Change in prevalence and antibiotic resistance of Enterococcus species isolated from blood cultures over an 8-year period

Development and Characterization of High-Throughput Caenorhabditis elegans - Enterococcus faecium Infection Model

The genus Enterococcus includes two Gram-positive pathogens of particular clinical relevance: E. faecalis and E. faecium. Infections with each of these pathogens are becoming more frequent, particularly in the case of hospital-acquired infections. Like most other bacterial species of clinical importance, antimicrobial resistance (and, specifically, multi-drug resistance) is an increasing threat, with both species considered to be of particular importance by the World Health Organization and the US Centers for Disease Control. The threat of antimicrobial resistance is exacerbated by the staggering difference in the speeds of development for the discovery and development of the antimicrobials versus resistance mechanisms. In the search for alternative strategies, modulation of host-pathogen interactions in general, and virulence inhibition in particular, have drawn substantial attention. Unfortunately, these approaches require a fairly comprehensive understanding of virulence determinants. This requirement is complicated by the fact that enterococcal infection models generally require vertebrates, making them slow, expensive, and ethically problematic, particularly when considering the thousands of animals that would be needed for the early stages of experimentation. To address this problem, we developed the first high-throughput C. elegans-E. faecium infection model involving host death. Importantly, this model recapitulates many key aspects of murine peritonitis models, including utilizing similar virulence determinants. Additionally, host death is independent of peroxide production, unlike other E. faecium-C. elegans virulence models, which allows the assessment of other virulence factors. Using this system, we analyzed a panel of lab strains with deletions of targeted virulence factors. Although removal of certain virulence factors (e.g., Δfms15) was sufficient to affect virulence, multiple deletions were generally required to affect pathogenesis, suggesting that host-pathogen interactions are multifactorial. These data were corroborated by genomic analysis of selected isolates with high and low levels of virulence. We anticipate that this platform will be useful for identifying new treatments for E. faecium infection.

Prevalence and phenotypic characterization of Enterococcus species isolated from clinical samples of pediatric patients in Jimma University Specialized Hospital, south west Ethiopia

OBJECTIVE

This study was done to determine the prevalence and phenotypic characterization of Enterococcus species isolated from clinical samples of pediatric patients in Jimma University Specialized Hospital, Southwest Ethiopia.

RESULTS

The overall prevalence of Enterococci species was 5.5% (22/403). Five (22.7%) of Enterococci species were vancomycin resistant. Haemolysin, gelatinase and biofilm production was seen among 45.5, 68.2 and 77.3% of isolates respectively. The overall rate of antibiotic resistance was 95.5% (21/22). High resistance was observed against norfloxacin (87.5%), and tetracycline (77.3%). Whereas, low resistance (36.5%) was observed against ciprofloxacin and eighteen (80.8%) of the isolates were multi-drug resistant.

Evolution of virulence in Enterococcus faecium, a hospital-adapted opportunistic pathogen

Enterococci are long-standing members of the human microbiome and they are also widely distributed in nature. However, with the surge of antibiotic-resistance in recent decades, two enterococcal species (Enterococcus faecalis and Enterococcus faecium) have emerged to become significant nosocomial pathogens, acquiring extensive antibiotic resistance. In this review, we summarize what is known about the evolution of virulence in E. faecium, highlighting a specific clone of E. faecium called ST796 that has emerged recently and spread globally.

Evolutionary origins of the emergent ST796 clone of vancomycin resistant Enterococcus faecium

From early 2012, a novel clone of vancomycin resistant Enterococcus faecium (assigned the multi locus sequence type ST796) was simultaneously isolated from geographically separate hospitals in south eastern Australia and New Zealand. Here we describe the complete genome sequence of Ef_aus0233, a representative ST796 E. faecium isolate. We used PacBio single molecule real-time sequencing to establish a high quality, fully assembled genome comprising a circular chromosome of 2,888,087 bp and five plasmids. Comparison of Ef_aus0233 to other E. faecium genomes shows Ef_aus0233 is a member of the epidemic hospital-adapted lineage and has evolved from an ST555-like ancestral progenitor by the accumulation or modification of five mosaic plasmids and five putative prophage, acquisition of two cryptic genomic islands, accrued chromosomal single nucleotide polymorphisms and a 80 kb region of recombination, also gaining Tn1549 and Tn916, transposons conferring resistance to vancomycin and tetracycline respectively. The genomic dissection of this new clone presented here underscores the propensity of the hospital E. faecium lineage to change, presumably in response to the specific conditions of hospital and healthcare environments.

Molecular epidemiology of vancomycin resistant enterococci in a tertiary care hospital in Saudi Arabia

AIM

Vancomycin-resistant enterococci (VRE) are a major cause of nosocomial infections with high mortality and morbidity. There is limited data on the molecular characterization of VRE in Saudi Arabia. This study was carried out to investigate the premise that a shift in VRE epidemiology is occurring in our setting.

METHODS

Enterococcus species identification and susceptibility testing plus VRE phenotypic confirmation by vancomycin and teicoplanin E-test were carried out. Vancomycin resistance genes were detected by PCR. Strain typing was conducted using PFGE.

RESULTS

Among the strains of Enterococcus spp. investigated in this study, 17 (4.5%) were VRE. With the exception of one isolate from rectal swab, all others were clinical specimens with blood being the commonest source (n = 11; 64.7%), followed by urine (n = 3; 17.6%). The 17 VRE isolates were Enterococcus faecium (n/N = 13/17) and Enterococcus gallinarum (n/N = 4/17). Among E. faecium isolates, vanA(+)/vanB(+) (n/N = 8/13; 62%) exhibiting VanB phenotype were predominant. One of the five vanA(+)E. faecium isolates exhibited a VanB phenotype indicative of vanA genotype-VanB phenotype incongruence. E. gallinarum isolates exhibited a Van C phenotype although two were vanA(+)/vanC1(+). PFGE revealed a polyclonal distribution with eight pulsotypes.

CONCLUSION

These findings indicate an evolving VRE epidemiology with vanA(+)/vanB(+) isolates and vanA genotype-VanB phenotype incongruence isolates, which were previously described as colonizers, are now causing clinical infection.

Antimicrobial resistance profile of Enterococcus species isolated from intestinal tracts of hospitalized patients in Jimma, Ethiopia

Background

Multi-drug-resistant Enterococci colonizing the intestinal tract of hospitalized patients are the major source of infection as well as nosocomial spread. Despite worldwide increasing rate of multidrug resistant Enterococci colonization and infection among hospitalized patients, there is scarcity of data from resource limited setting. The present study aimed at determining the antimicrobial resistance profile of Enterococcus species from intestinal tracts of hospitalized patients in Jimma, Ethiopia.

Methods

The study was conducted among hospitalized patients at Jimma University Specialized Hospital, from January to July 2013. Fecal samples were collected and processed for bacterial isolation and susceptibility testing to antimicrobial agents. Stool samples were inoculated onto enterococcus selective media (Bile Esculin azide agar plate) with and without 6 µg/ml of vancomycin. The isolates were identified to genus and species level by cultural characteristics, Gram’s stain, catalase test, growth in 6.5% NaCl broth, growth at 45°C, motility test and by using API 20 Streptococcus system. Sensitivity testing was done using Kirby–Bauer disk diffusion method. Minimum inhibitory concentrations for vancomycin were determined using E-test strips.

