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PubMed1996

Genetics of glycopeptide resistance in enterococci.

Glycopeptide resistance in enterococci is phenotypically and genotypically heterogeneous. The genes responsible for inducible resistance to high levels of vancomycin and teicoplanin (VanA phenotype) are carried by the 10,851-bp Tn1546 transposon. Transposition of Tn1546 into self-transferable plasmids and subsequent transfer by conjugation appears to be responsible for the dissemination of this type of resistance. Nine polypeptides are encoded by Tn1546 that belong to five functional groups: transposition functions (ORF1 and ORF2), regulation of resistance gene expression (VanR and VanS), synthesis of depsipeptide D-Ala-D-lactate (VanH and VanA), hydrolysis of D-Ala-D-Ala-containing peptidoglycan precursors (VanX and VanY), and low-level teicoplanin resistance (VanZ). VanB-type resistance (various levels of resistance to vancomycin and susceptibility to teicoplanin) is also due to production of D-Ala-D-Lac. The VanB ligase of VanB-type strains is structurally and functionally similar to VanA. The vanB gene was found on composite transposon Tn1547, which, in turn, was part of larger conjugative chromosomally located elements (90 to 250 kb). In contrast to acquired VanA- and VanB-type resistance, VanC-type resistance (low level of resistance to vancomycin and susceptibility to teicoplanin) is an intrinsic property of motile enterococci. Resistance in these species is due to synthesis of dipeptide D-Ala-D-Ser by VanC ligases leading to production of cell wall precursors with reduced vancomycin affinity.

Anti-Bacterial Agents↗
PubMed1998

Antimicrobial resistance in staphylococci and enterococci in 10 Portuguese hospitals in 1996 and 1997. POSGAR. Portuguese Study Group of Antimicrobial Resistance.

During a 2-year period, 10 Portuguese hospitals located throughout the country studied antimicrobial susceptibilities of clinically relevant staphylococci and enterococci. Of more than 12,000 Staphylococcus aureus isolates tested, two main patterns were found, methicillin-sensitive organisms most of them resistant only to penicillin but a few to other antimicrobials and methicillin-resistant S. aureus (MRSA) strains (prevalence 48.2%) resistant to most of the antimicrobials tested and uniformly susceptible to vancomycin. Among coagulase-negative staphylococci (CNS), 71% of S. epidermidis (approximately 5,000 isolates tested) and 84% S. haemolyticus (approximately 1,000 isolates tested) were also resistant to methicillin as well as most other antimicrobials except vancomycin. Most of the 5,000 Enterococcus faecalis isolates tested were susceptible to ampicillin and vancomycin, in contrast to 650 E. faecium isolates, 70% of which were resistant to ampicillin and 20% to vancomycin and all other antibiotics. A high prevalence of aminoglycoside resistance occurred in both Enterococcus species. This survey showed that resistance profiles of staphylococci and enterococci hospital isolates have not changed in the last 5 years in Portugal, with the exception of the rise in vancomycin resistance in E. faecium. The high prevalence of methicillin resistance in S. aureus and in the CNS remains an issue of medical concern.

Anti-Bacterial Agents↗
PubMed1992

Mechanisms of resistance to growth inhibition and killing by beta-lactam antibiotics in enterococci.

Enterococci are characterized by an intrinsic resistance to growth inhibition by beta-lactam antibiotics. The low susceptibility of enterococci to beta-lactam antibiotics is associated with the synthesis of a particular penicillin-binding protein (PBP) that has a low affinity for beta-lactam agents. This protein appears to be capable of taking over the function of the other PBPs when they are saturated with beta-lactam molecules or inactivated by mutations. A quantitative correlation can be established between the binding of several beta-lactam molecules to the low-affinity PBP and the minimal inhibitory concentration for enterococcal strains. In contrast, the mechanism of enterococcal resistance to the bactericidal activity of beta-lactam agents that inhibit growth at relatively low concentrations appears to be associated with an alteration in the pattern of autolytic enzyme activity. In particular, lack of or poor activity of an autolytic enzyme appears to be responsible for the paradoxical bactericidal response often exhibited by clinical isolates of Enterococcus faecalis in the presence of penicillin.

Anti-Bacterial Agents↗
PubMed1992

Resistance of enterococci to aminoglycosides and glycopeptides.

