Low faecal carrier rate of vancomycin resistant enterococci in Norwegian hospital patients

Mobile genetic elements beyond the VanB-resistance dissemination among hospital-associated enterococci and other Gram-positive bacteria

An increasing resistance to vancomycin among clinically relevant enterococci, such as Enterococcus faecalis and Enterococcus faecium is a cause of a great concern, as it seriously limits treatment options. The vanB operon is one of most common determinants of this type of resistance. Genes constituting the operon are located in conjugative transposons, such as Tn1549-type transposons or, more rarely, in ICEEfaV583-type structures. Such elements show differences in structure and size, and reside in various sites of bacterial chromosome or, in the case of Tn1549-type transposons, are also occasionally associated with plasmids of divergent replicon types. While conjugative transposition contributes to the acquisition of Tn1549-type transposons from anaerobic gut commensals by enterococci, chromosomal recombination and conjugal transfer of plasmids appear to represent main mechanisms responsible for horizontal dissemination of vanB determinants among hospital E. faecalis and E. faecium. This review focuses on diversity of genetic elements harbouring vanB determinants in hospital-associated strains of E. faecium and E. faecalis, the mechanisms beyond vanB spread in populations of these bacteria, and provides an overview of the vanB-MGE distribution among other enterococci and Gram-positive bacteria as potential reservoirs of vanB genes.

Characterization of an Enterococcus gallinarum Isolate Carrying a Dual vanA and vanB Cassette

The ability of vancomycin resistance determinants to be horizontally transferred within enterococci species is a concern. Identification and characterization of vancomycin-resistant enterococci (VRE) in a clinical isolate have a significant impact on infection control practices. In this study, we describe a clinical isolate of Enterococcus gallinarum exhibiting high-level resistance to vancomycin and teicoplanin. The genetic characterization of this isolate showed the presence of vanA and vanB genes in addition to the naturally carried vanC gene. vanA was identified on pA6981, a 35,608-bp circular plasmid with significant homology to plasmid pS177. The vanB operon was integrated into the bacterial chromosome and showed a high level of homology to previously reported Tn1549 and Tn5382. To the best of our knowledge, this is the first report of E. gallinarum carrying both vanA and vanB operons, indicating the importance of identifying the vancomycin resistance mechanism in non-E. faecium and non-E. faecalis enterococcal species.

Zero prevalence of vancomycin-resistant enterococci among Swedish preschool children

OBJECTIVES

Enterococci are a natural part of the bacterial flora of humans, animals, and insects and are frequently found in the community. Vancomycin-resistant enterococci (VRE) have emerged as a growing problem, associated with high morbidity and mortality. The aim of this study was to investigate the prevalence of VRE among healthy Swedish preschool children and ascertain whether they constitute a reservoir for the bacteria.

METHODS

In total, 313 individual diapers were collected from preschools in Uppsala, Sweden. Fecal samples were screened by analyzing the color change in a broth followed by polymerase chain reaction for vanA and vanB genes, which are associated with vancomycin resistance.

RESULTS

Neither vanA nor vanB genes could be detected from the samples.

CONCLUSIONS

Preschool children in Uppsala do not constitute a reservoir for VRE. The zero prevalence is consistent with the overall decline in VRE prevalence in Sweden during the last years.

ICESluvan, a 94-kilobase mosaic integrative conjugative element conferring interspecies transfer of VanB-type glycopeptide resistance, a novel bacitracin resistance locus, and a toxin-antitoxin stabilization system

