Reduction in glycopeptide resistance in vancomycin-resistant enterococci as a result of vanA cluster rearrangements

Genetic description of VanD phenotype vanA genotype in vancomycin-resistant Enterococcus faecium isolates from a Bone Marrow Transplantation Unit

BACKGROUND

Vancomycin-resistant Enterococcus faecium (VREfm) is an important agent of hospital-acquired infection. VanA phenotype is characterized by resistance to high levels of vancomycin and teicoplanin and is encoded by the vanA gene, whereas VanD phenotype is characterized by resistance to vancomycin and susceptibility or intermediate resistance to teicoplanin; however, some isolates carry a VanD phenotype with a vanA genotype, but there are many gaps in the knowledge about the genetic mechanisms behind this pattern.

OBJECTIVE

To characterize the genetic structure, clonality, and mobile genetic elements of VRE isolates that display a VanD-vanA phenotype.

RESULTS

All vanA VRE-fm isolates displayed minimum inhibitory concentration (MIC) for vancomycin > 32µg/mL and intermediate or susceptible MIC range for teicoplanin (8-16µg/mL). The isolates were not clonal, and whole-genome sequencing analysis showed that they belonged to five different STs (ST478, ST412, ST792, ST896, and ST1393). The absence of some van complex genes were observed in three isolates: Ef5 lacked vanY and vanZ, Ef2 lacked vanY, and Ef9 lacked orf1 and orf2; moreover, another three isolates had inverted positions of orf1, orf2, vanR, and vanS genes. IS1542 was observed in all isolates, whereas IS1216 in only five. Moreover, presence of other hypothetical protein-encoding genes located downstream the vanZ gene were observed in six isolates.

CONCLUSION

VRE isolates can display some phenotypes associated to vanA genotype, including VanA and VanB, as well as VanD; however, further studies are needed to understand the exact role of genetic variability, rearrangement of the transposon Tn1546, and presence of insertion elements in isolates with this profile.

Antimicrobial Resistance of Enterococcus sp. Isolated from Sheep and Goat Cheeses

This study aimed to calculate the proportion of antibiotic resistance profiles of Enterococcus faecium, E. faecalis, and E. durans isolated from traditional sheep and goat cheeses obtained from a selected border area of Slovakia with Hungary (region Slanské vrchy). A total of 110 Enterococcus sp. were isolated from cheese samples, of which 52 strains (E. faecium (12), E. faecalis (28), E. durans (12)) were represented. After isolation and identification by polymerase chain reaction and matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry, the enterococci (E. faecium, E. faecalis, and E. durans) were submitted to susceptibility tests against nine antimicrobial agents. In general, strains of E. faecalis were more resistant than E. durans and E. faecium. A high percentage of resistance was noted in E. faecalis to rifampicin (100%), vancomycin (85.7%), teicoplanin (71.4%), erythromycin (71.4%), minocycline (57.1%), nitrofurantoin (57.1%), ciprofloxacin (14.3%), and levofloxacin (14.3%). E. durans showed resistance to rifampicin (100%), teicoplanin (100%), vancomycin (66.7%), erythromycin (66.7%), nitrofurantoin (66.7%), and minocycline (33.3%), and E. faecium showed resistance to vancomycin, teicoplanin, and erythromycin (100%). Multidrug-resistant strains were confirmed in 80% of the 52 strains in this study. Continuous identification of Enterococcus sp. and monitoring of their incidence and emerging antibiotic resistance is important in order to prevent a potential risk to public health caused by the contamination of milk and other dairy products, such as cheeses, made on farm level.

Transmission dynamics of a linear vanA-plasmid during a nosocomial multiclonal outbreak of vancomycin-resistant enterococci in a non-endemic area, Japan

The spread of vancomycin-resistant enterococci (VRE) is a major threat in nosocomial settings. A large-scale multiclonal VRE outbreak has rarely been reported in Japan due to low VRE prevalence. We evaluated the transmission of vancomycin resistance in a multiclonal VRE outbreak, conducted biological and genomic analyses of VRE isolates, and assessed the implemented infection control measures. In total, 149 patients harboring VanA-type VRE were identified from April 2017 to October 2019, with 153 vancomycin-resistant Enterococcus faecium isolated being grouped into 31 pulsotypes using pulsed-field gel electrophoresis, wherein six sequence types belonged to clonal complex 17. Epidemic clones varied throughout the outbreak; however, they all carried vanA-plasmids (pIHVA). pIHVA is a linear plasmid, carrying a unique structural Tn1546 containing vanA; it moves between different Enterococcus spp. by genetic rearrangements. VRE infection incidence among patients in the "hot spot" ward correlated with the local VRE colonization prevalence. Local prevalence also correlated with vancomycin usage in the ward. Transmission of a novel transferrable vanA-plasmid among Enterococcus spp. resulted in genomic diversity in VRE in a non-endemic setting. The prevalence of VRE colonization and vancomycin usage at the ward level may serve as VRE cross-transmission indicators in non-intensive care units for outbreak control.