Result

Overall, Enterococci were isolated from 114 (76%) of the study subjects. The isolates were Enterococcus faecium (35.1%) followed by Enterococcusfaecalis (29.8%), Enterococcus gallinarum (17.5%), Enterococcuscasseliflavus (8.8%) and Enterococcusdurans (8.8%). Among 114 tested Enterococci isolates, 41 (36%) were resistant to ampicillin, 62 (54.4%) to streptomycin and 39 (34.2%) to gentamycin. Other alternative antibiotics to treat mixed nosocomial infection caused by Enterococci also showed high rate of resistance in vitro: ciprofloxacin (50% of resistance), norfloxacin (49.1%), erythromycin (63.2%), tetracycline (64.9%), chloramphenicol (34.2%), and nitrofrantoin (32.4%). Multiple drug resistance was observed among 89.5% of E. faecium and E. faecalis. Vancomycin resistant Enterococci were observed in 5% of E. faecium isolates.

Conclusion

This study reveals high rate of fecal colonization by multidrug-resistant Enterococci and prevalence of vancomycin resistance strains. Thus periodic surveillance of antibacterial susceptibilities is recommended to detect emerging resistance and to prevent the spread of antibacterial-resistant strains.

Genetic relatedness and risk factor analysis of ampicillin-resistant and high-level gentamicin-resistant enterococci causing bloodstream infections in Tanzanian children

Background

While enterococci resistant to multiple antimicrobials are spreading in hospitals worldwide, causing urinary tract, wound and bloodstream infections, there is little published data on these infections from Africa.

Methods

We assessed the prevalence, susceptibility patterns, clinical outcome and genetic relatedness of enterococcal isolates causing bloodstream infections in children in a tertiary hospital in Tanzania, as part of a prospective cohort study of bloodstream infections among 1828 febrile children admitted consecutively from August 2001 to August 2002.

Results

Enterococcal bacteraemia was identified in 2.1% (39/1828) of admissions, and in 15.3% (39/255) of cases of culture-confirmed bloodstream infections. The case-fatality rate in children with Enterococcus faecalis septicaemia (28.6%, 4/14) was not significantly different from those with Enterococcus faecium septicaemia (6.7%, 1/15, p = 0.12). E. faecium isolates commonly had combined ampicillin-resistance and high-level gentamicin resistance (HLGR), (9/17), while E. faecalis frequently displayed HLGR (6/15), but were ampicillin susceptible. None of the tested enterococcal isolates displayed vancomycin resistance by Etest or PCR for vanA and vanB genes. Multi-locus sequence-typing (MLST) showed that the majority of E. faecium (7/12) belonged to the hospital associated Bayesian Analysis of Population Structure (BAPS) group 3–3. Pulsed-field gel electrophoresis (PFGE) indicated close genetic relationship particularly among E. faecium isolates, but also among E. faecalis isolates. There was also correlation between BAPS group and PFGE results. Risk factors for enterococcal bloodstream infection in univariate analysis were hospital-acquired infection and clinical diagnosis of sepsis with unknown focus. In multivariate analysis, neonates in general were relatively protected from enterococcal infection, while both prematurity and clinical sepsis were risk factors. Malnutrition was a risk factor for enterococcal bloodstream infection among HIV negative children.

Conclusion

This is the first study to describe bloodstream infections caused by ampicillin-resistant HLGR E. faecium and HLGR E. faecalis in Tanzania. The isolates of E. faecium and E. faecalis, respectively, showed high degrees of relatedness by genotyping using PFGE. The commonly used treatment regimens at the hospital are insufficient for infections caused by these microbes. The study results call for increased access to microbiological diagnostics to guide rational antibiotic use in Tanzania.

Vancomycin-resistant Enterococcus faecium Bacteremia in a tertiary care hospital: epidemiology, antimicrobial susceptibility, and outcome

Vancomycin-resistant Enterococcus faecium (VREF) has emerged as a relevant multidrug-resistant pathogen and potentially lethal etiology of health care associated infections worldwide. The objective of this retrospective cohort study was to assess factors associated with mortality in patients with VREF bacteremia in a major tertiary referral hospital in Southern Brazil. All documented cases of bacteremia identified between May 2010 and July 2012 were evaluated. Cox regression was performed to determine whether the characteristics related to the host or antimicrobial treatment were associated with the all-cause 30-day mortality. In total, 35 patients with documented VREF bacteremia were identified during the study period. The median APACHE-II score of the study population was 26 (interquartile range: 10). The overall 30-day mortality was 65.7%. All VREF isolates were sensitive to linezolid, daptomycin, and quinupristin-dalfopristin. Linezolid was the only antimicrobial agent with in vitro activity against VREF that was administered to the cohort. After multivariate analysis, linezolid treatment (HR, 0.08; 95% CI, 0.02–0.27) and presence of acute kidney injury at the onset of bacteremia (HR, 4.01; 95% CI, 1.62–9.94) were independently associated with mortality. Presentation with acute kidney injury and lack of treatment with an effective antibiotic poses risk for mortality in patients with VREF bacteremia.

Prevalence of vancomycin resistant Enterococci and associated risk factors among clients with and without HIV in Northwest Ethiopia: a cross-sectional study

BACKGROUND

Enterococci are the most important multidrug resistant organisms associated with immunocompromised patients. Data are lacking about the epidemiology of vancomycin resistant Enterococci (VRE) in Ethiopia. This study aimed to assess the prevalence of VRE, their susceptibility patterns to different antibiotics and associated risk factors in fecal samples of Human Immunodeficiency Virus (HIV) positive and HIV negative clients.

METHODS

A cross sectional study was carried out in a total of 226 (113 HIV positive and 113 HIV negative) clients, from July 1/2013 to September 30/2013 at the University of Gondar Teaching Hospital. Data on socio-demographic characteristics and risk factors were collected with a short interview guided by pre-tested structured questionnaire. The enterococci were isolated and identified from stool sample using standard bacteriological procedures. Kary Bauer disk diffusion method was used to determine the susceptibility patterns of Enterococci isolates. Data were entered and analyzed using SPSS version 20 statistical package.

RESULTS

The overall colonization of Enterococci was 88.9% (201/226) of which 11 (5.5%) were VRE. The prevalence of VRE among clients with and without HIV infections were 8(7.8%) and 3(3.1%), respectively. Ninety percent of the Enterococci isolates (181/201) were resistant to two or more antibiotics tested. Isolates of Enterococci recovered from stool samples of HIV infected patients were more resistant to amoxicillin and amoxicillin-calvulinic acid than HIV negative clients (P < 0.05). Antibiotic treatment for the last 2 weeks was found to be the risk factor that showed statistically significant association with the presence of high VRE colonization. However, the socio-demographic variables and factors such as malnutrition, leucopenia, thromobocytopenia, anaemia, duration of Highly Active Antiretroviral Therapy, CD4 cell count, stage of WHO and drinking alcohol were not associated with VRE (P > 0.05).

CONCLUSION

The high prevalence of VRE in this study signals the emergence of VRE in the study area. Prior antibiotic treatment was associated with VRE colonization. Therefore, rational use of antibiotics and more detailed study using phenotypic and genotypic methods are needed.

The cell wall architecture of Enterococcus faecium: from resistance to pathogenesis

The cell wall of Gram-positive bacteria functions as a surface organelle that continuously interacts with its environment through a plethora of cell wall-associated molecules. Enterococcus faecium is a normal inhabitant of the GI tract of mammals, but has recently become an important etiological agent of hospital-acquired infections in debilitated patients. Insights into the assembly and function of enterococcal cell wall components and their interactions with the host during colonization and infection are essential to explain the worldwide emergence of E. faecium as an important multiantibiotic-resistant nosocomial pathogen. Understanding the biochemistry of cell wall biogenesis and principles of antibiotic resistance at the molecular level may open up new frontiers in research on enterococci, particularly for the development of novel antimicrobial strategies. In this article, we outline the current knowledge on the most important antimicrobial resistance mechanisms that involve peptidoglycan synthesis and the role of cell wall constituents, including lipoteichoic acid, wall teichoic acid, capsular polysaccharides, LPxTG cell wall-anchored surface proteins, WxL-type surface proteins and pili, in the pathogenesis of E. faecium.