High-level resistance to aminoglycosides in enterococci often is mediated by aminoglycoside-modifying enzymes, and the corresponding genes generally are located on self-transferable plasmids. These enzymes are similar to those in staphylococci but differ from the modifying enzymes of gram-negative bacteria. Three classes of enzymes are distinguished, depending upon the reaction catalyzed. All but amikacin and netilmicin confer high-level resistance to the antibiotics that are modified in vitro. However, the synergistic activity of these last two antibiotics in combination with beta-lactam agents can be suppressed, as has always been found in relation to high-level resistance to the aminoglycosides. Acquisition of glycopeptide resistance by enterococci recently was reported. Strains of two phenotypes have been distinguished: those that are resistant to high levels of vancomycin and teicoplanin and those that are inducibly resistant to low levels of vancomycin and susceptible to teicoplanin. In strains of Enterococcus faecium highly resistant to glycopeptides, we have characterized plasmids ranging from 34 to 40 kilobases that are often self-transferable to other gram-positive organisms. The resistance gene vanA has been cloned, and its nucleotide sequence has been determined. Hybridization experiments showed that this resistance determinant is present in all of our enterococcal strains that are highly resistant to glycopeptides. The vanA gene is part of a cluster of plasmid genes responsible for synthesis of peptidoglycan precursors containing a depsipeptide instead of the usual D-alanyl-D-alanine terminus. Reduced affinity of glycopeptides to these precursors confers resistance to the antibiotics.

Aminoglycosides↗
PubMed1992

Contribution of animal models in the search for effective therapy for endocarditis due to enterococci with high-level resistance to gentamicin.

Earlier studies suggest that ampicillin and amoxicillin are more effective than other beta-lactam agents in killing enterococci, although beta-lactam agents are slowly and incompletely bactericidal against most strains of Enterococcus faecalis. We previously showed that continuous infusion of ampicillin is more effective than intermittent administration in decreasing the number of enterococci in valvular vegetations of rats with catheter-induced endocarditis that are treated for 5 days. In this model, we found ampicillin plus sulbactam more effective than ampicillin alone against a beta-lactamase-producing enterococcal strain with high-level resistance to gentamicin. Daptomycin therapy produced results approximately equal to those of ampicillin plus sulbactam. Vancomycin and teicoplanin given for 5 days at doses producing equivalent serum levels had approximately equal efficacy. However, 10-day therapy with low-dose teicoplanin was considerably more effective than similar treatment with vancomycin. High-dose teicoplanin for 5 days produced sterile valves in 82% of the animals studied.

Ampicillin↗
PubMed1997

Enterococci acquire new kinds of resistance.

In recent years, enterococci have become increasingly resistant to a broad range of antimicrobial agents. The development of high-level resistance to aminoglycosides, penicillins, and glycopeptides singly and in combination has important clinical implications. Strains of Enterococcus faecium that are resistant to every useful available antibiotic have been described. Resistance to penicillin can be due to overproduction of penicillin-binding protein (which has low affinity for penicillins) or to production of beta-lactamase. High-level resistance of enterococci to gentamicin is due to the synthesis of a modifying enzyme. In this case, the synergistic activity of the combination of penicillin with any aminoglycoside (except for streptomycin) is totally abolished. Acquired resistance to glycopeptides is often plasmid-mediated and is associated with a major epidemic potential since certain plasmids are self-transferable from E. faecium to a variety of gram-positive organisms, including Staphylococcus aureus.

Cross Infection↗
PubMed1986

Comparative bactericidal activity of penicillin-netilmicin and penicillin-gentamicin against enterococci.

The synergistic bactericidal activity of netilmicin in combination with penicillins was compared with that of gentamicin and streptomycin against 16 clinical isolates of enterococci. In a macrodilution chessboard assay against multiple combinations of penicillin, gentamicin and netilmicin, bactericidal activity uniformly occurred at two- to four-fold lower concentrations of penicillin + netilmicin than with penicillin + gentamicin. With four strains, penicillin + netilmicin produced up to ten-fold greater killing than penicillin + gentamicin after 6 h of incubation. With one strain, 3 X log10 greater killing occurred with netilmicin after 24 h. Netilmicin was two- to four-fold more active than gentamicin when combined with penicillinase-resistant penicillins. The bactericidal activity of netilmicin against enterococci is equal to or greater than that of gentamicin, either alone or when combined with penicillins.

Drug Synergism↗
PubMed1986

Preliminary observations on the influence of antibiotics on the ecology of Escherichia coli and the enterococci in the faecal flora of healthy young chickens.