Phenotypic and Molecular Characterization of Plasmid-Mediated Virulence and Antimicrobial Resistance Traits among Multidrug Resistant Enterococcus spp. in Egypt

Enterococcus spp. are remarkable multidrug resistant (MDR) bacteria that are causing serious healthcare-associated infections. The current study investigated the frequency of Enterococcus spp., antimicrobial susceptibility, biofilm formation and the presence of some plasmid-mediated virulence characters and antimicrobial resistance determinants in enterococcal isolates from Egyptian hospitals in Cairo. Enterococcus bacterial isolates were recovered from different clinical specimens and identified using biochemical testing and KB005A HiStrep™ identification kit. Kirby-Bauer disc diffusion method and/or broth microdilution method were used to determine the antimicrobial susceptibility patterns. Phenotypic assays were performed to study biofilm formation and cytolysin and gelatinase production. PCR assays targeting the plasmid-carried genes aac(6’)-aph(2’), aph(3)-IIIa, vanA, agg and cylA were performed. In this study, 50 isolates of diverse Enterococcus spp. were identified with E. faecium was the most frequently isolated one. High resistance profiles were determined against tested antimicrobials and all isolates were MDR. Moderate biofilm formation was detected in 20% of isolates, 18% showed complete blood hemolysis and 12% produced gelatinase. All isolates carried the tested aminoglycosides resistance genes, while vanA was found only in 4 isolates (8%). The virulence genes agg and cylA were detected in 4% and 32% of isolates, respectively. In conclusion, E. faecium was the most prevalent species. The entire isolates set were MDR and the plasmid-carried aminoglycoside resistance genes were extensively disseminated among MDR isolates. Thus, regular surveillance studies, from the area of study or other geographical regions in Egypt, and strict infection control measures are required to monitor the emerging MDR enterococci.

Tagging the vanA gene in wastewater microbial communities for cell sorting and taxonomy of vanA carrying cells

Failure to understand the microbial ecology driving the proliferation of antibiotic resistance in the environment prevents us from developing strategies to limit the spread of antibiotic resistant infectious disease. In this study, we developed for the first time a tyramide signal amplification-fluorescence in situ hybridization-fluorescence-activated cell sorting protocol (TSA-FISH-FACS) for the characterization of all vanA carrying bacteria in wastewater samples. Firstly, we validated the TSA-FISH protocol through microscopy in pure cultures and wastewater influent. Then, samples were sorted and quantified by FACS and qPCR. Significantly higher percentage tagging of cells was detected in vanA carrying pure cultures and wastewater samples spiked with vanA carrying cells as compared to vanA negative Gram positive strains and non-spiked wastewater samples respectively. qPCR analysis targeting vanZ, a regulating gene in the vanA cluster, showed its relative abundance was significantly greater in Enterococcus faecium ATCC 700221-spiked and positively sorted samples compared to the E. faecium spiked and negatively sorted samples. Phylogenetic analysis was then performed. Although further efforts are needed to overcome technical problems, we have, for the first time, demonstrated sorting bacterial-cells carrying antibiotic resistance genes from wastewater samples through a TSA-FISH-FACS protocol and provided insight into the microbial ecology of vancomycin resistant bacteria. Future potential applications using this approach will include the separation of members of an environmental microbial community (cultured and hard-to-culture) to allow for metagenomics on single cells or, in the case of clumping, targeting a smaller portion of the community with a priori knowledge that the target gene is present.

Characterization of clinical enterococci isolates, focusing on the vancomycin-resistant enterococci in a tertiary hospital in China: based on the data from 2013 to 2018

Background

Vancomycin-resistant Enterococcus spp. (VRE) have spread all over the world. The present study aims to investigate the species distribution, specimen type and susceptibilities of Enterococcal species collected from Nanjing Drum Tower Hospital from 2013 to 2018. Additionally, distribution of VRE and prevalence of van gene among VRE isolates were also analyzed.

Methods

The susceptibilities of 3913 Enterococcus isolates were retrospectively investigated. Among these strains, 60 VRE strains were further anazlyed in this study. The minimum inhibitory concentrations (MICs) of the VRE strains towards vancomycin, teicoplanin and linezolid were determined by E-test. Polymerase chain reaction (PCR) and DNA sequencing were used to investigate the prevalence of van genes among VRE. Furthermore, the sequence types (STs) of VRE strains were explored by multi-locus sequence typing (MLST).

Results

Among the 3913 enterococci isolates, Enterococcus faecalis (n = 1870, 47.8%) and Enterococcus faecium (1738, 44.4%) were the main isolates. These Enterococcus strains were mainly isolated from urine (n = 1673, 42.8%), followed by secretions (n = 583, 14.9%) and ascites (n = 554, 14.2%). VRE displayed a decreasing trend year by year. Molecular analysis revealed that 49 out of 60 VRE isolates carried vanA gene, 10 carried vanM, and 1 carried both vanA and vanM genes. Sixteen distinct STs were identified among the 58 VREM, with ST78 (n = 16), ST192 (n = 8) and ST570 (n = 7) being the most dominant ones.