A 94-kb integrative conjugative element (ICESluvan) transferable to Enterococcus faecium and Enterococcus faecalis from an animal isolate of Streptococcus lutetiensis consists of a mosaic of genetic fragments from different Gram-positive bacteria. A variant of ICESluvan was confirmed in S. lutetiensis from a patient. A complete Tn5382/Tn1549 with a vanB2 operon is integrated into a streptococcal ICESde3396-like region harboring a putative bacteriophage exclusion system, a putative agglutinin receptor precursor, and key components of a type IV secretion system. Moreover, ICESluvan encodes a putative MobC family mobilization protein and a relaxase and, thus, in total has all genetic components essential for conjugative transfer. A 9-kb element within Tn5382/Tn1549 encodes, among others, putative proteins similar to the TnpX site-specific recombinase in Faecalibacterium and VanZ in Paenibacillus, which may contribute to the detected low-level teicoplanin resistance. Furthermore, ICESluvan encodes a novel bacitracin resistance locus that is associated with reduced susceptibility to bacitracin when transferred to E. faecium. The expression of a streptococcal pezAT toxin-antitoxin-encoding operon of ICESluvan in S. lutetiensis, E. faecium, and E. faecalis was confirmed by reverse transcription (RT)-PCR, indicating an active toxin-antitoxin system which may contribute to stabilizing ICESluvan within new hosts. Junction PCR and DNA sequencing confirmed that ICESluvan excised to form a circular intermediate in S. lutetiensis, E. faecalis, and E. faecium. Transfer between E. faecalis cells was observed in the presence of helper plasmid pIP964. Sequence analysis of the original S. lutetiensis donor and enterococcal transconjugants showed that ICESluvan integrates in a site-specific manner into the C-terminal end of the chromosomal tRNA methyltransferase gene rumA.

The Prevalence of Fecal Colonization of Enterococci, the Resistance of the Isolates to Ampicillin, Vancomycin, and High-Level Aminoglycosides, and the Clonal Relationship Among Isolates

The gastrointestinal tract carriage of enterococci was searched in 150 hospitalized patients and 100 outpatients, and clonal relatedness of the isolates and their resistance to ampicillin, vancomycin, and high-level streptomycin and gentamicin were investigated. A stool sample or rectal swab collected from each patient was inoculated into appropriate media within an hour. Enterococcus species were identified by using conventional biochemical tests, API-20 Strep assay, and BBL crystal kit. Antibiotic susceptibility tests were performed using Kirby-Bauer disk diffusion method. A polymerase chain reaction (PCR) was used to detect vanA and vanB genes. Pulsed-field gel electrophoresis (PFGE) and arbitrarily primed-polymerase chain reaction (AP-PCR) methods were used for molecular typing of the strains. Enterococci were isolated from 90 (60%) of the specimens collected from 150 inpatients. Of these 90 isolates, 37 (41%) had high-level gentamicin resistance, 36 (40%) had high-level streptomycin resistance, and 50 (55.6%) had ampicillin resistance. Fecal colonization was found in 30% of the outpatients. Resistances to ampicillin, high-level streptomycin, and gentamicin were 13%, 10%, and 3%, in these patients' isolates, respectively. No vancomycin-resistant enterococci were detected by both agar diffusion and PCR assays in our study. Both typing procedures were applied on 78 Enterococcus strains isolated from inpatients. AP-PCR typing showed that 30 (50.8%) of the 59 E. faecium and 5 (50%) of the 10 E. faecalis strains were clonally related. These values were found to be 12 (20.3%) and two (20%) by PFGE, respectively. The typing procedures did not find any clustered strains in the six E. durans and three E. avium isolates. Neither PFGE nor AP-PCR result was significantly different among the sensitive and resistant strains. Our results indicate that the high prevalence of colonization with ampicillin and highlevel aminoglycoside-resistant enterococci is an important problem in our medical center. The high clonal diversity among the isolates indicates limited spread of antibiotic-resistant strains between patients.

Comparative analysis of amplified fragment length polymorphism and pulsed field gel electrophoresis in a hospital outbreak and subsequent endemicity of ampicillin-resistantEnterococcus faecium

Reliable molecular methods for determination of relatedness between bacterial isolates have become increasingly important to evaluate outbreaks and endemic situations with nosocomial pathogens. In the present study Simpson's index of diversity with calculated confidence intervals was used to compare amplified fragment length polymorphism (AFLP) and pulsed field gel electrophoresis (PFGE) analysis of a hospital outbreak of ampicillin-resistant Enterococcus faecium and subsequent endemicity. The outbreak, in a Norwegian tertiary hospital, of infections caused by these enterococci started in 1995 and increased in 1996 after which the situation turned endemic. The purpose of this study was to compare the two methods in this setting and to determine the length of time during an outbreak that these methods are sufficiently valid to be of value for hospital infection control efforts. One hundred and sixty clinical isolates from urine specimens collected during the period 1995-1999 were included. The findings indicate that PFGE and AFLP are equally discriminative and could in this setting be used for typing purposes over the whole 5-year period.

