Skip to main page content

• HOME
• Current Issue
• Archive
• Alerts
• About ASM
• Contact us
• Tech Support
• Journals.ASM.org

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Giovanetti, E. Articles by Liñares, J. Search for Related Content PubMed PubMed Citation Articles by Giovanetti, E. Articles by Liñares, J.

 Previous Article  |  Next Article 

Antimicrobial Agents and Chemotherapy, December 2007, p. 4535-4536, Vol. 51, No. 12
0066-4804/07/$08.00+0     doi:10.1128/AAC.01155-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

LETTER TO THE EDITOR

Expressed and Unexpressed tet(M) Genes and the erm(B)-Carrying Tn1116 Transposon in Streptococcus pyogenes and Streptococcus pneumoniae

Top LETTER REFERENCES LETTER{nbsp} REFERENCES{nbsp}

 
It was exciting to read, in an excellent countrywide survey of erythromycin-resistant Streptococcus pneumoniae in Spain just published by Calatayud et al. (3), that Tn1116—a novel erm(B)-carrying element that we have recently described in Italian isolates of Streptococcus pyogenes and published in a recent issue of this journal (2)—was detected in 16 out of their 125 test strains. However, more careful reading reveals that the element detected in the Spanish pneumococci is not Tn1116, but a new structure.

Tn1116 is a composite element of ca. 50 kb (2) resulting from the insertion of an erm(B)-containing DNA fragment into a defective Tn5397, a Tn916-related transposon originally found in Clostridium difficile (6) where the conventional int (integrase) and xis (excisase) genes (4) are replaced by the tndX (resolvase) gene (7). Most interestingly, in Tn1116 the erm(B)-containing DNA is inserted into the coding sequence of the tet(M) gene of the defective Tn5397, at base 15,019 of its published sequence (accession no. AF333235). Therefore, although detectable by PCR using suitable primers, the tet(M) gene in Tn1116 is incomplete and silent, due to the lack of the portion of the gene upstream of the insertion. [The nucleotide sequence of Tn1116 between erm(B) and tndX has been deposited under accession no. AM411377.] Accordingly, a distinguishing feature of Tn1116-carrying strains, among S. pyogenes isolates with erm(B)-mediated erythromycin resistance, is the association between a tet(M) genotype and a tetracycline-susceptible phenotype.

In contrast, all of the 16 Spanish pneumococci putatively carrying Tn1116 harbored the erm(B), tet(M), and tndX genes but were tetracycline resistant (3). This means that, unlike in Tn1116, tet(M) was complete and was regularly expressed. It should be noted that the tet(M)-specific primer pair (1) used by Calatayud et al. (3) would be unable to detect the incomplete tet(M) of Tn1116, because the forward primer targets the initial, lacking portion of the gene.

If this pneumococcal element—sharing with Tn1116 an erm(B), tet(M), and tndX genotype but associated with an erythromycin-resistant and tetracycline-resistant phenotype instead of an erythromycin-resistant and tetracycline-susceptible phenotype—is not Tn1116, it is nevertheless an interesting new element warranting further investigation. The crucial issue is the location of the erm(B) gene: the insertion of erm(B)-containing DNA into a Tn5397-related element outside the coding sequence of tet(M) may be a working hypothesis, but an actual linkage of erm(B) with tet(M) and tndX is still to be proved. On the other hand, PCR data suggest that erm(B) is neither on Tn916-like elements with conventional int and xis genes (4, 5, 7) nor on Tn917 (8). A completely new organization cannot be ruled out. Finally, it seems likely (though not expressly stated by the authors) (3) that the 16 isolates in question also share the iMLS_B phenotype of erythromycin resistance. This would entail that they represent a particular clone relatively widespread among erythromycin-resistant pneumococci in Spain but less prevalent in other countries, where iMLS_B pneumococci are very uncommon.

