Prevalence of vancomycin-resistant enterococci in fecal samples from hospitalized patients and nonhospitalized controls in a cattle-rearing area of France

Molecular characterization of clinical and environmental isolates of vancomycin-resistant Enterococcus faecium and Enterococcus faecalis from a teaching hospital in Wales

The present study describes the first molecular characterization of environmental and clinical isolates of vancomycin-resistant enterococci (VRE) in Wales. Over a 3-month period (May-July 2000), 134 isolates of VRE (89 Enterococcus faecium and 45 Enterococcus faecalis) were isolated from the patient environment of the University Hospital of Wales (UHW) in Cardiff, Wales, UK. In addition, over the same time-period, 24 clinical isolates of VRE (20 isolates of E. faecium and four isolates of E. faecalis) were obtained from 14 patients. All study isolates were subjected to PFGE typing and their van genotypes were determined by using multiplex PCR. The vanA PCR product (231 bp) was evident in 146 (92 %) of 158 VRE isolates; the remaining 12 isolates (8 %) were positive for the vanB gene. All isolates of E. faecalis were found to be vanA-positive. In total, 16 PFGE banding profiles (pulsotypes) were observed for environmental isolates of E. faecium, whilst eight pulsotypes were found for isolates of E. faecalis. Some of these pulsotypes were isolated from multiple sites, whereas others were more restricted in their distribution. Eleven pulsotypes were evident for clinical isolates and eight of these (representing 11 isolates) were also encountered in environmental isolates. Eleven clinical isolates of E. faecium (55 %) shared an identical pulsotype that was not detected in environmental isolates. These results demonstrate a heterogeneous environmental population of VRE and an association of certain strains with clinical isolates. Predominance of a single pulsotype (not detected in the environment) amongst clinical isolates suggests non-environmental transmission between patients.

Risk factors for new detection of vancomycin-resistant enterococci in acute-care hospitals that employ strict infection control procedures

Accurate assessment of the risk factors for colonization with vancomycin-resistant enterococci (VRE) among high-risk patients is often confounded by nosocomial VRE transmission. We undertook a 15-month prospective cohort study of adults admitted to high-risk units (hematology, renal, transplant, and intensive care) in three teaching hospitals that used identical strict infection control and isolation procedures for VRE to minimize nosocomial spread. Rectal swab specimens for culture were regularly obtained, and the results were compared with patient demographic factors and antibiotic exposure data. Compliance with screening was defined as "optimal" (100% compliance) or "acceptable" (minor protocol violations were allowed, but a negative rectal swab specimen culture was required within 1 week of becoming colonized with VRE). Colonization with VRE was detected in 1.56% (66 of 4,215) of admissions (0.45% at admission and 0.83% after admission; the acquisition time was uncertain for 0.28%), representing 1.91% of patients. No patients developed infection with VRE. The subsequent rate of new acquisition of VRE was 1.4/1,000 patient days. Renal units had the highest rate (3.23/1,000 patient days; 95% confidence interval [CI], 1.54 to 6.77/1,000 patient days). vanB Enterococcus faecium was the most common species (71%), but other species included vanB Enterococcus faecalis (21%), vanA E. faecium (6%), and vanA E. faecalis (2%). The majority of isolates were nonclonal by pulsed-field gel electrophoresis analysis. Multivariate analysis of risk factors in patients with an acceptable screening suggested that being managed by a renal unit (hazard ratio [HR] compared to the results for patients managed in an intensive care unit, 4.6; 95% CI, 1.2 to 17.0 [P = 0.02]) and recent administration of either ticarcillin-clavulanic acid (HR, 3.6; 95% CI, 1.1 to 11.6 [P = 0.03]) or carbapenems (HR, 2.8; 95% CI, 1.0, 8.0 [P = 0.05]), but not vancomycin or broad-spectrum cephalosporins, were associated with acquisition of VRE. The relatively low rates of colonization with VRE, the polyclonal nature of most isolates, and the possible association with the use of broad-spectrum antibiotics are consistent with either the endogenous emergence of VRE or the amplification of previously undetectable colonization with VRE among high-risk patients managed under conditions in which the risk of nosocomial acquisition was minimized.