Molecular epidemiology of enterococcal bacteremia in Australia

Enterococci are a major cause of health care-associated infections and account for approximately 10% of all bacteremias globally. The aim of this study was to determine the proportion of enterococcal bacteremia isolates in Australia that are antimicrobial resistant, with particular emphasis on susceptibility to ampicillin and the glycopeptides, and to characterize the molecular epidemiology of the Enterococcus faecalis and Enterococcus faecium isolates. From 1 January to 31 December 2011, 1,079 unique episodes of bacteremia were investigated, of which 95.8% were caused by either E. faecalis (61.0%) or E. faecium (34.8%). The majority of bacteremias were health care associated, and approximately one-third were polymicrobial. Ampicillin resistance was detected in 90.4% of E. faecium isolates but was not detected in E. faecalis isolates. Vancomycin nonsusceptibility was reported in 0.6% and 36.5% of E. faecalis and E. faecium isolates, respectively. Unlike Europe and the United States, where vancomycin resistance in E. faecium is predominately due to the acquisition of the vanA operon, 98.4% of E. faecium isolates harboring van genes carried the vanB operon, and 16.1% of the vanB E. faecium isolates had vancomycin MICs at or below the susceptible breakpoint of the CLSI. Although molecular typing identified 126 E. faecalis pulsed-field gel electrophoresis pulsotypes, >50% belonged to two pulsotypes that were isolated across Australia. E. faecium consisted of 73 pulsotypes from which 43 multilocus sequence types were identified. Almost 90% of the E. faecium isolates were identified as CC17 clones, of which approximately half were characterized as ST203, which was isolated Australia-wide. In conclusion, the Australian Enterococcal Sepsis Outcome Programme (AESOP) study has shown that although they are polyclonal, enterococcal bacteremias in Australia are frequently caused by ampicillin-resistant vanB E. faecium.

Impact of enterococcal colonization and infection in solid organ transplantation recipients from the Swiss transplant cohort study

BACKGROUND

The burden of enterococcal infections has increased over the last decades with vancomycin-resistant enterococci (VRE) being a major health problem. Solid organ transplantation is considered as a risk factor. However, little is known about the relevance of enterococci in solid organ transplantation recipients in areas with a low VRE prevalence.

METHODS

We examined the epidemiology of enterococcal events in patients followed in the Swiss Transplant Cohort Study between May 2008 and September 2011 and analyzed risk factors for infection, aminopenicillin resistance, treatment, and outcome.

RESULTS

Of the 1234 patients, 255 (20.7%) suffered from 392 enterococcal events (185 [47.2%] infections, 205 [52.3%] colonizations, and 2 events with missing clinical information). Only 2 isolates were VRE. The highest infection rates were found early after liver transplantation (0.24/person-year) consisting in 58.6% of Enterococcus faecium. The highest colonization rates were documented in lung transplant recipients (0.33/person-year), with 46.5% E. faecium. Age, prophylaxis with a betalactam antibiotic, and liver transplantation were significantly associated with infection. Previous antibiotic treatment, intensive care unit stay, and lung transplantation were associated with aminopenicillin resistance. Only 4/205 (2%) colonization events led to an infection. Adequate treatment did not affect microbiological clearance rates. Overall mortality was 8%; no deaths were attributable to enterococcal events.

CONCLUSIONS

Enterococcal colonizations and infections are frequent in transplant recipients. Progression from colonization to infection is rare. Therefore, antibiotic treatment should be used restrictively in colonization. No increased mortality because of enterococcal infection was noted.

Comparative analysis of the complete genome of an epidemic hospital sequence type 203 clone of vancomycin-resistant Enterococcus faecium

Background

In this report we have explored the genomic and microbiological basis for a sustained increase in bloodstream infections at a major Australian hospital caused by Enterococcus faecium multi-locus sequence type (ST) 203, an outbreak strain that has largely replaced a predecessor ST17 sequence type.

Results

To establish a ST203 reference sequence we fully assembled and annotated the genome of Aus0085, a 2009 vancomycin-resistant Enterococcus faecium (VREfm) bloodstream isolate, and the first example of a completed ST203 genome. Aus0085 has a 3.2 Mb genome, comprising a 2.9 Mb circular chromosome and six circular plasmids (2 kb–130 kb). Twelve percent of the 3222 coding sequences (CDS) in Aus0085 are not present in ST17 E. faecium Aus0004 and ST18 E. faecium TX16. Extending this comparison to an additional 12 ST17 and 14 ST203 E. faecium hospital isolate genomes revealed only six genomic regions spanning 41 kb that were present in all ST203 and absent from all ST17 genomes. The 40 CDS have predicted functions that include ion transport, riboflavin metabolism and two phosphotransferase systems. Comparison of the vancomycin resistance-conferring Tn1549 transposon between Aus0004 and Aus0085 revealed differences in transposon length and insertion site, and van locus sequence variation that correlated with a higher vancomycin MIC in Aus0085. Additional phenotype comparisons between ST17 and ST203 isolates showed that while there were no differences in biofilm-formation and killing of Galleria mellonella, ST203 isolates grew significantly faster and out-competed ST17 isolates in growth assays.

Conclusions

Here we have fully assembled and annotated the first ST203 genome, and then characterized the genomic differences between ST17 and ST203 E. faecium. We also show that ST203 E. faecium are faster growing and can out-compete ST17 E. faecium. While a causal genetic basis for these phenotype differences is not provided here, this study revealed conserved genetic differences between the two clones, differences that can now be tested to explain the molecular basis for the success and emergence of ST203 E. faecium.

Characterization of hospital-associated lineages of ampicillin-resistant Enterococcus faecium from clinical cases in dogs and humans

Ampicillin-resistant Enterococcus faecium (ARE) has rapidly emerged worldwide and is one of the most important nosocomial pathogens. However, very few reports are available on ARE isolates from canine clinical cases. The objective of this study was to characterize ARE strains of canine clinical origin from a veterinary teaching hospital in Canada and to compare them with human strains. Ten ARE strains from dogs and humans were characterized by multilocus sequence typing (MLST), pulsed field gel electrophoresis (PFGE), antibiotic susceptibility and biofilm activities, presence of rep-families, CRISPR-cas and putative virulence genes. All ARE strains (n = 10) were resistant to ciprofloxacin and lincomycin. Resistances to tetracycline (n = 6), macrolides (n = 6), and to high concentrations of gentamicin, kanamycin and streptomycin (n = 5) were also observed. Canine ARE isolates were found to be susceptible to vancomycin whereas resistance to this antibiotic was observed in human strains. Ampicillin resistance was linked to PBP5 showing mutations at 25 amino acid positions. Fluoroquinolone resistance was attributable to ParC, GyrA, and GyrB mutations. Data demonstrated that all canine ARE were acm (collagen binding protein)-positive and that most harbored the efaA_fm gene, encoding for a cell wall adhesin. Biofilm formation was observed in two human strains but not in canine strains. Two to five rep-families were observed per strain but no CRISPR sequences were found. A total of six STs (1, 18, 65, 202, 205, and 803) were found with one belonging to a new ST (ST803). These STs were identical or closely related to human hospital-associated lineages. This report describes for the first time the characterization of canine ARE hospital-associated strains in Canada and also supports the importance of prudent antibiotic use in veterinary medicine to avoid zoonotic spread of canine ARE.

Analysis of the tolerance of pathogenic enterococci and Staphylococcus aureus to cell wall active antibiotics

OBJECTIVES

Tolerance refers to the phenomenon that bacteria do not significantly die when exposed to bactericidal antibiotics. Enterococci are known for their high tolerance to these drugs, but the molecular reasons why they resist killing are not understood. In a previous study we showed that the superoxide dismutase (SOD) is implicated in this tolerance. This conclusion was based on the results obtained with one particular strain of Enterococcus faecalis and therefore the objective of the present communication was to analyse whether dependence of tolerance on active SOD is a general phenomenon for enterococci and another Gram-positive pathogen, Staphylococcus aureus.