Top LETTER REFERENCES LETTER{nbsp} REFERENCES{nbsp}

 

1
1. Amezaga, M. R., P. E. Carter, P. Cash, and H. McKenzie. 2002. Molecular epidemiology of erythromycin resistance in Streptococcus pneumoniae isolates from blood and noninvasive sites. J. Clin. Microbiol. 40:3313-3318.[Abstract/Free Full Text]
2
2. Brenciani, A., A. Bacciaglia, M. Vecchi, L. A. Vitali, P. E. Varaldo, and E. Giovanetti. 2007. Genetic elements carrying erm(B) in Streptococcus pyogenes and association with tet(M) tetracycline resistance gene. Antimicrob. Agents Chemother. 51:1209-1216.[Abstract/Free Full Text]
3
3. Calatayud, L., C. Ardanuy, E. Cercenado, A. Fenoll, E. Bouza, R. Pallares, R. Martin, and J. Linares. 2007. Erythromycin-resistant Streptococcus pneumoniae isolated in Spain: serotypes, clones, and mechanisms of resistance. Antimicrob. Agents Chemother. 51:3240-3246.[Abstract/Free Full Text]
4
4. Clewell, D. B., S. E. Flannagan, and D. D. Jaworski. 1995. Unconstrained bacterial promiscuity: the Tn916-Tn1545 family of conjugative transposons. Trends Microbiol. 3:229-236.[CrossRef][Medline]
5
5. Cochetti, I., E. Tili, M. Vecchi, A. Manzin, M. Mingoia, P. E. Varaldo, and M. P. Montanari. 2007. New Tn916-related elements causing erm(B)-mediated erythromycin resistance in tetracycline-susceptible pneumococci. J. Antimicrob. Chemother. 60:127-131.[Abstract/Free Full Text]
6
6. Mullany, P., M. Wilks, I. Lamb, C. Clayton, B. Wren, and S. Tabaqchali. 1990. Genetic analysis of a tetracycline resistance element from Clostridium difficile and its conjugal transfer to and from Bacillus subtilis. J. Gen. Microbiol. 136:1343-1349.[Abstract/Free Full Text]
7
7. Roberts, A. P., P. A. Johanesen, D. Lyras, P. Mullany, and J. I. Rood. 2001. Comparison of Tn5397 from Clostridium difficile, Tn916 from Enterococcus faecalis and the CW459tet(M) element from Clostridium perfringens shows that they have similar conjugation regions but different insertion and excision modules. Microbiology 147:1243-1251.[Abstract/Free Full Text]
8
8. Shaw, J. H., and D. B. Clewell. 1985. Complete nucleotide sequence of macrolide-lincosamide-streptogramin B-resistance transposon Tn917 in Streptococcus faecalis. J. Bacteriol. 164:782-796.[Abstract/Free Full Text]

						E. Giovanetti A. Brenciani A. Bacciaglia M. P. Montanari P. E. Varaldo* Institute of Microbiology and Biomedical Sciences Polytechnic University of Marche 60020 Ancona, Italy
						* Phone: 39 071 2206294 Fax: 39 071 2206293 E-mail: pe.varaldo{at}univpm.it

Authors' Reply

Top LETTER REFERENCES LETTER{nbsp} REFERENCES{nbsp}

 
We appreciate the thoughtful and convincing comments by Giovanetti and colleagues about the possible mobile element that could carry the erm(B) and tet(M) genes together with the tndX resolvase in 16 of 125 erythromycin-resistant pneumococci isolated in a countrywide survey in Spain (2). We agree with the authors that these genes erm(B), tet(M), and tndX might be carried by a new mobile element, because the 16 pneumococci were tetracycline resistant and had positive detection of tet(M) gene, whereas the S. pyogenes isolates carrying Tn1116 had an incomplete and silent tet(M) gene and were tetracycline susceptible (1).

