Emergence of CC17 Enterococcus faecium: from commensal to hospital-adapted pathogen

Dogs leaving the ICU carry a very large multi-drug resistant enterococcal population with capacity for biofilm formation and horizontal gene transfer

The enterococcal community from feces of seven dogs treated with antibiotics for 2–9 days in the veterinary intensive care unit (ICU) was characterized. Both, culture-based approach and culture-independent 16S rDNA amplicon 454 pyrosequencing, revealed an abnormally large enterococcal community: 1.4±0.8×10⁸ CFU gram⁻¹ of feces and 48.9±11.5% of the total 16,228 sequences, respectively. The diversity of the overall microbial community was very low which likely reflects a high selective antibiotic pressure. The enterococcal diversity based on 210 isolates was also low as represented by Enterococcus faecium (54.6%) and Enterococcus faecalis (45.4%). E. faecium was frequently resistant to enrofloxacin (97.3%), ampicillin (96.5%), tetracycline (84.1%), doxycycline (60.2%), erythromycin (53.1%), gentamicin (48.7%), streptomycin (42.5%), and nitrofurantoin (26.5%). In E. faecalis, resistance was common to tetracycline (59.6%), erythromycin (56.4%), doxycycline (53.2%), and enrofloxacin (31.9%). No resistance was detected to vancomycin, tigecycline, linezolid, and quinupristin/dalfopristin in either species. Many isolates carried virulence traits including gelatinase, aggregation substance, cytolysin, and enterococcal surface protein. All E. faecalis strains were biofilm formers in vitro and this phenotype correlated with the presence of gelE and/or esp. In vitro intra-species conjugation assays demonstrated that E. faecium were capable of transferring tetracycline, doxycycline, streptomycin, gentamicin, and erythromycin resistance traits to human clinical strains. Multi-locus variable number tandem repeat analysis (MLVA) and pulsed-field gel electrophoresis (PFGE) of E. faecium strains showed very low genotypic diversity. Interestingly, three E. faecium clones were shared among four dogs suggesting their nosocomial origin. Furthermore, multi-locus sequence typing (MLST) of nine representative MLVA types revealed that six sequence types (STs) originating from five dogs were identical or closely related to STs of human clinical isolates and isolates from hospital outbreaks. It is recommended to restrict close physical contact between pets released from the ICU and their owners to avoid potential health risks.

Changes in vancomycin-resistant Enterococcus faecium causing outbreaks in Brazil

Enterococci have been implicated in severe human infections as a consequence of associated determinants of virulence and antimicrobial resistance. The majority of vancomycin-resistant Enterococcus faecium (VRE(fm)) connected to outbreaks worldwide pertains to the clonal complex 17 (CC17). In Brazil, the majority of VRE(fm) involved in outbreaks reported so far are not related to CC17. VRE(fm) strains responsible for an outbreak and sporadic cases in hospitals located in the city of Campinas, Brazil, were compared to other VRE(fm) strains in the country. Twenty-two out of 23 E. faecium were vancomycin-resistant and harboured the vanA gene. One vancomycin-susceptible E. faecium (VSE(fm)) strain was included in this study because it was isolated from a patient who one week later harboured a VRE(fm). All strains, except VSE, showed the same alteration in the VanA element characterised by deletion of the left extremity of the transposon and insertion of IS1251 between the vanS and vanH genes. Genes codifying virulence factors such as collagen-adhesin protein, enterococcal surface protein and hyaluronidase were detected in the VRE(fm) and VSE(fm) studied. Both pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) revealed that VRE(fm) and VSE(fm) strains have a clonal relationship. New sequence types (STs) were identified by MLST as ST447, ST448, ST478 and ST412 but all belonged to the CC17. The present study revealed that VRE(fm) outbreaks in Brazil were caused by strains that did not share a common evolutionary history, and that VRE(fm) strains belonging to CC17 could be predominant in Brazil as in other countries.

Analysis of PBP5 of early U.S. isolates of Enterococcus faecium: sequence variation alone does not explain increasing ampicillin resistance over time

Recent studies have shown that ampicillin resistance has increased steadily over the past 3 decades within U.S. Enterococcus faecium isolates. Analysis of the predicted PBP5 protein of 41 isolates showed a consensus PBP5 pattern for the 9 isolates with MICs of <4 μg/ml that is distinctly different from the PBP5 consensus of the 32 isolates with MICs of >4 μg/ml with ∼5% difference between these; however, there were no consistent amino acid changes that correlated with specific increases in the MICs of ampicillin within the latter group. Analysis of three other genes encoding cell wall/surface proteins also showed that there are two distinct evolutionary groups for each gene, but with occasional mixing of genes, consistent with a species that evolves by recombination.