METHODS

Mutants deficient in SOD activity were constructed in pathogenic enterococci. The wild-type sodA gene was cloned into an expression vector and transformed into SOD-deficient strains for complementation with varying levels of SOD activity. Previously constructed SOD-deficient strains of S. aureus were also included in this study. Tolerance to vancomycin and penicillin was then tested.

RESULTS

We demonstrated that the dependence on SOD of tolerance to vancomycin and penicillin is a common trait of antibiotic-susceptible pathogenic enterococci. By varying the levels of expression we could also show that tolerance to vancomycin is directly correlated to SOD activity. Interestingly, deletion of the sodA gene in a non-tolerant Enterococcus faecium strain did not further sensitize the mutant to bactericidal antibiotics. Finally, we showed that the SOD enzymes of S. aureus are also implicated in tolerance to vancomycin.

CONCLUSION

High tolerance of enterococci to cell wall active antibiotics can be reversed by SOD deficiency.

Microbiological and clinical characteristics of vancomycin-resistant Enterococcus faecium bacteraemia in Taiwan: implication of sequence type for prognosis

OBJECTIVES

Vancomycin-resistant enterococci (VRE), particularly vancomycin-resistant Enterococcus faecium (VREfm), have emerged among the leading pathogens causing hospital-acquired infections worldwide. We aimed to examine whether there were newly introduced clones contributing to this increase and to assess the risk factors for mortality in patients with VREfm bacteraemia.

METHODS

Between 2003 and 2010, all medical records of adult patients diagnosed with VREfm bacteraemia at a university hospital in Taiwan were reviewed. Antibiotic susceptibility, genotyping and multilocus sequence typing of the VREfm isolates were performed.

RESULTS

During the study period, the prevalence of non-duplicated blood VRE isolates increased significantly from 3.9% in 2003 to 18.9% in 2010 (P < 0.0001). One-hundred-and-forty-nine patients with VREfm bacteraemia were noted and 102 isolates of VREfm were available for microbiological characterization. All isolates were susceptible to daptomycin and linezolid. Sequence type (ST) 18 and ST414 were the two predominant emerging STs from 2009 to 2010, accounting for 29.7% and 25.0% of all isolates, respectively. Patients who received immunosuppressives, had a high Charlson comorbidity index or experienced septic shock had a significantly higher 14 day mortality rate. Patients who had bacteraemia caused by ST414 isolates and received appropriate antibiotics had a lower 14 day mortality rate.

CONCLUSIONS

The prevalence of the VRE that caused bacteraemia increased from 2003 to 2010. This increase might be attributed to the clonal spread of VREfm belonging to ST18 and ST414. The all-cause 14 day mortality rate was lower in patients with bacteraemia due to VREfm isolates that belonged to ST414.

Comparative analysis of the first complete Enterococcus faecium genome

Vancomycin-resistant enterococci (VRE) are one of the leading causes of nosocomial infections in health care facilities around the globe. In particular, infections caused by vancomycin-resistant Enterococcus faecium are becoming increasingly common. Comparative and functional genomic studies of E. faecium isolates have so far been limited owing to the lack of a fully assembled E. faecium genome sequence. Here we address this issue and report the complete 3.0-Mb genome sequence of the multilocus sequence type 17 vancomycin-resistant Enterococcus faecium strain Aus0004, isolated from the bloodstream of a patient in Melbourne, Australia, in 1998. The genome comprises a 2.9-Mb circular chromosome and three circular plasmids. The chromosome harbors putative E. faecium virulence factors such as enterococcal surface protein, hemolysin, and collagen-binding adhesin. Aus0004 has a very large accessory genome (38%) that includes three prophage and two genomic islands absent among 22 other E. faecium genomes. One of the prophage was present as inverted 50-kb repeats that appear to have facilitated a 683-kb chromosomal inversion across the replication terminus, resulting in a striking replichore imbalance. Other distinctive features include 76 insertion sequence elements and a single chromosomal copy of Tn1549 containing the vanB vancomycin resistance element. A complete E. faecium genome will be a useful resource to assist our understanding of this emerging nosocomial pathogen.

Genomic diversification of enterococci in hosts: the role of the mobilome

Enterococci are ubiquitous lactic acid bacteria, possessing a flexible nature that allows them to colonize various environments and hosts but also to be opportunistic pathogens. Many papers have contributed to a better understanding of: (i) the taxonomy of this complex group of microorganisms; (ii) intra-species variability; (iii) the role of different pathogenicity traits; and (iv) some markers related to the character of host-specificity, but the reasons of such incredible success of adaptability is still far from being fully explained. Recently, genomic-based studies have improved our understanding of the genome diversity of the most studied species, i.e., E. faecalis and E. faecium. From these studies, what is becoming evident is the role of the mobilome in adding new abilities to colonize new hosts and environments, and eventually in driving their evolution: specific clones associated with human infections or specific hosts can exist, but probably the consideration of these populations as strictly clonal groups is only partially correct. The variable presence of mobile genetic elements may, indeed, be one of the factors involved in the evolution of one specific group in a specific host and/or environment. Certainly more extensive studies using new high throughput technologies are mandatory to fully understand the evolution of predominant clones and species in different hosts and environments.

Comparative analysis of the first complete Enterococcus faecium genome

Vancomycin-resistant enterococci (VRE) are one of the leading causes of nosocomial infections in health care facilities around the globe. In particular, infections caused by vancomycin-resistant Enterococcus faecium are becoming increasingly common. Comparative and functional genomic studies of E. faecium isolates have so far been limited owing to the lack of a fully assembled E. faecium genome sequence. Here we address this issue and report the complete 3.0-Mb genome sequence of the multilocus sequence type 17 vancomycin-resistant Enterococcus faecium strain Aus0004, isolated from the bloodstream of a patient in Melbourne, Australia, in 1998. The genome comprises a 2.9-Mb circular chromosome and three circular plasmids. The chromosome harbors putative E. faecium virulence factors such as enterococcal surface protein, hemolysin, and collagen-binding adhesin. Aus0004 has a very large accessory genome (38%) that includes three prophage and two genomic islands absent among 22 other E. faecium genomes. One of the prophage was present as inverted 50-kb repeats that appear to have facilitated a 683-kb chromosomal inversion across the replication terminus, resulting in a striking replichore imbalance. Other distinctive features include 76 insertion sequence elements and a single chromosomal copy of Tn1549 containing the vanB vancomycin resistance element. A complete E. faecium genome will be a useful resource to assist our understanding of this emerging nosocomial pathogen.

Population biology of Gram-positive pathogens: high-risk clones for dissemination of antibiotic resistance

Infections caused by multiresistant Gram-positive bacteria represent a major health burden in the community as well as in hospitalized patients. Staphylococcus aureus, Enterococcus faecalis and Enterococcus faecium are well-known pathogens of hospitalized patients, frequently linked with resistance against multiple antibiotics, compromising effective therapy. Streptococcus pneumoniae and Streptococcus pyogenes are important pathogens in the community and S. aureus has recently emerged as an important community-acquired pathogen. Population genetic studies reveal that recombination prevails as a driving force of genetic diversity in E. faecium, E. faecalis, S. pneumoniae and S. pyogenes, and thus, these species are weakly clonal. Although recombination has a relatively modest role driving the genetic variation of the core genome of S. aureus, the horizontal acquisition of resistance and virulence genes plays a key role in the emergence of new clinically relevant clones in this species. In this review, we discuss the population genetics of E. faecium, E. faecalis, S. pneumoniae, S. pyogenes and S. aureus. Knowledge of the population structure of these pathogens is not only highly relevant for (molecular) epidemiological research but also for identifying the genetic variation that underlies changes in clinical behaviour, to improve our understanding of the pathogenic behaviour of particular clones and to identify novel targets for vaccines or immunotherapy.