We agree with Giovanetti and colleagues that the Sweden^15A-25 clone is relatively widespread among erythromycin-resistant pneumococci in Spain. Fourteen (11.2%) of 125 erythromycin-resistant strains isolated in this study belonged to Sweden^15A-25 clone by pulsed-field gel electrophoresis and multilocus sequence typing and were isolated in different geographic areas of Spain (2). This clone represents nearly one-tenth of the erythromycin-resistant pneumococci isolated between 1997 and 2006 in our institution (unpublished data). The Sweden^15A-25 clone, first detected in Sweden in 1992, has a common antibiotic multiresistance pattern: low-level resistance to penicillin (MICs of 0.12 to 0.25 µg/ml) and resistance to erythromycin and clindamycin and has been detected in Portugal, Italy, France, the United States, and elsewhere (3) (www.spneumoniae.mlst.net). In addition, we have studied another 21 pneumococci belonging to Sweden^15A-25 clone isolated in our hospital during the period from 1997 to 2006. All of them had positive detection of erm(B), tet(M), and tndX genes, whereas the int, xis, tnpA, and tnpR genes were not detected. The same results were observed for the reference strain of this clone (http://www.sph.emory.edu/PMEN).

In our experience, the iMLS_B phenotype represents 5% of invasive erythromycin-resistant pneumococci isolated in our laboratory from adult patients over the last decade. However, this rate was higher (14.4%) in the nationwide study (2), which included both invasive and noninvasive pneumococci isolated from adults and children. Contrary to the assumption of Giovanetti and colleagues, the 18 iMLS_B strains of the nationwide study showed 12 different pulsed-field gel electrophoresis patterns and belonged to eight serotypes. Only two of these 18 inducible strains belonged to Sweden^15A-25 clone and had positive detection of erm(B), tet(M), and tndX genes, whereas the int, xis, tnpA, and tnpR genes were not detected.

In conclusion, we are in agreement with Giovanetti and colleagues about the possible presence of a new composite element that might carry erm(B), tet(M) and tndX genes associated with the Sweden^15A-25 clone.

Top LETTER REFERENCES LETTER{nbsp} REFERENCES{nbsp}

 

1
1. Brenciani, A., A. Bacciaglia, M. Vecchi, L. A. Vitali, P. E. Varaldo, and E. Giovanetti. 2007. Genetic elements carrying erm(B) in Streptococcus pyogenes and association with tet(M) tetracycline resistance gene. Antimicrob. Agents Chemother. 51:1209-1216.[Abstract/Free Full Text]
2
2. Calatayud, L., C, Ardanuy, E. Cercenado, A. Fenoll, E. Bouza, R. Pallares, R. Martin, and J. Linares. 2007. Serotypes, clones, and mechanisms of resistance of erythromycin-resistant Streptococcus pneumoniae isolates collected in Spain. Antimicrob. Agents Chemother. 51:3240-3246.[Abstract/Free Full Text]
3
3. Sa-Leao, R., A. Tomasz, I. S. Sanches, A. Brito-Avo, S. E. Vilhelmsson, K. G. Kristinsson, and H. de Lencastre. 2000. Carriage of internationally spread clones of Streptococcus pneumoniae with unusual drug resistance patterns in children attending day care centers in Lisbon, Portugal. J. Infect. Dis. 182:1153-1160.[CrossRef][Medline]

						Laura Calatayud Carmen Ardanuy Josefina Liñares* Microbiology Department Hospital Universitari de Bellvitge-IDIBELL Feixa Llarga s/n 08907 L'Hospitalet de Llobregat Barcelona, Spain
						* Phone: 34 93 260 7930. Fax: 34 93 260 7547. E-mail: fina.linares{at}csub.scs.es

---

Antimicrobial Agents and Chemotherapy, December 2007, p. 4535-4536, Vol. 51, No. 12
0066-4804/07/$08.00+0     doi:10.1128/AAC.01155-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

• Varaldo, P. E., Montanari, M. P., Giovanetti, E. (2009). Genetic Elements Responsible for Erythromycin Resistance in Streptococci. Antimicrob. Agents Chemother. 53: 343-353 [Full Text]  

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Giovanetti, E. Articles by Liñares, J. Search for Related Content PubMed PubMed Citation Articles by Giovanetti, E. Articles by Liñares, J.