Genetic detection and multilocus sequence typing of vanA-containing Enterococcus strains from mullets fish (Liza ramada)

Enterococci have emerged as important nosocomial and community-acquired pathogens in humans. The presence of vanA-enterococci was investigated in 103 fecal samples recovered from mullets fish (Liza ramada). All fecal samples were inoculated in Slanetz-Bartley agar plates supplemented with 4 mg/L of vancomycin for vancomycin-resistant enterococci (VRE) recovery and two isolates/sample were characterized. Antibiotic susceptibility was tested for 11 antibiotics by disk diffusion and agar dilution methods. VRE identification was performed by biochemical and molecular methods. Additionally, the mechanisms of resistance to glycopeptides (vanA, vanB, vanC1, vanC2, and vanD) and other antibiotics [erm(A), erm(B), tet(L), tet(M), aph(2'')-aac(6'), aph(3')-IIIa, ant(6'), vat(D), vat(E)] as well as the presence of enterococcal surface protein (esp) and hyl virulence factors were investigated. vanA-Enterococcus faecium isolates were recovered from 4 of 103 tested samples, and they showed glycopeptide and erythromycin resistances. Three of them were also ampicillin resistant, two showed resistance to tetracycline, ciprofloxacin, and kanamycin, and one showed resistance to gentamicin. The tet(M) and erm(B) genes were found in all tetracycline- and erythromycin-resistant strains, respectively. The aph(3')-III and aph(2'')-aac(6') genes were identified in the kanamycin- and gentamicin-resistant isolates, respectively. The IS1216 element was identified within vanX-vanY region of Tn1546 in two vanA isolates. The hyl and esp virulence genes were found in four and two isolates, respectively. vanA-strains were ascribed to sequence types ST280 (two isolates) and ST273 (two isolates), including both lineages into the clonal complex CC17. Mullets fish can excrete VRE in their feces and may be a reservoir for such resistant bacteria that can be transmitted to other animals including humans.

IS element IS16 as a molecular screening tool to identify hospital-associated strains of Enterococcus faecium

Background

Hospital strains of Enterococcus faecium could be characterized and typed by various molecular methods (MLST, AFLP, MLVA) and allocated to a distinct clonal complex known as MLST CC17. However, these techniques are laborious, time-consuming and cost-intensive. Our aim was to identify hospital E. faecium strains and differentiate them from colonizing and animal variants by a simple, inexpensive and reliable PCR-based screening assay. We describe here performance and predictive value of a single PCR detecting the insertion element, IS16, to identify hospital E. faecium isolates within a collection of 260 strains of hospital, animal and human commensal origins.

Methods

Specific primers were selected amplifying a 547-bp fragment of IS16. Presence of IS16 was determined by PCR screenings among the 260 E. faecium isolates. Distribution of IS16 was compared with a prevalence of commonly used markers for hospital strains, esp and hyl_Efm. All isolates were typed by MLST and partly by PFGE. Location of IS16 was analysed by Southern hybridization of plasmid and chromosomal DNA.

Results

IS16 was exclusively distributed only among 155 invasive strains belonging to the clonal complex of hospital-associated strains ("CC17"; 28 MLST types) and various vancomycin resistance genotypes (vanA/B/negative). The five invasive IS16-negative strains did not belong to the clonal complex of hospital-associated strains (CC17). IS16 was absent in all but three isolates from 100 livestock, food-associated and human commensal strains ("non-CC17"; 64 MLST types). The three IS16-positive human commensal isolates revealed MLST types belonging to the clonal complex of hospital-associated strains (CC17). The values predicting a hospital-associated strain ("CC17") deduced from presence and absence of IS16 was 100% and thus superior to screening for the presence of esp (66%) and/or hyl_Efm (46%). Southern hybridizations revealed chromosomal as well as plasmid localization of IS16.

Conclusions

This simple screening assay for insertion element IS16 is capable of differentiating hospital-associated from human commensal, livestock- and food-associated E. faecium strains and thus allows predicting the epidemic strengths or supposed pathogenic potential of a given E. faecium isolate identified within the nosocomial setting.