Two separate replicated experiments are described. In the first the influence of oxytetracycline on the Escherichia coli flora was assessed, while in the second the effect of tylosin on the enterococci was investigated. In both experiments the administration of the antibiotic was associated with an increase in the average proportion of isolates resistant to the agent although in experiment 1 the agent had no apparent influence on either the total number of E. coli strains, differentiated by biotype and resistance pattern, or the number of 'new' strains per sampling. On the other hand significant differences were noted between the two replicates and also in relation to the age of the birds. In the second experiment fewer enterococcal strains were isolated from the birds dosed with tylosin but since fewer strains on average were isolated from the samples collected prior to dosing it is probable that this difference was due to factors other than the influence of the antibiotic. The enterococci were speciated and the two most commonly isolated were Streptococcus faecalis and S. faecium. The isolation rate of each was expressed as a proportion of the total number of enterococcal isolates per sample and when considered in relation to both dosing and the age of the bird the interaction dosing X age was statistically significant for both species. However, the differences did not appear particularly great and it was possible that the differences were of no practical importance from an ecological point of view.

Animals↗
PubMed1990

Synergy between penicillin and gentamicin against enterococci.

The role of active uptake in aminoglycoside activity against penicillin-treated enterococci was studied by viable counts and ATP determinations. Penicillin and gentamicin gave synergistic bactericidal and post-antibiotic effects (PAEs) which were partially reduced by sodium azide, an electron transport inhibitor, and totally blocked in the presence of both sodium azide and EDTA, which chelates divalent cations. EDTA and gentamicin showed marked synergy in both 'killing curve' and PAE experiments. This synergy was completely inhibited by sodium azide. The data indicate that the activity of gentamicin against enterococci that have been damaged by penicillin or EDTA is energy-dependent. This is consistent with present theories of gentamicin uptake via transportation drive by a protonmotive force.

Adenosine Triphosphate↗
PubMed1995

In-vitro activity of two glycylcyclines against enterococci resistant to other agents.

Two new glycylcyclines, CL 329,998 and CL 331,002, were tested for in-vitro activity against 178 clinical strains of enterococci which were resistant to one or more of the commonly used agents (ampicillin, high level gentamicin, vancomycin and teicoplanin). Both glycylcyclines demonstrated good activity (MICs < or = 0.5 mg/L) against all isolates tested, including those strains which demonstrated multiple resistance. As resistant enterococci are increasing in importance, new agents with activity against these strains are urgently required. Glycylcyclines have in-vitro activity which suggests they may be useful agents for treatment of infections caused by these organisms.

Anti-Bacterial Agents↗
PubMed2000

Enterococci with reduced susceptibility to vancomycin in New Zealand.

This study was conducted to determine the prevalence of vancomycin-resistant enterococci (VRE) in the stools of hospitalized patients with possible antibiotic-associated diarrhoea. From 176 faecal samples collected during 1997 and 1998, 66 strains of enterococci were recovered using vancomycin enrichment techniques. Only six of these displayed reduced susceptibility to vancomycin (MIC 8-12 mg/L). All VRE were positive for the presence of the vanC gene. Based on motility, pigment production and automated Gram-positive identification (GPI Vitek card), four of these six VRE isolates were identified as Enterococcus gallinarum. The remaining two isolates were non-motile and therefore were considered to be Enterococcus faecium. However, 16S rDNA sequence analysis and positive methyl-alpha-D-glucopyranoside tests indicated that they were non-motile species of E. gallinarum. This is consistent with the intrinsic, low-level vanC-1-mediated resistance associated with this species. Pulsed-field gel electrophoresis analysis comparisons between the VRE indicated genetic relatedness between some strains. This work confirms that vancomycin-resistant E. faecium and Enterococcus faecalis are rare in New Zealand.

Anti-Bacterial Agents↗
PubMed2001

Antimicrobial susceptibility patterns of enterococci in intensive care units in Sweden evaluated by different MIC breakpoint systems.

