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A vancomycin-dependent VanA-type Enterococcus faecalis strain isolated in Japan from chicken imported from China.

AIMS: The characterization of KC122.1, which is a vancomycin-dependent VRE (Vancomycin-resistant enterococci) (Enterococcus faecalis) and the first case in Japan of a VRE isolate obtained from chicken meat imported from China. METHODS AND RESULTS: PCR amplification of vanA, vanS and ddl gene and direct sequencing of the PCR products were performed. KC122.1 was a VanA-type VRE showing high-level vancomycin resistance and low-level teicoplanin resistance, and its vanS gene had three point mutations. The ddl gene of KC122.1 was sequenced and two changes were found at the ninth codon (GCC-GAC) and the stop codon (TAA-CAA). The latter change was also found in the laboratory strain E. faecalis FA2-2. CONCLUSIONS: Three point mutations in vanS resulted in high-level vancomycin resistance and low-level teicoplanin resistance. The change at the ninth codon resulted in the inactivation of the ddl gene and vancomycin-dependent growth. An eight amino acid extension at the C-terminal did not impair the function of the D-Ala : D-Ala ligase. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first example of the isolation of VRE from chicken meat imported from China and the first vancomycin-dependent VRE from a nonhuman source.

Animals↗

Evaluation of Chromocult enterococci agar for the isolation and selective enumeration of Enterococcus spp. in broilers.

AIMS: To investigate the productivity and specificity of a new chromogenic enterococci selective medium (Chromocult enterococci agar) recently developed by Merck. METHODS AND RESULTS: The study was carried out comparing Chromocult enterococci agar with MRS agar (Merck), a basal lactic acid bacteria medium in current use. A total of 216 faecal samples from poultry were collected and enterococci populations were counted. Likewise, 100 randomly selected strains were identified for each medium. The differences found between the two media were analysed and discussed. CONCLUSIONS: A good sensitivity of 98% was obtained for Chromocult agar and all false-positive isolates obtained were identified as Leuconostoc spp. However significant differences (P<0.01) were obtained between the enterococci species isolation rates identified from these two media, suggesting the poor growth of some species in Chromocult enterococci agar. Viable counts of Enterococcus spp. obtained with MRS agar were significantly higher than those obtained with Chromocult enterococci agar. SIGNIFICANCE AND IMPACT OF THE STUDY: The use of chromogenic media for microbiological analysis is increasing. Independent studies are important to evaluate newly developed chromogenic media.

Agar↗

Survival of Listeria monocytogenes and Enterococcus faecium in sludge evaluated by real-time PCR and culture methods.

AIMS: This study evaluates the behaviour in spiked sludge of a pathogenic bacteria, Listeria monocytogenes, by cultural and molecular techniques, and compares its survival with the one of a faecal indicator, Enterococcus faecium. METHODS AND RESULTS: Listeria monocytogenes strain Scott A and E. faecium(T) were followed for 17 days after inoculation in sludge. Kinetics of survival depended on the bacteria and on the technique used [most probable number method, direct plate count or real-time quantitative PCR (qPCR)]. The concentration of L. monocytogenes decreased rapidly regardless of the technique, but the decrease was much more dramatic with culture techniques than with qPCR. On the contrary, the concentrations of culturable E. faecium(T) were stable. CONCLUSIONS: The results suggest that the cells of L. monocytogenes strain Scott A might have entered a viable, but nonculturable (VBNC) status, whereas cells of the indicator bacteria, E. faecium(T), maintained themselves better and stayed culturable. SIGNIFICANCE AND IMPACT OF THE STUDY: The difference of survival kinetics in the sludge of a faecal indicator (E. faecium) and a pathogenic bacterium (L. monocytogenes) may be linked to the fact that they either enter or do not enter into a VBNC status.

Bacterial Toxins↗

Molecular characterization of Enterococcus faecium isolated from hospitalized patients in Korea.