The recombinase IntA is required for excision of esp-containing ICEEfm1 in Enterococcus faecium

Comparative genome analysis of Enterococcus faecium recently revealed that a genomic island containing the esp gene, referred to as the esp-containing pathogenicity island (esp PAI), can be transferred by conjugation and contains a partial Tn916-like element and an integrase gene, intA. Here, we characterize the role of intA in the excision of the esp PAI. An intA insertion-deletion mutant in E. faecium E1162 (E1162ΔintA) was constructed and in trans complemented with wild-type intA (E1162ΔintA::pEF30). Circular intermediates (CI) of excised esp PAI were determined using inverse PCR analysis on purified chromosomal DNA from strains E1162, E1162Δesp, E1162ΔintA, and E1162ΔintA::pEF30. In E1162 and E1162Δesp, CI of the esp PAI were detected. No CI were detected in E1162ΔintA, while in the complemented strain E1162ΔintA::pEF30 CI formation was restored, indicating that intA is essential for excision and subsequent mobilization of the esp-containing genomic island in E. faecium. Based on the fact that this island can be mobilized and is self-transmissible, we propose to change the name of the esp PAI to ICEEfm1.

Genotyping of Enterococcus faecalis and Enterococcus faecium isolates by use of a set of eight single nucleotide polymorphisms

A single nucleotide polymorphism (SNP) genotyping method for Enterococcus faecalis and Enterococcus faecium was developed using the "Minimum SNPs" program. SNP sets were interrogated using allele-specific real-time PCR. SNP typing subdivided clonal complexes 2 and 9 of E. faecalis and 17 of E. faecium, members of which cause the majority of nosocomial infections globally.

A genetic element present on megaplasmids allows Enterococcus faecium to use raffinose as carbon source

Enterococcus faecium is a commensal of the gastrointestinal tract of humans and animals. Since the 1990s, it has also emerged as a nosocomial pathogen. Little is known about carbon metabolism of E. faecium even though the ability to utilize different sugars could be an important factor in adapting to different ecological niches. In this study we identify an E. faecium gene cluster that is responsible for the metabolism of the α-galactoside sugar raffinose. Phenotypic testing of seven E. faecium isolates of which the genomes were previously sequenced showed that one isolate (strain E980) could grow on raffinose. Genome analysis identified a gene cluster containing two genes encoding α-galactosidases (termed agaA and agaB) that was uniquely present in E980. The agaA and agaB genes were significantly more frequently found in strains that are phylogenetically related to E980 and were more prevalent in surveillance isolates from hospital and community sources than in isolates from clinical infections. Disruption of the α-galactosidase gene agaB, but not of agaA, disabled growth on raffinose in strain E980. In all strains agaA and agaB are carried on megaplasmids that are between 150 and 300 kb in size. Filter-mating experiments showed that the megaplasmid of E980 can be transferred to a plasmidless recipient which then gains the ability to grow on raffinose. The observation that raffinose utilization by E. faecium is a trait carried by megaplasmids indicates that these megaplasmids can have important roles in shaping the competitive fitness of E. faecium in the environment, for example by expanding the metabolic repertoire of this organism.

Multidrug-resistant enterococci lack CRISPR-cas

Clustered, regularly interspaced short palindromic repeats (CRISPR) provide bacteria and archaea with sequence-specific, acquired defense against plasmids and phage. Because mobile elements constitute up to 25% of the genome of multidrug-resistant (MDR) enterococci, it was of interest to examine the codistribution of CRISPR and acquired antibiotic resistance in enterococcal lineages. A database was built from 16 Enterococcus faecalis draft genome sequences to identify commonalities and polymorphisms in the location and content of CRISPR loci. With this data set, we were able to detect identities between CRISPR spacers and sequences from mobile elements, including pheromone-responsive plasmids and phage, suggesting that CRISPR regulates the flux of these elements through the E. faecalis species. Based on conserved locations of CRISPR and CRISPR-cas loci and the discovery of a new CRISPR locus with associated functional genes, CRISPR3-cas, we screened additional E. faecalis strains for CRISPR content, including isolates predating the use of antibiotics. We found a highly significant inverse correlation between the presence of a CRISPR-cas locus and acquired antibiotic resistance in E. faecalis, and examination of an additional eight E. faecium genomes yielded similar results for that species. A mechanism for CRISPR-cas loss in E. faecalis was identified. The inverse relationship between CRISPR-cas and antibiotic resistance suggests that antibiotic use inadvertently selects for enterococcal strains with compromised genome defense.

