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

Emergence of vanA gene among vancomycin-resistant enterococci in a tertiary care hospital of North - East India

BACKGROUND & OBJECTIVES

Vancomycin-resistant enterococci (VRE) have become one of the most challenging nosocomial pathogens with the rapid spread of the multi-drug resistant strain with limited therapeutic options. It is a matter of concern due to its ability to transfer vancomycin resistant gene to other organisms. The present study was undertaken to determine the emergence of vancomycin-resistant enterococci and the vanA gene among the isolates in a tertiary care hospital of North-East India.

METHODS

A total of 67 consecutive enterococcal isolates from different clinical samples were collected and identified by using the standard methods. Antibiogram was done by disk diffusion method and VRE was screened by the disk diffusion and vancomycin supplement agar dilution method. The minimum inhibitory concentration (MIC) value for vancomycin was determined by E-test. The VRE isolates were analyzed by PCR for vanA gene.

RESULTS

A total of 54 (81%) Enterococcus faecalis and 13 (19%) E. faecium were detected among the clinical isolates and 16 (24%) were VRE. The VRE isolates were multidrug resistant and linezolid resistance was also found to be in three. MIC range to vancomycin was 16-32 µg/ml among the VRE. The vanA gene was found in nine of 16 VRE isolates.

INTERPRETATION & CONCLUSIONS

Emergence of VRE and presence of vanA in a tertiary care hospital setting in North-East India indicate toward a need for implementing infection control policies and active surveillance.

Vancomycin-resistant enterococci: Troublemaker of the 21st century

The emergence of multidrug-resistant and vancomycin-resistant enterococci during the last decade has made it difficult to treat nosocomial infections. Although various enterococcal species have been identified, only two (Enterococcus faecalis and Enterococcus faecium) are responsible for the majority of human infections. Vancomycin is an important therapeutic alternative against multidrug-resistant enterococci but is associated with a poor prognosis. Resistance to vancomycin dramatically reduces the therapeutic options for enterococcal infections. The bacterium develops resistance by modifying the C-terminal d-alanine of peptidoglycan to d-lactate, creating a d-Ala-d-Lac sequence that effectively reduces the affinity of vancomycin for the peptidoglycan by 1000-fold. Moreover, the resistance genes can be transferred from enterococci to Staphylococcus aureus, thereby posing a threat to patient safety and also a challenge for treating physicians. Judicious use of vancomycin and broad-spectrum antibiotics must be implemented, but strict infection control measures must also be followed to prevent nosocomial transmission of these organisms. Furthermore, improvements in clinical practice, rotation of antibiotics, herbal drugs, nanoantibiotics and the development of newer antibiotics based on a pharmacogenomic approach may prove helpful to overcome dreadful vancomycin-resistant enterococcal infections.

DNA microarray detection of antimicrobial resistance genes in diverse bacteria

High throughput genotyping is essential for studying the spread of multiple antimicrobial resistance. A test oligonucleotide microarray designed to detect 94 antimicrobial resistance genes was constructed and successfully used to identify antimicrobial resistance genes in control strains. The microarray was then used to assay 51 distantly related bacteria, including Gram-negative and Gram-positive isolates, resulting in the identification of 61 different antimicrobial resistance genes in these bacteria. These results were consistent with their known gene content and resistance phenotypes. Microarray results were confirmed by polymerase chain reaction and Southern blot analysis. These results demonstrate that this approach could be used to construct a microarray to detect all sequenced antimicrobial resistance genes in nearly all bacteria.

Epidemiology and mechanisms of glycopeptide resistance in enterococci

PURPOSE OF REVIEW

This review updates epidemiologic trends and our understanding of glycopeptide resistance in enterococci.

RECENT FINDINGS

Colonization and infection rates with vancomycin resistant enterococci continue to increase throughout the world while factors contributing to this rise continue to be defined. While no interventions exist to eradicate colonization, infection control procedures are cost effective and decrease the prevalence of vancomycin resistant enterococcal colonization and infection. New molecular methods show great promise in strengthening our ability to detect colonization with these bacteria. Furthermore, our understanding of the origin of vancomycin resistant enterococci continues to grow. Paenibacillus species found in soil have been found to carry homologues of vanA-associated glycopeptide resistance genes found in enterococci. Also, additional evidence supports previous data that VanB-associated resistance may have been horizontally transferred from gastrointestinal tract bacteria to enterococci. Finally, glycopeptide resistance has been transferred to methicillin-resistant Staphylococcus aureus in clinical practice on several occasions.

SUMMARY

The prevalence of vancomycin resistant enterococci will likely continue to increase. Implementation of infection control strategies, in conjunction with deployment of advanced technologies for detection of vancomycin resistant enterococci, may curb this rise. The emergence of vancomycin resistant S. aureus is of concern.