Effect of routine use of a multiplex PCR for detection of vanA- and vanB- mediated enterococcal resistance on accuracy, costs and earlier reporting

Chlorhexidine bathing for the prevention of colonization and infection with multidrug-resistant microorganisms in a hematopoietic stem cell transplantation unit over a 9-year period: Impact on chlorhexidine susceptibility

Health care associated infections (HAIs) are currently among the major challenges to the care of hematopoietic stem cell transplantation (HSCT) patients. The objective of the present study was to evaluate the impact of 2% chlorhexidine (CHG) bathing on the incidence of colonization and infection with vancomycin-resistant Enterococcus (VRE), multidrug-resistant (MDR) gram-negative pathogens, and to evaluate their CHG minimum inhibitory concentration (MIC) after the intervention.A quasi-experimental study with duration of 9 years was conducted. VRE colonization and infection, HAI rates, and MDR gram-negative infection were evaluated by interrupted time series analysis. The antibacterial susceptibility profile and mechanism of resistance to CHG were analyzed in both periods by the agar dilution method in the presence or absence of the efflux pump inhibitor carbonyl cyanide-m-chlorophenyl hydrazone (CCCP) and presence of efflux pumps (qacA/E, qacA, qacE, cepA, AdeA, AdeB, and AdeC) by polymerase chain reaction (PCR).The VRE colonization and infection rates were significantly reduced in the postintervention period (P = 0.001). However, gram-negative MDR rates in the unit increased in the last years of the study. The CHG MICs for VRE increased during the period of exposure to the antiseptic. A higher MIC at baseline period was observed in MDR gram-negative strains. The emergence of a monoclonal Pseudomonas aeruginosa clone was observed in the second period.Concluding, CHG bathing was efficient regarding VRE colonization and infection, whereas no similar results were found with MDR gram-negative bacteria.

Evaluation of vancomycin resistance 3 multiplexed PCR assay for detection of vancomycin-resistant enterococci from rectal swabs

Background

Active screening for vancomycin-resistant enterococci (VRE) using rectal specimens is recommended to limit the spread of antimicrobial resistance within certain high-risk populations. We evaluated the diagnostic performance of Vancomycin Resistance 3 Multiplexed Tandem PCR assay (AusDiagnostics, Australia), a rapid multiplex real-time PCR assay that detects vanA and/or vanB.

Methods

Two-hundred-and-eleven rectal swabs from Hematology and Oncology unit were submitted for VRE surveillance via direct detection of vanA and/or vanB by culture and by using Vancomycin Resistance 3 Multiplexed Tandem PCR assay. Enterococci were identified to the species level by using standard biochemical tests and BD Phoenix Automated Microbiology System (BD Diagnostic Systems, USA). Vancomycin susceptibility of enterococci was determined using Etest (BioMerieux, France).

Results

Compared to the culture method, Vancomycin Resistance 3 Multiplexed Tandem PCR assay had a sensitivity of 84.0%, specificity of 98.8%, positive predictive value (PPV) of 91.3%, and negative predictive value (NPV) of 97.6%. The assay failed to detect 18 (8.5%) specimens because of the presence of PCR inhibitors; of the remaining 193 specimens, 25 (12.9%) were positive, 23 for vanA, and 2 for vanB. Although both sensitivity and specificity for vanA VRE was 100% compared to the culture method, all vanB-positive specimens tested negative by VRE culture.

Conclusions

Vancomycin Resistance 3 Multiplexed Tandem PCR assay is a rapid and laborsaving option for VRE surveillance for direct use on rectal swabs. However, the high rate of PCR failure owing to the inhibitors in the specimens and the low specificity for vanB should be considered when interpreting the results.

Comparison of the BD GeneOhm VanR assay to culture for identification of vancomycin-resistant enterococci in rectal and stool specimens

Active screening for vancomycin-resistant enterococci (VRE) in rectal and stool specimens has been recommended to limit the spread of antimicrobial resistance within certain high-risk populations. Directly from 502 rectal swabs and stool specimens, we evaluated the diagnostic performance of the BD GeneOhm VanR assay (BD GeneOhm, San Diego, CA), a rapid real-time PCR test that detects the presence of vanA and/or vanB genes. The VanR assay was compared to culture consisting of both bile-esculin-azide agar with 6 mug/ml vancomycin (BEAV agar) (BD Diagnostics, Sparks, MD) and BEAV broth with 8 mug/ml vancomycin (Hardy Diagnostics, Santa Maria, CA). Enterococci were identified to the species level using standard biochemical tests and a Phoenix automated microbiology system (BD Diagnostics, Sparks, MD). The susceptibility of the enterococci to vancomycin and teicoplanin was determined using an Etest (AB Biodisk, Solna, Sweden). VRE were initially isolated from 147 cultures, and the VanR assay detected 142 of the 147 positive cultures for a sensitivity of 96.6%. The specificity was 87.0% (309/355) largely due to false positives seen with the vanB portion of the assay. The sensitivity when testing rectal swabs was 98.3%, and the sensitivity for stool samples was 95.4% (P = 0.643). The specificity of rectal swabs was comparable to that of the stool specimens (87.5% and 86.5%, respectively). When used only to detect VanA resistance, the VanR assay was 94.4% (136/144) sensitive and 96.4% (345/358) specific, with positive and negative predictive values of 91.3% and 97.7%, respectively. In summary, the BD GeneOhm VanR assay is a good screening test for VRE in our population of predominantly vanA-colonized patients. However, patient samples testing only vanB positive should be confirmed by another method for the presence of VRE.