For many bacteria, including the opportunistically pathogenic enterococci, antibiotic resistance is mediated by acquisition of new DNA and is frequently encoded on mobile DNA elements such as plasmids and transposons. Certain enterococcal lineages have recently emerged that are characterized by abundant mobile DNA, including numerous viruses (phage), and plasmids and transposons encoding multiple antibiotic resistances. These lineages cause hospital infection outbreaks around the world. The striking influx of mobile DNA into these lineages is in contrast to what would be expected if a self (genome)-defense system was present. Clustered, regularly interspaced short palindromic repeat (CRISPR) defense is a recently discovered mechanism of prokaryotic self-defense that provides a type of acquired immunity. Here, we find that antibiotic resistance and possession of complete CRISPR loci are inversely related and that members of recently emerged high-risk enterococcal lineages lack complete CRISPR loci. Our results suggest that antibiotic therapy inadvertently selects for enterococci with compromised genome defense.

Failure of vancomycin treatment for meningitis caused by vancomycin-susceptible Enterococcus faecium

This case report describes a nosocomial vancomycin-sensitive Enterococcus faecium meningitis with poor response to vancomycin. E. faecium infections continue to represent a therapeutic challenge in Europe, even in countries where vancomycin resistance is still rare. In the case of vancomycin-sensitive E. faecium meningitis, intravenous chloramphenicol should be considered as a treatment option.

Enterococcal surface protein contributes to persistence in the host but is not a target of opsonic and protective antibodies in Enterococcus faecium infection

Enterococci are important nosocomial pathogens with multiple intrinsic and acquired resistances to antibiotics. In the past, the majority of infections were caused by Enterococcus faecalis; however, an increase in Enterococcus faecium clinical isolates has been observed in recent years. The enterococcal surface protein (Esp) is expressed on the surface of most E. faecium clinical isolates and has been shown to be involved in biofilm formation. Here, E. faecium E1162 and its previously created insertion-deletion mutant of the esp gene, E. faecium E1162Δesp, were compared in a mouse bacteraemia model. Anti-Esp serum was tested for its capacity to mediate opsonophagocytic killing of E1162 in vitro and to protect against E. faecium bacteraemia. The inactivation of esp attenuated E. faecium virulence with reduced numbers of bacteria recovered from the kidneys in animals infected with the mutant compared to the wild-type strain (P=0.035). Passive immunization with rabbit polyclonal serum raised against the recombinant N-terminal Esp protein did not protect mice against E. faecium bacteraemia (P>0.05). In contrast, mice passively immunized with polyclonal antiserum raised against lipoteichoic acid (LTA) from E. faecalis had lower numbers of E. faecium E1162 in the blood compared to mice immunized with normal rabbit serum. These results suggest that Esp contributes to E. faecium persistence in the host. However, in contrast to LTA, Esp does not seem to be a target for protective antibodies in E. faecium strain E1162 in mouse bacteraemia.

Multiple copies of functional, Tet(M)-encoding Tn916-like elements in a clinical Enterococcus faecium isolate

Tn916 and similar elements are very common in clinical enterococcal isolates, and are responsible for transmission of a variety of resistance determinants. It is commonly assumed that clinical strains carrying Tn916 have a single copy, although the actual number of copies in clinical isolates has never been systematically studied. We report a clinical isolate of Enterococcus faecium in which three distinct and excision-proficient copies of Tn916-like elements are present in the genome. All of the elements contain tet(M) genes, at least one of which confers resistance to tetracycline and minocycline. Two elements (Tn6085a, Tn6085b) are indistinguishable, containing an inserted 2758bp Group II intron at the start of open reading frame Tn916ORF_06. The third (Tn6084) also contains the intron, but also has an ISEfa11 integrated upstream of tet(M). All three copies are able to excise from plasmid vectors when cloned in E. coli, and at least two of the elements can transfer to an E. faecium recipient strain. These data indicate that nearly identical Tn916-like elements encoding Tet(M)-mediated tetracycline/minocycline resistance can coexist in clinical E. faecium isolates.