Transferable vanB2 Tn5382-containing elements in fecal streptococcal strains from veal calves

Three vancomycin-resistant veal calf fecal streptococci, identified as Streptococcus gallolyticus (n = 2) and Streptococcus lutetiensis, were shown to harbor vanB2 Tn5382-like elements earlier described in enterococci. One S. gallolyticus strain had a 1,495-bp IS256-related element inserted in vanS(B). The vanB2 Tn5382 element present in the plasmid-free S. lutetiensis strain was transferable to Enterococcus faecium BM4105-RF, Enterococcus faecalis JH2-2, and its recombination-deficient derivative, UV202. The transfer frequencies were comparable between recipient strains (from 1 x 10(-7) to 7 x 10(-6)). All transconjugants acquired a vanB-containing chromosomal insert of approximately 100 kb, apparently by site-specific integration. Secondary transconjugants were not observed in intraspecies retransfer experiments. These observations are consistent with a conjugative, selftransmissible, integrative element that might be involved in the interspecies spread of vanB2 resistance determinants. Two JH2-2-derived transconjugants had also gained additional copies of large vanB-containing chromosomal fragments, a process that involves unexplained mechanisms that seems to require functional host cell-dependent recombination mechanisms.

Molecular characterization of ampicillin-resistant Enterococcus faecium isolates from hospitalized patients in Norway

The genetic relationship of 81 ampicillin-resistant and 21 ampicillin-susceptible Enterococcus faecium isolates from clinical infections and rectal screening in hospitalized patients in Norway was studied by pulsed-field gel electrophoresis (PFGE) and amplified fragment length polymorphism (AFLP). PFGE showed 55 different banding patterns, and 65 of the isolates could be grouped into one large group. With AFLP, 46 patterns were discerned, and 74 isolates clustered in one group. In general, the isolates had a higher degree of similarity than with PFGE. The purK gene, which is one of the targets of the E. faecium multilocus sequence typing scheme, was sequenced. Eleven different purK alleles could be discerned, with the majority of isolates (n = 80) harboring allele 1. With only two exceptions, all strains carrying purK-1 clustered in the same PFGE and AFLP groups, indicating a good correlation between PFGE type, AFLP type, and purK allele. Genetic polymorphism of a 571-bp PCR fragment of the C-terminal domain of the penicillin-binding protein 5 gene (pbp5) was determined, and sequence differences were associated with the level of ampicillin resistance. This study indicates that the majority of ampicillin-resistant E. faecium strains in Norway belong to a distinct genetic lineage of closely related genotypes. Rectal and clinical isolates were generally indistinguishable, and differences in clonal distribution and allele polymorphism were found mainly between ampicillin-resistant and -susceptible isolates.

Enterococcus gallinarum endocarditis occurring on native heart valves

We report the first case of Enterococcus gallinarum endocarditis developing on normal native heart valves. Using phenotypic and molecular methods, a precise identification of this naturally vancomycin-resistant species allowed an optimal antibiotic therapy and the patient's recovery.

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.

Fecal carriage of vancomycin- and ampicillin-resistant Enterococci observed in Swedish adult patients with diarrhea but not among healthy subjects

During a 1-y prospective study between 1 October 1996 and 30 September 1997, fecal samples from 786 adult patients with diarrhea and 203 healthy control subjects were screened for vancomycin-resistant Enterococci (VRE) and ampicillin-resistant Enterococci (ARE). The carriage rates of VRE and ARE were 0.4% and 6%, respectively among patients and 0% among controls. The 3 VRE isolates were all VanA and were obtained from patients who had been abroad (Thailand, Spain, France) within the previous 3 months. Thirteen of the 45 patients with ARE (29%) had been abroad within 2 weeks of the onset of diarrhea. These findings suggest a potential risk of introduction of antibiotic-resistant Enterococci in Swedish hospitals by patients receiving treatment for diarrhea after traveling abroad.

