Direct detection of vanB2 using the Roche LightCycler vanA/B detection assay to indicate vancomycin-resistant enterococcal carriage--sensitive but not specific

Enterococci as a One Health indicator of antimicrobial resistance

The rapid increase of antimicrobial-resistant bacteria in humans and livestock is concerning. Antimicrobials are essential for the treatment of disease in modern day medicine, and their misuse in humans and food animals has contributed to an increase in the prevalence of antimicrobial-resistant bacteria. Globally, antimicrobial resistance is recognized as a One Health problem affecting humans, animals, and environment. Enterococcal species are Gram-positive bacteria that are widely distributed in nature. Their occurrence, prevalence, and persistence across the One Health continuum make them an ideal candidate to study antimicrobial resistance from a One Health perspective. The objective of this review was to summarize the role of enterococci as an indicator of antimicrobial resistance across One Health sectors. We also briefly address the prevalence of enterococci in human, animal, and environmental settings. In addition, a 16S RNA gene-based phylogenetic tree was constructed to visualize the evolutionary relationship among enterococcal species and whether they segregate based on host environment. We also review the genomic basis of antimicrobial resistance in enterococcal species across the One Health continuum.

Gastrointestinal Colonization with Vancomycin-Resistant Enterococci In Hospitalized and Outpatients

BACKGROUND

The incidence of infection and intestinal colonization with vancomycin resistant enterococci (VRE) is increasing in many countries in the last decade. Concerning the difficult antimicrobial treatment of infections caused by VRE, decreasing the incidence and prevalence of these infections is an important factor in VRE-induced morbidity and mortality control.

AIM

To determine the prevalence of gastrointestinal colonization with vancomycin resistant enterococci in hospitalized and outpatients, and to determine the genetic base of the vancomycin resistance in VRE isolates.

MATERIAL AND METHODS

Seven hundred and eighty stool specimens were investigated for the gastrointestinal carriage of vancomycin-resistant enterococci (VRE). Susceptibility to vancomycin was tested in all isolates by disk-diffusion test and E-test (AB Biodisk, Sweden). Determined vancomycin resistant enterococci were than tested for detection of vanA, vanB and vanC genes by PCR.

RESULTS

Vancomycin resistant strains of enterococci were isolated from 46 (16.1 %) of the 285 hospitalized patients and 5 (7.7 %) of the 65 patients living in the community (p < 0.05). The most of the highly resistant enterococci strains to vancomycin (95.2 %), were identified as E. faecium. Minimal inhibitory concentrations (MICs) to vancomycin in all 39 vanA genotypes of E. faecium and two vanA genotypes of E. fecalis were > 256 μg/ml. Three vanB genotypes of E. faecium and one vanB genotype of E. faecalis had MICs of 32 μg/ml. All six vanC genotypes of E. gallinarum had MICs of 8 μg/ml. All vanA genotypes of VRE were highly resistant to vancomycin, with MICs above 256 μg/ml. Three vanB genotypes of VR E. faecium and one VR E. fecalis were resistant, with MICs 32 μg/ml. vanC genotypes of VR E. gallinarum were intermediate resistant to vancomycin with MICs of 8 μg/ml.

CONCLUSIONS

The prevalence of vancomycin resistant enterococci in Republic of Macedonia was 2-fold higher in hospitalized than in outpatients. VanA genotype was dominant in isolates of E. faecium and it was highly associated with the MIC values above the 256 μg/ml. Since most of the enterococcal infections are endogenous, there is a need for screening the colonization of patient's intestinal flora with VRE at the hospital entry. Identification and genotyping of faecal enterococci, together with their susceptibility testing to vancomycin, could be useful marker for the infection control.

[Vancomycin-resistant enterococci (VRE). Recent results and trends in development of antibiotic resistance]

Enterococci (mainly E. faecalis, E. faecium) are important nosocomial pathogens predominantly affecting older and/or immunocompromised patients. The bacteria possess a broad spectrum of intrinsic and acquired antibiotic resistance properties. Among these, the transferrable glycopeptide resistance of the vanA and vanB genotypes in vancomycin-resistant enterococci (VRE; reservoir: E. faecium) as well as resistance to last resort antibiotics (e.g. linezolid and tigecycline) are of special concern. Enterococci (including VRE) are easily transferred in hospitals; however, colonizations are far more frequent than infections. Resistance frequencies for vancomycin in clinical E. faecium isolates have remained at a relatively constant level of 8-15% (but with local or regional variations) in recent years whereas frequencies for teicoplanin resistance have shown a slight decrease. Glycopeptide resistance trends correlate with a spread of hospital-associated E. faecium strains carrying the vanA and, with rising frequency in recent years, the vanB gene cluster, the latter being associated with teicoplanin susceptibility. This increased occurrence of vanB-positive E. faecium strains may be caused by an increased use of antibiotics selecting enterococci and VRE as well as due to methodological reasons (e.g. reduced EUCAST MIC-breakpoints for glycopeptides; increased use and sensitive performance of chromogenic VRE agars, increased use of molecular diagnostic assays).