Biocidal efficacy of copper alloys against pathogenic enterococci involves degradation of genomic and plasmid DNAs

The increasing incidence of nosocomial infections caused by glycopeptide-resistant enterococci is a global concern. Enterococcal species are also difficult to eradicate with existing cleaning regimens; they can survive for long periods on surfaces, thus contributing to cases of reinfection and spread of antibiotic-resistant strains. We have investigated the potential use of copper alloys as bactericidal surfaces. Clinical isolates of vancomycin-resistant Enterococcus faecalis and Enterococcus faecium were inoculated onto copper alloy and stainless steel surfaces. Samples were assessed for the presence of viable cells by conventional culture, detection of actively respiring cells, and assessment of cell membrane integrity. Both species survived for up to several weeks on stainless steel. However, no viable cells were detected on any alloys following exposure for 1 h at an inoculum concentration of <or=10(4) CFU/cm(2). Analysis of genomic and plasmid DNA from bacterial cells recovered from metal surfaces indicates substantial disintegration of the DNA following exposure to copper surfaces that is not evident in cells recovered from stainless steel. The DNA fragmentation is so extensive, and coupled with the rapid cell death which occurs on copper surfaces, that it suggests that mutation is less likely to occur. It is therefore highly unlikely that genetic information can be transferred to receptive organisms recontaminating the same area. A combination of effective cleaning regimens and contact surfaces containing copper could be useful not only to prevent the spread of viable pathogenic enterococci but also to mitigate against the occurrence of potential resistance to copper, biocides, or antibiotics and the spread of genetic determinants of resistance to other species.

Multidrug-resistant Enterococcus faecium meningitis in a toddler: characterization of the organism and successful treatment with intraventricular daptomycin and intravenous tigecycline

A case of enterococcal meningitis in a toddler is presented. The organism was highly resistant to all drugs previously used for pediatric Gram-positive meningitis. She was successfully treated with intraventricular and intravenous daptomycin and intravenous tigecycline. The organism was characterized as a member of CC17, a notorious emerging nosocomial clone of Enterococcus faecium.

High-level ciprofloxacin resistance among hospital-adapted Enterococcus faecium (CC17)

Hospital-adapted Enterococcus faecium differ from their colonising variants in humans and animals by additional genomic content. Molecular typing based on multilocus sequence typing (MLST) allows allocation of isolates to specific clonal complexes (CCs), such as CC17 for hospital-adapted strains. Acquired ampicillin resistance is a specific feature of these hospital isolates, especially in Europe. A few recent reports have described acquired high-level ciprofloxacin resistance as a supposed feature of hospital-adapted E. faecium strains. In the present retrospective analysis, ciprofloxacin minimum inhibitory concentrations (MICs) of 609 clinical isolates from German hospital patients (1997-2007) were determined and a breakpoint for high-level resistance was deduced (>16mg/L). Acquired high-level ciprofloxacin resistance was distributed among isolates of 26 different MLST types (all CC17), indicating a wide prevalence of this acquired resistance trait among the hospital-adapted E. faecium population. High-level ciprofloxacin resistance was linked to gyrA and parC mutations in 98 investigated isolates. Eleven different allele types or combinations thereof were identified. Their allocation to specific MLST and pulsed-field gel electrophoresis (PFGE) types revealed differences in the emergence and spread of corresponding mutations and strains.

Spread of vancomycin-resistant Enterococcus faecium in two haematological centres in Russia

This paper describes the clonal diversity of vancomycin-resistant Enterococcus faecium isolated from patients with haematological malignancies in Russia. Pulsed-field gel electrophoresis (PFGE) typing of 129 vanA-positive E. faecium strains revealed 23 independent restriction profiles with two predominant clonal types. Multilocus sequence typing (MLST) of 16 strains selected from two predominant PFGE types showed that they belong to the epidemic clonal complex (CC) 17. Tn1546-like elements of isolates were compared with the prototype element from E. faecium BM4147 by polymerase chain reaction (PCR). Four different Tn1546 types were distinguished according to structural alternations. Polymorphism in the orf1 and vanSH genes was detected. However, a significant prevalence of the prototype Tn1546 was revealed. Tn1546-like elements with the same structures were observed in strains of different PFGE types. The virulence genes esp, gelE and hyl were detected by PCR in 118 isolates (91%), 87 isolates (67%) and 35 isolates (27%), respectively. In contrast, agg and cylA genes were not found. The detection frequency of esp was higher in epidemic strains than in sporadic ones (100% vs. 56%; P<0.05). This study describes a genetically variable population of vancomycin-resistant E. faecium in two Russian haematological centres. The spread of vancomycin resistance was mostly due to the distribution of the two subclones of E. faecium CC17, enriched with the virulence marker esp. At the same time, dissemination of an altered Tn1546 also occurred.