AIMS: Multilocus sequence typing (MLST) was performed for vancomycin-resistant Enterococcus faecium (VREF) from diverse geographical areas in Korea to obtain insights into the genetic relationships with other molecular profiles. To understand the diversity of lineages, vancomycin-susceptible E. faecium (VSEF) were included. METHODS AND RESULTS: A total of 60 E. faecium isolates were analysed by MLST and esp profile. Molecular typing of Tn1546 of 30 VREF strains was evaluated by overlapping PCR of Tn1546 and DNA sequencing. Seven sequence types (ST) were found among 30 VSEF isolates, and four STs were found among 30 VREF isolates. The types most frequently encountered were ST 78 (26 isolates) and ST 203 (16 isolates). Of the 60 E. faecium isolates, 35 isolates were positive for the esp gene. On molecular typing of Tn1546, all VREF isolates were divided into four main types. Strains with the same ST showed divergence in Tn1546 types and strains with the same Tn1546 type represented different STs. CONCLUSIONS: An association between Tn1546 typing and MLST was not found. SIGNIFICANCE AND IMPACT OF THE STUDY: These results suggest that the horizontal spread of Tn1546 between strains plays a major role in the dissemination of vancomycin resistance in Korea.

Bacterial Typing Techniques↗

The enumeration of chlorine-injured Escherichia coli and Enterococcus faecalis is enhanced under conditions where reactive oxygen species are neutralized.

AIM: To investigate the effect of neutralization of reactive oxygen species (ROS-neutralized conditions) on the enumeration of chlorine-injured Escherichia coli and Enterococcus faecalis using selective and nonselective media. METHODS: Pure cultures of E. coli NCTC8912 and Ent. faecalis NCTC775 were injured using dilute sodium hypochlorite, at free chlorine levels of 0.6 and 0.9 microg ml(-1), respectively, and then enumerated at 37 degrees C by surface plate counts on nonselective nutrient (N) agar and on several selective media, either under (i) standard aerobic conditions; (ii) aerobic conditions using growth medium, supplemented with 0.05%-w/v sodium pyruvate, to neutralize peroxides; or (iii) conditions designed to neutralize ROS, using a combination of 0.05%-w/v sodium pyruvate in the growth medium, together with incubation in an anaerobic jar. RESULTS: The counts obtained on the nonselective medium were lowest under aerobic conditions in unsupplemented medium, higher in pyruvate-supplemented (peroxide-neutralized) medium and highest for ROS-neutralized conditions. Counts for the selective media were often lower than those for nonselective N (nutrient) agar, with enhancement under peroxide-neutralized conditions and a further increase in counts under ROS-neutralized conditions. Broadly similar observations were made for three other strains of each organism. CONCLUSIONS: Chlorine-injured E. coli and Ent. faecalis become sensitive to ROS, giving higher counts under ROS-neutralized enumeration conditions than under conventional aerobic conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: The enhancement in counts observed under ROS-neutralized conditions indicate that the addition of pyruvate to the growth medium may not fully counteract the effects of sublethal injury under aerobic conditions, which is a novel observation. Thus, ROS-neutralized conditions may be required for optimal enumeration of faecal indicator bacteria. Furthermore, the lower counts, obtained using selective media indicate that the sensitivity of chlorine-injured bacteria to selective agents is not necessarily reversed under ROS-neutralized conditions.

Bacteriological Techniques↗

Systemic inflammatory response syndrome in nosocomial bloodstream infections with Pseudomonas aeruginosa and Enterococcus Species: comparison of elderly and nonelderly patients.

OBJECTIVES: To determine whether the systemic inflammatory response syndrome (SIRS), clinical course, and outcome of monomicrobial nosocomial bloodstream infection (BSI) due to Pseudomonas aeruginosa or Enterococcus spp. is different in elderly patients than in younger patients. DESIGN: Historical cohort study. SETTING: An 820-bed tertiary care facility. PARTICIPANTS: One hundred twenty-seven adults with P. aeruginosa or enterococcal BSI. MEASUREMENTS: SIRS scores were determined 2 days before the first positive blood culture through 14 days afterwards. Elderly patients (> or =65, n=37) were compared with nonelderly patients (<65, n=90). Variables significant for predicting mortality in univariate analysis were entered into a logistic regression model. RESULTS: No difference in SIRS was detected between the two groups. No significant difference was noted in the incidence of organ failure, 7-day mortality, or overall mortality between the two groups. Univariate analysis revealed that Acute Physiology And Chronic Health Evaluation (APACHE) II score of 15 or greater at BSI onset; adjusted APACHE II score (points for age excluded) of 15 or greater at BSI onset; and respiratory, cardiovascular, renal, hematological, and hepatic failure were predictors of mortality. Age, sex, use of empirical antimicrobial therapy, and infection with imipenem-resistant P. aeruginosa or vancomycin-resistant enterococci did not predict mortality. Multivariate analysis revealed that hematological failure (odds ratio (OR)=8.1, 95% confidence interval (CI)=2.78-23.47), cardiovascular failure (OR=4.7, 95% CI=1.69-13.10), and adjusted APACHE II > or = 15 at BSI onset (OR=3.1, 95% CI=1.12-8.81) independently predicted death. CONCLUSION: Elderly patients did not differ from nonelderly patients with respect to severity of illness before or at the time of BSI. Elderly patients with pseudomonal or enterococcal BSIs did not have a greater mortality than nonelderly patients.