Clustering of polyclonal VanB-type vancomycin-resistant Enterococcus faecium in a low-endemic area was associated with CC17-genogroup strains harbouring transferable vanB2-Tn5382 and pRUM-like repA containing plasmids with axe-txe plasmid addiction systems

VanB-type vancomycin-resistant Enterococcus faecium isolates (n = 17) from 15 patients at the Örebro University hospital in Sweden during a span of 18 months was characterized. All patients had underlying disorders and received broad-spectrum antimicrobial therapy. Pulsed-field gel electrophoresis (PFGE) grouped 14 isolates in three PFGE types and three isolates in unique PFGE patterns. All isolates had multi-locus sequence types [ST17 (n = 5); ST18 (n = 3); ST125 (n = 7); ST262 (n = 1); ST460 (n = 1)] belonging to the successful hospital-adapted clonal complex 17 (CC17), harboured CC17-associated virulence genes, were vanB2-positive and expressed diverse vancomycin minimum inhibitory concentration (MICs; 8 to > 256 mg/L). Isolate 1 had a unique PFGE type and a chromosomal transferable vanB2-Tn5382 element. Interestingly, the other five PFGE types had Tn5382 located on plasmids containing pRUM-like repA and a plasmid addiction system (axe-txe) shown by co-hybridization analysis of PFGE-separated S1-nuclease digested total DNA. The resistance plasmids were mainly of 120-kb and supported intraspecies vanB transfer. Two strains were isolated from patient 6 and we observed a possible transfer of the vanB2-resistance genes from PFGE type III ST460 to a more successful PFGE type I ST125. This latter PFGE type I ST125 became the predominant type afterwards. Our observations support the notion that vanB-type vancomycin-resistant Enterococcus faecium can persist in a low-endemic area through successful clones and plasmids with stability functions in hospital patients with known risk factors.

Transition of Enterococcus faecium from commensal organism to nosocomial pathogen

The Gram-positive species Enterococcus faecium has long been thought of as a harmless commensal of the mammalian GI tract. In the last two decades, however, E. faecium has become an important cause of nosocomial bacteremias. These infections are often difficult to treat owing to the resistance of E. faecium to a large number of antibiotics. In this article, we review the recent transition of E. faecium from commensal to nosocomial pathogen. We focus on population biology-based studies, which suggest that several clonal populations of E. faecium are mostly responsible for causing infections. We also discuss the role of the accessory genome of E. faecium in contributing to the infectious phenotype and examine the role that surface proteins of E. faecium may have in colonization and infection.

Dogs are a reservoir of ampicillin-resistant Enterococcus faecium lineages associated with human infections

Ampicillin resistance is a marker for hospital-associated Enterococcus faecium. Feces from 208 dogs were selectively screened for the occurrence of ampicillin-resistant E. faecium (AREF). AREF was detected in 42 (23%) of 183 dogs screened in a cross-sectional study in the United Kingdom and in 19 (76%) of 25 dogs studied longitudinally in Denmark. AREF carriage was intermittent in all dogs studied longitudinally. Multilocus sequence typing of 63 canine AREF isolates revealed the presence of 13 distinct sequence types. Approximately 76% of the isolates belonged to hospital-adapted clonal complex 17 (CC17), including those of sequence types ST-78 and ST-192, which are widespread in European and Asian hospitals. Longitudinal screening of 18 healthy humans living in contact with 13 of the dogs under study resulted in the identification of a single, intermittent CC17 carrier. This person carried one of the sequence types (ST-78) recovered from his dog. Based on PCR and Southern hybridization analyses, the putative virulence gene cluster from orf903 to orf907 was widespread in canine AREF isolates (present in 97%), whereas orf2351 (present in 26% of isolates) and orf2430 (present in 31%) were strongly associated with CC17-related sequence types (P<0.05). Surprisingly, esp and hyl were not detected in any of the isolates. The antimicrobial resistance profiles of canine AREF isolates generally differed from those previously described for clinical human isolates. The results indicate that dogs are frequent carriers of CC17-related lineages and may play a role in the spread of this nosocomial pathogen. The distinctive virulence and antimicrobial resistance profiles observed among canine AREF isolates raise interesting questions about the origin and evolution of the strains causing human infections.

Distribution of genes encoding MSCRAMMs and Pili in clinical and natural populations of Enterococcus faecium

Enterococcus faecium has recently emerged as an important cause of nosocomial infections. We previously identified 15 predicted surface proteins with characteristics of MSCRAMMs and/or pili and demonstrated that their genes were frequently present in 30 clinical E. faecium isolates studied; one of these, acm, has been studied in further detail. To determine the prevalence of the other 14 genes among various E. faecium populations, we have now assessed 433 E. faecium isolates, including 264 isolates from human clinical infections, 69 isolates from stools of hospitalized patients, 70 isolates from stools of community volunteers, and 30 isolates from animal-related sources. A variable distribution of the 14 genes was detected, with their presence ranging from 51% to 98% of isolates. While 81% of clinical isolates carried 13 or 14 of the 14 genes tested, none of the community group isolates and only 13% of animal isolates carried 13 or 14 genes. The presence of these genes was most frequent in endocarditis isolates, with 11 genes present in all isolates, followed by isolates from other clinical sources. The number of genes significantly associated with clinical versus fecal or animal origin (P = 0.04 to <0.0001) varied from 10 to 13, depending on whether comparisons were made against individual clinical subgroups (endocarditis, blood, and other clinical isolates) or against all clinical isolates combined as one group. The strong association of these genes with clinical isolates raises the possibility that their preservation/acquisition has favored the adaptation of E. faecium to nosocomial environments and/or patients.

Enterococcal surface protein Esp is not essential for cell adhesion and intestinal colonization of Enterococcus faecium in mice

Background

Enterococcus faecium has globally emerged as a cause of hospital-acquired infections with high colonization rates in hospitalized patients. The enterococcal surface protein Esp, identified as a potential virulence factor, is specifically linked to nosocomial clonal lineages that are genetically distinct from indigenous E. faecium strains. To investigate whether Esp facilitates bacterial adherence and intestinal colonization of E. faecium, we used human colorectal adenocarcinoma cells (Caco-2 cells) and an experimental colonization model in mice.

Results

No differences in adherence to Caco-2 cells were found between an Esp expressing strain of E. faecium (E1162) and its isogenic Esp-deficient mutant (E1162Δesp). Mice, kept under ceftriaxone treatment, were inoculated orally with either E1162, E1162Δesp or both strains simultaneously. Both E1162 and E1162Δesp were able to colonize the murine intestines with high and comparable numbers. No differences were found in the contents of cecum and colon. Both E1162 and E1162Δesp were able to translocate to the mesenteric lymph nodes.

Conclusion

These results suggest that Esp is not essential for Caco-2 cell adherence and intestinal colonization or translocation of E. faecium in mice.