Analysis of clonality and antibiotic resistance among early clinical isolates of Enterococcus faecium in the United States

BACKGROUND

The Enterococcus faecium genogroup, referred to as clonal complex 17 (CC17), seems to possess multiple determinants that increase its ability to survive and cause disease in nosocomial environments.

METHODS

Using 53 clinical and geographically diverse US E. faecium isolates dating from 1971 to 1994, we determined the multilocus sequence type; the presence of 16 putative virulence genes (hyl(Efm), esp(Efm), and fms genes); resistance to ampicillin (AMP) and vancomycin (VAN); and high-level resistance to gentamicin and streptomycin.

RESULTS

Overall, 16 different sequence types (STs), mostly CC17 isolates, were identified in 9 different regions of the United States. The earliest CC17 isolates were part of an outbreak that occurred in 1982 in Richmond, Virginia. The characteristics of CC17 isolates included increases in resistance to AMP, the presence of hyl(Efm) and esp(Efm), emergence of resistance to VAN, and the presence of at least 13 of 14 fms genes. Eight of 41 of the early isolates with resistance to AMP, however, were not in CC17.

CONCLUSIONS

Although not all early US AMP isolates were clonally related, E. faecium CC17 isolates have been circulating in the United States since at least 1982 and appear to have progressively acquired additional virulence and antibiotic resistance determinants, perhaps explaining the recent success of this species in the hospital environment.

Frequent occurrence of multidrug-resistant CC17 Enterococcus faecium among clinical isolates in Sweden

AIMS

To screen for the globally spread cluster of Enterococcus faecium, clonal complex 17 (CC17) and characterize the genetic profile of Swedish clinical Ent. faecium isolates.

METHODS

A total of 203 consecutive isolates collected from 2004 to 2007 from patients with bacteraemia in Sweden. All isolates were genotyped using multiple-locus variable-number tandem repeat analysis (MLVA) and 20 isolates representing different MLVA types (MT) were chosen for multilocus sequence typing (MLST). Minimal inhibitory concentrations against clinically relevant antibiotics were determined with agar dilution. Presence of the virulence genes esp and hyl was investigated using PCR.

RESULTS

A total of 65% (n = 109) of all isolates belonged to MT-1, and the second most common MLVA type was MT-159 (13%, n = 21). MLST analysis confirmed the presence of CC17 during the entire study period. The number of isolates resistant to gentamicin and vancomycin, as well as the presence of hyl, increased significantly during the investigation period.

CONCLUSIONS

The present study demonstrates that nosocomial infections caused by Ent. faecium CC17 are commonly occurring in Sweden.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report of CC17 Ent. faecium in Sweden. The increase of antibiotic resistance and virulence indicates that these strains are further adapting to the hospital environment.

Cross-transmission of clinical Enterococcus faecium in relation to esp and antibiotic resistance

AIMS

To investigate clonality among clinical Enterococcus faecium isolates and normal intestinal microflora isolates as well as cross-transmission between patients in relation to the presence of the esp gene and antibiotic resistance.

METHODS AND RESULTS

Blood-culture isolates (n = 101) deriving from tertiary, secondary and primary hospitals were analysed. Antibiotic susceptibility was investigated. Polymerase chain reaction and pulsed-field gel electrophoresis were used for detection of esp and genotyping, respectively. Nearly half (43%) of the patients included were involved in a cross-transmission event with Ent. faecium. These strains disseminated both within and between all hospitals. The antibiotic resistance and presence of esp were highest in isolates from the tertiary hospital. Isolates harbouring esp showed less genetic diversity compared with esp negative ones.

CONCLUSIONS

Cross-transmission with Ent. faecium between patients was readily detected, indicating that hospital-adapted clones circulate within and between hospitals. Acquired characteristics, such as antibiotic resistance and esp, seem to accumulate in the isolates disseminating in the tertiary hospital.

SIGNIFICANCE AND IMPACT OF THE STUDY

It is important to characterize Ent. faecium isolates causing infections and to determine the extent of dissemination in order to prevent further spread of these pathogens.

Comparison of two chromogenic media for selective isolation of vancomycin-resistant enterococci from stool specimens

Two chromogenic media (Chromagar VRE and chromID VRE [C-ID]) performed equally well in the direct detection of vancomycin-resistant enterococci (VRE) in stool specimens after an overnight enrichment step and a 48-h incubation period, with a sensitivity of 98.2% (56/57) for both and specificities of 96.5% (195/202) and 97.5% (197/202), respectively. However, assigning discriminatory colony color was sometimes difficult, especially on C-ID. In order to facilitate simple species identification, biochemical key reactions were implemented.