Age Factors↗

Clostridium difficile and vancomycin-resistant enterococcus: the new nosocomial alliance.

OBJECTIVES: The aims of this study were to determine the frequency of the association between Clostridium difficile (C. difficile) and vancomycin-resistant Enterococcus (VRE) and delineate the role of C. difficile coinfection as a predictor of VRE infection versus colonization and adverse outcome. METHODS: Patients with both C. difficile colitis and VRE (CD/VRE) were compared to patients with VRE alone with regard to demographics, comorbidity, prior antibiotic therapy, and coinfection with methicillin-resistant Staphylococcus aureus and funguria. C. difficile as a predictor of VRE infection (VRE-I) versus colonization (VRE-C) and adverse outcome was also studied. RESULTS: Eighty-nine patients with VRE infection or colonization were studied. This included 31 cases of VRE-I and 58 VRE-C. C. difficile was isolated in 17 (19.1%) of patients; of these C. difficile was isolated before VRE in 9 patients and after VRE in 8. The two groups did not differ in age, residence, or comorbidity. C. difficile coinfection was not predictive of VRE-I versus VRE-C, nor was it associated with increased length of stay or mortality. However, the mortality rates in both groups was high, around 30%. A significant association was noted between the use of vancomycin and metronidazole (before the isolation of VRE) and C. difficile coinfection (p = 0.03 and p = 0.001, respectively). A high incidence of nosocomial coinfection with methicillin-resistant Staphylococcus aureus, funguria, and gram-negative sepsis was noted in both groups; the association with funguria was statistically significant (p = 0.029). CONCLUSIONS: In conclusion, C. difficile coinfection is common in patients with VRE infection or colonization and is significantly associated with other nosocomial dilemmas like funguria. This may result in the emergence of highly virulent pathogens including vancomycin-resistant C. difficile, posing new challenges in the management of nosocomial diarrheas.

Aged↗

Horizontal transfer of tet(M) and erm(B) resistance plasmids from food strains of Lactobacillus plantarum to Enterococcus faecalis JH2-2 in the gastrointestinal tract of gnotobiotic rats.

Two wild-type strains of Lactobacillus plantarum previously isolated from fermented dry sausages were analysed for their ability to transfer antibiotic resistance plasmids in the gastrointestinal tract. For this purpose, we used gnotobiotic rats as an in vivo model. Rats were initially inoculated with the recipient Enterococcus faecalis JH2-2 at a concentration of 10(10) CFU mL(-1). After a week, either of the two donors L. plantarum DG 522 (harbouring a tet(M)-containing plasmid of c. 40 kb) or L. plantarum DG 507 [harbouring a tet(M)-containing plasmid of c. 10 kb and an erm(B)-containing plasmid of c. 8.5 kb] was introduced at concentrations in the range of 10(8)-10(10) CFU mL(-1). Two days after donor introduction, the first transconjugants (TCs) were detected in faecal samples. The detected numbers of tet(M)-TCs were comparable for the two donors. In both cases, this number increased to c. 5 x 10(2) CFU g(-1) faeces towards the end of the experiment. For erm(B)-TCs, the number was significantly higher and increased to c. 10(3) CFU g(-1) faeces. To our knowledge, this is the first study showing in vivo transfer of wild-type antibiotic resistance plasmids from L. plantarum to E. faecalis.