Conclusions

E. faecalis and E. faecium were the major enterococci strains which are the main pathogens of urinary traction infections; vanA and vanM were the main determinants conferring resistance to vancomycin; ST78, ST192 and ST570 were the leading STs of VREM which displayed a decreasing trend of prevalence year by year.

Antimicrobial resistance of major clinical pathogens in South Korea, May 2016 to April 2017: first one-year report from Kor-GLASS

The Korean government established an antimicrobial resistance (AMR) surveillance system, compatible with the Global AMR Surveillance System (GLASS): Kor-GLASS. We describe results from the first year of operation of the Kor-GLASS from May 2016 to April 2017, comprising all non-duplicated clinical isolates of major pathogens from blood, urine, faeces and urethral and cervical swabs from six sentinel hospitals. Antimicrobial susceptibility tests were carried out by disk diffusion, Etest, broth microdilution and agar dilution methods. Among 67,803 blood cultures, 3,523 target pathogens were recovered. The predominant bacterial species were Escherichia coli (n = 1,536), Klebsiella pneumoniae (n = 597) and Staphylococcus aureus (n = 584). From 57,477 urine cultures, 6,394 E. coli and 1,097 K. pneumoniae were recovered. Bloodstream infections in inpatients per 10,000 patient-days (10TPD) were highest for cefotaxime-resistant E. coli with 2.1, followed by 1.6 for meticillin-resistant Sta. aureus, 1.1 for imipenem-resistant Acinetobacter baumannii, 0.8 for cefotaxime-resistant K. pneumoniae and 0.4 for vancomycin-resistant Enterococcus faecium. Urinary tract infections in inpatients were 7.7 and 2.1 per 10TPD for cefotaxime-resistant E. coli and K. pneumoniae, respectively. Kor-GLASS generated well-curated surveillance data devoid of collection bias or isolate duplication. A bacterial bank and a database for the collections are under development.

Detection of Vancomycin Resistance among Enterococcus faecalis and Staphylococcus aureus

INTRODUCTION

Vancomycin remains the drug of choice for resistant gram positive infections caused by Enterococcus spp and Methicillin resistant Staphylococcus aureus (MRSA). Increased use of vancomycin has led to frank resistance and increase in MIC (MIC creep). Vancomycin intermediate Staphylococcus aureus (VISA), Vancomycin resistant Staphylococcus aureus (VRSA) & Vancomycin resistant Enterococci (VRE) are important emerging nosocomial pathogens resulting in treatment failures.

AIM

This study was undertaken to detect vancomycin resistance among clinical isolates of Staphylococcus aureus and Enterococcus faecalis by phenotypic and genotypic methods.

MATERIALS AND METHODS

The study was conducted in a 1850 bedded university teaching hospital from November 2013 to April 2014. Non-repetitive, consecutive clinically significant Staphylococcus aureus (109) and Enterococcus faecalis (124) were included in this study. They were identified up to species level by conventional and automated methods. Susceptibility to various antibiotics was tested by disc diffusion method. MIC of vancomycin was determined by agar dilution method. Inducible resistance to clindamycin was detected by the D test. Methicillin resistance in Staphylococcus aureus (MRSA) was screened using cefoxitin disc. All isolates were subjected to polymerase chain reaction (PCR) to detect van A and van B genes.

RESULTS

Out of 109 Staphylococcus aureus isolates, 54 were MRSA. By MIC there was no resistance observed to vancomycin.MIC50 was 1μg/ml. None of the isolates harboured van A and van B. Among Enterococcus faecalis, sixteen isolates (12.9%) and four isolates (3.2%) exhibited resistance to vancomycin and teicoplanin by disc diffusion respectively. All isolates were susceptible to linezolid. Van A was detected in 2, van B in 7 and one had both van A and van B.

CONCLUSION

PCR remains the gold standard for diagnosis of vancomycin resistance. There was no resistance observed to vancomycin among Staphylococci though the MIC creep detected is a cause for concern. Eight percent of Enterococci were vancomycin resistant.

Comparison of vanA gene mRNA levels between vancomycin-resistant Enterococci presenting the VanA or VanB phenotype with identical Tn1546-like elements

BACKGROUND/PURPOSE

During the routine screening of vancomycin-resistant Enterococci faecium (VREfm) we found that VanA phenotype-vanA genotype and VanB phenotype-vanA genotype isolates had an identical Tn1546-like element structure. This study aimed to evaluate the genetic background and vanA gene expression to identify the mechanisms of the development of the VanB phenotype-vanA genotype VREfm.

METHODS

Twelve VREfm isolates were collected from a 1500-bed tertiary-care teaching hospital in Beijing. Genetic variations of the Tn1546-like element were determined by an overlapping polymerase chain reaction assay and sequencing. The genetic background was determined by pulsed-field gel electrophoresis and mutilocus sequence typing. vanA gene expression was evaluated using a TaqMan quantitative real-time polymerase chain reaction.

