Related Experiment Videos
Diversity of VanA glycopeptide resistance elements in enterococci from humans and nonhuman sources
N Woodford1, A M Adebiyi, M F Palepou
1Antibiotic Reference Unit and Laboratory of Hospital Infection, Central Public Health Laboratory, London, United Kingdom. nwoodfor@phis.co.uk
Abstract:
Elements mediating VanA glycopeptide resistance in 106 diverse enterococci from humans and nonhuman sources were compared with the prototype VanA transposon, Tn1546, in Enterococcus faecium BM4147. The isolates included 64 from individual patients at 15 hospitals in the United Kingdom (isolated between 1987 and 1996) and 42 from nonhuman sources in the United Kingdom (27 from raw meat, 7 from animal feces, and 8 from sewage). VanA elements were assigned to 24 groups (designated groups A to X) with primers that amplified 10 overlapping fragments of Tn1546. Ten groups of elements were found only in human enterococci, eight groups of elements were unique to nonhuman strains, and six groups of elements were common in enterococci from all sources. Elements indistinguishable from Tn1546 (group A) were observed more frequently in enterococci from nonhuman sources (34 versus 9%) but were identified in enterococci that caused outbreaks in hospital patients between 1987 and 1995. The most common group found in human enterococci (group H; 33%) was rarely observed in enterococci from other sources (5%). Group H elements differed from Tn1546 in three regions and included a novel insertion sequence, designated IS1542, between orf2 and vanR. The VanA elements of 14 other groups had a similar insertion at this position and/or distinct insertions at other positions. We conclude that VanA elements in enterococci are heterogeneous, although all show regions of homology with Tn1546. Furthermore, the elements most common among the human and nonhuman enterococci studied were different. This approach may be useful for monitoring the evolution of VanA resistance and may also be applicable in local "snapshot" epidemiological studies. However, as transposition events involving insertion sequences accounted for the differences observed between several groups, the stability of the elements must be assessed before their true epidemiological significance can be determined.
Insights
VanA glycopeptide resistance elements in enterococci show significant diversity between human and nonhuman sources. Understanding these variations is key to tracking resistance evolution and epidemiology.
Area of Science:
- Microbiology
- Molecular Biology
- Epidemiology
Background:
- VanA-mediated glycopeptide resistance is a significant public health concern.
- Enterococci are important reservoirs for antibiotic resistance genes.
- The VanA transposon, Tn1546, is the prototype element mediating this resistance.
Purpose of the Study:
- To compare VanA elements in enterococci from human and nonhuman sources.
- To investigate the diversity and evolution of VanA resistance elements.
- To assess the epidemiological significance of different VanA element groups.
Main Methods:
- Comparative analysis of VanA elements using PCR amplification of Tn1546 fragments.
- Typing of VanA elements from 106 enterococcal isolates (64 human, 42 nonhuman).
- Identification of novel insertion sequences and variations within VanA elements.
Main Results:
- VanA elements were classified into 24 groups based on sequence homology to Tn1546.
- Distinct groups of VanA elements were prevalent in human versus nonhuman enterococci.
- Elements indistinguishable from Tn1546 were more common in nonhuman sources, while a novel variant (group H) dominated human isolates.
Conclusions:
- VanA elements in enterococci exhibit significant heterogeneity, with distinct profiles in human and nonhuman reservoirs.
- The presence of a novel insertion sequence (IS1542) contributes to this diversity.
- Monitoring VanA element evolution and stability is crucial for understanding resistance epidemiology.