randomized study

OBJECTIVE

To improve walking and other aspects of physical function with a progressive 6-month exercise program in patients with multiple sclerosis (MS).

METHODS

MS patients with mild to moderate disability (Expanded Disability Status Scale scores 1.0 to 5.5) were randomly assigned to an exercise or control group. The intervention consisted of strength and aerobic training initiated during 3-week inpatient rehabilitation and continued for 23 weeks at home. The groups were evaluated at baseline and at 6 months. The primary outcome was walking speed, measured by 7.62 m and 500 m walk tests. Secondary outcomes included lower extremity strength, upper extremity endurance and dexterity, peak oxygen uptake, and static balance. An intention-to-treat analysis was used.

RESULTS

Ninety-one (96%) of the 95 patients entering the study completed it. Change between groups was significant in the 7.62 m (p = 0.04) and 500 m walk tests (p = 0.01). In the 7.62 m walk test, 22% of the exercising patients showed clinically meaningful improvements. The exercise group also showed increased upper extremity endurance as compared to controls. No other noteworthy exercise-induced changes were observed. Exercise adherence varied considerably among the exercisers.

CONCLUSIONS

Walking speed improved in this randomized study. The results confirm that exercise is safe for multiple sclerosis patients and should be recommended for those with mild to moderate disability.

Increased substitution of phosphate groups in lipopolysaccharides and lipid A of the polymyxin-resistant pmrA mutants of Salmonella typhimurium: a 31P-NMR study

De-O-acylated lipopolysaccharides (LPS) of three polymyxin-resistant Salmonella typhimurium pmrA mutants and their parent strains were analysed by 31P-NMR (nuclear magnetic resonance) in order to assess, in relation to polymyxin resistance, the types and degree of substitution of phosphates of the LPS and lipid A. In the pmrA mutant LPS phosphate diesters predominated over phosphate monoesters, whereas the latter were more abundant in the parent wild-type LPS. The increase in the proportion of phosphate diesters was traced to both the core oligosaccharide and the lipid A part. In the latter, the ester-linked phosphate at position 4' was to a large extent (79-88%) substituted with 4-amino-4-deoxy-L-arabinose, whereas in the wild-type LPS the 4'-phosphate was mainly present as monoester. In each LPS, regardless of the pmrA mutation, the glycosidically linked phosphate of lipid A was largely unsubstituted.

Outer membrane permeability barrier to azithromycin, clarithromycin, and roxithromycin in gram-negative enteric bacteria

Mutations which severely affect the function of the outer membrane of Escherichia coli and Salmonella typhimurium (lpxA and firA mutations of lipid A synthesis and rfaE mutation of the lipopolysaccharide inner-core synthesis) were found to decrease the MICs of erythromycin, roxithromycin, clarithromycin, and azithromycin by factors of 32 to 512, 32 to 1,024, 64 to 512, and 16 to 64, respectively. The sensitization factors for three other hydrophobic antibiotics (rifampin, fusidic acid, and mupirocin) ranged from 16 to 300. The outer membrane permeability-increasing agents polymyxin B nonapeptide (3 micrograms/ml) and deacylpolymyxin B (1 microgram/ml) sensitized wild-type E. coli to azithromycin by factors of 10 and 30, respectively. Quantitatively very similar sensitization to the other macrolides took place. Polymyxin-resistant pmrA mutants of S. typhimurium displayed no cross-resistance to azithromycin. Proteus mirabilis mutants which were sensitized to polymyxin by a factor of > or = 300 to > or = 1,000 had a maximal two- to fourfold increase in sensitivity to azithromycin. These results indicate that azithromycin and the other new macrolides use the hydrophobic pathway across the outer membrane and that the intact outer membrane is an effective barrier against them. Furthermore, the results indicate that azithromycin, in contrast to polymyxin, does not effectively diffuse through the outer membrane by interacting electrostatically with the lipopolysaccharide.

Outer membrane permeability barrier disruption by polymyxin in polymyxin-susceptible and -resistant Salmonella typhimurium

In contrast to their polymyxin-susceptible parent strains, polymyxin-resistant Salmonella typhimurium mutants (pmrA strains) did not lose their outer membrane permeability barrier to macromolecules such as lysozyme and periplasmic proteins upon polymyxin treatment. The sensitization of pmrA strains to deoxycholate-induced lysis required 10-times-higher polymyxin concentrations than did the sensitization of the parent strains. These findings indicate that the pmrA mutation affects the outer membrane and decreases its susceptibility to polymyxin. By contrast, the pmrA mutants did not differ from their parents in the uptake of gentian violet after treatment with polymyxin, suggesting a degree of specificity in the pmrA effect in the outer membrane.

