The mef (E)-Carrying Genetic Element (mega) of Streptococcus pneumoniae : Insertion Sites and Association with Other Genetic Elements

Abstract

The structure of the macrolide efflux genetic assembly (mega) element, its genomic locations, and its association with other resistance determinants and genetic elements were investigated in 16 Streptococcus pneumoniae isolates carrying mef(E), of which 1 isolate also carried tet(M) and 4 isolates also carried tet(M) and erm(B). All isolates carried a mega element of similar size and structure that included the operon mef(E)-msr(D) encoding the efflux transport system. Among tetracycline-susceptible isolates, six different integration sites were identified, five of which were recognized inside open reading frames present in the R6 genome. In the five isolates also carrying tet(M), mega was inserted in different genetic contexts. In one isolate, it was part of previously described Tn916-like element Tn2009. In another isolate, mega was inserted in a transposon similar to Tn2009 that also included an erm(B) element. This new composite transposon was designated Tn2010. Neither Tn2009 nor Tn2010 could be transferred by conjugation to pneumococcal or enterococcal recipients. In the three isolates in which mega was not physically linked with tet(M), this gene was associated with erm(B) in transposon Tn3872, a Tn916-like element. Homologies between the chromosomal insertions of these composite transposons and sequences of multidrug-resistant pneumococcal genomes in the databases indicate the presence of preferential sites for the integration of composite Tn916-like elements carrying multiple resistance determinants in S. pneumoniae.

Resistance to the tetracyclines and macrolide-lincosamide-streptogramin group of antibiotics and its genetic linkage – a review

“…A new Tn6079 conjugative transposon of the Tn916/Tn1545-like family that harbours two tetracycline resistance genes [tet(M)and tet(L)], and one gene conferring MLS B resistance [erm(T)] was recently identified in samples from an infant faecal fosmid library [31]. The presence of genetic determinants of resistance to both tetracyclines and MLS antibiotics was also described for other large transposons, such as the CTnDOT family, Tn2009, Tn2010, Tn2017, Tn3872, Tn5253, Tn6058, Tn5385, Tn6002 and Tn6003 that arose as a combination of smaller transposons [20,27,32,33,34].…”

“…An excellent review on this topic was recently published and is recommended for more information on the subject [19]; however the main focus of this study are transposons carrying both resistance determinants, against tetracycline and MLS antibiotics, some of which belong to the Tn916 transposon family and will be discussed in detail. Elements associated with MLS resistance are the Tn917 transposon that carries the erm(B) gene [26] or MEGA element (macrolide efflux genetic assembly, 5.5kb) that carries the mef(E)-msr(D)operon [27]. The Tn916 transposon family has a broad host range and transfer readily to a wide variety of Gram-positive and Gram-negative bacteria [19].…”

“…The association between mefEmsrD and tet(M) was found in Tn2009 transposons that have the MEGA element inserted into a Tn916-like structure [20]. In addition to that, Tn2010 and Tn2017 carry the erm(B) gene due to the insertion of the erm(B) element or Tn917, respectively, into a Tn2009 like structure [27,39]. Tn6002 is an element resulting from the insertion of an erm(B)-containing DNA fragment (the erm(B) element) into Tn916 [33,40].…”

Genetic Resistance Elements Carrying mef Subclasses Other than mef (A) in Streptococcus pyogenes

“…mega is frequently found associated with other resistance genes in composite transposons, the most common being the 23.5-kb element Tn2009, found in S. pneumoniae and in Gram-negative bacteria, where mega is associated with Tn916 carrying tet(M) (10, 18). Other composite elements similar to Tn2009 are Tn2010 and Tn2017, both also harboring erm(B) (7,8).Another mef subclass, mef(I), has been found in S. pneumoniae to be embedded in a genetic element that also contains tet(M) and catQ. This element, designated the 5216IQ complex of 30.5 kb, includes portions derived from Tn5252 and Tn916, genetic elements frequently found in S. pneumoniae, in association with a novel element enclosing mef(I) and catQ and designated the IQ element (17).…”

“…mega is frequently found associated with other resistance genes in composite transposons, the most common being the 23.5-kb element Tn2009, found in S. pneumoniae and in Gram-negative bacteria, where mega is associated with Tn916 carrying tet(M) (10, 18). Other composite elements similar to Tn2009 are Tn2010 and Tn2017, both also harboring erm(B) (7,8).…”