Identification of VanB-Type Vancomycin Resistance in Enterococcus gallinarum from Japan

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.

Identification of Enterococcus faecium and Enterococcus faecalis as vanC-type Vancomycin-Resistant Enterococci (VRE) from sewage and river water in the provincial city of Miyazaki, Japan

As a first step for assessing the risk to human health posed by vancomycin-resistant enterococci (VRE) in the aquatic environment, we screened sewage and urban river water samples from Miyazaki, Japan for VRE. Because vancomycin-resistant organisms are not as prevalent in sewage and river water as vancomycin-susceptible organisms, the samples were screened by minimum inhibitory concentration test using the vancomycin-supplemented membrane-Enterococcus indoxyl-β-d-glucoside (mEI) agar. The isolates, presumed to be enterococci, were identified using 16S rRNA sequencing analysis. The percentages of VRE isolates screened using 4 μg mL(-1) vancomycin-supplemented mEI agar from sewage and urban river water samples were 12% and 24%, respectively. The vancomycin-resistant genes vanC1 and vanC2/3 were detected in the isolates from both samples by PCR analysis. All enterococci isolates containing vanC1, which is a specific gene for vanC-type of VRE, were identified as Enterococcus casseliflavus/gallinarum. Further, 92% enterococci isolates containing vanC2/3 were identified as E. casseliflavus/gallinarum, the remaining isolates containing vanC2/3 were E. faecium (4%) and E. faecalis (4%). Thereafter, the distribution of E. faecium and E. faecalis, which are the major types of enterococci in humans containing vanC2/3, was observed in the water samples collected.

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.

Bacteremia caused by VanC-type enterococci in a university hospital in Japan: a 6-year survey

We retrospectively examined the clinical and microbiological characteristics of bacteremia caused by intrinsically vancomycin-resistant (VanC-type) enterococci in a university hospital in Japan. Five cases of Enterococcus gallinarum and four of Enterococcus casseliflavus bacteremia were identified during the 6 years of the survey. Of the nine cases, five were related to neutropenic states with hematologic diseases and four were related to biliary tract infection with hepatobiliary or pancreatic diseases. VanC-type enterococci were associated with 12% of all the enterococcal bacteremias, indicating that these species cause bacteremia more frequently in Japan than in previously reported areas.

No regional spread of vancomycin-resistant enterococci with vanA or vanB in Kitakyushu, Japan

Outbreaks of vancomycin-resistant enterococci (VRE) infection occur sporadically in Japan, and their frequency has been gradually increasing. We experienced a nosocomial outbreak of VRE in two hospitals in the city of Kitakyushu, and the spread of VRE strains was suspected in this area. To examine the prevalence rate of infection and colonization of VRE in Kitakyushu, we screened a total of 24 297 clinical samples from patients in hospitals and clinics in Kitakyushu from October through December 2002 for VRE. The isolates screened as positive for VRE accounted for 2.3% (566/24 297) of the tested clinical samples. Polymerase chain reaction (PCR) analyses for vanA, vanB, vanC1, and vanC2/3 were performed to confirm the screening test results. Neither vanA nor vanB genes were detected in any isolates. The 265 vanC1-positive isolates were Enterococcus gallinarum, and the 150 vanC2/3-positive isolates were E. casseliflavus. Other Enterococcus species were negative in this PCR-detection test. In this study, the PCR procedure was considered reliable and successful because although neither vanA nor vanB was detected, vanC1 and vanC2/3 were completely detectable. Therefore, we concluded that the regional spread of VRE with vanA and vanB had not occurred in Kitakyushu in 2002. In the near future, the prevalence of VRE with vanA or vanB is likely to increase in Japan, as it has in other countries. We should continue to find and prevent nosocomial outbreaks of infection and colonization by VRE.

Surveillance of vancomycin-resistant Enterococcus in hospitals in Ibaraki prefecture

We surveyed the prevalence of vancomycin-resistant Enterococcus (VRE) in six hospitals in Ibaraki prefecture. Three hundred and fifty-five fecal specimens were examined and 18 Enterococcus intermediately resistant to vancomycin were isolated. All of them were vanC genotypes (16 vanC-1 and 2 vanC-2 genotypes) and susceptible or intermediately resistant to ampicillin, teicoplanin, linezolid, and quinupristin-dalfopristin. Neither the vanA nor vanB gene was detected. Two of the vanC genotypes were not motile. We concluded that VRE of either VanA or VanB phenotype or those highly resistant to the antibiotics commonly used against enterococcal infection were not epidemic in this prefecture to date. In addition, we consider that detection of vancomycin-resistant genes should be encouraged for the characterization of VRE, because the vanC genotypes are occasionally motility-negative and can be misinterpreted as other Enterococcus species.

