Heat resistance of nosocomial enterococci

Persistent environmental reservoirs for Vancomycin-resistant enterococci requiring repeated decontamination to achieve eradication

V ancomycin-resistant enterococci (VRE) are increasingly recognised nosocomial pathogens in clinical areas with high antibiotic usage. Patients with chronic renal failure, including those requiring haemodialysis, are at particular risk. Investigation and control of an outbreak of VRE in two renal wards, highlighting mattresses as reservoirs and environmental measures to control VRE are reported in this paper. Outbreak control measures included standard isolation in accordance with the Recommendations of the Hospital Infection Control Practices Advisory Committee (HICPAC). Patients were screened on admission and weekly using a rectal swab. The inanimate environment including mattresses was also screened. Enhanced environmental decontamination was performed on a daily basis.

The outbreak continued over a 20-week period with most cases occurring in the first 6 weeks. The results of screening indicated that 59 (13%) of 451 patients and 54 (8.3%) of 647 environmental samples were positive for VRE. VRE was isolated from 35 (8%) of 433 mattresses, 12 (8.1%) of 148 environmental ledges, 4 (8%) of 50 toilets, and 3 (18.8%) of 16 items of cleaning equipment. Molecular typing indicated that a predominant strain was also implicated in mattress contamination, thus highlighting a potential and important reservoir for transmission of VRE. Difficulty with eradication of VRE from the environment was encountered despite enhanced cleaning regimens and a doubling of use of disinfectant was necessary.

Restriction of antibiotics, hand hygiene, hygiene and education are the cornerstone of VRE prevention and control. Lessons from this outbreak highlight the role of the environment in VRE transmission and the need for attention to the environment, especially mattress decontamination.

Functional genomic analysis of bile salt resistance in Enterococcus faecium

Background

Enterococcus faecium is a Gram-positive commensal bacterium of the mammalian intestinal tract. In the last two decades it has also emerged as a multi-resistant nosocomial pathogen. In order to survive in and colonize the human intestinal tract E. faecium must resist the deleterious actions of bile. The molecular mechanisms exploited by this bacterium to tolerate bile are as yet unexplored.

Results

In this study we used a high-throughput quantitative screening approach of transposon mutant library, termed Microarray-based Transposon Mapping (M-TraM), to identify the genetic determinants required for resistance to bile salts in E. faecium E1162. The gene gltK, which is predicted to encode a glutamate/aspartate transport system permease protein, was identified by M-TraM to be involved in bile resistance. The role of GltK in bile salt resistance was confirmed by the subsequent observation that the deletion of gltK significantly sensitized E. faecium E1162 to bile salts. To further characterize the response of E. faecium E1162 to bile salts, we performed a transcriptome analysis to identify genes that are regulated by exposure to 0.02% bile salts. Exposure to bile salts resulted in major transcriptional rearrangements, predominantly in genes involved in carbohydrate, nucleotide and coenzyme transport and metabolism.

Conclusion

These findings add to a better understanding of the molecular mechanisms by which E. faecium responds and resists the antimicrobial action of bile salts.

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.

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

For many years, Enterococcus faecium was considered to be a commensal of the digestive tract, which only sporadically caused opportunistic infections in severely ill patients. Over the last two decades, vancomycin-resistant E. faecium (VREF) has emerged worldwide as an important cause of nosocomial infections, especially in immunocompromised patients. The global Vancomycin-resistant enterococci (VRE) epidemic was preceded by the emergence of ampicillin-resistant E. faecium (AREfm) in the United States in the early 1980s, followed by the rapid emergence of VRE in the 1990s. A similar increase of VRE may occur in countries with still low levels of VRE in hospitals (such as The Netherlands), but increasing incidence of AREfm infections. Molecular epidemiological studies of both human- and animal-derived E. faecium isolates using multilocus sequence typing revealed the existence of host-specific genogroups, including a specific genetic lineage designated CC17, associated with hospital-related isolates. These strains were characterized by ampicillin and quinolone resistance. In addition, the majority of these CC17 isolates contain over hundred hospital-clade-specific genes, including mobile elements, phage genes and plasmid sequences, hypothetical and membrane proteins and antibiotic and regulatory genes and a putative pathogenicity island including the esp gene.