Three hundred and twenty-two (322) clinical isolates were collected from patients admitted to intensive care units (ICUs) at eight Swedish hospitals between December 1996 and December 1998. Of the isolates, 244 (76%) were Enterococcus faecalis, 74 (23%) were Enterococcus faecium and four (1%) were other Enterococcus spp. MICs of ampicillin, imipenem, meropenem, piperacillin/tazobactam, ciprofloxacin, trovafloxacin, clinafloxacin, gentamicin, streptomycin, vancomycin, teicoplanin, quinupristin/dalfopristin, linezolid and evernimicin were determined by Etest. Susceptible and resistant isolates were defined according to the species-related MIC breakpoints of the British Society for Antimicrobial Chemotherapy (BSAC), the National Committee for Clinical Laboratory Standards (NCCLS) and the Swedish Reference Group for Antibiotics (SRGA). Tentative breakpoints were applied for new/experimental antibiotics. Multidrug resistance among enterococci in ICUs is not uncommon in Sweden, particularly among E. faecium, and includes ampicillin resistance and concomitant resistance to fluoroquinolones. Almost 20% of E. faecalis isolates showed high-level resistance to gentamicin and concomitant resistance to fluoroquinolones. Vancomycin-resistant enterococci were only found sporadically. Among the new antimicrobial agents, linezolid and evernimicin showed the best activity against all enterococcal isolates. There was good concordance between the BSAC, NCCLS and SRGA breakpoints in detecting resistance. When applying the SRGA breakpoints for susceptibility, isolates were more frequently interpreted as intermediate. This might indicate earlier detection of emerging resistance using the SRGA breakpoint when the native population is considered susceptible, but with the risk that isolates belonging to the native susceptible population will be incorrectly interpreted as intermediate.

Anti-Bacterial Agents↗
PubMed2001

In vitro activity of LY333328 (oritavancin) against Gram-positive aerobic cocci and synergy with ciprofloxacin against enterococci.

Gram-positive cocci are a major cause of nosocomial bacteraemias and are often resistant to most antibiotics. The emergence of enterococci with reduced susceptibility to vancomycin has created an urgent need for novel antibiotics to combat infections associated with these bacteria. In this study the in vitro activity of LY333328 (oritavancin), a semi-synthetic glycopeptide, was evaluated. LY333328 was effective against all strains of staphylococci, streptococci and enterococci tested. A combination of LY333328 and ciprofloxacin was additive for 50% of Enterococcus faecium strains resistant to both vancomycin and ciprofloxacin, and for 100% of vancomycin-susceptible and either ciprofloxacin-susceptible or -resistant strains.

Anti-Bacterial Agents↗
PubMed2004

Molecular study of vancomycin-resistant enterococci isolated from humans and from food in a cattle-rearing area of France.

OBJECTIVES: Study possible links between vancomycin-resistant enterococci strains isolated from human stool samples and from pork or poultry food products. METHODS: One hundred and eleven vancomycin-resistant enterococci strains (15 VanA and 96 VanC) were isolated from human stool samples and from pork or poultry food products. Characterization of the Tn1546-like element of the 15 VanA strains was realized by restriction analysis of PCR products and polymorphism study. The 96 strains of VanC phenotype (75 Enterococcus gallinarum and 21 Enterococcus casseliflavus) were analysed by pulsed-field gel electrophoresis (PFGE). RESULTS: In the study described here, polymorphism of the Tn1546-like element enabled the establishment of five groups. Groups III, IV and V were found only in human strains. Groups I and II were found to occur in strains isolated from humans and from food, suggesting a possible transfer of the Tn1546-like element. The isolates from Group I harboured the whole Tn1546 element. In Group II, the five strains possessed a novel Tn1546-like element, characterized by a single-nucleotide difference in the vanX gene and a deletion upstream from the nucleotide 164. Analysis by PFGE of the 75 E. gallinarum strains revealed 20 different patterns. One pattern was shared by isolates from pork food and human samples. None of the 21 E. casseliflavus strains tested was found to share similar PFGE patterns. CONCLUSIONS: Results tend to support the possible transfer of the Tn1546-like element between strains of VanA phenotype. Concerning VanC phenotype strains, the transfer was not demonstrated.

Agriculture↗
PubMed2005

Evidence of vancomycin resistance gene transfer between enterococci of human origin in the gut of mice harbouring human microbiota.

OBJECTIVES: Potential intra- and inter-species transfers of vancomycin resistance genes (vanA gene cluster) between Enterococcus strains were evaluated in the gut of heteroxenic mice harbouring a human microbiota. METHODS: Mice colonized with a stable population of E. faecium 64/3 or E. faecalis JH2-2 recipient strain and harbouring an enterococci-free human microbiota were obtained. Donor strain E. faecium HC-VI2 of clinical origin was administered orogastrically to these mice and transfers were evaluated over time in faecal samples. RESULTS: Only intraspecies transfers were detected in the digestive tract (DT) of mice harbouring a human microbiota. E. faecium 64/3 transconjugants were detected at several sampling times over the 60 day experiment to levels up to 10(3) cfu/g of faeces, but they did not steadily colonize the DT. CONCLUSIONS: Here, we show for the first time that transfer of the vanA gene cluster can occur between Enterococcus strains in the DT colonized with a human microbiota and in the absence of selective pressure. The colonization properties of other enterococci transconjugants and the influence of vancomycin intake should be further investigated since transfers in the DT of animals and humans might contribute to emergence and dissemination of new vancomycin-resistant bacteria.