RESULTS

For the 12 isolates, six isolates with the VanA phenotype-vanA genotype and six with the VanB phenotype-vanA genotype were identified. According to the structure analysis of the Tn1546-like elements, our isolates were divided into two types. In the four isolates of type A, IS1542 and IS1216V were inserted into the orf2-vanR and vanX-vanY regions, respectively. In the eight isolates of type D, a similar insertion as type A occurred, except for an ISEfa4 insertion into IS1542. A significant difference in vanA gene expression was observed between the VanA and VanB phenotype isolates in type A, but not in type D. Mutilocus sequence typing and pulsed-field gel electrophoresis analysis showed that these isolates have a different genetic background.

CONCLUSION

Our results indicated that the occurrence of the VanB phenotype-vanA genotype might not completely depend on the structure of Tn1546-like elements and vanA gene expression.

Outbreak of vancomycin-susceptible Enterococcus faecium containing the wild-type vanA gene

Accurate detection of vancomycin-resistant enterococci (VRE) is essential in preventing transmission in health care settings. Chromogenic media are widely used for screening VRE because of fast turnaround times (TAT) and high sensitivity. We report an outbreak of Enterococcus faecium bearing vanA yet susceptible to vancomycin (vancomycin-variable Enterococcus [VVE]). Between October 2009 to March 2011, clinical and screening specimens (n=14,747) were screened for VRE using VRE-selective medium and/or PCR. VVE isolates were genotyped to determine relatedness. Plasmids from these isolates were characterized by sequencing. Overall, 52 VVE isolates were identified, comprising 15% of all VRE isolates identified. Isolates demonstrated growth on Brilliance VRE agar (Oxoid) at 24 h of incubation but did not grow on brain heart infusion agar with 6 μg/ml vancomycin (Oxoid) or bile esculin azide agar with 6 μg/ml vancomycin (Oxoid) and were susceptible to vancomycin. Genotyping of 20 randomly selected VVE isolates revealed that 15/20 were identical, while 5 were highly related. PCR of the VVE transposon confirmed the presence of vanHAXY gene cluster; however, vanS (sensor) and vanR (regulator) genes were absent. The outbreak was controlled through routine infection control measures. We report an emergence of a fit strain of E. faecium containing vanA yet susceptible to vancomycin. Whether this new strain represents VRE has yet to be determined; however, unique testing procedures are required for reliable identification of VVE.

Molecular epidemiology of vancomycin-resistant enterococci isolated from non-tertiary-care and tertiary-care hospitals in Korea

This study compared the molecular characteristics of vancomycin-resistantEnterococcus faecium(VREF) isolates recovered from 20 non-tertiary-care hospitals (36 isolates) and three tertiary-care hospitals (26 isolates) in diverse geographical areas of Korea from October 2010 to April 2011. All isolates carried thevanAgene only, but 42% and 73% of non-tertiary and tertiary-care isolates expressed the VanB phenotype (teicoplanin minimum inhibitory concentration ⩽16 μg/ml). All isolates harboured insertion sequences, IS1542and IS1216V, within Tn1546. The isolates from tertiary-care hospitals tended to have reduced Tn1546lengths by deletion of sequences adjacent to IS elements. Multilocus sequence typing revealed eight sequence types within clonal complex 17 (CC17), but DNA fingerprinting by rep-PCR did not show clonal relatedness between the intra- and inter-hospital isolates. These results suggest thatvanA, which has prevailed in tertiary-care hospitals of Korea since the 1990s, had been transferred horizontally to non-tertiary-care hospitals while the genetic rearrangement driven by evolutionary adaptation to adverse environments may have occurred in tertiary-care hospitals.

Phenotypic & genotypic characterization of vancomycin resistant Enterococcus isolates from clinical specimens

BACKGROUND & OBJECTIVES

Enterococci have emerged as important nosocomial pathogens and emergence of resistance to many of the antimicrobials used for Gram-positive organisms has made the management of infections due to Enterococcus species difficult. Resistance to glycopeptide antibiotics, especially vancomycin is of special concern. This study was undertaken to perform a phenotypic and genotypic characterization of vancomycin resistant Enterococcus (VRE) isolates obtained from clinical samples in a tertiary care hospital in southern India.

METHODS

Susceptibility testing was performed for Enterococcus isolates collected over a period of one year (November 2008-October 2009). Minimum inhibitory concentrations (MIC) of vancomycin and teicoplanin were determined for the isolates by the agar dilution method. Genotypic characterization of VRE isolates was done by performing multiplex polymerase chain reaction (PCR) for detecting the various vancomycin resistance genes.

RESULTS

Of the 367 isolates of Enterococcus species isolated, 32 were found to be resistant to vancomycin after MIC testing. VanA was the commonest phenotype of vancomycin resistance and the commonest genotype was vanA. Among the other important findings of the study was the presence of heterogeneity in isolates of VRE with the vanA gene cluster with regards to resistance to teicoplanin and the coexistence of vanA and vanC1 gene clusters in an isolate of E. gallinarum which conferred high level glycopeptide resistance to the isolate.