Outer membrane permeability barrier in Escherichia coli mutants that are defective in the late acyltransferases of lipid A biosynthesis

The tight packing of six fatty acids in the lipid A constituent of lipopolysaccharide (LPS) has been proposed to contribute to the unusually low permeability of the outer membrane of gram-negative enteric bacteria to hydrophobic antibiotics. Here it is shown that the Escherichia coli msbB mutant, which elaborates defective, penta-acylated lipid A, is practically as resistant to a representative set of hydrophobic solutes (rifampin, fusidic acid, erythromycin, clindamycin, and azithromycin) as the parent-type control strain. The susceptibility index, i.e., the approximate ratio between the MIC for the msbB mutant and that for the parent-type control, was maximally 2.7-fold. In comparison, the rfa mutant defective in the deep core oligosaccharide part of LPS displayed indices ranging from 20 to 64. The lpxA and lpxD lipid A mutants had indices higher than 512. Furthermore, the msbB mutant was resistant to glycopeptides (vancomycin, teicoplanin), whereas the rfa, lpxA, and lpxD mutants were susceptible. The msbB htrB double mutant, which elaborates even-more-defective, partially tetra-acylated lipid A, was still less susceptible than the rfa mutant. These findings indicate that hexa-acylated lipid A is not a prerequisite for the normal function of the outer membrane permeability barrier.

Susceptibility of gram-negative bacteria to polymyxin B nonapeptide

Subinhibitory concentrations of polymyxin B nonapeptide sensitized all 21 polymyxin-susceptible gram-negative bacterial strains studied to hydrophobic antibiotics such as fusidic acid, novobiocin, and erythromycin. The susceptibility increases were usually 30- to 300-fold. The strains included representatives of Escherichia coli with different O- and K-antigens, Klebsiella pneumoniae, Klebsiella oxytoca, Enterobacter cloacae, Enterobacter agglomerans, Salmonella typhimurium, Acinetobacter calcoaceticus, Pseudomonas aeruginosa, and Pseudomonas maltophilia. In contrast, polymyxin-resistant strains (Proteus mirabilis, Proteus vulgaris, Morganella morganii, Providencia stuartii, and Serratia marcescens) were resistant to the action of polymyxin B nonapeptide.

The lipid A biosynthesis mutation lpxA2 of Escherichia coli results in drastic antibiotic supersusceptibility

The conditionally lethal lpxA2 mutant of Escherichia coli, which lacks detectable UDP-N-acetylglucosamine acyltransferase activity and which produces greatly reduced amounts of lipid A after a shift to 42 degrees C (S. Galloway and C. R. H. Raetz, J. Biol. Chem. 265:6394-6402, 1990), was found to be, at conditions which promote normal growth, remarkably susceptible to a number of antibiotics. The MICs of hydrophobic antibiotics, such as rifampin, erythromycin, clindamycin, and fusidic acid, were 32- to greater than 128-fold lower for the lpxA2 strain than for the parent type strain, and those of the peptide antibiotics vancomycin and bacitracin were 32- and 256-fold lower, respectively. Futhermore, the lpxA2 strain was found to be sensitive to hypoosmotic conditions. Comparisons with the other characterized outer membrane permeability mutants, such as the heptose-deficient strains of E. coli and Salmonella typhimurium, the acrA and abs mutants of E. coli, and the ssc-1 and class SS-B mutants of S. typhimurium, indicated that the lpxA2 mutant had characteristically the most antibiotic-supersusceptible phenotype. These findings advocate the possible use of the lpxA2 strain as a tool in various fields of basic and applied bacterial research in which the impermeability of the outer membrane currently poses problems.

Neonatal Candida parapsilosis outbreak with a high case fatality rate

A Candida parapsilosis outbreak of 58 cases in a neonatal intensive care unit lasted for 55 months. Patients infected by or colonized with C. parapsilosis were mainly very low birth weight infants (birth weight < 1500 g). Their mean birth weight was 817 g and their mean gestational age was 28 weeks. Statistical analysis including logistic regression confirmed that prematurity was the main risk factor. The analysis also suggested that C. parapsilosis infection (or colonization) was associated with a poor prognosis. In infants with gestational age < 29 weeks the risk for death in C. parapsilosis-infected patients was 16-fold greater than in those with no C. parapsilosis infection. The case fatality rate of C. parapsilosis patients was higher than that of the controls (9 of 23 vs. 1 of 40; P < 0.0001). The outbreak was most likely a result of cross-infection because C. parapsilosis could be isolated only from the patients and from the hands of four nurses immediately after they had cared for a colonized patient. Cessation of the outbreak was temporally associated with long term parenteral fluconazole (6 mg/kg/day) prophylaxis.