Animals↗
PubMed2006

Cell preparation of Enterococcus faecalis strain EC-12 prevents vancomycin-resistant enterococci colonization in the cecum of newly hatched chicks.

The use of antimicrobials in broilers is considered to be a cause of the appearance of vancomycin-resistant enterococci (VRE). Once VRE penetration occurs, whatever its origin, it is difficult to expel the enterococci from the intestine because of their multiple resistance, whether natural or acquired. In this study, we evaluated the prevention of VRE colonization by the dietary supplementation of a cell-wall preparation of Enterococcus faecalis strain EC-12 (EC-12) in newly hatched broilers that were challenged by experimental infection with VRE. The chicks were fed a basal diet supplemented with 0.05% (wt/wt) EC-12 powder for 15 d. The control group and that administered Lactobacillus sp. were fed the basal diet. The VRE challenge was administered orally when the chicks were 2 d old (d 0). Dietary EC-12 reduced VRE colonization in the intestine from d 3 to 14. Total IgA in the cecal digesta and total IgG in the serum were higher on d 14 in the EC-12 treatment group. However, VRE-specific and EC-12-specific antibodies were not affected in serum. Hence, it appeared that dietary EC-12 stimulated the gut immune system and reinforced the immune reaction against the VRE challenge to accelerate its defecation from the chick intestine.

Animals↗
PubMedDate not supplied

Alternate antimicrobial therapy for vancomycin-resistant enterococci burn wound infections.

Survival after a major thermal burn is precarious and fraught with difficult complications associated with hypermetabolism, gut or respiratory dysfunction, and infection. Clinicians must be cognizant of a new threat to the patient with burn injuries--the emergence of vancomycin-resistant enterococci (VRE). In an analysis of 31 clinical isolates obtained during acute burn hospitalization, an optimal antimicrobial therapy for VRE has been identified. All VRE cultures were inoculated to the MicroScan Gram-Positive Breakpoint Combo Panel #8 (Dade Microscan, Inc, Sacramento, Calif), which speciates the enterococci, provides antimicrobial susceptibility patterns (including vancomycin) and a biotype, and examines streptomycin and gentamicin synergy. Eleven (35.5%) of the 31 isolates were identified as E faecium and 20 (64.5%) as E faecalis. All isolates were susceptible to chloramphenicol and tetracycline, whereas only half were sensitive to gentamicin synergy screen. All other antimicrobials screened against VRE were either ineffective or of limited effect. Our preliminary data supports the initiation of chloramphenicol therapy when a VRE burn wound infection is encountered or suspected.

Anti-Bacterial Agents↗
PubMed1997

Evaluation of arbitrarily primed PCR analysis and pulsed-field gel electrophoresis of large genomic DNA fragments for identification of enterococci important in human medicine.

The increasing problems encountered with enterococcal nosocomial infections and the intrinsic and acquired resistance of the enterococci to different antimicrobial compounds highlight the need for a rapid identification technique. Enterococcus faecalis is readily identified by biochemical tests, but species differentiation within the Enterococcus faecium and Enterococcus gallinarum species groups is less well established. In the present study, 66 strains representing the most prevalent human enterococci were used to develop a PCR-based species-specific identification protocol. Whole-cell protein analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis was used as a reference method for species identification. In addition, the genomic SmaI macro-restriction fragment distribution of all of the strains was examined by pulsed-field gel electrophoresis (PFGE). Oligonucleotide D11344-primed PCR was as discriminative as whole-cell protein analysis and resulted in more easily interpreted band patterns. This PCR-based technique allowed identification of clinical isolates by visual examination of the DNA profiles obtained. The inability of both methods to discriminate between Enterococcus casseliflavus and Enterococcus flavescens brought into question the species status of E. flavescens. PFGE did not result in species-discriminative DNA bands or band patterns, but proved to be superior for interpretation of interstrain relationships.

Bacterial Typing Techniques↗