INTERPRETATION & CONCLUSIONS

Enterococcus species have emerged as important nosocomial pathogens in our patients with a capacity to cause a variety of infections. The vancomycin resistance among Enterococcus isolates was 8.7 per cent in our study which was high compared to other Indian studies. VanA was the commonest phenotype of glycopeptide resistance and vanA was the commonest vancomycin resistance gene. The study also demonstrates phenotypic as well as genotypic heterogeneity among isolates of VRE from clinical specimens.

Acquired inducible antimicrobial resistance in Gram-positive bacteria

A major contributor to the emergence of antibiotic resistance in Gram-positive bacterial pathogens is the expansion of acquired, inducible genetic elements. Although acquired, inducible antibiotic resistance is not new, the interest in its molecular basis has been accelerated by the widening distribution and often 'silent' spread of the elements responsible, the diagnostic challenges of such resistance and the mounting limitations of available agents to treat Gram-positive infections. Acquired, inducible antibiotic resistance elements belong to the accessory genome of a species and are horizontally acquired by transformation/recombination or through the transfer of mobile DNA elements. The two key, but mechanistically very different, induction mechanisms are: ribosome-sensed induction, characteristic of the macrolide-lincosamide-streptogramin B antibiotics and tetracycline resistance, leading to ribosomal modifications or efflux pump activation; and resistance by cell surface-associated sensing of β-lactams (e.g., oxacillin), glycopeptides (e.g., vancomycin) and the polypeptide bacitracin, leading to drug inactivation or resistance due to cell wall alterations.

[Mechanism of VanB Phenotype in Vancomycin-Resistant Enterococci carrying vanA gene.]

BACKGROUND

Recently, vancomycin-resistant enterococci (VRE) with the vanA genotype that are susceptible to teicoplanin have been described in Japan, Taiwan, and Korea. The investigators suggested three point mutations in the putative sensor domain of vanS or impairment of accessory proteins VanY and VanZ as an explanation for the VanB phenotype-vanA genotype VRE. In this study, we analyzed Tn1546-like elements to determine the molecular mechanisms responsible for the impaired glycopeptide resistance of clinical VRE isolates with VanB phenotype-vanA genotype from Korea.

METHODS

From 2001 to 2004, 28 clinical isolates of Enterococcus faecium with VanB phenotypevanA genotype were collected from 8 different university hospitals in diverse geographic areas in Korea. For structural analysis of Tn1546-like elements, PCR amplifications for internal regions of Tn1546 were performed. The purified PCR products were directly sequenced with an ABI Prism 3100 DNA sequencer.

RESULTS

The sequence data of the vanS regulatory gene revealed that none of the isolates had any point mutations in this gene. All 28 isolates had a complete or incomplete deletion of vanY gene. Of these, 13 strains represented a complete deletion of vanZ, and 2 strains showed the deletion of nucleotides near the end point of vanX.

CONCLUSIONS

The mechanism of VanB phenotype-vanA genotype in VRE isolates from Korea is not point mutations of vanS but the rearrangements of vanX, vanY and vanZ.

vanA-containing Enterococcus faecium susceptible to vancomycin and teicoplanin because of major nucleotide deletions in Tn1546

OBJECTIVES

During the course of routine screening for vancomycin-resistant enterococci (VRE), we found six Enterococcus faecium isolates positive for vanA by PCR, but susceptible to vancomycin and teicoplanin by phenotypic testing. The aim of this study was to characterize the genetic composition of the Tn1546 vanA gene cluster of these isolates.

METHODS

The E. faecium isolates were characterized by antibiotic susceptibility, PFGE and structural analysis of the Tn1546 elements. Plasmids extracted from these isolates were used to determine the presence of the Tn1546 vanA gene cluster by PCR and the genomic organization of the deleted Tn1546 element by primer walking DNA sequencing.

RESULTS

The vancomycin-susceptible vanA-positive E. faecium isolates showed three PFGE patterns, and were missing the vanR and vanS genes that are responsible for the activation of transcription of resistance genes. Primer walking sequencing revealed that these genes were completely deleted and that interruptions in the vanA cluster were in the vicinity of insertion sequence elements.

CONCLUSIONS

The presence of vancomycin-susceptible vanA-positive E. faecium in clinical samples results from major deletions in the Tn1546 vanA operon. Our findings support the essential role of vanR and vanS for the expression of resistance to vancomycin in enterococci.

Molecular characterization of vancomycin-resistant enterococci in a Chinese hospital between 2003 and 2009

From June 2003 to December 2009, 98 isolates of vancomycin-resistant enterococci (VRE) were cultured from clinical specimens taken from patients admitted to a 1,500-bed tertiary-care teaching hospital in Beijing, China. Isolates were characterized by pulsed-field gel electrophoresis and multilocus sequence typing. We investigated the structure of the vanA gene cluster and the distribution of the virulence markers esp, hyl, gelE, asa1, and cylA by polymerase chain reaction. Our results indicate that multilocus sequence typing revealed five novel sequence types and one new allele. VRE faecium (VREfm) isolates were heterogeneous in their vanA cluster types and in the presence of virulence genes. We also observed inconsistency between genotype and phenotype in VREfm isolates. The outbreak with VREfm in our hospital appears polyclonal, whereas VRE faecalis characterization indicated dissemination of a particular clone. After 2007, VRE faecalis was completely replaced by VREfm, which has since been the predominant species in our hospital. VRE appears to be in an evolutionary flux in our hospital.