Characterization of a vancomycin-resistant Enterococcus faecalis (VREF) isolate from a dog with mastitis: further evidence of a clonal lineage of VREF in New Zealand

We report here on the characterization of a vancomycin-resistant Enterococcus faecalis (VREF) isolated from a dog with mastitis. The isolate was positive for the vanA, ermB, and tet(M) genes, with vanA and ermB carried on the same transferable plasmid. Comparison of this isolate with VREF from poultry and human sources in New Zealand demonstrated identical SmaI macrorestriction patterns and Tn1546-like elements. This is further evidence of a clonal lineage of VREF in New Zealand.

Assessing risks for a pre-emergent pathogen: virginiamycin use and the emergence of streptogramin resistance in Enterococcus faecium

Vancomycin-resistant enterococci (VRE) are an important cause of hospital-acquired infections and an emerging infectious disease. VRE infections were resistant to standard antibiotics until quinupristin/dalfopristin (QD), a streptogramin antibiotic, was approved in 1999 for the treatment of vancomycin-resistant Enterococcus faecium infections in people. After that decision, the practice of using virginiamycin in agriculture for animal growth promotion came under intense scrutiny. Virginiamycin, another streptogramin, threatens the efficacy of QD in medicine because streptogramin resistance in enterococci associated with food animals may be transferred to E faecium in hospitalised patients. Policy makers face an unavoidable conundrum when assessing risks for pre-emergent pathogens; good policies that prevent or delay adverse outcomes may leave little evidence that they had an effect. To provide a sound basis for policy, we have reviewed the epidemiology of E faecium and streptogramin resistance and present qualitative results from mathematical models. These models are based on simple assumptions consistent with evidence, and they establish reasonable expectations about the population-genetic and population-dynamic processes underlying the emergence of streptogramin-resistant E faecium (SREF). Using the model, we have identified critical aspects of SREF emergence. We conclude that the emergence of SREF is likely to be the result of an interaction between QD use in medicine and the long-term use of virginiamycin for animal growth promotion. Virginiamycin use has created a credible threat to the efficacy of QD by increasing the mobility and frequency of high-level resistance genes. The potential effects are greatest for intermediate rates of human-to-human transmission (R0 approximately equal 1).

A clonal lineage of VanA-type Enterococcus faecalis predominates in vancomycin-resistant Enterococci isolated in New Zealand

Avoparcin was used as a feed additive in New Zealand broiler production from 1977 until June 2000. We report here on the effects of the usage and discontinuation of avoparcin on the prevalence of vancomycin-resistant enterococci (VRE) in broilers. Eighty-two VRE isolates were recovered from poultry fecal samples between 2000 and mid-2001. VRE isolates were only obtained from broiler farms that were using, or had previously used, avoparcin as a dietary supplement. Of these VRE isolates, 73 (89%) were VanA-type Enterococcus faecalis and nine (11%) were VanA-type Enterococcus faecium. All E. faecalis isolates were found to have an identical or closely related pulsed-field gel electrophoresis (PFGE) pattern of SmaI-digested DNA and were susceptible to both ampicillin and gentamicin. The PFGE patterns of the nine E. faecium isolates were heterogeneous. All VRE contained both the vanA and ermB genes, which, regardless of species or PFGE pattern, resided on the same plasmid. Eighty-seven percent of the VRE isolates also harbored the tet(M) gene, while for 63 and 100%, respectively, of these isolates, the avilamycin and bacitracin MICs were high (>or=256 microg/ml). Five of eight vancomycin-resistant E. faecalis isolates recovered from humans in New Zealand revealed a PFGE pattern identical or closely related to that of the E. faecalis poultry VRE isolates. Molecular characterization of Tn1546-like elements from the VRE showed that identical transposons were present in isolates from poultry and humans. Based on the findings presented here, a clonal lineage of VanA-type E. faecalis dominates in VRE isolated from poultry and humans in New Zealand.

