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 Previous Article

Antimicrobial Agents and Chemotherapy, April 2008, p. 1587-1588, Vol. 52, No. 4
0066-4804/08/$08.00+0     doi:10.1128/AAC.01502-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

LETTER TO THE EDITOR

RmtD 16S RNA Methylase in Epidemiologically Unrelated SPM-1-Producing Pseudomonas aeruginosa Isolates from Brazil


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We read with interest the article by Doi et al. (2) suggesting that the coproduction of the metallo-β-lactamase SPM-1 and the RmtD 16S RNA methylase is highly prevalent among imipenem-resistant Pseudomonas aeruginosa isolates from Brazil. SPM-1 is widespread among Brazilian carbapenem-resistant P. aeruginosa isolates, and isolates carrying blaSPM-1 have been observed in distinct regions of this country (3). The majority of SPM-1-producing isolates belong to a unique molecular clone identified by pulsed-field gel electrophoresis and automated ribotyping (3). The findings of Doi et al. (2) led us to test a very broad collection of epidemiologically unrelated blaSPM-1-carrying P. aeruginosa strains recovered from diverse Brazilian regions for the presence of rmtD.

We evaluated 26 epidemiologically unrelated SPM-1-producing P. aeruginosa clinical isolates collected from different patients during 2002 in 10 Brazilian cities located in nine states (Table 1). These isolates belonged to 16 different ribogroups, and six isolates belonged to the major ribotype spread throughout the country (ribotype 72-3). Screening for rmtD was performed by PCR using the primers rmtD-F (5'-GAG CGA ACT GAA GGA AAA AC-3') and rmtD-R (5'-CAG CAC GTA AAA CAG CTC-3'), which produce a 730-bp product. Amplicons were sequenced on both strands by using the ABIPrism 377 system (Applied Biosystems, Foster City, CA). The nucleotide sequences were analyzed using the Lasergene software package (DNASTAR, Madison, WI), and the sequences obtained were compared to sequences available over the Internet (http://www.ncbi.nlm.nih.gov/blast/Blast.cgi).


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  		TABLE 1. Characteristics of the 26 epidemiologically unrelated SPM-1-producing P. aeruginosa clinical isolates from different regions in Brazil

 
Among the 26 isolates, rmtD was detected in only 4 (15.4%) strains. This rate is much lower than the results obtained previously (51.0%), implying that the production of RmtD is not prevalent among SPM-1-producing isolates with distinct genetic backgrounds and/or from different geographic areas in Brazil.

blaSPM-1 is different from other metallo-β-lactamase genes that are carried in class 1 integrons also harboring aminoglycoside resistance genes as part of other gene cassettes (5) in that blaSPM-1 is embedded in a distinct genetic element (4) where the correlation of β-lactam and aminoglycoside resistance is not as evident. However, many SPM-1-producing isolates are resistant to other antimicrobial agents, including aminoglycosides. Recently, Carvalho et al. (1) reported that all 13 SPM-1-producing P. aeruginosa isolates found in another Brazilian state carried a class 1 integron, named In163, harboring two aminoglycoside resistance genes, aacA4 and aadA7, showing that aminoglycoside resistance among SPM-1-producing isolates can be also encoded by distinct resistance mechanisms other than the RmtD 16S RNA methylase gene.


   ACKNOWLEDGMENTS
 
The isolates evaluated were collected during a study sponsored by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP research grant 2001/033497) and kindly provided by Professor Ana C. Gales, M.D., Ph.D.