Loss of vancomycin resistance not completely dependent on the Tn1546 element in Enterococcus faecium isolates

We investigated characteristics of 3 Enterococcus faecium strains (SHY-1, SHY-2, and SHY-3) isolated successively from 1 patient. In vitro susceptibility testing was performed using broth microdilution method. Change of vancomycin MIC was monitored during incubation with vancomycin for SHY-3 strain. Genetic backgrounds were determined both by multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE). In addition, the genetic variations among Tn1546 element were investigated by polymerase chain reaction (PCR) assay and sequencing. vanA and vanX expression of 3 strains was evaluated using quantitative real-time (qRT)-PCR method. Although all the strains possessed the vanA gene, SHY-3 was susceptible to glycopeptides, while SHY-1 and SHY-2 were resistant to glycopeptides. Judged by MLST and PFGE, 3 strains have the same genetic background. The vancomycin resistance of SHY-3 was not recovered after exposure to vancomycin. The vanA and vanX genes were expressed in strains SHY-1 and SHY-2 but not in strain SHY-3, although the SHY-2 and SHY-3 strains shared the same arrangement of the van gene cluster, a common 88-bp deletion in vanS gene. Our results indicate that vancomycin resistance might not be completely dependent on the Tn1546 element.

Analysis of methods commonly used for glycopeptide and oxazolidinone susceptibility testing in Enterococcus faecium isolates

The susceptibility to teicoplanin, vancomycin and linezolid of 30 clinical isolates of Enterococcus faecium was tested by Vitek 2, Phoenix, Etest, broth microdilution and disc diffusion tests. The vanA and vanB resistance genes and the 23S rRNA gene G2576T mutation were detected by PCR and PCR-RFLP, respectively. Resistance rates to teicoplanin ranged from 3 % for Vitek 2 to 57.6 % for the Phoenix test, and those to vancomycin ranged from 56.7 % for Vitek 2 to 86.7 % for the Phoenix test. Only two out of 25 strains carrying the vanA gene were univocally recognized as the VanA phenotype. The only strain with the G2576T mutation did not carry the vanA gene and showed resistance to linezolid by the disc diffusion, Vitek 2 and broth dilution methods (MIC >8 μg ml−1), but was susceptible when tested with the Phoenix test and Etest (MIC ≤4 μg ml−1). Therefore, the resistance to glycopeptides and linezolid was not univocally detected by the susceptibility testing methods used in this study.

[Microbiological and epidemiological characteristics of vancomycin-dependent enterococci]

BACKGROUND

Vancomycin-dependent enterococci (VDE) are clinically equivalent to vancomycin-resistant enterococci (VRE), but more difficult to detect. This study was purposed to characterize VDE microbiologically and epidemiologically.

METHODS

The patients from whom VDE were detected from April 2007 to March 2008 were investigated. For available isolates, minimal inhibitory concentrations (MICs) of and the levels of dependence on vancomycin and teicoplanin were measured by E test (AB Biodisk, Sweden), and a test for reversion of VDE to non-dependent VRE (NDVRE) and pulsed field gel electrophoresis (PFGE) were performed. Patients' demographic and clinical findings were reviewed via electronic medical records.

RESULTS

VDE were recovered from 6 (2.2%) of 272 patients carrying VRE during this study period. All patients were already colonized or infected by VRE and treated with vancomycin for 13 to 107 days. VDE were isolated from pleural fluid (one), urine (four), and stool (one). All isolates carried vanA with vancomycin MICs of >256 microg/mL, but two of them had intermediate susceptibilities to teicoplanin. Because 4 VDE isolates were reverted to NDVRE with single passage, vancomycin dependence was measurable for only two isolates as equal and above 0.064 and 0.5 microg/mL respectively, and was reverted after 5 and 7 passages, respectively. Six VDE isolates showed no related clones in PFGE analysis, and 3 of 4 available pairs of initial VRE isolates and subsequent VDE isolates were identical clones.

CONCLUSIONS

VDE were not rare and seemed to emerge independently from VRE with a prolonged use of vancomycin. Vancomycin-dependence was reverted within several passages.

VanB phenotype-vanA genotype Enterococcus faecium with heterogeneous expression of teicoplanin resistance

Six VanB phenotype-vanA genotype isolates of Enterococcus faecium with heterogeneous expression of teicoplanin resistance which gave rise to an outbreak at a Korean tertiary care teaching hospital have IS1216V in the coding region of vanS. This could be the underlying cause of the VanB phenotype-vanA genotype with heterogeneous expression of teicoplanin resistance.