Expression of two distinct types of pili by a hospital-acquired Enterococcus faecium isolate

Surface filamentous structures designated pili, and implicated in virulence, have been found on the surfaces of several Gram-positive pathogens. This work describes the conditional expression of two phenotypically distinct pilus-like structures, designated PilA and PilB, on the surface of a hospital-adapted Enterococcus faecium bloodstream isolate. E. faecium is an emerging Gram-positive opportunistic pathogen that can cause severe disease, particularly in immunocompromised patients. Expression of PilA- and PilB-type pili was analysed during different phases of growth in broth culture. During growth, PilA and PilB pilin subunits were expressed around the cross-wall in early-exponential-phase cells. Polymerization and migration of short PilB-type pili towards the poles occurred in cells from the exponential phase and long polymerized pili were expressed at the poles of cells grown to stationary phase. In contrast, PilA-type pili were not expressed in broth culture, but only when cells were grown on solid media. Furthermore, surface expression of the PilA- and PilB-type pili was regulated in a temperature-dependent manner, as polymerization of two distinct types of pili at the surface only occurred when cells were grown at 37 degrees C; no pili were observed on cells grown at 21 degrees C. Hospital-aquired E. faecium isolates were specifically enriched in pilin gene clusters, suggesting that conditional expression of pili may contribute to E. faecium pathogenesis.

Emergence of clonal complex 17 Enterococcus faecium in The Netherlands

The global emergence of vancomycin-resistant Enterococcus faecium has been characterized as the clonal spread of clonal complex 17 (CC17) E. faecium. CC17 was defined upon multilocus sequence typing and is characterized by resistance to quinolones and ampicillin and the presence of the enterococcal surface protein (Esp) in the majority of isolates. The recently noticed increased incidence of vancomycin-susceptible CC17 E. faecium infections in our hospital initiated a nationwide study to determine ecological changes among enterococcal infections. The data and strain collections were obtained from 26 (38%) and 9 (14%) of 66 microbiology laboratories in The Netherlands. E. faecium and E. faecalis were distinguished by multiplex PCR; all E. faecium isolates were genotyped by multiple-locus variable-number tandem-repeat analysis (MLVA), and the presence of esp was identified by PCR. Average numbers of ampicillin-resistant enterococcal isolates from normally sterile body sites per hospital increased from 5 +/- 1 in 1994 to 25 +/- 21 in 2005. Among all enterococcal bloodstream infections, the proportions of ampicillin-resistant E. faecium (AREF) increased from 4% in 1994 to 20% in 2005 (P < 0.001). All E. faecalis isolates were susceptible to ampicillin, whereas 78% of the E. faecium isolates were resistant (49% of these contained esp). Genotyping revealed that 86% of AREF isolates belonged to CC17, including four dominant MLVA types found in > or = 3 hospitals, accounting for 64% of the AREF isolates. Infections caused by CC17 E. faecium has increased nationwide, especially in university hospitals due to the clonal spread of four MLVA types, and seems associated with acquisition of the esp gene.

Five genes encoding surface-exposed LPXTG proteins are enriched in hospital-adapted Enterococcus faecium clonal complex 17 isolates

Most Enterococcus faecium isolates associated with hospital outbreaks and invasive infections belong to a distinct genetic subpopulation called clonal complex 17 (CC17). It has been postulated that the genetic evolution of CC17 involves the acquisition of various genes involved in antibiotic resistance, metabolic pathways, and virulence. To gain insight into additional genes that may have favored the rapid emergence of this nosocomial pathogen, we aimed to identify surface-exposed LPXTG cell wall-anchored proteins (CWAPs) specifically enriched in CC17 E. faecium. Using PCR and Southern and dot blot hybridizations, 131 E. faecium isolates (40 CC17 and 91 non-CC17) were screened for the presence of 22 putative CWAP genes identified from the E. faecium TX0016 genome. Five genes encoding LPXTG surface proteins were specifically enriched in E. faecium CC17 isolates. These five LPXTG surface protein genes were found in 28 to 40 (70 to 100%) of CC17 and in only 7 to 24 (8 to 26%) of non-CC17 isolates (P < 0.05). Three of these CWAP genes clustered together on the E. faecium TX0016 genome, which may comprise a novel enterococcal pathogenicity island covering E. faecium contig 609. Expression at the mRNA level was demonstrated, and immunotransmission electron microscopy revealed an association of the five LPXTG surface proteins with the cell wall. Minimal spanning tree analysis based on the presence and absence of 22 CWAP genes revealed grouping of all 40 CC17 strains together with 18 hospital-derived but evolutionary unrelated non-CC17 isolates in a distinct CWAP-enriched cluster, suggesting horizontal transfer of CWAP genes and a role of these CWAPs in hospital adaptation.

Enterococcal surface protein Esp is important for biofilm formation of Enterococcus faecium E1162

Enterococci have emerged as important nosocomial pathogens with resistance to multiple antibiotics. Adhesion to abiotic materials and biofilm formation on medical devices are considered important virulence properties. A single clonal lineage of Enterococcus faecium, complex 17 (CC17), appears to be a successful nosocomial pathogen, and most CC17 isolates harbor the enterococcal surface protein gene, esp. In this study, we constructed an esp insertion-deletion mutant in a clinical E. faecium CC17 isolate. In addition, initial adherence and biofilm assays were performed. Compared to the wild-type strain, the esp insertion-deletion mutant no longer produced Esp on the cell surface and had significantly lower initial adherence to polystyrene and significantly less biofilm formation, resulting in levels of biofilm comparable to those of an esp-negative isolate. Capacities for initial adherence and biofilm formation were restored in the insertion-deletion mutant by in trans complementation with esp. These results identify Esp as the first documented determinant in E. faecium CC17 with an important role in biofilm formation, which is an essential factor in infection pathogenesis.

Ecological replacement of Enterococcus faecalis by multiresistant clonal complex 17 Enterococcus faecium

The proportion of enterococcal infections caused by ampicillin-resistant Enterococcus faecium (AREfm) in a European hospital increased from 2% in 1994 to 32% in 2005, with prevalence rates of AREfm endemicity of up to 35% in at least six hospital wards. Diabetes mellitus, three or more admissions in the preceding year, and use of beta-lactams and fluoroquinolones, were all associated with AREfm colonisation. Of 217 AREfm isolates that were genotyped, 97% belonged to clonal complex 17 (CC17). This ecological change mimics events preceding the emergence of vancomycin-resistant E. faecium (VREF) in the USA and may presage the emergence of CC17 VREF in European hospitals.

Monoclonal antibodies recognizing the Enterococcus faecalis collagen-binding MSCRAMM Ace: conditional expression and binding analysis

Enterococci are opportunistic pathogens known to cause numerous clinical infections and complications in humans. Adhesin-mediated binding to extracellular matrix (ECM) proteins of the host is thought to be a crucial step in the pathogenesis of these bacterial infections. Adhesin of collagen from Enterococcus faecalis (Ace) is a cell-wall anchored protein of E. faecalis that has been shown to be important for bacterial binding to the ECM. In this report, we characterize the conditions for Ace expression and demonstrate Ace binding to mammalian epithelial and endothelial cells as well as to collagens found in the ECM. To further characterize Ace expression and function, we report the generation of a panel of monoclonal antibodies (mAbs) directed against this important E. faecalis virulence factor. Through the use of multiple in vitro assays, surface plasmon resonance and flow cytometry, we have characterized this panel of mAbs which may prove to be not only beneficial in studies that address the precise biological role of adhesion of E. faecalis, but may also serve as beneficial therapeutic agents against E. faecalis infections.

Enterococcal Infection in Children

From relative obscurity, enterococci have become a leading cause of nosocomial infection. This has been attributed, in part, to the growth in susceptible host populations, increased use of intravascular devices, prolonged hospital stay, and widespread antibiotics use. Furthermore, the facility with which enterococci acquire resistance characteristics coupled with their capacity to survive in the environment renders them uniquely suited as nosocomial opportunists and have resulted in global dissemination of resistant strains. Debate continues as to whether most serious infections arise from a person's indigenous flora or dissemination of virulent clones. Enterococci are normal inhabitants of the human gastrointestinal tract. Classically associated with endocarditis and wound and urinary tract infections, increasingly they are a cause of nosocomial bacteremia. The rise in incidence of serious enterococcal infection has been particularly evident in neonatal, paediatric intensive care, and haematology/oncology units. Spread of resistant phenotypes has posed a difficult therapeutic challenge. We have been rescued, albeit perhaps only temporarily, by the addition of newer agents, such as linezolid, to the therapeutic armamentarium. However, there is no room for complacency. Linezolid resistance already has been reported. Efforts must continue to focus on prevention of the emergence and dissemination of resistance through policies of rational antibiotic use, infection control and education.