Performance of three chromogenic VRE screening agars, two Etest(®) vancomycin protocols, and different microdilution methods in detecting vanB genotype Enterococcus faecium with varying vancomycin MICs

Frequencies of vanB-type Enterococcus faecium increased in Europe during the last years. VanB enterococci show various levels of vancomycin MICs even below the susceptible breakpoint challenging a reliable diagnostics. The performance of 3 chromogenic vancomycin-resistant enterococci (VRE) screening agars, 2 Etest® vancomycin protocols, and different microdilution methods to detect 129 clinical vanB E. faecium strains was investigated. Altogether, 112 (87%) were correctly identified as VanB-type Enterococcus by microdilution MICs. An Etest® macromethod protocol was more sensitive than the standard protocol while keeping sufficient specificity in identifying 15 vanA/vanB-negative strains. Three chromogenic VRE agars performed similarly with 121 (94%), 123 (95%), and 124 (96%) vanB isolates that grew on Brilliance™ VRE Agar, CHROMagar™ VRE, and chromID™ VRE agar, respectively. Using identical media and conditions, we did not identify different growth behaviour on agar and in broth. A few vanB strains showed growth of microcolonies inside the Etest® vancomycin inhibition zones, suggesting a VanB heteroresistance phenotype.

Vancomycin-resistant vanB-type Enterococcus faecium isolates expressing varying levels of vancomycin resistance and being highly prevalent among neonatal patients in a single ICU

BACKGROUND

Vancomycin-resistant isolates of E. faecalis and E. faecium are of special concern and patients at risk of acquiring a VRE colonization/infection include also intensively-cared neonates. We describe here an ongoing high prevalence of VanB type E. faecium in a neonatal ICU hardly to identify by routine diagnostics.

METHODS

During a 10 months' key period 71 E. faecium isolates including 67 vanB-type isolates from 61 patients were collected non-selectively. Vancomycin resistance was determined by different MIC methods (broth microdilution, Vitek® 2) including two Etest® protocols (McFarland 0.5/2.0. on Mueller-Hinton/Brain Heart Infusion agars). Performance of three chromogenic VRE agars to identify the vanB type outbreak VRE was evaluated (BrillianceTM VRE agar, chromIDTM VRE agar, CHROMagarTM VRE). Isolates were genotyped by SmaI- and CeuI-macrorestriction analysis in PFGE, plasmid profiling, vanB Southern hybridisations as well as MLST typing.

RESULTS

Majority of vanB isolates (n = 56, 79%) belonged to a single ST192 outbreak strain type showing an identical PFGE pattern and analyzed representative isolates revealed a chromosomal localization of a vanB2-Tn5382 cluster type. Vancomycin MICs in cation-adjusted MH broth revealed a susceptible value of ≤4 mg/L for 31 (55%) of the 56 outbreak VRE isolates. Etest® vancomycin on MH and BHI agars revealed only two vanB VRE isolates with a susceptible result; in general Etest® MIC results were about 1 to 2 doubling dilutions higher than MICs assessed in broth and values after the 48 h readout were 0.5 to 1 doubling dilutions higher for vanB VRE. Of all vanB type VRE only three, three and two isolates did not grow on BrillianceTM VRE agar, chromIDTM VRE agar and CHROMagarTM VRE, respectively. Permanent cross contamination via the patients' surrounding appeared as a possible risk factor for permanent VRE colonization/infection.

CONCLUSIONS

Low level expression of vanB resistance may complicate a proper routine diagnostics of vanB VRE and mask an ongoing high VRE prevalence. A high inoculum and growth on rich solid media showed the highest sensitivity in identifying vanB type resistance.