Diversity of Tn1546 and its role in the dissemination of vancomycin-resistant enterococci in Portugal

We characterized the molecular diversity of vanA vancomycin-resistant enterococci (VRE; 176 isolates/87 pulsed-field gel electrophoresis types) from different sources and cities in Portugal (1996 to 2004): (i) food animals (FA; n = 38 isolates out of 31 samples), hospitalized humans (HH; n = 101/101), healthy human volunteers (HV; n = 7/4), and environmental sources (n = 30/10). Some strains were isolated from different hosts and persistently recovered for years. Twenty-four Tn1546 variants were identified, all located on plasmids (30 to 250 kb). Some Tn1546 variants were associated with specific sources such as FA (3 types), HH (11 types), or HV (1 type), while others were recovered from isolates of different origins (8 types). Polymorphisms in the central vanRSHA region of Tn1546 were scarcely detected, while alterations upstream of vanR and downstream of vanA were frequently identified involving mutations (vanS and vanX), deletions (vanY), insertions (IS1216V, ISEf1, and IS19; sequences with or without homology with others available in GenBank databases), and different genetic rearrangements. Most Tn1546 variants contained IS1216V (14 types) or ISEf1 (6 types). IS1216V was found alone or associated with an IS3-like element at different orientations and positions in Tn1546 from human, animal, and environmental samples. ISEf1 was located within vanX-vanY region at nucleotide 9044 of Tn1546 variants mostly associated with clinical isolates, suggesting a common genetic platform. IS19 was observed within the vanX-vanY region in one Tn1546 variant from poultry. Recent spread of VRE in Portugal reflects a complex epidemiology involving both clonal spread and plasmid dissemination containing a variety of Tn1546 types. Apparent Tn1546 heterogeneity among enterococci from human, animal, and environmental sources might reflect frequent genetic exchange events and evolution of particular widely disseminated genetic elements.

Increasing rates of vancomycin resistance among Enterococcus faecium isolated from German hospitals between 2004 and 2006 are due to wide clonal dissemination of vancomycin-resistant enterococci and horizontal spread of vanA clusters

Results of national and international surveillance studies revealed increasing rates of vancomycin-resistant Enterococcus faecium (VREF) among German hospital patients since 2003. To investigate the molecular background of vanA-type glycopeptide resistance, 51 clinical VREF isolated between 2004 and 2006 and originating from 19 German hospitals representing 10 Federal States have been investigated. Isolates were characterised by multi-locus sequence typing (MLST), SmaI macrorestriction analysis in pulsed-field gel electrophoresis (PFGE), and multiple-locus variable-number tandem repeat analysis (MLVA). Phylogenetic relatedness between strains was identified using BioNumerics and eBURST software. Distribution of virulence markers esp and hyl(Efm) was investigated by PCR. The structure of the vanA gene clusters was investigated by PCR, long-template PCR, sequencing and Southern hybridisations. The 51 VREF were rather diverse constituting different strain types, different virulence markers and vanA clusters. Within this diversity we found supportive data for a dissemination of related--already vancomycin-resistant--E. faecium among various hospitals and Federal States and for spread of identical vanA gene clusters among clonally different strain types within single hospitals. In conclusion, the increase in the rates of VREF among German hospital patients within the last 2 years might be rather complex and due to different molecular events and scenarios.

The first molecular analysis of clinical isolates of VanA-type vancomycin-resistant Enterococcus faecium strains in Mainland China

AIMS

The aim of this study was to examine two VanA-type vancomycin-resistant Enterococcus faecium (VRE) strains that had been isolated from patients resident in mainland China. This is the first molecular analysis of clinical VRE strains being isolated in mainland China.

METHODS AND RESULTS

Two VanA-type VRE isolates were isolated from in-patients at hospitals located in the Chinese cities Beijing and Dalian and were designated C264 and I125. The plasmids pC264V (40 kbp) and pI125V (370 kbp) that were isolated from C264 and I125, respectively, carried a Tn1546-like element encoding VanA resistance. The vancomycin-resistant plasmids pC264V and pI125V were transferred by filter mating at frequencies of 10(-7) and 10(-4) respectively. Sequence analysis of pC264V revealed that two IS1216V sequences and an IS1542 sequence were present within the Tn1546-like element. pI125V had two IS1216V insertions in the Tn1546-like element.

CONCLUSIONS

The two VanA-type vancomycin-resistant E. faecium (VRE) strains C264 and I125 were isolated from in-patients in Chinese hospitals. The vancomycin-resistant conjugative plasmids pC264V and pI125V plasmids isolated from these strains carried the Tn1546-like element. The Tn1546-like element was found to contain the insertion sequences IS1216V and IS1542.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first molecular analysis of VanA-type VRE strains from patients resident in mainland China.

High frequency of vancomycin-resistant Enterococcus faecium isolates with VanB phenotype and vanA genotype in Korean hospitals

A total of 59 vancomycin-resistant Enterococcus faecium (VREF) clinical isolates were collected from 8 Korean hospitals for 2 months in 2004. They were investigated by genotyping for glycopeptide resistance, multilocus sequence typing (MLST), esp repeat profiling, and structural analysis of Tn1546-like element. Nine of 59 VREF isolates (15.3%) from 5 hospitals in Korea showed VanB phenotype, but they contained vanA gene. MLST and esp repeat profiling indicated that E. faecium isolates with VanB phenotype and vanA genotype occurred from independent genetic background except 3 isolates from 1 hospital. Structural analysis of Tn1546 also showed that these isolates were not clonally related. Data showed a relatively high frequency of VREF isolates with incongruence between phenotype and genotype for glycopeptide resistance in Korean hospitals.

