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 Schmitz, F.-J. Articles by Schwarz, S. Search for Related Content PubMed PubMed Citation Articles by Schmitz, F.-J. Articles by Schwarz, S.

 Previous Article  |  Next Article 

Antimicrobial Agents and Chemotherapy, May 2001, p. 1603-1604, Vol. 45, No. 5
0066-4804/01/$04.00+0   DOI: 10.1128/AAC.45.5.1603-1604.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

LETTERS TO THE EDITOR

Structural Alterations in the Translational Attenuator of Constitutively Expressed erm(A) Genes in Staphylococcus aureus

	LETTER

The expression of the predominant macrolide resistance genes in staphylococci, erm(A) and erm(C) (2, 7), is either inducible by 14- and 15-membered macrolides via translational attenuation or constitutive. Constitutively expressed erm(A) and erm(C) genes are of particular clinical relevance since they also confer resistance to 16-membered macrolides, lincosamides, streptogramin B antibiotics, and the new ketolide drugs. To date, very few data on the molecular basis of constitutive erm(A) gene expression in naturally occurring staphylococci are available (8).

In this study, we examined 64 clinical Staphylococcus aureus isolates from humans, collected at 24 European university hospitals within the SENTRY program (5, 6). All 64 isolates carried constitutively expressed erm(A) genes and exhibited the respective resistance phenotype as confirmed by MIC determination (5, 6). A previously described PCR assay (8) served for the detection of structural alterations in the erm(A) regulatory region. All 64 PCR amplicons were sequenced and compared to the sequence of the inducibly expressed erm(A) gene of Tn554 (3).

Five different types of structural alterations were seen: deletions of 83, 121, 123 bp and two closely related tandem duplications of 25 bp each (Fig. 1). The two tandem duplications of 25 bp (5'-TAAGGAGAAGGTTATAATGAACCAG-3' and 5'-GGAGAAGGTTATAATGAACCAGAAA-3') were detected in 1 and 51 isolates, respectively, and comprised the erm(A)-associated ribosome binding site (AGAAGG) as well as the inverted repeat 6 (IR6) sequence (GGTTATAATGAAC). The 83-bp deletion found in two of the isolates comprised the entire open reading frame (ORF) of the 19-amino-acid (aa) peptide including IR3. The 121-bp deletion detected in nine isolates and the 123-bp deletion observed in a single isolate are closely related. Both types of deletions comprise the ORF of the 19-aa peptide as well as the part immediately downstream of it which includes the IR4 and IR5 sequences. These deletions and tandem duplications favored the formation of mRNA secondary structures which allowed translation of the erm(A) transcripts in the absence of inducers.

View larger version (32K): [in this window] [in a new window]   FIG. 1.   Regulatory regions of the inducibly expressed erm(A) gene of Tn554 (2) and the constitutively expressed erm(A) genes analyzed in this study. SD1 to -3, Shine-Dalgarno sequences of the ORFs of the 15-aa peptide, the 19-aa peptide and the erm(A) gene, respectively; arrows, IR1 to IR6; stippled box, truncated erm(A) gene present in isolates which exhibit the 25-bp tandem duplications. Positions numbering corresponds to the Tn554 sequence (database accession no. K02987).

The data show that tandem duplications and deletions of different sizes account for constitutive erm(A) gene expression in naturally occurring S. aureus isolates. So far, deletions of 26 to 141 bp, a tandem duplication of 12 bp, and a point mutation, all of which cause constitutive erm(A) gene expression, have been derived under in vitro selection in the presence of noninducers (3, 4). Thus, these data on in vivo-occurring mutations in the erm(A) translational attenuator in human isolates complement both the in vitro-derived mutations (3, 4) and the mutation seen in a naturally occurring S. intermedius isolate of avian origin (8), thus confirming that similar mutations can arise in vivo and in vitro (1). The development of constitutive erm(C) and erm(A) mutants is a fast and irreversible process. Under in vitro conditions constitutive mutants can be obtained after overnight cultivation in the presence of noninducers (1, 3, 7, 9), and reversion to the inducible type has not been observed in any such mutants. Thus, noninducers, such as lincosamides or streptogramins, should not be recommended for the control of staphylococci which exhibit an inducible macrolide-lincosamide-streptogramin B resistance phenotype.