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  1. Carvalho, A. P., R. M. Albano, D. N. de Oliveira, D. A. Cidade, L. M. Teixeira, and A. Marques Ede. 2006. Characterization of an epidemic carbapenem-resistant Pseudomonas aeruginosa producing SPM-1 metallo-β-lactamase in a hospital located in Rio de Janeiro, Brazil. Microb. Drug Resist. 12:103-108.[CrossRef][Medline]
  2. Doi, Y., A. C. Ghilardi, J. Adams, D. de Oliveira Garcia, and D. L. Paterson. 2007. High prevalence of metallo-β-lactamase and 16S rRNA methylase coproduction among imipenem-resistant Pseudomonas aeruginosa isolates in Brazil. Antimicrob. Agents Chemother. 51:3388-3390.[Abstract/Free Full Text]
  3. Gales, A. C., L. C. Menezes, S. Silbert, and H. S. Sader. 2003. Dissemination in distinct Brazilian regions of an epidemic carbapenem-resistant Pseudomonas aeruginosa producing SPM metallo-β-lactamase. J. Antimicrob. Chemother. 52:699-702.[Abstract/Free Full Text]
  4. Poirel, L., M. Magalhaes, M. Lopes, and P. Nordmann. 2004. Molecular analysis of metallo-β-lactamase gene blaSPM-1-surrounding sequences from disseminated Pseudomonas aeruginosa isolates in Recife, Brazil. Antimicrob. Agents Chemother. 48:1406-1409.[Abstract/Free Full Text]
  5. Walsh, T. R., M. A. Toleman, L. Poirel, and P. Nordmann. 2005. Metallo-β-lactamases: The quiet before the storm? Clin. Microbiol. Rev. 18:306-325.[Abstract/Free Full Text]
Mariana Castanheira*
Thomas R. Fritsche
Hélio S. Sader
Ronald N. Jones
JMI Laboratories
345 Beaver Kreek Centre, Suite A
North Liberty, Iowa 52317

* Phone: (319) 665-3370, Fax: (319) 665-3371, E-mail: mariana-castanheira{at}jmilabs.com


Authors' Reply


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The foregoing letter by Castanheira et al. examined the occurrence of rmtD in epidemiologically unrelated, SPM-1-producing Pseudomonas aeruginosa isolated in various parts of Brazil and provided valuable additional data on the epidemiology of this novel gene. They reported a much lower incidence of rmtD (15.4%) among their study isolates than among the isolates in our previous report (51.0%) (1).

There may be several factors for the apparently discordant results. First, the isolates in our study were collected mostly from large tertiary hospitals in the São Paulo metropolitan area, where the antibiotic selection pressure may be higher than the national average. Indeed, a significant number of rmtD-positive isolates in our study were obtained from a large tertiary hospital in São Paulo. Second, all of the SPM-1-producing isolates in our report belonged to a single epidemic clone that coproduced RmtD. Third, the isolates in our study were collected between 2005 and 2006, while those in the study by Castanheira et al. were from 2002. Also, it would be interesting to know how many of the isolates studied by Castanheira et al. were actually resistant or highly resistant to aminoglycosides, whereas the majority of our isolates were. Finally, we found a number of imipenem-resistant isolates in different clonal groups that produced RmtD but not SPM-1 (1).

Equivalent data from the authors may provide further insight into the clinical impact of this phenomenon in Brazil at the national level. Both the authors and we recently reported identification of RmtD-producing Enterobacteriaceae in Brazil (2, 3). We now thus need to keep vigilant eyes on the occurrence of rmtD not only in P. aeruginosa but also in Enterobacteriaceae.


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  1. Doi, Y., A. C. Ghilardi, J. Adams, D. de Oliveira Garcia, and D. L. Paterson. 2007. High prevalence of metallo-β-lactamase and 16S rRNA methylase coproduction among imipenem-resistant Pseudomonas aeruginosa isolates in Brazil. Antimicrob. Agents Chemother. 51:3388-3390.[Abstract/Free Full Text]
  2. Fritsche, T. R., G. H. Miller, R. N. Jones, and E. S. Armstrong. 2007. Abstr. 47th Intersci. Conf. Antimicrob. Agents Chemother., abstr. C2-2053.
  3. Yamane, K., F. Rossi, M. G. Barberino, J. M. Adams-Haduch, Y. Doi, and D. L. Paterson. 2008. 16S ribosomal RNA methylase RmtD produced by Klebsiella pneumoniae in Brazil. J. Antimicrob. Chemother. 61:746-747.[Free Full Text]
Yohei Doi*
Division of Infectious Diseases
University of Pittsburgh Medical Center
Pittsburgh, Pennsylvania 15213

Doroti de Oliveira Garcia
Instituto Adolfo Lutz
São Paulo, Brazil

David L. Paterson
Royal Brisbane and Women's Hospital
University of Queensland
Brisbane, Australia

* Phone: (412) 648-6401
Fax: (412) 648-6399
E-mail: doiy{at}dom.pitt.edu

Antimicrobial Agents and Chemotherapy, April 2008, p. 1587-1588, Vol. 52, No. 4
0066-4804/08/$08.00+0     doi:10.1128/AAC.01502-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.




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