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.

Sudden increase of vancomycin-resistant enterococcal infections in a Korean tertiary care hospital: possible consequences of increased use of oral vancomycin

A sudden increase in vancomycin-resistant enterococci (VRE) infections was noted in 1998 in a tertiary care hospital in Korea. All of the VRE isolated in 1998 in the hospital were VanA type and most were multidrug-resistant Enterococcus faecium. The increase in VRE was probably due to the increased use of oral vancomycin to treat Clostridium difficile infections and clonal as well as horizontal spread. More restricted oral vancomycin use and stricter infection control measures are required to achieve a better control of the spread of VRE.

Meningitis caused by Enterococcus gallinarum in patients with ventriculoperitoneal shunts

Vancomycin-resistant enterococci have recently emerged as significant nosocomial pathogens. Here we describe two Japanese patients, a 57-year-old man and a 12-year-old boy, with ventriculoperitoneal shunts for hydrocephalus who developed meningitis caused by vancomycin-resistant Enterococcus gallinarum. The infection of the central nervous system in these two patients may have been associated with E. gallinarum derived from the gut. Removal of the shunts and antimicrobial treatment promoted apparent improvement in these patients. The risk factors and management of vancomycin-resistant enterococcal infections in the central nervous system are discussed.

Epidemiological study of vancomycin-resistant enterococcus isolated from a single medical university hospital in Japan

Since 1998 more than 50 reports have described the isolation of high-level vancomycin-resistant enterococci (VRE) in Japan. Here, we report on our clinical isolates of VRE and an epidemiological study carried out using chemical and genetic techniques. VRE isolates were screened for high resistance to vancomycin (VCM) with a cutoff value of 6 microg/ml and VCM-resistant gene was confirmed by polymerase chain reaction (PCR). The epidemiological studies used pulsed-field gel electrophoresis (PFGE) and plasmid analysis. Six strains of VRE were isolated from six different patients on two wards during a 3-months period. All of the isolates possessed vanA on their plasmid, and the isolates were divided into two similar groups. Furthermore, three different patterns were defined by PFGE. Although all of the asymptomatic carriers were hospitalized for more than 3 months, we were able to prevent an outbreak of VRE in our hospital by using our guidelines for infection control, which are stricter than those for methicillin-resistant Staphylococcus aurens. From the results of this epidemiological study, we propose that there was a possibility of contamination in this hospital, and that three of the six isolates may have acquired vanA independently. In this study, we demonstrated that infection control, according to appropriate prevention guidelines, as well as regular surveillance for VRE, are essential for designing interventions to prevent the further spread of VRE.

Two sporadic cases of infections due to Klebsiella pneumoniae resistant to expanded-spectrum cephalosporins in Japan

TEM- or SHV-type extended-spectrum beta-lactamases (ESBLs) are of clinical concern in Europe and the United States, whereas bacterial strains producing such types of ESBLs have not been reported in Japan. We report here two cases of infection due to Klebsiella pneumoniae resistant to extended-spectrum cephalosporins in Japan. A ceftadizime-resistant K. pneumoniae strain (minimum inhibitory concentration; 32 &mgr;g/ml) was isolated transiently from the sputum of an 87-year-old woman with acute myocardial infarction and pneumonia (patient 1). Ceftadizime-susceptible and -resistant (minimum inhibitory concentration; >/=8 &mgr;g/ml) K. pneumoniae strains were isolated over a month from the blood, ascites, and feces of a 44-year-old man after bone marrow transplantation for acute lymphoblastic leukemia (patient 2); this patient died of K. pneumoniae sepsis and peritonitis followed by multiple organ failure. These isolates produced penicillinase, which was inhibited by clavulanic acid. A polymerase chain reaction (PCR) study showed that both isolates carried the SHV or LEN genes, but not the TEM, Toho-1, and IMP-1 genes. The pulsed-field gel electrophoresis profile of the strain isolated from patient 1 was genetically distinguishable from the profiles of the strains isolated from patient 2. It appeared that mutation of the beta-lactamase gene may have occurred in the body of patient 2, since the genotypes of the ceftadizime-susceptible and -resistant isolates from this patient were identical. Another 12 strains of K. pneumoniae, isolated from other patients in the same wards during the period in which the K. pneumoniae strains were isolated from patients 1 and 2, did not produce ESBLs and showed different genotypes. The results suggest that these isolates of resistant K. pneumoniae did not spread by cross transmission in the hospital and that the two cases were sporadic. Surveillance of these types of resistant bacteria is necessary, since they may well be present in other hospitals in Japan. Although the organisms are suspected to produce SHV-type ESBLs or LEN-1 variant beta-lactamases, further studies are necessary to specify the resistance genes.