	FOOTNOTES

^* Phone: 49-5141-384673

Fax: 49-5141-381849

E-mail: stefan.schwarz{at}fal.de

	REFERENCES

1.	Lampson, B. C., and J. T. Parisi. 1986. Naturally occurring Staphylococcus epidermidis plasmid expressing constitutive macrolide-lincosamide-streptogramin B resistance contains a deleted attenuator. J. Bacteriol. 166:479-483[Abstract/Free Full Text].
2.	Leclercq, R., and P. Courvalin. 1991. Bacterial resistance to macrolide, lincosamide, and streptogramin antibiotics by target modification. Antimicrob. Agents Chemother. 35:1267-1272[Free Full Text].
3.	Murphy, E. 1985. Nucleotide sequence of ermA, a macrolide-lincosamide-streptogramin B determinant in Staphylococcus aureus. J. Bacteriol. 162:633-640[Abstract/Free Full Text].
4.	Sandler, P., and B. Weisblum. 1988. Erythromycin-induced stabilization of ermA messenger RNA in Staphylococcus aureus and Bacillus subtilis. J. Mol. Biol. 203:905-915[CrossRef][Medline].
5.	Schmitz, F.-J., R. Sadurski, A. Kray, M. Boos, R. Geisel, K. Köhrer, J. Verhoef, and A. C. Fluit. 2000. Prevalence of macrolide-resistance genes in Staphylococcus aureus and Enterococcus faecium isolates from 24 European university hospitals. J. Antimicrob. Chemother. 45:891-894[Abstract/Free Full Text].
6.	Schmitz, F.-J., J. Verhoef, A. C. Fluit, and the SENTRY Participants Group. 1999. Prevalence of resistance to MLS antibiotics in 20 European university hospitals participating in the European SENTRY surveillance program. J. Antimicrob. Chemother. 43:783-792[Abstract/Free Full Text].
7.	Weisblum, B. 1995. Insights into erythromycin action from studies of its activity as inducer of resistance. Antimicrob. Agents Chemother. 39:797-805[Medline].
8.	Werckenthin, C., and S. Schwarz. 2000. Molecular analysis of the translational attenuator of a constitutively expressed erm(A) gene from Staphylococcusintermedius. J. Antimicrob. Chemother. 46:785-788[Abstract/Free Full Text].
9.	Werckenthin, C., S. Schwarz, and H. Westh. 1999. Structural alterations in the translational attenuator of constitutively expressed ermC genes. Antimicrob. Agents Chemother. 43:1681-1685[Abstract/Free Full Text].

					Franz-Josef Schmitz Jasmina Petridou Nadine Astfalk Sibylle Scheuring Karl Köhrer Institut für Medizinische Mikrobiologie und Virologie Heinrich-Heine Universität Düsseldorf Düsseldorf, Germany
					Jan Verhoef Ad C. Fluit Eijkman-Winkler  Institute for Medical Microbiology University Medical Center Utrecht Utrecht, The Netherlands
					Stefan Schwarz* Institut für Tierzucht und Tierverhalten Bundesforschungsanstalt für Landwirtschaft Dörnbergstrasse 25-27 29223 Celle, Germany

This article has been cited by other articles:

• Depardieu, F., Podglajen, I., Leclercq, R., Collatz, E., Courvalin, P. (2007). Modes and Modulations of Antibiotic Resistance Gene Expression. Clin. Microbiol. Rev. 20: 79-114 [Abstract] [Full Text]  
• Doktor, S. Z., Shortridge, V. (2005). Differences in the DNA Sequences in the Upstream Attenuator Region of erm(A) in Clinical Isolates of Streptococcus pyogenes and Their Correlation with Macrolide/Lincosamide Resistance. Antimicrob. Agents Chemother. 49: 3070-3072 [Abstract] [Full Text]  
• Schmitz, F.-J., Petridou, J., Jagusch, H., Astfalk, N., Scheuring, S., Schwarz, S. (2002). Molecular characterization of ketolide-resistant erm(A)-carrying Staphylococcus aureus isolates selected in vitro by telithromycin, ABT-773, quinupristin and clindamycin. J Antimicrob Chemother 49: 611-617 [Abstract] [Full Text]  
• Schmitz, F.-J., Petridou, J., Milatovic, D., Verhoef, J., Fluit, A. C., Schwarz, S. (2002). In vitro activity of new ketolides against macrolide-susceptible and -resistant Staphylococcus aureus isolates with defined resistance gene status. J Antimicrob Chemother 49: 580-582 [Full Text]  
• Schmitz, F.-J., Witte, W., Werner, G., Petridou, J., Fluit, A. C., Schwarz, S. (2001). Characterization of the translational attenuator of 20 methicillin-resistant, quinupristin/dalfopristin-resistant Staphylococcus aureus isolates with reduced susceptibility to glycopeptides. J Antimicrob Chemother 48: 939-941 [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 Schmitz, F.-J. Articles by Schwarz, S. Search for Related Content PubMed PubMed Citation Articles by Schmitz, F.-J. Articles by Schwarz, S.