Vancomycin-resistant enterococci (VRE) in broiler flocks 5 years after the avoparcin ban

The glycopeptide growth promoter avoparcin was banned from animal production in Denmark in 1995. In this study, we investigated the occurrence of vancomycin-resistant enterococci (VRE) in broiler flocks in the absence of the selective pressure exerted by the use of avoparcin. One hundred sixty-two broiler flocks from rearing systems with different histories of avoparcin exposure were investigated for the presence of VRE. Using a direct selective plating procedure, VRE were isolated from 104 of 140 (74.3%) broiler flocks reared in broiler houses previously exposed to avoparcin on conventional and extensive indoor broiler farms. In contrast, only 2 of 22 (9.1%) organic broiler flocks reared on free-range farms with no history of previous exposure to avoparcin were VRE-positive. Furthermore, the occurrence of VRE over time in flocks reared in broiler houses previously exposed to avoparcin was investigated. Results obtained by direct selective plating showed no significant decrease in the proportion of VRE-positive flocks during the study period (1998-2001). This study demonstrated the extensive occurrence of VRE in broiler flocks more than 5 years after the avoparcin ban in Denmark, and indicates that VRE may persist in the absence of the selective pressure exerted by avoparcin. The results differ markedly from previously published Danish surveillance data on VRE in broilers. This may reflect differences in isolation procedures.

Vancomycin-resistant enterococci in shellfish, unchlorinated waters, and chicken

Vancomycin-resistant enterococci (VRE) have been a cause of increasing concern chiefly regarding the infection of hospital patients. There is suspicion, but limited evidence, that food and environmental spread may be important. Biomonitoring by examination of bivalve shellfish was used to assess the occurrence of VRE entering the environment. Using pre-enrichment and Lewisham and Slanetz and Bartley agars, 2/125 (1.6%) of shellfish were found to contain enterococci resistant to high levels of vancomycin. Lewisham agar allows relatively rapid identification of VRE. In a second phase of the work using pre-enrichment and Slanetz and Bartley agar, 4/151 (2.7%) shellfish and 5/27 (18.5%) raw chickens contained VRE. Using filtration and pre-enrichment, no VRE were found in 54 unchlorinated water samples. The study shows that environmental prevalence of VRE is low, and that raw chickens are frequently contaminated.

Enterococci from foods

Enterococci have recently emerged as nosocomial pathogens. Their ubiquitous nature determines their frequent finding in foods as contaminants. In addition, the notable resistance of enterococci to adverse environmental conditions explains their ability to colonise different ecological niches and their spreading within the food chain through contaminated animals and foods. Enterococci can also contaminate finished products, such as fermented foods and, for this reason, their presence in many foods (such as cheeses and fermented sausages) can only be limited but not completely eliminated using traditional processing technologies. Enterococci are low grade pathogens but their intrinsic resistance to many antibiotics and their acquisition of resistance to the few antibiotics available for treatment in clinical therapy, such as the glycopeptides, have led to difficulties and a search for new drugs and therapeutic options. Enterococci can cause food intoxication through production of biogenic amines and can be a reservoir for worrisome opportunistic infections and for virulence traits. Clearly, there is no consensus on the acceptance of their presence in foodstuffs and their role as primary pathogens is still a question mark. In this review, the following topics will be covered: (i) emergence of the enterococci as human pathogens due to the presence of virulence factors such as the production of adhesins and aggregation substances, or the production of biogenic amines in fermented foods; (ii) their presence in foods; (iii) their involvement in food-borne illnesses; (iv) the presence, selection and spreading of antibiotic-resistant enterococci as opportunistic pathogens in foods, with particular emphasis on vancomycin-resistant enterococci.

High prevalence of vancomycin-resistant enterococci in Swedish sewage

In Europe the use of the growth promoter avoparcin is considered to have selected for vancomycin-resistant enterococci (VRE). Sweden ceased using avoparcin in 1986, and only occasional cases of VRE from hospitals have been reported since 1995. Within the framework of a European study, samples from urban raw sewage, treated sewage, surface water, and hospital sewage in Sweden (n = 118) were screened for VRE. Surprisingly, VRE were isolated from 21 of 35 untreated sewage samples (60%), from 5 of 14 hospital sewage samples (36%), from 6 of 32 treated sewage samples (19%), and from 1 of 37 surface water samples. Thirty-five isolates from 33 samples were further characterized by geno- and phenotyping, MIC determination, and PCR analysis. Most isolates (30 of 35) carried the vanA gene, and the majority (24 of 35) of the isolates were Enterococcus faecium. Most of the VRE were multiresistant. The typing revealed high diversity of the isolates. However, one major cluster with seven identical or similar isolates was found. These isolates came from three different sewage treatment plants and were collected at different occasions during 1 year. All VRE from hospital sewage originated from one of the two hospitals studied. That hospital also had vancomycin consumption that was 10-fold that of the other. We conclude that VRE were commonly found in sewage samples in Sweden. The origin might be both healthy individuals and individuals in hospitals. Possibly, antimicrobial drugs or chemicals released into the sewage system may sustain VRE in the system.

