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Antimicrobial Agents and Chemotherapy, May 2009, p. 1921-1925, Vol. 53, No. 5
0066-4804/09/$08.00+0     doi:10.1128/AAC.01065-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Characterization of Macrolide Efflux Pump mef Subclasses Detected in Clinical Isolates of Streptococcus pyogenes Isolated between 1999 and 2005

J. Blackman Northwood,^1* M. Del Grosso,² L. R. Cossins,¹ M. D. Coley,¹ R. Creti,² A. Pantosti,² and D. J. Farrell¹

Quotient Bioresearch Ltd., Fordham, United Kingdom,¹ Department of Infectious, Parasitic and Immune-Mediated Diseases, Istituto Superiore di Sanità, Rome, Italy²

Received 7 August 2008/ Returned for modification 7 November 2008/ Accepted 20 February 2009

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The macrolide efflux mechanism of resistance, mef, was characterized in community-acquired respiratory tract infections with Streptococcus pyogenes. Fifty-four (4.6%) M phenotype isolates were screen tested as negative for mef(A). Of these 54 isolates, 5 (0.4%), 27 (2.3%), and 1 (0.1%) were considered to be mef(I) positive, a novel mosaic variant of mef, or a novel subclass of mef, respectively. This study shows (i) the definitive presence of mef(E) in S. pyogenes and its global distribution, (ii) the presence of a mosaic variant of mef composed of mef(A) and mef(E), (iii) the previously undescribed presence of mef(I) in S. pyogenes, and (iv) the presence of a novel subclass of mef in S. pyogenes.

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Macrolide resistance (Mac^r) due to the presence of an efflux pump was first described in Staphylococcus aureus (17). This type of Mac^r is known as M type and is characterized by a phenotype that has a low-level resistance to the 14- and 15-ring-membered macrolides but no resistance to the type B streptogramins and the lincosamides. The mef(A) gene was described in Streptococcus pyogenes in 1996 (GenBank accession number U70055) (4). Later, a further variant, mef(E), was identified in Streptococcus pneumoniae (18) (GenBank accession number U83667). It was considered that these subclasses of the mef gene were species specific (4, 18).

There has been some debate over the nomenclature of the mef gene. Based on the fact that the mef subclasses show 80% homology, it has been suggested that both subclasses should be designated mef(A) (13) with further designation by subclass should the need arise. Klaassen and Mouton have argued the need to identify mef(A) and mef(E) separately due to the fact that each gene originated from a different transposable element, Tn1207.1 and mega, respectively (6), and that the erythromycin MICs associated with mef(A) are higher than the erythromycin MICs associated with mef(E) (1).

In this paper, notation of the mef gene will be done according to its subclass, e.g., mef(A) subclass mef(E) will be represented as mef(E).

Since the discovery of mef(A) and mef(E), further subclasses have been published. The subclass mef(I) was found to be present in S. pneumoniae in the IQ element, which is different from Tn1207.1 and the mega element (11). mef(I) was shown to be 91.4% identical to mef(A) and 93.6% identical to mef(E). Extending this subclass, mef(O) has been described in S. pyogenes, which is 97% identical to the mef gene present in Streptococcus dysgalactiae (15).

In this report, we definitively prove the existence of mef(E) and mef(I) in S. pyogenes and describe a novel subclass and a mosaic variant of mef in S. pyogenes.

(This paper was presented in part at the 47th ICAAC in Chicago, IL.)

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Bacterial isolates. The 1,175 macrolide-resistant isolates of S. pyogenes showing the M phenotype were obtained from a global surveillance study of clinical isolates collected between 1999 and 2005. The countries represented by these organisms were Belgium, Brazil, Canada, France, Germany, Guatemala, Japan, Mexico, Portugal, Russia, South Korea, Spain, Taiwan, and the United States. These isolates were determined to be mef only by a previously described PCR-based method (9). Thirty-three isolates of S. pyogenes collected in the same period, found to contain the mef(A) gene and sequenced for confirmation, were used for MIC comparison.