The clinical consequences of antimicrobial resistance

The continued evolution of antimicrobial resistance in the hospital and more recently in the community threatens to seriously compromise our ability to treat serious infections. The major success of the seven-valent Streptococcus pneumoniae vaccine at reducing both infection and resistance has been followed by the emergence of previously minor serotypes that express multiresistance. The almost universal activity of cephalosporins and fluoroquinolones against community Escherichia coli strains has been compromised by the spread of CTX-M beta-lactamase-producing, fluoroquinolone-resistant strains, and the emergence of community-onset methicillin-resistant Staphylococcus aureus, particularly in the United States, has forced us to re-think our empirical treatment guidelines for skin and soft-tissue infections. Finally, our most potent and reliable class of antibiotics, the carbapenems, is compromised by the growth, primarily in intensive care units, of multiresistant Klebsiella pneumoniae, Acinetobacter baumanni, and Pseudomonas aeruginosa. The lack of a robust pipeline of new agents, particularly against resistant Gram-negative bacteria, emphasizes the importance of optimizing our use of current antimicrobials and promoting strict adherence to established infection control practices.

Cotransfer of antibiotic resistance genes and a hylEfm-containing virulence plasmid in Enterococcus faecium

The hyl(Efm) gene (encoding a putative hyaluronidase) has been found almost exclusively in Enterococcus faecium clinical isolates, and recently, it was shown to be on a plasmid which increased the ability of E. faecium strains to colonize the gastrointestinal tract. In this work, the results of mating experiments between hyl(Efm)-containing strains of E. faecium belonging to clonal cluster 17 and isolated in the United States and Colombia indicated that the hyl(Efm) gene of these strains is also carried on large plasmids (>145 kb) which we showed transfer readily from clinical strains to E. faecium hosts. Cotransfer of resistance to vancomycin and high-level resistance (HLR) to aminoglycosides (gentamicin and streptomycin) and erythromycin was also observed. The vanA gene cluster and gentamicin resistance determinants were genetically linked to hyl(Efm), whereas erm(B) and ant(6)-I, conferring macrolide-lincosamide-streptogramin B resistance and HLR to streptomycin, respectively, were not. A hyl(Efm)-positive transconjugant resulting from a mating between a well-characterized endocarditis strain [TX0016 (DO)] and a derivative of a fecal strain of E. faecium from a healthy human volunteer (TX1330RF) exhibited increased virulence in a mouse peritonitis model. These results indicate that E. faecium strains use a strategy which involves the recruitment into the same genetic unit of antibiotic resistance genes and determinants that increase the ability to produce disease. Our findings indicate that the acquisition of the hyl(Efm) plasmids may explain, at least in part, the recent successful emergence of some E. faecium strains as nosocomial pathogens.

Dispersion of multidrug-resistant Enterococcus faecium isolates belonging to major clonal complexes in different Portuguese settings

The population structure of 56 Enterococcus faecium isolates selected from a collection of enterococci from humans, animals, and the environment in Portugal (1997 to 2007) was analyzed by multilocus sequence typing. We identified 41 sequence types clustering into CC17, CC5, CC9, CC22 and CC94, all clonal lineages comprising isolates from different hosts. Our findings highlight the role of community-associated hosts as reservoirs of enterococci able to cause human infections.

Antimicrobial resistance: its emergence and transmission

New concepts have emerged in the past few years that help us to better understand the emergence and spread of antimicrobial resistance (AMR). These include, among others, the discovery of the mutator state and the concept of mutant selection window for resistances emerging primarily through mutations in existing genes. Our understanding of horizontal gene transfer has also evolved significantly in the past few years, and important new mechanisms of AMR transfer have been discovered, including, among others, integrative conjugative elements and ISCR (insertion sequences with common regions) elements. Simultaneously, large-scale studies have helped us to start comprehending the immense and yet untapped reservoir of both AMR genes and mobile genetic elements present in the environment. Finally, new PCR- and DNA sequencing-based techniques are being developed that will allow us to better understand the epidemiology of classical vectors of AMR genes, such as plasmids, and to monitor them in a more global and systematic way.