Animals↗

Cytokine-inducing glycolipids in the lipoteichoic acid fraction from Enterococcus hirae ATCC 9790.

Five high molecular weight glycolipids capable of stimulating human peripheral whole-blood cell cultures to cause interleukin 6 (IL-6) and tumor necrosis factor (TNF)-alpha induction were isolated from one of the lipoteichoic acid fractions (LTA-2) extracted from Enterococcus hirae ATCC 9790 (Tsutsui et al., (1991) FEMS Microbiol. Immunol. 76, 211-218) by a combination of hydrophobic interaction and anion-exchange chromatographies. This purification procedure resulted in a remarkable increase in the cytokine-inducing activities on the weight basis of isolated glycolipids (a maximum of 36- and 17-fold increases of IL-6 and TNF-alpha induction, respectively). The total yield of these bioactive glycolipids amounted to 6 wt% of the parent LTA-2 fraction, while the recovery rate in terms of the cytokine-inducing activities was estimated to be sufficient. The chemical composition and the profile, using SDS-PAGE, revealed that all of the isolated bioactive components were high molecular weight glycolipids, which were distinct from each other and from the parent LTA-2 fraction. These findings suggest that the IL-6 and TNF-alpha-inducing activities previously noted in the parent LTA-2 fraction are not attributable to a chemical entity, the structure of which had been proposed elsewhere (Fischer, W. (1990) in Glycolipids, Phosphoglycolipids and Sulfoglycolipids (Kates, M. ed.) pp. 123-234, Plenum Press, New York), but to the other high molecular weight glycolipids described here.

Animals↗

A lipoteichoic acid fraction of Enterococcus hirae activates cultured human monocytic cells via a CD14-independent pathway to promote cytokine production, and the activity is inhibited by serum components.

To elucidate the cellular activation mechanisms of lipoteichoic acid (LTA) compared with those of lipopolysaccharide (LPS), a quantitatively major LTA fraction, QM-1M, was prepared from hot phenol-water extracts of Enterococcus hirae (ATCC 9790) by hydrophobic octyl-Sepharose chromatography and by ion-exchange membrane (QMA-Mem Sep 1010) chromatography as a 60% 1-propanol- and 1 M NaCl-eluted fraction. Unlike the reference Escherichia coli LPS, QM-1M did not demonstrate any ability to induce cytokines in a human whole blood culture system in this study, whereas QM-1M induced a few cytokines such as interleukin (IL)-8 and tumor necrosis factor-alpha in human monocytic THP-1 cell and human peripheral mononuclear cell (PBMC) cultures in the absence of serum. Fetal calf and human sera decreased the above cytokine induction by QM-1M in THP-1 and PBMC cultures, whereas sera increased activities of the reference LPS. IL-8 induction in the absence of serum in response to QM-1M was demonstrated to proceed through a CD14-independent pathway unlike the reference LPS.

Cell Line↗

Enterococcus faecalis aggregation substance promotes opsonin-independent binding to human neutrophils via a complement receptor type 3-mediated mechanism.

Enterococcus faecalis aggregation substance (AS) mediates efficient adhesion between bacteria, thereby facilitating plasmid exchange as an integral part of a bacterial sex pheromone system. We examined the interaction of AS-bearing E. faecalis with human neutrophils (PMNs), an important component of the host defense system. AS promoted a markedly increased opsonin-independent bacterial binding to PMNs. Adhesion was dependent on the expression of the enterococcal Asc10 protein, which contains two Arg-Gly-Asp (RGD) sequences, and addition of exogenous RGD-containing peptides inhibited AS-mediated binding by 66%. AS-mediated adhesion was inhibited by 85% by anti-human complement receptor type 3 (CR3) monoclonal antibodies or by use of PMNs from a patient with leukocyte adhesion deficiency. However, AS-bearing E. faecalis cells were unable to bind to CHO-Mac-1 cells, expressing functionally active CR3, suggesting the potential need for additional PMN surface receptors for bacterial adhesion. Monoclonal antibodies against integrin-associated protein (CD47) and L-selectin, both of which may interact with CR3 and bind to ligands on E. faecalis, also inhibited AS-dependent binding. The non-opsonic binding of E. faecalis to PMNs may play an important role in this organism's pathogenesis.