Isolate preparation. All isolates were subcultured from storage (–70°C freezer or plates stored at 4°C) onto horse blood agar and incubated overnight at 36°C in 5 to 6% CO₂. An aliquot (100 µl) of RNase/DNase-free H₂O (Sigma, Poole, United Kingdom) was added to each of the 96 wells of a MicroAmp plate (Applied Biosystems, Warrington, United Kingdom). For each isolate, a confluent area of growth was sampled using a 1-µl plastic loop and transferred to a well in the MicroAmp plate. The plate was incubated at 95°C for 8 min in a PE 9700 thermocycler (Applied Biosystems, Warrington, United Kingdom) and then placed in a Jouan C4.12 centrifuge (Jouan Ltd., Ilkeston, United Kingdom) at 2,290 x g for 5 min. The resultant supernatant was used for TaqMan Probe analysis. DNA template preparation for sequencing analysis was carried out using the DNA Template Preparation Kit (14).

MIC determination. MICs were determined for erythromycin, clarithromycin, azithromycin, clindamycin, and tetracycline using the Clinical and Laboratory Standards Institute guidelines for broth microdilution methods (5).

High-throughput screening for the macrolide efflux mechanism mef. A plus/minus assay for the characterization of mef was performed using the ABI PRISM 7000 sequence detection system with the manufacturer's standard assay parameters and conditions (Applied Biosystems). The primers (mefEF2 and mefER2) and probe (mefEP2) used, which were designed using the mef(E) sequence (NCBI accession number U83667) and the Primer Express software package (Applied Biosystems), are shown in Table 1.

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TABLE 1. PCR and sequencing primers and probes used for characterization of the mef gene

Amplification of the mef gene. Amplification of the mef gene was performed using primers MEF3 and MEF4 listed in Table 1. Further PCR primers, mef 8 F and mef 6 R, were required for isolate MB56Spyo002. The cycling parameters were as follows: 94°C for 2 min; 35 cycles of 94°C for 30 s, 50°C for 30 s, and 72°C for 40 s; 72°C for 7 min. Discrimination between mef(A), mef(E), mef(I), and mef(O) was performed by comparing each sequence to the sequences with GenBank accession numbers U70055 [mef(A)], U83667 [mef(E)], AJ971089 [mef(I)], and DQ016305 [mef(O)]. Each PCR mixture contained 5 µl of extracted DNA, 2.5 U of Platinum Taq (Invitrogen Ltd., Paisley, United Kingdom), 1x Platinum Taq PCR buffer, 200 µmol of each deoxynucleotide triphosphate (dATP, dCTP, dGTP, and dTTP), 2.5 mmol of MgCl₂, 25 pmol of the forward primer, and 25 pmol of the reverse primer. All amplifications of genes, and amplicons for sequencing were performed in a PE 9700 thermocycler. PCR products were detected by electrophoresis on agarose gels incorporating ethidium bromide and visualized using UV transillumination.

Sequencing of PCR products. PCR products were prepared for cycle sequencing using shrimp alkaline phosphatase (SAP) (GE Healthcare, Little Chalfont, United Kingdom) and exonuclease I (GE Healthcare) treatment. Briefly, 5 µl of each PCR product was added to 5 µl of reaction mixture (1 U SAP and 1 U exonuclease I in DNase/RNase-free H₂O) and incubated at 37°C for 60 min, followed by 75°C for 15 min to inactivate the enzymes. Each sample was then diluted 1 in 5 by adding 40 µl of DNase/RNase-free H₂O. The primers used for sequencing were as previously published (6, 15, 16). A further sequencing primer, listed in Table 1 (mef 5 R), was used in the original amplification, while primers mef 8 F and mef 6 R were used as sequencing primers for the mef 8 F and mef 6 R PCR amplification. Each diluted SAP/exonuclease I nuclease-treated product (5 µl) was added to 15 µl of a reaction mixture containing 1 µl Ready Reaction Mix (Applied Biosystems, Warrington, United Kingdom), 4 µl of 5x sequencing buffer (Applied Biosystems), 9.5 µl of RNase- and DNase-free sterile distilled H₂O (Sigma, Poole, United Kingdom), and 3.2 pmol of each target-specific forward and reverse primer. The cycling parameters were 25 cycles of 96°C for 10 s, 50°C for 5 s, and 60°C for 4 min.