Molecular analysis of vanA enterococci isolated from humans and animals in northeastern Italy

A total of 53 vancomycin-resistant vanA-positive enterococci isolates from poultry farms (17 Enterococcus faecium; 8 Enterococcus durans) and from different hospitals (23 E. faecium; 5 Enterococcus faecalis) in northeastern Italy were compared on the basis of their antibiotic susceptibilities, their SmaI pulsed-field gel electrophoresis (PFGE) patterns, and the organization of their Tn1546-related elements. Ampicillin resistance was similar in both groups of isolates (52 and 60.7%, respectively), whereas human strains were more resistant to high-level gentamicin and streptomycin. A total of 52% of animal strains and 60% of human strains were resistant to tetracycline, and 56% and 46.4% to quinupristin/dalfopristin, respectively. In E. faecium and E. durans animal isolates, nine and six distinct PFGE patterns, respectively, were found: in two instances indistinguishable isolates were found from different farms. In E. faecium and E. faecalis human isolates, nine and six distinct PFGE patterns, respectively, were found; among E. faecium strains, 12 were identical or closely related and were isolates from the same hospital. Elements mediating vanA-glycopeptide resistance were characterized by PCR with primers that amplified 10 overlapping fragments of Tn1546. A total of 84.6% of animal strains and 64.2% of human strains contained elements indistinguishable from the prototype Tn1546. In addition, nine different types were identified, but none was common to animal and human strains.

Human infections caused by glycopeptide-resistant Enterococcus spp: are they a zoonosis?

Following the detection of glycopeptide-resistant enterococci (GRE) in 1986 and their subsequent global dissemination during the 1990s, many studies have attempted to identify the reservoirs and lines of resistance transmission as a basis for intervention. The eradication of reservoirs and the prevention of GRE spread is of major importance for two reasons: (i) the emergence of high-level glycopeptide resistance in invasive enterococcal clinical isolates that are already multiresistant, has left clinicians with therapeutic options that are only at the experimental stage; and (ii) the resistance genes may spread to more virulent bacterial species such as Staphylococcus aureus, Streptococcus pneumoniae and Clostridium difficile. VanA-type strains, resistant to high levels of both vancomycin and teicoplanin, are the most commonly encountered enterococci with acquired glycopeptide resistance in humans. A widespread VanA-type GRE reservoir was detected early in farm animals that were exposed to the glycopeptide growth-promoter avoparcin. Numerous studies have provided indirect evidence for the transfer of VanA-type GRE and their resistance determinants from animal reservoirs to humans. The data collected have expanded our understanding of the promiscuous nature of antibiotic resistance, and have provided the groundwork for logical decision-making with the objective of deterring the dissemination of resistant bacteria and of their resistance genes.

Transient intestinal carriage after ingestion of antibiotic-resistant Enterococcus faecium from chicken and pork

BACKGROUND

Antibiotic-resistant enterococci are often present in retail meats, but it is unclear whether the ingestion of these contaminants leads to sustained intestinal carriage.

METHODS

We conducted a randomized, double-blind study in 18 healthy volunteers. Six ingested a mixture of 10(7) colony-forming units (CFU) of two glycopeptide-resistant strains of Enterococcus faecium obtained from chicken purchased at a grocery store, six ingested 10(7) CFU of a streptogramin-resistant strain of E. faecium obtained from a pig at slaughter, and six ingested 10(7) CFU of a glycopeptide-susceptible and streptogramin-susceptible strain of E. faecium from chicken purchased at a grocery store. Suspensions of enterococci were prepared in 250 ml of whole milk and were well within the amounts deemed acceptable by Danish food regulations. Stool samples were collected before exposure, daily for 1 week after ingestion, and at 14 and 35 days. Resistant enterococci in stools were identified by selective culture techniques; further molecular characterization of the organisms was also conducted.

RESULTS

At the outset, none of the subjects were colonized with glycopeptide-resistant or streptogramin-resistant E. faecium. After ingestion of the study strains, these same strains were isolated from the stools of all subjects, in various concentrations. The test strain was isolated in stool from 8 of 12 subjects on day 6, and from 1 of 12 on day 14. All stool samples were negative at 35 days.