Mobile genetic elements and their contribution to the emergence of antimicrobial resistant Enterococcus faecalis and Enterococcus faecium

Mobile genetic elements (MGEs) including plasmids and transposons are pivotal in the dissemination and persistence of antimicrobial resistance in Enterococcus faecalis and Enterococcus faecium. Enterococcal MGEs have also been shown to be able to transfer resistance determinants to more pathogenic bacteria such as Staphylococcus aureus. Despite their importance, we have a limited knowledge about the prevalence, distribution and genetic content of specific MGEs in enterococcal populations. Molecular epidemiological studies of enterococcal MGEs have been hampered by the lack of standardized molecular typing methods and relevant genome information. This review focuses on recent developments in the detection of MGEs and their contribution to the spread of antimicrobial resistance in clinically relevant enterococci.

Comparison of PCR and culture for screening of vancomycin-resistant Enterococci: highly disparate results for vanA and vanB

We compared PCR to conventional culture for the detection of vancomycin-resistant enterococci (VRE) in 30,835 rectal samples over a 3-year period. The positive and negative predictive values of vanB PCR were 1.42% and 99.9%, respectively. A positive vanB result by PCR is poorly predictive and necessitates culture for differentiation of VRE-positive and -negative individuals.

Real time PCR for the rapid detection of vanA gene in surface waters and aquatic macrophyte by molecular beacon probe

Enterococci serve as an "indicator" of fecal contamination for recreational water quality. The vancomycin-resistant-enterococci (VRE) are emerging environmental contaminants in the surface waters. The aim ofthis study wasto develop a rapid and specific molecular beacon probe (MBP)-based real-time PCR assay for detection of vanA gene in surface waters and aquatic macrophyte. The limit of detection (LOD) of the MBP assay was 1 CFU/mL of VRE [r = 0.943; PCR efficiency = 99.7%] in 2-fold dilution format within 2.5 h and demonstrated high specificityfor environmental enterococci isolates exhibiting VanA phenotype (n=25). VRE were detected from downstream surface waters of the rivers impacted by point sources of pollution and recreational activities.The probe detected vanA gene in rootmat associated microbiota of E. crassipes (Mart) Solms. an aquatic nuisance weed, at eutrophic sites of the surface waters (ANOVA p < 0.001). In addition, the assay enabled detection of otherwise nondetectable vanA gene concentration in the upstream sites of two Indian rivers (Student's ttest p < 0.001). The MBP assay developed can be used for sensitive and rapid detection of VRE in surface waters and identification of nonpoint sources of pollution for implementation of preventive measures to protect human health.

Vancomycin-resistant Enterococcus – A Review From a Singapore Perspective

Introduction: Vancomycin-resistant enterococcus (VRE) can cause serious infections in vulnerable, immunocompromised patients. Materials and Methods: In this article, we summarise current data on epidemiology, detection, treatment and prevention of VRE. Results: VRE was first isolated in Singapore in 1994 and until 2004 was only sporadically encountered in our public hospitals. After 2 outbreaks in 2004 and in 2005, VRE has become established in our healthcare institutions. Multiple studies have shown that VRE spreads mainly via contaminated hands, cloths and portable equipment carried by healthcare workers. Conclusions: Only a comprehensive programme (consisting of active surveillance, isolation of colonised/infected patients, strict adherence to proper infection control practices and anti-microbial stewardship) can limit the spread of these organisms. In addition to monitoring the compliance with traditional infection control measures, new strategies that merit consideration include pre-emptive isolation of patients in high-risk units and molecular techniques for the detection of VRE. Keywords: Antibiotic resistance, Infection control, Outbreaks, Surveillance

Comparative study of selective chromogenic (chromID VRE) and bile esculin agars for isolation and identification of vanB-containing vancomycin-resistant enterococci from feces and rectal swabs

The new chromogenic agar chromID VRE (cIDVRE; bioMérieux) was compared with bile esculin agar (BD) containing 6 mg/liter vancomycin for the detection of colonization with vanB-containing vancomycin-resistant enterococci (VRE). At 48 h of incubation, the results obtained with both media were comparable. However, cIDVRE detected significantly more VRE at 24 h (39.3% versus 21.3%, P = 0.003), and its use may facilitate the timely implementation of infection control procedures.

High rates of fecal carriage of nonenterococcal vanB in both children and adults

We examined the rate of fecal carriage of vanB in the absence of cultivable vancomycin-resistant enterococci in three distinct populations (children, community adults, and hemodialysis patients). Nonenterococcal vanB carriage was similarly high in hemodialysis patients (45%) and community adults (63%; P = 0.066) and significantly more common among community adults than children (27%; P = 0.001).