Mosaic structure characterization. The method used to emphasize the mosaic structure of mef was similar to a previously published method (12).

MLST. Multilocus sequence typing (MLST) was performed as previously described (8). Sequence types were determined using the MLST database (http://www.mlst.net).

All sequencing was performed on an ABI PRISM 3100 Genetic Analyzer (Applied Biosystems). Sequence analysis was performed using the DNAStar analysis program (DNAStar, Madison, WI).

emm typing. Total DNA was prepared by a Chelex-based procedure using the InstaGene Matrix (Bio-Rad Laboratories). Primers and PCR conditions for the amplification of the emm gene were according to the Centers for Disease Control and Prevention protocol (2). Distinct reference emm types (designated subtype 0) share less than 92% sequence identity over the first 90 bases encoding the deduced processed M protein. New subtypes of known types are dictated by any base change observed within the 150 bases predicted to encode the processed N terminus of the M protein. New types and subtypes are assigned by the curator of the Centers for Disease Control and Prevention streptococcal M protein gene database as described previously after inspection of the sequence data (http://www.cdc.gov/ncidod/biotech/strep/assigning.htm).

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High-throughput screening results. Of the 28,892 clinical isolates of S. pyogenes collected between 1999 and 2005, 1,175 tested positive for mef previously; 54 (4.6%) of those were negative for mef(A), and 1,121 (95.4%) were mef(A) by the TaqMan probe plus/minus assay.

mef sequencing results. The 54 isolates that tested negative for mef(A) with the TaqMan plus/minus assay were confirmed as negative for mef(A) by sequencing of the mef gene. Of these 54 isolates, 21 were considered to be mef(E) positive. Twelve isolates were 100% identical to the mef(E) gene sequenced in S. pneumoniae (Table 2); one isolate (GenBank accession number EU870851) was 100.0% identical to mef(E) except for a 1,218-bp insertion at position 456 corresponding to an insertion sequence (IS) 96% identical to the previously published ISSdy1 of S. dysgalactiae (GenBank accession no. AJ250837) and belonging to the IS3 family; six isolates were 99.9% homologous to mef(E), with one of the six having a stop codon at amino acid position 133 (GenBank accession number EU870853); one isolate (GenBank accession number EU870854) was 98.9% homologous to mef(E), with amino acid deletions at amino acid positions 233 to 235 (FVYdel); and one isolate was 97.8% homologous to mef(E). Five isolates (0.02%) were 97.5% identical to mef(I) at the nucleotide level (GenBank accession number EU870852). These isolates' mef(I) sequences had a single-nucleotide polymorphism (SNP) in the stop codon of the mef gene, resulting in a longer open reading frame by 9 bases. One isolate (MB56Spyo029) showed the greatest homology to mef(E), but its identity was only 96.0% (GenBank accession number EU870855). This novel mef sequence had the same SNP in the stop codon as mef(I), resulting in an open reading frame longer by 9 bases.

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TABLE 2. Numbers of isolates with a specific mef subclass and their percent identity

Twenty-seven isolates showed >96.7% identity to the nearest, most similar gene, mef(E). Sequence analysis of the mef genes of these isolates, in comparison with mef(A) and mef(E), revealed a mosaic structure in which the 5' region was identical to that of mef(A) and the 3' region was identical to that of mef(E) (Fig. 1). There were three different sequences of the mef mosaic variants identified within the 27 isolates, mef mosaic variant 1, mef mosaic variant 2, and mef mosaic variant 3 (GenBank accession numbers EU870856, EU870857, and EU870858, respectively).