Evaluation of chromogenic media for the isolation of vancomycin-resistant enterococci from stool samples

AIMS

This study sought to evaluate the performance of two chromogenic media designed for the isolation of vancomycin-resistant enterococci (VRE) and compare them with a traditional bile-esculin medium for the isolation of VRE from stool samples.

METHODS AND RESULTS

A total of 285 stool samples were inoculated onto Chromogenic VRE Agar (AES VRE agar; AES Chemunex), chromID VRE (bioMérieux) and VRE Agar (Oxoid) both directly and also following broth enrichment. In total 18 strains of vancomycin-resistant Enterococcus faecium were recovered, including 17 harbouring the vanA gene and one with vanB. On direct culture, the sensitivity of the three media was 66.7%, 77.8% and 44.4% and after broth enrichment 66.7%, 83.3% and 77.8% using AES VRE Agar, chromID VRE and Oxoid VRE Agar respectively.

CONCLUSIONS

All three media are useful tools for the isolation of VRE from stool samples. AES VRE Agar and bioMérieux chromID VRE are easier to use than Oxoid VRE Agar due to diffusion of black coloration from the latter.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study to evaluate the performance of AES VRE Agar and the first to compare two media containing synthetic chromogens for the isolation of VRE.

A pan-European survey of antimicrobial susceptibility towards human-use antimicrobial drugs among zoonotic and commensal enteric bacteria isolated from healthy food-producing animals

OBJECTIVES

The aim of the study was to study antimicrobial susceptibility in Escherichia coli, Salmonella, Campylobacter and Enterococcus recovered from chickens, pigs and cattle using uniform methodology.

METHODS

Intestinal samples were taken at slaughter in five EU countries per host and bacteria isolated in national laboratories. MICs were determined in a central laboratory of key antimicrobials used in human medicine. Clinical resistance was based on CLSI breakpoints and decreased susceptibility on EFSA epidemiological cut-off values.

RESULTS

Isolation rates from a total of 1500 samples were high for E. coli (n=1465), low for Salmonella (n=205) and intermediate for Campylobacter (n=785) and Enterococcus (n=718). Resistance prevalence varied among antibiotics, bacteria, hosts and countries. For E. coli and Salmonella, clinical resistance to newer compounds (cefepime, cefotaxime, ciprofloxacin) was absent or low, but a decreased susceptibility was apparent, particularly in chickens. Clinical resistance to older compounds (except colistin and gentamicin) was variable and higher. For Campylobacter jejuni from chickens, ciprofloxacin resistance was markedly higher than in isolates from cattle. Clinical resistance to erythromycin was absent for both hosts; decreased susceptibility very low. Similar trends were determined for Campylobacter coli, but C. jejuni was less resistant. None of the enterococcal strains was resistant to linezolid, but a few displayed resistance to ampicillin or vancomycin. Resistance prevalence to quinupristin/dalfopristin was clearly higher.

CONCLUSIONS

Antimicrobial resistance among enteric organisms in food animals varied among countries, particularly for older antimicrobials, but clinical resistance to essential compounds used to treat disease in humans was generally zero or low. In the absence of clinical resistance to newer compounds in E. coli and Salmonella, the apparent decreased susceptibility should be monitored carefully.

Microbes in gastrointestinal health and disease

Most, if not all, animals coexist with a complement of prokaryotic symbionts that confer a variety of physiologic benefits. In humans, the interaction between animal and bacterial cells is especially important in the gastrointestinal tract. Technical and conceptual advances have enabled rapid progress in characterizing the taxonomic composition, metabolic capacity, and immunomodulatory activity of the human gut microbiota, allowing us to establish its role in human health and disease. The human host coevolved with a normal microbiota over millennia and developed, deployed, and optimized complex immune mechanisms that monitor and control this microbial ecosystem. These cellular mechanisms have homeostatic roles beyond the traditional concept of defense against potential pathogens, suggesting these pathways contribute directly to the well-being of the gut. During their coevolution, the bacterial microbiota has established multiple mechanisms to influence the eukaryotic host, generally in a beneficial fashion, and maintain their stable niche. The prokaryotic genomes of the human microbiota encode a spectrum of metabolic capabilities beyond that of the host genome, making the microbiota an integral component of human physiology. Gaining a fuller understanding of both partners in the normal gut-microbiota interaction may shed light on how the relationship can go awry and contribute to a spectrum of immune, inflammatory, and metabolic disorders and may reveal mechanisms by which this relationship could be manipulated toward therapeutic ends.