**Table 1.**

**77**

*Mobile Genetic Elements in Vancomycin-Resistant* Enterococcus faecium *Population*

*vanB1-3*, based on nucleotidic sequence differences. *vanB2* subtype is the most commonly spreaded in clinical enterococci. Also, is part of conjugative Tn, Tn*1549*

Tn*5382*-like. The first description of a *vanB2*-Tn*1549*-like element in pheromone responsive plasmids (pCF10-like) carried by *E. faecalis* was reported at Japan. *vanB1* has only been described for certain isolates as part of composite Tn or an integrative

Tn associated with two insertion sequences: IS*1216V* and IS*1251* [49].

It has been described that some *vanA* genotype isolates had a new type F Tn*1546*

The *vanM* cluster is similar to *vanA*, *vanB*, and *vanD*, while *vanL* and *vanN* are similar to *vanC*. The *vanM* operon has been described in VREfm isolates and showed a close genetic arrangement to *vanD* and *in vitro* transferable resistance by conjuga

tion. The *vanN* operon is the most recently identified gene cluster described in *E. faecium* and is a similar operon to *vanG*, but can be transferred by MGEs only in this enterococcal species. The IS elements can produce structural alterations in the genes, and as a consequence leads to changes of resistance phenotype. The *vanA* gene cluster is prone to IS-mediated alterations, modifying sometimes the vancomycin resistance phenotype, as being susceptible to glycopeptides but with possibility to revert to a resistant phenotype. These bacteria were named vancomycin-variable enterococci (VVE), which could cause serious clinical issues because of their pos

sibility to escape of detection and surveillance as well as facilitating the horizontal

An additional operon (*vanF*) was described but only in *Paenibacillus popilliae*. This *vanF* cluster has a high similarity to the amino acid sequences /



*DOI: http://dx.doi.org/10.5772/intechopen.88389*

conjugative element [21, 43–48].

*Schematic diagram of van operon. Adapted from [40].*

**Figure 1.**

transfer of vancomycin resistance [50–52].

*Main phenotypic and genotypic features of glycopeptide-resistant enterococci.*

*Mobile Genetic Elements in Vancomycin-Resistant* Enterococcus faecium *Population DOI: http://dx.doi.org/10.5772/intechopen.88389*

**Figure 1.** *Schematic diagram of van operon. Adapted from [40].*

*vanB1-3*, based on nucleotidic sequence differences. *vanB2* subtype is the most commonly spreaded in clinical enterococci. Also, is part of conjugative Tn, Tn*1549*/ Tn*5382*-like. The first description of a *vanB2*-Tn*1549*-like element in pheromone responsive plasmids (pCF10-like) carried by *E. faecalis* was reported at Japan. *vanB1* has only been described for certain isolates as part of composite Tn or an integrative conjugative element [21, 43–48].

It has been described that some *vanA* genotype isolates had a new type F Tn*1546* Tn associated with two insertion sequences: IS*1216V* and IS*1251* [49].

The *vanM* cluster is similar to *vanA*, *vanB*, and *vanD*, while *vanL* and *vanN* are similar to *vanC*. The *vanM* operon has been described in VREfm isolates and showed a close genetic arrangement to *vanD* and *in vitro* transferable resistance by conjugation. The *vanN* operon is the most recently identified gene cluster described in *E. faecium* and is a similar operon to *vanG*, but can be transferred by MGEs only in this enterococcal species. The IS elements can produce structural alterations in the genes, and as a consequence leads to changes of resistance phenotype. The *vanA* gene cluster is prone to IS-mediated alterations, modifying sometimes the vancomycin resistance phenotype, as being susceptible to glycopeptides but with possibility to revert to a resistant phenotype. These bacteria were named vancomycin-variable enterococci (VVE), which could cause serious clinical issues because of their possibility to escape of detection and surveillance as well as facilitating the horizontal transfer of vancomycin resistance [50–52].

An additional operon (*vanF*) was described but only in *Paenibacillus popilliae*. This *vanF* cluster has a high similarity to the amino acid sequences

*Pathogenic Bacteria*

**76**

**Phenotype**

Resistance

MICvan

MICtei Expression

Mobiltiy Precursor

Operon Subtypes Required genes for

*vanH*, *vanA*,

*vanHB*, *vanB*,

*vanHD*, *vanD*,

*vanE*,

*vanG*,

*vanL*, *vanXY1*,

*vanHM*,

*vanN*,

*vanC*,

*vanXYC*, *vanT*

*vanXYN*,

*vanTN*

*vanM*, *vanXM*

*vanTm*, *vanTr1*

*vanXYG*,

*vanTG*

*vanXYE*,

*vanTE*

*MIC, minimum inhibitory concentration (mg/L); van, vancomycin; tei, teicoplanin; I, inducible; C, constitutive; N/A, not applies. Adapted from [39, 40].*

*vanXD*

*vanXB*

*vanX*

expression

**Table 1.**

*Main phenotypic and genotypic features of glycopeptide-resistant enterococci.*

**VanA** Acquired 16–>1000

16–512

I Yes Ala-Lac

*vanA* N/A

B1-B3

D1-D5

N/A

G1-G2

N/A

N/A

N/A

C1-C4

*vanB*

*vanD*

*vanE*

*vanG*

*vanL*

*vanM*

*vanN*

*vanC*

Ala-Lac

Ala-Lac

Ala-Ser

Ala-Ser

Ala-Ser

Ala-Lac

Ala-Ser

Ala-Ser

Yes

No

No

Yes

No

Yes

Yes

No

I

C

I

I

I

I

C

I, C

0.25–2

2–64

0.5

0.5

0.5

96

0.5

0.12–2

4–>1000

16–128

8–32

16

8

>256

16

2–32

Acquired

Acquired

Acquired

Acquired

Acquired

Acquired

Acquired

Intrinsic

**VanB**

**VanD**

**VanE**

**VanG**

**VanL**

**VanM**

**VanN**

**VanC**

of the *vanA* operon, and *P. popilliae* has been proposed as a possible origin for vancomycin resistance in enterococci [53].