Increased outer membrane resistance to ethylenediaminetetraacetate and cations in novel lipid A mutants

Polymyxin-resistant pmrA mutants of Salmonella typhimurium differed from their parents in that they were resistant to tris(hydroxymethyl)aminomethane-ethylenediaminetetraacetate-lysozyme, tris(hydroxymethyl)aminomethane-ethylenediaminetetraacetate-deoxycholate, and tris(hydroxymethyl)aminomethane-ethylenediaminetetraacetate-bacitracin. Tris(hydroxymethyl)aminomethane-ethylenediaminetetraacetate released about 50% less lipopolysaccharide from the pmrA strains than from the parental strains when the bacteria were grown in L-broth containing 2 mM Ca2+. Protamine, polylysine, octapeptin, benzalkonium chloride, cold NaCl, cold MgCl2, or cold tris(hydroxymethyl)aminomethane hydrochloride (pH 7.2) caused no leakage or markedly less leakage of periplasmic beta-lactamase from a pmrA mutant than from its parent strain. pmrA mutants were more resistant than their parent strains to protamine and polylysine but not to octapeptin or benzalkonium chloride, as measured by the ability of these agents to kill the bacteria or to sensitize them to deoxycholate-induced lysis. The pmrA strains did not differ from their parent strains in sensitivity to several antibiotics, in porin function (as measured by cephaloridine diffusion across the outer membrane), or in outer membrane-associated phospholipase A activity.

Decreased binding of polymyxin by polymyxin-resistant mutants of Salmonella typhimurium

Polymyxin-resistant pmrA strains were shown to absorb only about 25% of the amount of polymyxin absorbed by the corresponding polymyxin-sensitive parent strains. The lipopolysaccharide from the pmrA strains bound less polymyxin than the lipopolysaccharide from the parent strains.

New Salmonella typhimurium mutants with altered outer membrane permeability

We describe three new classes of Salmonella typhimurium mutants with increased sensitivity to hydrophobic agents. In contrast to many previously described mutants, the phage sensitivity pattern of these mutants did not give any indication of defective lipopolysaccharide. Furthermore, they had no detectable changes in their phospholipid or outer membrane protein composition, and their growth rate and cell morphology were normal. Class B mutants were nearly as sensitive to novobiocin, fusidic acid, erythromycin, rifampin, and clindamycin as are deep rough (heptoseless) mutants; in addition they were sensitive to methicillin, penicillin (to which heptoseless mutants are resistant), gentian violet, and anionic and cationic detergents. Class A and C mutants had less sensitive, but characteristic phenotypes. None of the three classes were sensitive to serum bactericidal action. The class B mutation mapped between map positions 7 and 11 on the S. typhimurium chromosome, and the class C mutation mapped between positions 5 and 7. The map position for the class A mutation remained undefined, but it was separate from the class B and C mutations and, like those, did not correspond to any gene loci known to participate in the synthesis of major outer membrane constituents.

vanA and vanB incorporate into an endemic ampicillin-resistant vancomycin-sensitive Enterococcus faecium strain: effect on interpretation of clonality

Clonal spread and horizontal transfer in the spread of vancomycin resistance genes were investigated. Multiplex PCR, pulsed-field gel electrophoresis (PFGE), hybridization of enterococcal plasmids with the vanA and vanB probes, and sequencing of a fragment of vanB were used in the analysis. Before May 1996, 12 vancomycin-resistant Enterococcus faecium (VRE) isolates were found in Finland. Between May 1996 and October 1997, 156 VRE isolates were found in the Helsinki area. Between December 1997 and April 1998, fecal samples from 359 patients were cultured for VRE. One new case of colonization with VRE was found. During the outbreak period, 88% (137 of 155) of the VRE isolates belonged to two strains (VRE types I and II), as determined by PFGE. Each VRE type I isolate possessed vanB, and five isolates also had vanA. Of the 34 VRE type II isolates, 27 possessed vanA and 7 possessed vanB. Fifteen of 21 (71%) ampicillin-resistant, vancomycin-sensitive E. faecium (VSE) isolates found during and after the outbreak period in one ward were also of type II. Two VSE type II isolates were found in the hospital before the outbreak in 1995. By PFGE, the three groups (vanA, vanB, or no van gene) of type II shared the same band differences with the main type of VRE type II with vanA. None of the differences was specific to or determinative for any of the groups. Our material suggests that vanA and vanB incorporate into an endemic ampicillin-resistant VSE strain.