The prevalence of faecal carriage of ampicillin-resistant and high-level gentamicin-resistant enterococci among inpatients at 10 major Norwegian hospitals

From March to October 1999, 854 patients hospitalized at 10 major Norwegian hospitals were screened for rectal carriage of ampicillin-resistant enterococci (ARE) and high-level gentamicin-resistant enterococci (HLGRE). A total of 59 ARE carriers (prevalence 6.9%, range 0-22% among hospitals) and 28 HLGRE carriers (prevalence 3.3%, range 1-11%) were detected. All ARE or HLGRE strains were susceptible to vancomycin, whereas 77% of the ARE isolates were resistant to ciprofloxacin. All the ARE strains were identified as Enterococcus faecium, and 48% of these were genomically closely related as shown by PFGE. Specific point mutations in the pbp5 gene were associated with reduced susceptibility to ampicillin. The adjusted risk of becoming a carrier of ARE was related to the use of glycopeptides [odds ratio (OR) = 4.8], the use of any antimicrobial agent (OR = 3.1) and more than one hospital admission during the last six months (OR = 2.0). Twenty-five of 28 HLGRE isolates were Enterococcus faecalis. The aacA/aphD genes were detected in 26 (93%) and the aphA3 in 19 (68%) of the HLGRE isolates. Sixty-four percent of the HLGRE isolates belonged to two PFGE clusters. Consumption of antimicrobial agents was also a significant risk factor for HLGRE colonization (OR = 5.4), while prescription of penicillins was associated with reduced risk (OR = 0.28).

VanA-type vancomycin-resistant enterococci (VRE) remain prevalent in poultry carcasses 3 years after avoparcin was banned

Avoparcin was used as a growth promoting feed additive in Norwegian broiler and turkey production from 1986 until it was banned in 1995, when an association between vancomycin-resistant enterococci (VRE) and avoparcin use became apparent. A recent study regarding faecal samples documented a continuing high prevalence of VRE among Norwegian poultry 3 years after avoparcin was banned. In the present study, carcasses of broilers and turkeys from farms where avoparcin had previously been in use and carcasses of layer chickens from farms where avoparcin had never been used were examined for the presence of VRE. One carcass from each of 150 different farms was included. By a direct plating method, VRE were isolated from 30 of 100 samples of broilers and turkeys, but not from any samples of layer chickens. When an enrichment step was included, VRE were isolated from a total of 81 of the 100 samples of broilers and turkeys and from nine of the 50 samples of layer chickens. All VRE isolated were highly resistant to vancomycin (MIC > or = 256 microg/ml) and possessed the vanA gene. These results correspond to the prevalence of VRE recently documented in faecal samples from Norwegian poultry. The present study reveals a high prevalence of VRE in broiler and turkey carcasses. Consequently, consumers are exposed to VRE when handling raw poultry meat, although the public health significance of such exposure is unclear.

Continuing high prevalence of VanA-type vancomycin-resistant enterococci on Norwegian poultry farms three years after avoparcin was banned

Avoparcin was used as a feed additive in Norwegian broiler and turkey production from 1986 until 1995. It was banned due to the selection of VanA-type vancomycin-resistant enterococci (VRE) in animal husbandry and to reduce the potential for human exposure to VRE. The aim of the present study was to investigate the prevalence of VRE carriage in Norwegian poultry farmers and their poultry three years after avoparcin was banned. Corresponding faecal samples from poultry and humans on farms where avoparcin had previously been used (exposed farms, n = 73) and farms where avoparcin had never been used (unexposed farms, n = 74) were analysed for the presence of VRE. For each farm, one sample from the poultry house and one sample from the farmer were obtained. VRE were isolated from 72 of 73 (99%) and eight of 74 (11%) poultry samples from exposed and unexposed farms, respectively. VRE were isolated from 13 of 73 (18%) and one of 74 (1%) farmer samples from exposed and unexposed farms, respectively. All VRE isolates were highly resistant to vancomycin and possessed the vanA gene, as shown by PCR. The high prevalence of VRE is in accordance with previous Norwegian studies, and shows a remarkable stability of the VanA resistance determinant in an apparently non-selective environment.

Prevalence and determinants of fecal colonization with vancomycin-resistant Enterococcus in hospitalized patients in The Netherlands

OBJECTIVE

To determine the prevalence and determinants of fecal carriage of vancomycin-resistant enterococci (VRE) in intensive care unit (ICU), hematology-oncology, and hemodialysis patients in The Netherlands.

DESIGN

Descriptive, multicenter study, with yearly 1-week point-prevalence assessments between 1995 and 1998.

POPULATION

All patients hospitalized on the testing days in ICUs and hematology-oncology wards in nine hospitals in The Netherlands were included.

