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Category: Clinical Microbiology
Enterococcus, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555816728/9781555814632_Chap21-1.gif /docserver/preview/fulltext/10.1128/9781555816728/9781555814632_Chap21-2.gifAbstract:
Current criteria for inclusion in the genus Enterococcus and for the description of new enterococcal species encompass a polyphasic approach resulting from a combination of different molecular techniques (frequently involving DNA-DNA reassociation experiments, 16S rRNA gene sequencing, and whole-cell protein profiling analysis) and phenotypic tests. Several other molecular methods, mostly nucleic acid-based assays, have been used as additional tools to assess the phylogenetic relationships among enterococcal species and to formulate the description of new species, but their use is still limited. Positive catalase testing has also been reported for strains of Enterococcus haemoperoxidus and Enterococcus silesiacus when cultivated on blood-containing agar media. Phenotypic characteristics are used for the identification of Enterococcus species and some physiologically related species of other gram-positive cocci. Serologic tests for detecting antibody responses to different enterococcal antigens have been proposed. In addition to the intrinsic resistance traits, enterococci have acquired different genetic determinants that confer resistance to several classes of antimicrobial agents, including chloramphenicol, tetracyclines, macrolides, lincosamides and streptogramins, aminoglycosides, β-lactams, glycopeptides, quinolones, and even some of the more recently available drugs, such as linezolid, daptomycin, and quinupristin-dalfopristin. Antimicrobial resistance can be classified as either intrinsic or acquired. Molecular methods have been used to detect specific antimicrobial resistance genes and have substantially contributed to the understanding of the spread of acquired resistance among enterococci, especially resistance to vancomycin. However, because of their high specificity, molecular methods do not detect antimicrobial resistance due to mechanisms not targeted by the testing, including emerging resistance mechanisms.
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Phylogenetic tree based on comparative analysis of the 16S rDNA sequences, showing the relationships among the type strains of species of Enterococcus. Vagococcus fluvialis was used as an outgroup, and bootstrap values at the nodes are displayed as percentages.
Phylogenetic tree based on comparative analysis of the 16S rDNA sequences, showing the relationships among the type strains of species of Enterococcus. Vagococcus fluvialis was used as an outgroup, and bootstrap values at the nodes are displayed as percentages.
Phenotypic characteristics used for the identification of Enterococcus species and some physiologically related species of other gram-positive cocci
a Abbreviations and symbols: MAN, mannitol; SOR, sorbose; ARG, arginine; ARA, arabinose; SBL, sorbitol; RAF, raffinose; TEL, 0.04% tellurite; MOT, motility; PIG, pigment; SUC, sucrose; PYU, pyruvate; MGP, methyl-α-D-glucopyranoside; TRE, trehalose; XYL, xylose; GAL, 2-naphthyl-β-D-galactopyranoside; +, 90% or more of the strains are positive; –, 90% or more of the strains are negative; V, variable (11 to 89% of the strains are positive).
b Phenotypic characteristics are based on data from type strains.
c Late positive (3 days' incubation or longer).
d Occasional exceptions occur (<3% of strains show atypical reactions).
e w, weak reaction.
Phenotypic characteristics used for the identification of Enterococcus species and some physiologically related species of other gram-positive cocci
a Abbreviations and symbols: MAN, mannitol; SOR, sorbose; ARG, arginine; ARA, arabinose; SBL, sorbitol; RAF, raffinose; TEL, 0.04% tellurite; MOT, motility; PIG, pigment; SUC, sucrose; PYU, pyruvate; MGP, methyl-α-D-glucopyranoside; TRE, trehalose; XYL, xylose; GAL, 2-naphthyl-β-D-galactopyranoside; +, 90% or more of the strains are positive; –, 90% or more of the strains are negative; V, variable (11 to 89% of the strains are positive).
b Phenotypic characteristics are based on data from type strains.
c Late positive (3 days' incubation or longer).
d Occasional exceptions occur (<3% of strains show atypical reactions).
e w, weak reaction.
Types of resistance to glycopeptides among members of the genus Enterococcus
a R, resistant; S, susceptible; I, intermediate.
b Subtypes exist: vanB1-3; vanC1-4; vanD1-5; and vanG1-2.
c D-Ala-D-Lac, D-alanine–D-lactate; D-Ala-D-Ser, D-alanine–D-serine.
Types of resistance to glycopeptides among members of the genus Enterococcus
a R, resistant; S, susceptible; I, intermediate.
b Subtypes exist: vanB1-3; vanC1-4; vanD1-5; and vanG1-2.
c D-Ala-D-Lac, D-alanine–D-lactate; D-Ala-D-Ser, D-alanine–D-serine.