Persistence of vancomycin-resistant enterococci (VRE) in broiler houses after the avoparcin ban

The glycopeptide growth promoter avoparcin was banned from animal production in the EU in 1997 due to concern for the spread of vancomycin-resistant enterococci (VRE) from food animals to humans. In recent Norwegian and Danish studies, extensive occurrence of VRE on broiler farms and in broiler flocks after the avoparcin ban has been reported. The present study was undertaken to investigate the epidemiology of VRE on broiler farms in the absence of the selective pressure exerted by avoparcin. Environmental samples were obtained from five broiler houses after depopulation, cleaning, and disinfection of the houses between rotations, and two consecutive broiler flocks from each house were sampled by taking cloacal swabs from the broilers at the time of slaughter. A total of 69 vancomycin-resistant Enterococcus faecium isolates obtained from broiler flocks and broiler houses were subjected to molecular typing by pulsed-field gel electrophoresis (PFGE). Forty-one PFGE-profiles were observed. VRE with indistinguishable or highly similar PFGE profiles were isolated from consecutive broiler flocks and from environmental samples from the houses in which the flocks were reared, whereas VRE-isolates from different broiler houses and from flocks reared in different houses appeared to be genetically unrelated. These findings indicated that VRE was transmitted between consecutive broiler flocks by clones of resistant bacteria surviving in the broiler houses despite cleaning and disinfection between rotations. Thus, the extensive occurrence of VRE in broiler flocks after the avoparcin ban may be explained by persistence of VRE in the broiler house environment.

Vancomycin-resistant enterococci: 15 years and counting

We review the history of vancomycin-resistant enterococci (VRE) and propose a causal model illustrating the roles of exposure to VRE reservoirs, patient characteristics, antimicrobial exposure, and prevalence of VRE in the progression from potential VRE reservoirs to active disease in hospitalized patients. Differences in VRE colonization and VRE infection are discussed with respect to hospital surveillance methodology and implications for interventions. We further document clonal transmission of VRE in a large, urban, teaching hospital and demonstrate VRE susceptibility to a wide array of antimicrobial agents. This model can guide the identification of mutable factors that are focal points for intervention.

Antibiotic-resistant enterococci: the mechanisms and dynamics of drug introduction and resistance

Enterococci possess a vast array of mechanisms to resist the lethal effects of most antimicrobial drugs currently approved for therapeutic use in humans, thus presenting a considerable therapeutic challenge. This review summarizes current concepts regarding the mechanisms of resistance, as well as the emergence, proliferation, and epidemiology of resistant enterococci.

Prevalence of glycopeptide and aminoglycoside resistance in Enterococcus and Listeria spp. in low microbial load diets of neutropenic hospital patients

Low microbial load diets for patients with haematological malignancy were examined for enterococci and listeria using pre-enrichment, enrichment and selective plating. Enterococci were highly prevalent and their ecology diverse; 100/211 samples yielded 132 isolates made up of 67 strains distinguishable by PFGE. Listeria monocytogenes was not found. Screening of enterococci for antibiotic resistance showed low level vancomycin resistance (6-12 microg/ml) in six isolates of E. gallinarum and high level streptomycin resistance (> or = 1000 microg/ml) in eight isolates from various foods. No strains showing high level glycopeptide or gentamicin resistance were found. The high prevalence of enterococci in food processed for safety indicates a possible route for the acquisition of antibiotic-resistant strains by vulnerable hospital patients.

Vancomycin-resistant enterococci

After they were first identified in the mid-1980s, vancomycin-resistant enterococci (VRE) spread rapidly and became a major problem in many institutions both in Europe and the United States. Since VRE have intrinsic resistance to most of the commonly used antibiotics and the ability to acquire resistance to most of the current available antibiotics, either by mutation or by receipt of foreign genetic material, they have a selective advantage over other microorganisms in the intestinal flora and pose a major therapeutic challenge. The possibility of transfer of vancomycin resistance genes to other gram-positive organisms raises significant concerns about the emergence of vancomycin-resistant Staphylococcus aureus. We review VRE, including their history, mechanisms of resistance, epidemiology, control measures, and treatment.