METHODS

Rectal swabs obtained from 1,112 patients were screened for enterococci in a selective broth and subcultured on selective media with and without 6 mg/L vancomycin. Resistance genotypes were determined by polymerase chain reaction. Further characterization of VRE strains was done by pulsed-field gel electrophoresis (PFGE). We studied possible determinants of VRE colonization with a logistic regression analysis model. Determinants analyzed included gender, age, and log-transformed length of prior hospital stay.

RESULTS

The results showed that 614 (55%) of 1,112 patients were colonized with vancomycin-sensitive enterococci, and 15 (1.4%) of 1,112 carried VRE. No increase in VRE colonization was observed from 1995 to 1998. Eleven strains were identified as Enterococcus faecium and four as Enterococcus faecalis. All E faecium and one E faecalis carried the vanA gene; the other E faecalis strains harbored the vanB gene. PFGE revealed that three vanB VRE isolated from patients hospitalized in one single ICU were related, suggesting nosocomial transmission. Though higher age seemed associated with VRE colonization, exclusion of patients with the nosocomial strain from the regression analysis decreased this relation to nonsignificant. Duration of hospital stay was not associated with VRE colonization.

CONCLUSION

VRE colonization in Dutch hospitals is an infrequent phenomenon. Although nosocomial spread occurs, most observed cases were unrelated, which suggests the possibility of VRE acquisition from outside the hospital. Prolonged hospital stay, age, and gender proved unrelated to VRE colonization.

Nosocomial outbreak of ampicillin resistant Enterococcus faecium: risk factors for infection and fatal outcome

A nosocomial outbreak caused by ampicillin resistant Enterococcus faecium (ARE) was detected at a Norwegian university hospital in January 1995. Prior to this outbreak, ARE were not common in this hospital or other hospitals in Norway. During 1995 and 1996, a total of 149 cases with clinical ARE infection were detected prospectively. A case control study was performed by allocating controls matched for gender, age and ward of admission. Altogether, 123 case control pairs with mean age 70.1 years were included. Isolates from 89 (72. 4%) of the cases were identical or related to the defined outbreak strain as determined by pulsed-field gel electrophoresis (PFGE). In 75 of the patients (60.9%), ARE caused urinary tract infection, five (4.1%) had bacteraemia, 33 (26.8%) had wound infection and 10 (8.1%) had other infections. In a logistic regression model for 1:1 matched samples, the following factors were identified as significant risk factors for ARE infection: underlying neurological disease (OR=33.5), prescription of antimicrobial agents for more than 10 days (OR=8. 99), prescription of cephalosporins (OR=4.69), underlying gastrointestinal disease (OR=3.36) and length of hospital stay per day (OR=1.04). The intrahospital death rate for the cases was 18.7% compared with 8.9% for the controls, corresponding to an excess mortality attributable to ARE infection of 9.8%. A history of carbapenem prescription was the only independent factor contributing to death (OR=5.64) when comparing ARE patients dying in hospital to those surviving.

The use of avoparcin as a growth promoter and the occurrence of vancomycin-resistant Enterococcus species in Norwegian poultry and swine production

This study documents a strong and statistically significant association between the use of the glycopeptide avoparcin as a growth promoter in Norwegian poultry production and the occurrence of vancomycin-resistant Enterococcus species (VRE). Avoparcin was approved as a feed additive for broilers and turkeys in Norway in 1986 and was banned from June 1, 1995. In a survey conducted in Norway between June, 1995 and March, 1997, VRE were isolated from fecal samples from 106 out of 109 poultry houses previously exposed to avoparcin (97%) and from six out of 33 poultry houses never exposed to avoparcin (18%) (RR = 5.35). Samples from previously exposed poultry houses were collected in three time periods. The proportion of positive samples remained high (96-98%), in all three time periods indicating a persistence of vancomycin resistance among enterococci for more than a year and a half after the withdrawal of avoparcin. VRE were also isolated from six out of 10 poultry farmers living on farms previously exposed to avoparcin, and from none of 16 farmers living on farms never exposed to avoparcin. Moreover, VRE were isolated from 68 out of the 225 broiler carcasses investigated (30%). The resistance to vancomycin was a high-level type (MIC > or = 256 microg/ml) mediated by the vanA gene. For comparison, VRE could only be isolated from two out of 147 fecal samples from Norwegian flocks of swine (1%). Because avoparcin never has been used in Norwegian swine production, this observation strengthens the association between the use of avoparcin in animal husbandry and the occurrence of VRE.