Pathogenesis of implant infections by enterococci

Enterococci are commensals of human and animal intestinal tract that have emerged in the last decades as a major cause of nosocomial infections of bloodstream, urinary tract and in infected surgical sites. Enterococcus faecalis is responsible for ca. 80% of all enterococcal infections while Enterococcus faecium accounts for most of the others; among the most relevant risk factors for development of enterococcal infections is the presence of implanted devices. The pathogenesis of such infections is poorly understood, but several virulence factors have been proposed. Among them, the ability to form biofilm has recently been shown to be one of the most prominent features of this microorganism, allowing colonization of inert and biological surfaces, while protecting against antimicrobial substances, and mediating adhesion and invasion of host cells and survival within professional phagocytes. Biofilm formation has been shown to be particularly important in the development of prosthetic valve enterococcal endocarditis and stent occlusion. Enterococci are also able to express other surface factors that may support colonization of both inert and biological surfaces, and that may be involved in the invasion of, and survival within, the host cell.

Construction of improved temperature-sensitive and mobilizable vectors and their use for constructing mutations in the adhesin-encoding acm gene of poorly transformable clinical Enterococcus faecium strains

Inactivation by allelic exchange in clinical isolates of the emerging nosocomial pathogen Enterococcus faecium has been hindered by lack of efficient tools, and, in this study, transformation of clinical isolates was found to be particularly problematic. For this reason, a vector for allelic replacement (pTEX5500ts) was constructed that includes (i) the pWV01-based gram-positive repAts replication region, which is known to confer a high degree of temperature intolerance, (ii) Escherichia coli oriR from pUC18, (iii) two extended multiple-cloning sites located upstream and downstream of one of the marker genes for efficient cloning of flanking regions for double-crossover mutagenesis, (iv) transcriptional terminator sites to terminate undesired readthrough, and (v) a synthetic extended promoter region containing the cat gene for allelic exchange and a high-level gentamicin resistance gene, aph(2'')-Id, to distinguish double-crossover recombination, both of which are functional in gram-positive and gram-negative backgrounds. To demonstrate the functionality of this vector, the vector was used to construct an acm (encoding an adhesin to collagen from E. faecium) deletion mutant of a poorly transformable multidrug-resistant E. faecium endocarditis isolate, TX0082. The acm-deleted strain, TX6051 (TX0082Deltaacm), was shown to lack Acm on its surface, which resulted in the abolishment of the collagen adherence phenotype observed in TX0082. A mobilizable derivative (pTEX5501ts) that contains oriT of Tn916 to facilitate conjugative transfer from the transformable E. faecalis strain JH2Sm::Tn916 to E. faecium was also constructed. Using this vector, the acm gene of a nonelectroporable E. faecium wound isolate was successfully interrupted. Thus, pTEX5500ts and its mobilizable derivative demonstrated their roles as important tools by helping to create the first reported allelic replacement in E. faecium; the constructed this acm deletion mutant will be useful for assessing the role of acm in E. faecium pathogenesis using animal models.

Global spread of vancomycin-resistant Enterococcus faecium from distinct nosocomial genetic complex

Vancomycin-resistant enterococci (VRE) have caused hospital outbreaks worldwide, and the vancomycin-resistance gene (vanA) has crossed genus boundaries to methicillin-resistant Staphylococcus aureus. Spread of VRE, therefore, represents an immediate threat for patient care and creates a reservoir of mobile resistance genes for other, more virulent pathogens. Evolutionary genetics, population structure, and geographic distribution of 411 VRE and vancomycin-susceptible Enterococcus faecium isolates, recovered from human and nonhuman sources and community and hospital reservoirs in 5 continents, identified a genetic lineage of E. faecium (complex-17) that has spread globally. This lineage is characterized by 1) ampicillin resistance, 2) a pathogenicity island, and 3) an association with hospital outbreaks. Complex-17 is an example of cumulative evolutionary processes that improved the relative fitness of bacteria in hospital environments. Preventing further spread of this epidemic E. faecium subpopulation is critical, and efforts should focus on the early disclosure of ampicillin-resistant complex-17 strains.

Global Spread of Vancomycin-resistantEnterococcus faeciumfrom Distinct Nosocomial Genetic Complex

Vancomycin-resistant enterococci (VRE) have caused hospital outbreaks worldwide, and the vancomycin-resistance gene (vanA) has crossed genus boundaries to methicillin-resistant Staphylococcus aureus. Spread of VRE, therefore, represents an immediate threat for patient care and creates a reservoir of mobile resistance genes for other, more virulent pathogens. Evolutionary genetics, population structure, and geographic distribution of 411 VRE and vancomycin-susceptible Enterococcus faecium isolates, recovered from human and nonhuman sources and community and hospital reservoirs in 5 continents, identified a genetic lineage of E. faecium (complex-17) that has spread globally. This lineage is characterized by 1) ampicillin resistance, 2) a pathogenicity island, and 3) an association with hospital outbreaks. Complex-17 is an example of cumulative evolutionary processes that improved the relative fitness of bacteria in hospital environments. Preventing further spread of this epidemic E. faecium subpopulation is critical, and efforts should focus on the early disclosure of ampicillin-resistant complex-17 strains.

Linezolid in the treatment of vancomycin-resistant Enterococcus faecium in solid organ transplant recipients: report of a multicenter compassionate-use trial

Vancomycin-resistant Enterococcus faecium (VRE) is increasing in incidence in solid organ transplant recipients and has a high (up to 83%) associated mortality rate. Until recently, there have been no consistently effective antimicrobial therapies for VRE infection. Linezolid is a new antibiotic that belongs to the class of oxazolidinones approved by the FDA for the treatment of VRE infections, including those with bacteremia. Here, we report the experience with linezolid in an open-label, compassionate-use trial at 53 US centers for the treatment of documented VRE infections in patients with solid organ transplants. Eighty-five patients with solid organ transplants and documented VRE infections were studied. Blood cultures were positive for VRE in 43 patients, while 42 patients had other, non-rectal, sites of infection. Fifty-three patients responded well to treatment, with clinical resolution of the infection (62.4% survival rate). Of these, 47 had documented negative cultures post therapy. The mean duration of therapy for cured patients was 23.5 days. Thirty-two (37.6%) patients died, 28 due to sepsis and organ failure (32.9% failure rate), and 4 due to unrelated causes. Mortality rates for patients with bacteremia were comparable to mortality rates observed with patients who had positive cultures from other sites. Adverse reactions to linezolid included thrombocytopenia (4.7%), decreased leukocyte count (3.5%), and an increase in blood pressure (1.2%), none of which led to discontinuation of therapy. Linezolid appears to be a safe and effective treatment option for VRE, even in the presence of bacteremia, and may lead to decreased mortality in solid organ transplant recipients with VRE infection.