Vancomycin-resistant enterococci

After they were first identified in the mid-1980s, vancomycin-resistant enterococci (VRE) spread rapidly and became a major problem in many institutions both in Europe and the United States. Since VRE have intrinsic resistance to most of the commonly used antibiotics and the ability to acquire resistance to most of the current available antibiotics, either by mutation or by receipt of foreign genetic material, they have a selective advantage over other microorganisms in the intestinal flora and pose a major therapeutic challenge. The possibility of transfer of vancomycin resistance genes to other gram-positive organisms raises significant concerns about the emergence of vancomycin-resistant Staphylococcus aureus. We review VRE, including their history, mechanisms of resistance, epidemiology, control measures, and treatment.

Vancomycin-resistant enterococcus. Detection, epidemiology, and control measures

VRE have spread rapidly since their initial description in 1988. Although much has been learned about the epidemiology of VRE, further studies are needed to establish the reservoirs of the organism and the relative importance of various modes of transmission. There is considerable anecdotal evidence that nosocomial transmission of VRE can be thwarted by using measures such as those recommended by HICPAC, especially if they are implemented promptly after VRE have been introduced into hospitals.

Heat and chemical resistance of enterococci

Recent reports have highlighted the tolerance of vancomycin-resistant strains of enterococci to heat. This study examined the tolerance of vancomycin-resistant and sensitive strains of enterococci and an NCTC type strain to 65, 71 and 80 degrees C, and also to low concentrations of a chlorine-releasing agent, alcohol and glutaraldehyde. Variation in the tolerance to chemicals was observed but there was no correlation between vancomycin resistance and tolerance to chemical disinfectants. The NCTC type strain was killed within the time/temperature parameters set by the Department of Health for thermal washer/disinfectors, i.e. 65 degrees C for 10 min, 71 degrees C for 3 min and 80 degrees C for 1 min. However, the clinical strains showed varying resistance to heat, irrespective of their vancomycin susceptibility. One strain survived 80 degrees C for 3 min. These results showed that clinical isolates can be resistant to commonly used disinfection processes, although the practical significance of these results is debatable.

Heat tolerance of vancomycin resistant Enterococcus faecium

The heat tolerance of 27 Enterococcus faecium isolates in water was studied. Stationary phase cultures including vancomycin resistant and sensitive clinical and food isolates were exposed to heat at 60 degrees, 65 degrees, 71 degrees, and 80 degrees C for one, three, 10, and 30 minutes and the log10 reductions in bacterial counts were determined. Exposure at 71 degrees and 80 degrees C resulted in > 6 log10 reduction in viable counts for all isolates. Seven (24%) isolates survived (< 5 log10 reduction) heat at 65 degrees C for 10 minutes. The E faecium isolates were more resistant to heat than the two E faecalis reference strains. No differences in heat tolerance were observed between vancomycin sensitive and resistant strains or between isolates of human or food origin.

Current perspectives on glycopeptide resistance

In the last 5 years, clinical isolates of gram-positive bacteria with intrinsic or acquired resistance to glycopeptide antibiotics have been encountered increasingly. In many of these isolates, resistance arises from an alteration of the antibiotic target site, with the terminal D-alanyl-D-alanine moiety of peptidoglycan precursors being replaced by groups that do not bind glycopeptides. Although the criteria for defining resistance have been revised frequently, the reliable detection of low-level glycopeptide resistance remains problematic and is influenced by the method chosen. Glycopeptide-resistant enterococci have emerged as a particular problem in hospitals, where in addition to sporadic cases, clusters of infections with evidence of interpatient spread have occurred. Studies using molecular typing methods have implicated colonization of patients, staff carriage, and environmental contamination in the dissemination of these bacteria. Choice of antimicrobial therapy for infections caused by glycopeptide-resistant bacteria may be complicated by resistance to other antibiotics. Severe therapeutic difficulties are being encountered among patients infected with enterococci, with some infections being untreatable with currently available antibiotics.