The use of multiplex PCR to detect and differentiate food- and beverage-associated microorganisms: a review

Regarding food safety, rapid detection of microbial species is crucial to develop effective preventive and/or adjustment measures. Classical methods for determining the presence of certain species are time-consuming and labor-intensive, hence, molecular methods, which offer speed, sensitivity and specificity, have been developed to address this problem. Multiplex PCR (MPCR) is widely applied in the various fields of microbiology for the rapid differentiation of microbial species without compromising accuracy. This paper describes the method and reports on the state-of-the-art application of this technique to the identification of microorganisms vehiculated with foods and beverages. The identification of both pathogens and probiotics and the species important for food fermentation or deterioration will be discussed. Applications of MPCR in combination with other techniques are also reviewed. Potentials, pitfalls, limitations and future prospects are summarised.

Rapid detection and differentiation method of VanA, VanB and VanC phenotypes in vancomycin-resistant enterococci

We developed a simple method that can replace the polymerase chain reaction (PCR) to distinguish between vancomycin-resistant enterococci (VRE) with the vanA, vanB and vanC genes. The method is based on induction of teicoplanin resistance by vancomycin in vanB-VRE, while the two compounds have a synergistic effect in vanC-VRE. In addition, vanA-VRE shows resistance to both vancomycin and teicoplanin, and both the compounds can induce resistance to vanA-VRE. Utilising these properties, we attempted to develop a simple method to distinguish between vanA, vanB and vanC. We compared our simple method with the PCR method in 43 strains of vanA-VRE, 35 strains of vanB-VRE and 37 strains of vanC-VRE. The results were 100% consistent with that obtained by PCR.

Methods used for the isolation, enumeration, characterisation and identification of Enterococcus spp

This paper reviews the methodology applied for the identification and characterisation of enterococci and covers phenotypic, genotypic and phylogenetic techniques. Although conventional phenotypic typing schemes are useful for rapid and simple identification of enterococcal species for routine applications, other methods like standardised sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE), multilocus enzyme electrophoresis (MLEE), antimicrobial susceptibility testing, serotyping, pyrolysis mass spectrometry (pyMS) and vibrational spectroscopic methods allow a more in-depth characterisation of enterococci. Many of the recently described enterococcal species exhibit deviations from hitherto so-called classical enterococci with regard to their phenotypical properties. Therefore, genotypic methods have to be used to clarify their possible assignment to the genus Enterococcus. In this review, special emphasis is given on recently developed polymerase chain reaction (PCR)-based typing methods such as random amplified polymorphic DNA (RAPD), amplified fragment length polymorphism (AFLP), specific and random amplification (SARA) and modifications of PCR-ribotyping as well as pulsed-field gel electrophoresis (PFGE) and partial sequence analysis. The use of PCR and probes for genus and species identification of enterococci is also considered like the application of sequence data of conserved DNA regions (e.g., ribosomal ribonucleic acid (rRNA) genes) in the case of species identification.

Rapid detection of methicillin-resistant staphylococci from blood culture bottles by using a multiplex PCR assay

Rapid detection and accurate identification of methicillin-resistant staphylococci are critical for the effective management of infections caused by these organisms. We describe a multiplex PCR-based assay for the direct detection of methicillin-resistant staphylococci from blood culture bottles (BacT/Alert; Organon-Teknika, Durham, N.C.). A simple lysis method followed by a multiplex PCR assay designed to detect the nuc, mecA, and bacterial 16S rRNA genes was performed. A total of 306 blood culture specimens were collected over a period of 10 months from June 1998 to April 1999, consisting of 236 blood cultures growing staphylococci (including 124 methicillin-resistant Staphylococcus spp.), 50 positive blood cultures which grew organisms other than staphylococci, and 20 blood cultures that were negative for bacterial and fungal pathogens after 5 days of incubation and terminal subculture. DNA extraction, PCR, and detection could be completed in 2.5 h. Of the positive blood cultures with staphylococci, the multiplex PCR assay had a sensitivity and specificity of 99.2% and 100%, respectively. Our results show that rapid, direct detection of methicillin-resistant staphylococci is possible, allowing clinicians to make prompt and effective decisions for the management of patients with staphylococcal bacteremia.