CONCLUSIONS

The ingestion of resistant E. faecium of animal origin leads to detectable concentrations of the resistant strain in stools for up to 14 days after ingestion. The organisms survive gastric passage and multiply.

Vancomycin-resistant Enterococcus spp. isolated from wastewater and chicken feces in the United States

Vancomycin-resistant Enterococcus spp. (VRE) were isolated from sewage and chicken feces but not from other animal fecal sources (dog, cow, and pig) or from surface waters tested. VRE from hospital wastewater were resistant to > or =20 microg of vancomycin/ml and possessed the vanA gene. VRE from residential wastewater and chicken feces were resistant to 3 to 5 microg of vancomycin/ml and possessed the vanC gene.

Occurrence of vancomycin-resistant enterococci in pork and poultry products from a cattle-rearing area of France

Meat products were collected from public retail outlets and tested for the presence of vancomycin-resistant enterococci (VRE) in an area with a high prevalence of VRE reported in human fecal samples. VRE were detected in 66% of the samples, and a predominance of VanC strains was found, which is also true for human fecal samples.

Clinical prevalence, antimicrobial susceptibility, and geographic resistance patterns of enterococci: results from the SENTRY Antimicrobial Surveillance Program, 1997-1999

As part of the SENTRY Antimicrobial Resistance Surveillance Program, a total of 4998 strains of enterococci isolated from 1997 to 1999 were processed. The occurrence of enterococcal infections by species and site of infection was analyzed, as were the occurrence of vancomycin-resistant enterococci (VRE) and their resistance phenotypes and genotypes. Trends in antimicrobial susceptibility to a variety of agents (including experimental compounds) were also reported. Enterococci accounted for >9% of isolates from all bloodstream infections (BSIs) in North America. Ampicillin was active against strains from Latin America and Europe but not against those from the United States and Canada. US isolates were considerably more resistant to vancomycin (17% resistant strains in 1999) than were those from patients in the rest of the world. The highest proportion of VRE was observed among BSI isolates (81.7%). Quinupristin-dalfopristin, chloramphenicol, and doxycycline were the most active agents tested against VRE. The results of this study confirm the worldwide trend in increasing occurrence of enterococci and the emerging pattern of antimicrobial resistance among such isolates.

Treatment of methicillin-resistant Staphylococcus epidermidis infection following repair of an ulnar fracture and humeroradial joint luxation in a horse

A 27-month-old Rocky Mountain Horse was examined because of a fracture of the proximal portion of the ulna and luxation of the humeroradial joint (Monteggia fracture). Open reduction was performed, using a mechanical distractor, and the ulnar fracture was stabilized by application of a bone plate and screws. After surgery, the horse developed an infection of the surgical site, and bacterial culture of fluid from the surgical site yielded a pure growth of methicillin-resistant Staphylococcus epidermidis susceptible to oxytetracycline, erythromycin, rifampin, and vancomycin. Treatment with oxytetracycline did not result in a favorable clinical response. Therefore, the horse was treated systemically with vancomycin and rifampin, and vancomycin-impregnated polymethyl methacrylate beads were implanted at the surgical site. Six months after surgery, the horse was sound at a walk or trot, and bony union was evident on radiographs of the elbow joint.

Antibiotic resistance

Widespread resistance problems exist today in a global sense because of the incorporation of antibiotics with a high resistance potential into animal feeds and because of the uncontrolled use of antibiotics with a high resistance potential in the clinical setting. The only proven method of controlling nonoutbreak resistance problems in hospitals is to limit the hospital formulary to antibiotics with little or no resistance potential. The control of multiresistant organisms in outbreaks occurring in hospitals is best contained using appropriate infection control containment measures. Physicians treating infections in the community, with all other factors being equal, should preferentially select antibiotics with a low resistance potential. The titles and headings of much of the resistance literature are misleading. Articles should not contain fluoroquinolone resistant in the title when ciprofloxacin-resistant organisms are described. Many articles concerning penicillin-resistant pneumococci are entitled fluoroquinolone-resistant S. pneumoniae. These articles describe ciprofloxacin-resistant S. pneumoniae and not resistance to other fluoroquinolones. The same error is perpetuated in describing third-generation cephalosporins and carbapenems. Virtually all of the resistance problems associated with third-generation cephalosporins and carbapenems are due to ceftazidime or imipenem. More precise titling in the literature would remind physicians that antibiotic resistance is related to a specific agent and not class phenomena.