A novel putative enterococcal pathogenicity island linked to the esp virulence gene of Enterococcus faecium and associated with epidemicity

Enterococcus faecalis harbors a virulence-associated surface protein encoded by the esp gene. This gene has been shown to be part of a 150-kb putative pathogenicity island. A gene similar to esp has recently been found in Enterococcus faecium isolates recovered from hospitalized patients. In the present study we analyzed the polymorphism in the esp gene of E. faecium, and we investigated the association of esp with neighboring chromosomal genes. The esp gene showed considerable sequence heterogeneity in the regions encoding the nonrepeat N- and C-terminal domains of the Esp protein as well as differences in the number of repeats. DNA sequencing of chromosomal regions flanking the esp gene of E. faecium revealed seven open reading frames, representing putative genes implicated in virulence, regulation of transcription, and antibiotic resistance. These flanking regions were invariably associated with the presence or absence of the esp gene in E. faecium, indicating that esp in E. faecium is part of a distinct genetic element. Because of the presence of virulence genes in this gene cluster, the lower G+C content relative to that of the genome, and the presence of esp in E. faecium isolates associated with nosocomial outbreaks and clinically documented infections, we conclude that this genetic element constitutes a putative pathogenicity island, the first one described in E. faecium. Except for the presence of esp and araC, this pathogenicity island is completely different from the esp-containing pathogenicity island previously disclosed in E. faecalis.

Can Enterococcal Infections Initiate Sepsis Syndrome?

Enterococci are the third most common nosocomial bloodstream pathogen and frequently are the causative pathogen(s) of intra-abdominal, genitourinary, surgical wound, endovascular, or other serious infections. In addition to a diverse spectrum of intrinsic and acquired antimicrobial resistance mechanisms, some strains of enterococci exhibit numerous virulence factors that facilitate mucosal adherence, tissue invasiveness, endovascular attachment, and inflammation production. However, the opportunistic nature of enterococcal infection coupled with animal models of experimental enterococcal and mixed infection have caused many to question the independent capacity of this organism to incite severe sepsis or septic shock. Despite evidence suggesting that this organism possesses low intrinsic virulence, observational and interventional trials of enterococcal bacteremia and sepsis strongly support the notion that Enterococcus is capable of promulgating sepsis as a solitary or copathogen with more serious sequelae in the immunocompromised hosts. Monomicrobial enterococcal bacteremia appears to be increasing during the glycopeptide-resistant era, which bolsters the notion that pure enterococcal sepsis is a real entity.

[Oxazolidinones and glycopeptides]

We review the chemical structure, pharmacokinetics, antimicrobial spectrum, mechanisms of action and resistance, clinical use and adverse effects of oxazolidinones (linezolid) and glycopeptides. Oxazolidinones inhibit protein synthesis and glycopeptides cell wall synthesis. Antibacterial spectra cover grampositive pathogens, including multiresistant organisms. Linezolid has a 100% absorption and can be administered orally or intravenously; it is cleared by renal and hepatic routes, thus dose adjustments are not needed in moderate renal or hepatic failure. Oral absorption of glycopeptides is minimal. They are excreted by the kidneys (dose adjustments are needed in renal failure). The main clinical indications are the treatment of infections caused by grampositive pathogens; linezolid is also useful for infections caused by glycopeptide-resistant enterococcal infections. Linezolid can cause trombocytopenia when treatment lasted longer than two weeks. The main side effect of vancomycin is its nefrotoxicity and teicoplanin can cause fever.

Human health hazards associated with the administration of antimicrobials to slaughter animals. Part II. An assessment of the risks of resistant bacteria in pigs and pork

Risks for the consumer regarding the acquisition of resistant bacteria and/or resistance genes via the consumption of pork are discussed. In general, Salmonella spp. and Escherichia coli that originate from animals do not easily transfer their resistance genes to the resident intestinal flora of humans. The prevalence of resistant E. coli in humans seems more associated with being a vegetarian (odds ratio (OR) 1.89) than with the consumption of meat and meat products. Other risk factors are treatment with antimicrobials (OR 2-5), becoming hospitalized (OR 5.93), or working in a health setting (OR 4.38). In the Netherlands, annually an estimated 45,000 people (0-150,000) become a carrier of resistant E. coli and/or resistance genes that ori ginate from pigs, while an estimated 345,000 persons (175,000-600,000) become a carrier of resistant E. coli and/or resistance genes that originate from hospitals, e.g. other patients. Any problems with resistant Salmonella spp. that stem from pigs are, in fact, an integral part of the total problem of food-borne salmonellosis. Sometimes there are outbreaks of a specific multi-resistant clone of S. typhimurium that causes problems in both farm animals and humans. The probability that in the next 30 years there is no or maximally one outbreak of a specific clone that originates from pig herds is estimated at about 75%. Antimicrobials used as a growth promoter can have a measurable influence on the prevalence of resistant bacteria. The likely chain of events regarding avoparcin and the selection and dissemination of resistance against vancomycin in the enterococci gives the impression that the impact of the use of antimicrobials in animals on the prevalence of resistance in humans is largely determined by whether resistance genes are, or become, located on a self-transferable transposon. Furthermore, consumer health risks of antimicrobials used in slaughter pigs are mainly determined by the selection and dissemination of bacterial resistance and much less by the toxicological properties of any residues in pork. It is also concluded that most of the problems with resistant bacteria in humans are associated with the medical use of antimicrobials, and that the impact of particularly the veterinary use of antimicrobials is limited. However, the impact of antimicrobials used as a feed additive appears to be much greater than that of antimicrobials used for strictly veterinary purposes. The use of antimicrobials as a feed additive should therefore be seriously reconsidered.

Comparison of antimicrobial resistance phenotypes and resistance genes in Enterococcus faecalis and Enterococcus faecium from humans in the community, broilers, and pigs in Denmark

Enterococcus faecalis and E. faecium isolated from humans in the community (98 and 65 isolates), broilers (126 and 122), and pigs (102 and 88) during 1998 were tested for susceptibility to 12 different antimicrobial agents and for the presence of selected genes encoding resistance using PCR. Furthermore, the presence of vancomycin resistant enterococci was examined in 38 human stool samples using selective enrichment. Widespread resistance to chloramphenicol, macrolides, kanamycin, streptomycin, and tetracycline was found among isolates from all three sources. All E. faecium isolates from humans and pigs were susceptible to avilamycin, whereas 35% of isolates from broilers were resistant. All E. faecium isolates from humans were susceptible to vancomycin, whereas 10% and 17% of isolates from broilers and pigs, respectively, were resistant. A vancomycin resistant E. faecium isolate was found in one of the 38 human fecal samples examined using selective enrichment. All vancomycin resistant isolates contained the vanA gene, all chloramphenicol resistant isolates the cat(pIP501) gene, and all five gentamicin resistant isolates the aac6-aph2 gene. Sixty-one (85%) of 72 erythromycin resistant E. faecalis examined and 57 (90%) of 63 erythromycin resistant E. faecium isolates examined contained ermB. Forty (91%) of the kanamycin resistant E. faecalis and 18 (72%) of the kanamycin resistant E. faecium isolates contained aphA3. The tet(M) gene was found in 95% of the tetracycline resistant E. faecalis and E. faecium isolates of human and animal origin, examined. tet(K) was not observed, whereas tet(L) was detected in 17% of tetracycline resistant E. faecalis isolates and in 16% of the E. faecium isolates. tet(O) was not detected in any of the isolates from pigs, but was observed in 38% of E. faecalis isolates from broilers, in two E. faecalis isolates from humans and in three E. faecium isolates from broilers. tet(S) was not detected among isolates from animals, but was observed in 31% of E. faecalis and one E. faecium isolate from humans. This study showed a frequent occurrence of antimicrobial resistance and the presence of selected resistance genes in E. faecalis and E. faecium isolated from humans, broilers and pigs. Differences in the occurrence of resistance and tetracycline resistance genes were observed among isolates from the different sources. However, similar resistance patterns and resistance genes were detected frequently indicating that transmission of resistant enterococci or resistance genes takes place between humans, broilers, and pigs.

The epidemiology of vancomycin-resistant enterococci

Major differences in the epidemiology of vanA carrying enterococci exist between Europe and the USA, where these organisms have been well investigated. These differences are probably related to the differences in antibiotic use in humans and animals in both continents, but more research is needed before firm conclusions can be drawn.