Adhesins, Bacterial↗

Specific antibody promotes opsonization and PMN-mediated killing of phagocytosis-resistant Enterococcus faecium.

Many clinical isolates of Enterococcus faecium are resistant to neutrophil (PMN)-mediated phagocytosis and killing in the presence of normal human serum. We have now examined the ability of specific polyclonal rabbit antibodies to promote opsonization and killing of phagocytosis-resistant E. faecium. Immune rabbit serum generated against formalin-killed E. faecium TX0016, a phagocytosis-resistant strain, markedly promoted binding of TX0016 organisms to PMNs and PMN-mediated killing. These effects were dramatically reduced by (a) adsorption of immune serum with E. faecium TX0016, but not by adsorption with a strain of E. faecium susceptible to phagocytosis, and (b) incubation of immune serum with carbohydrate purified from TX0016, but not by incubation with a surface protein extract from TX0016. IgG purified from immune serum was unable by itself to promote bacterial binding to PMNs. However, specific IgG was able to promote binding to PMNs and PMN-mediated killing in the presence of normal human serum as a complement source, as were F(ab')(2) and Fab fragments produced from it, and the alternative pathway of complement was sufficient to promote IgG- and F(ab')(2)-mediated opsonization. PMN complement receptor type 3, but not complement receptor type 1, was involved in bacterial binding to PMNs induced by the combination of F(ab')(2) fragments and normal human serum. These results suggest that opsonization by antibodies potentially directed against bacterial carbohydrate, in conjunction with complement activation, has an important role in the host defense against phagocytosis-resistant E. faecium.

Animals↗

Identification of ABC transporters in vancomycin-resistant Enterococcus faecium as potential targets for antibody therapy.

The occurrence of an outbreak of septicaemias due to vancomycin-resistant Enterococcus faecium (VRE), in Manchester, UK, provided an opportunity to examine the antibody responses in patients infected by the same strain. Immunoblotting sera from 24 cases, six of whom died, showed an immunodominant cluster of antigens at 34, 54 and 97 kDa, with a statistically significant correlate between survival and immunoglobulin G to the 34 and 97 kDa bands (P<0.05). Screening a genomic expression library of VRE with seropositive serum and peritoneal dialysate from a survivor gave a recombinant clone with two contiguous open reading frames, the derived amino acid sequences of which both showed sequence homologue with ABC transporters, with a Walker A and Walker B motif and the signature sequence LSGGQ. The first open reading frame (putative VRE ABC1) showed 57% homologue with YbxA from Bacillus subtilis. A partial sequence (putative VRE ABC2) was also obtained, in the same recombinant clone, of a second ABC transporter with 72% homologue with ybaE from B. subtilis. Affinity selection with the seropositive serum and peritoneal dialysate used to screen the library showed that the eluted antibody bound to the 97, 54, 34 and 30 kDa bands. Direct amino acid sequencing identified this as a possible ABC transporter. Rabbit antiserum against peptides representing Walker A and an area adjacent to the Walker B site cross-reacted with bands at 34, 54, 97, 110 kDa and at 30, 34 and 54 kDa respectively. This therefore appeared to be an immunodominant complex of ABC transporters of which the smallest was the 30 kDa antigen. Epitope mapping of this antigen with seropositive patients' sera delineated three linear epitopes (KVGIV, FGPKNF and RVAI). The Walker A site represented by peptide 1 (GHNGSGKSTLAKTIN), epitope RVAI represented by peptides 2 (MRRVAIAGVLAMPRE) and 3 (ELSGGQMRRVAIAGV), epitope KVGIV represented by peptide 4 (LKPIRKKVGIVFQFP), and recombinant VRE ABC1 and VRE ABC2 expressed in Escherichia coli pBAD were then used to isolate human genetically recombinant antibodies from a phage antibody display library. An assessment of the protective potential of these antibodies was carried out in a mouse model of the infection. This study suggests that an ABC transporter homologue could be a target for antibody therapy against VRE infections.

ATP-Binding Cassette Transporters↗

Characterization of Ers, a PrfA-like regulator of Enterococcus faecalis.