Evaluation of clonality in enterococci isolated in Brazil carrying Tn1546-like elements associated with vanA plasmids

Fifty-one vancomycin-resistant enterococci samples isolated from different geographic regions in Brazil were studied. All the isolates harboured the vanA gene as demonstrated by PCR analysis, and in a majority of strains the gene was associated with a transferable plasmid of 70 kb. A single variant of the prototype Tn1546 associated with common transferable vanA-containing plasmids has spread among the enterococcal strains circulating in Brazil. The VanA element integrity in these enterococci strains and the different pulsed-field gel electrophoresis patterns suggest horizontal transmission of the vancomycin resistance transposon in Brazilian strains.

Epidemiology and mechanisms of glycopeptide resistance in enterococci

PURPOSE OF REVIEW

This review updates epidemiologic trends and our understanding of glycopeptide resistance in enterococci.

RECENT FINDINGS

Colonization and infection rates with vancomycin resistant enterococci continue to increase throughout the world while factors contributing to this rise continue to be defined. While no interventions exist to eradicate colonization, infection control procedures are cost effective and decrease the prevalence of vancomycin resistant enterococcal colonization and infection. New molecular methods show great promise in strengthening our ability to detect colonization with these bacteria. Furthermore, our understanding of the origin of vancomycin resistant enterococci continues to grow. Paenibacillus species found in soil have been found to carry homologues of vanA-associated glycopeptide resistance genes found in enterococci. Also, additional evidence supports previous data that VanB-associated resistance may have been horizontally transferred from gastrointestinal tract bacteria to enterococci. Finally, glycopeptide resistance has been transferred to methicillin-resistant Staphylococcus aureus in clinical practice on several occasions.

SUMMARY

The prevalence of vancomycin resistant enterococci will likely continue to increase. Implementation of infection control strategies, in conjunction with deployment of advanced technologies for detection of vancomycin resistant enterococci, may curb this rise. The emergence of vancomycin resistant S. aureus is of concern.

First nosocomial outbreak of vancomycin-resistant Enterococcus faecium expressing a VanD-like phenotype associated with a vanA genotype

Although enterococci expressing acquired vancomycin resistance phenotype have been reported increasingly worldwide, they have been rarely reported in France. From August to December 2004 we faced an outbreak of vancomycin-resistant Enterococcus faecium (VRE) isolates in the nephrology department at Bicêtre Hospital (K.-Bicêtre, France). The expression of the glycopeptide resistance varied among the 26 VRE isolates, with vancomycin MICs ranging from 12 to >256 microg/ml, whereas teicoplanin MICs ranged from 4 to 48 microg/ml. However, several strains appeared to be susceptible to glycopeptides according to disk diffusion testing and expressed resistance only after subculture with glycopeptides. In addition, a heterogeneous expression of glycopeptide resistance was also observed. This so-called VanD-like phenotype of resistance (low-level resistance to vancomycin and mostly susceptibility to teicoplanin) was surprisingly associated with a vanA gene. Plasmid extraction and mating-out experiments indicated that the vanA gene was located on a 200-kb self-transferable plasmid. Pulsed-field gel electrophoresis identified mostly dissemination of a single clone, whereas diffusion of the VanA-positive plasmid in different genomic backgrounds had also occurred. The vanA gene was part of a vanA-type operon for expression of resistance located on a Tn1546-like transposon. Sequencing of this transposon identified insertion of insertion sequence IS16 in the vanY gene that encodes a d,d-carboxypeptidase that might explain in part the peculiar VanD-type phenotype of resistance. This report is the first description of a VRE outbreak in France and underlines the difficulty in detecting this organism due to variability on the expression of the glycopeptide resistance trait, if any.

Molecular characterization of vancomycin-resistant Enterococcus faecium isolates from Korea

A total of 98 vancomycin-resistant Enterococcus faecium (VREF) isolates from four tertiary-care hospitals in Korea during the period between 1998 and 2004 were analyzed for genotypic characteristics using the multiplex PCR, multilocus sequence typing (MLST), pulsed-field gel electrophoresis (PFGE), and esp gene analysis. Ninety-two isolates of VREF with VanA phenotype and five of six isolates with VanB phenotype possessed the vanA gene. MLST analysis revealed 9 sequence types (STs), which belonged to a single clonal complex (CC78, clonal lineage C1). Five strains showing incongruence between phenotype and genotype (VanB-vanA) did not belong to the same genotypic clone. The esp gene was detected in all VREF strains, showing 12 different esp repeat profiles. Data suggest that an epidemic clonal group of VREF, CC78 with esp gene, is also present in Asia and has differentiated into multiple diverse genotypic clones during the evolutionary process.