We have identified a transcriptional regulator, named Ers (for enterococcal regulator of survival), of Enterococcus faecalis, an important opportunistic bacterium commonly recovered from hospitalized patients. Ers is a member of the Crp/Fnr family and is 69% similar to Srv, a PrfA-like regulator of Streptococcus pyogenes implicated in virulence, and is the E. faecalis protein most closely related to PrfA, a positive regulator of virulence genes in Listeria monocytogenes. In an in vivo-in vitro macrophage infection model, the survival of an ers mutant was highly significantly decreased compared with that of the parental strain JH2-2. This mutant was more than 10-fold more sensitive to oxidative challenge by hydrogen peroxide. In order to identify genes whose expression was under Ers control, the RNA levels of 31 likely candidates were measured by real-time quantitative PCR. The results indicate that ers may be autoregulated and that the locus ef0082 appears to be positively regulated by Ers. Nevertheless, mutation of ef0082 did not result in any detectable changes in the survival of the bacterium within murine macrophages.

Amino Acid Sequence↗

Effect of in vivo growth conditions upon expression of surface protein antigens in Enterococcus faecalis.

Western blotting of whole-cell preparations of Enterococcus faecalis showed the protein-antigen profiles to be markedly influenced by growth conditions. The E. faecalis-specific antigens of 40 and 37 kDa, which are prominent in endocarditis, were strongly expressed following growth in serum or brain heart infusion, but not after growth in a chemically defined medium. The expression of these antigens in vivo was demonstrated in cells grown as a biofilm on silastic discs in the peritoneum of rabbits. These in vivo culture conditions may be useful in studying the pathogenesis of E. faecalis infections and the effectiveness of antibiotic therapy.

Animals↗

Relationship of the chemical structure and immunobiological activities of lipoteichoic acid from Streptococcus faecalis (Enterococcus hirae) ATCC 9790.

Two molecular species of lipoteichoic acid (LTA 1 and LTA 2) were isolated from whole cells of Streptococcus faecalis (Enterococcus hirae) ATCC 9790 by hydrophobic chromatography on Octyl Sepharose CL-4B. Chemical analysis revealed that LTA 1 and LTA 2 contained two and four acyl lipid anchors respectively. LTA 1 was less active than LTA 2 in inducing cytokines, except interleukin-1 (IL-1), but their in vivo antitumour effects were similar. LTA 2 was a potent inducer of tumour necrosis factor (TNF) and interferon (IFN) production and had excellent antitumour activity against Meth A fibrosarcoma established in mice. Deacylation of LTA 2 by alkaline hydrolysis abolished these biological activities. The phosphatidylglycolipid fraction derived from LTA 2 after acid hydrolysis could also induce TNF, IFN, and IL-1 production, as well as having antitumour activity against Meth A fibrosarcoma. Therefore, the lipid anchor portion of S. faecalis LTA may play an important role in the manifestation of these various biological activities.

Animals↗

Mode of membrane insertion and sequence of a 32-amino acid peptide stretch of the penicillin-binding protein 4 of Enterococcus hirae.

Analysis of water-soluble derivatives of the Enterococcus hirae 75-kDa membrane-bound penicillin-binding protein 4 (PBP4) has yielded the amino acid sequence of a 32-amino acid polypeptide stretch. This peptide is similar to peptide segments known to occur in the N-terminal domain of high-Mr PBPs of class B. The E. hirae PBP4 probably belongs to the same class. It is anchored in the membrane at the N-terminus of the polypeptide chain.

Amino Acid Sequence↗

Environmental strains of Enterococcus faecium with inducible high-level resistance to glycopeptides.

High-level resistance to glycopeptides in Enterococcus faecium is associated with an inducible 39-kDa cytoplasmic membrane protein. The present paper shows that such glycopeptide-resistant E. faecium strains can not only be isolated in a definite clinical setting but also from waste water of sewage treatment plants. Nearer characterization of these and of clinical isolates by resistance pattern, biotyping, and genotyping (DNA-fingerprinting with pulsed-field gel electrophoresis) has shown that different glycopeptide-resistant E. faecium strains have been isolated from clinical sources and from waste water.

DNA Fingerprinting↗