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FIG. 1. Diagrammatic representation of the mosaic nature of mef. The numbers represent nucleotide positions in the mef gene. Nucleotide positions 1 to 569, 1100 to 1150, and 1152 to 1218 are identical to mef(A). Nucleotide positions 570 to 617, 619 to 1051, and 1053 to 1099 are identical to mef(E). Nucleotides at positions 618 and 1052 in the mosaic variant are the same as the nucleotides present in mef(A). The nucleotide at position 1151 is identical to that in mef(E).

MLST results. mef(E)-positive S. pyogenes isolates were from six separate clonal complexes (CC) (predicted founders, sequence type 15 [ST15], ST36, ST37, ST46, ST55, and ST75) and one new ST, ST317, which has yet to be grouped on the MLST website. Isolates carrying mef(I) were all within the CC whose predicted founder was ST36. The novel mef subclass ST394 was a singleton in the MLST database. MLST analysis of the mosaic variants of mef showed four different STs, ST39, ST421, ST422, and ST423. All isolates were from the CC whose predicted founder was ST39, with no more than one allelic variation. The genetic relatedness of these isolates is shown by the dendrogram in Fig. 2.

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FIG. 2. MLST-based dendrogram of the genetic relationships among 54 S. pyogenes isolates. The genetic distances between the strains are indicated. Strain names have been shortened, with * representing MB56Spyo. Therefore, *003 is MB56Spyo003. The percentage of nucleotides identical to the most similar mef subclass; distinguishing features, e.g., stop codon, deletion (del), or insertion (ins); the emm type; and the ST/CC are indicated.

emm-typing results. mef(E)-positive S. pyogenes isolates were from seven different emm types, 2.0, 3.1, 6.4, 9.2, 12.0, 22.0, and 36.2, with most of them showing emm type 12.0. Of the five mef(I)-positive S. pyogenes isolates, four were found to be a new emm type, 12.42, and one was emm type 12.0. The isolate carrying the novel mef subclass was found to be emm type 25.0. Isolates containing the mef mosaic variant were from three different emm subtypes, 4.0, 4.7, and 4.9.

MIC results. The MIC₅₀, MIC₉₀, and MIC ranges are shown in Table 3. Isolates containing mef(E) had an erythromycin MIC₅₀ of 8 µg/ml, 1 dilution lower than that of isolates containing mef(A) (16 µg/ml) but the same as the MIC₅₀ of the mosaic variant of mef (8 µg/ml). The tetracycline MIC₅₀ values for mef(E), mef(A), and the mosaic variant were 32 µg/ml, 0.25 µg/ml, and 32 µg/ml, respectively.

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TABLE 3. Distribution of MIC50, MIC90, and MIC ranges between mef(E), mef(A), and the mosaic variant

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From these results, it is possible to definitively confirm the presence of mef(E) in S. pyogenes. Isolates containing mef(E) were identified in North America, South America, Western Europe, and the Far East, suggesting that this gene has a wide geographical distribution. Although the majority of S. pyogenes isolates carry the mef(A) gene, it is no longer possible to suggest that the mef subclasses are species specific. There are seven published sequences of mef(E) in GenBank, either as mef(E) or as part of a large element (accession numbers AB011259, AB426620, AB426624, AB426625, AB42662, AF274302, and AF376746). All were 100% identical to the original mef(E) sequence described in S. pneumoniae (10). In this report, it has been shown that there is greater variation in the subclass mef(E) found in S. pyogenes than the mef(E) found in S. pneumoniae. These variations include (i) an SNP resulting in a stop codon, (ii) the presence of an IS of the IS3 family inside mef(E), (iii) a deletion of 3 amino acids, and (iv) identity of only 97.8% compared with the reference sequence of mef(E), equivalent to 27 SNPs.

It has also been shown that mef(I) is present in S. pyogenes, which to our knowledge has not been reported before. In this project, it has been possible to demonstrate a further mef that shows variation from all of the previously reported mef subclasses, but before adding to an already confused nomenclature of the mef gene, it is important to determine which transposons this and the previously reported mef genes are associated with in order to reduce the number of mef subclasses.

The presence of a mosaic variant of mef in S. pyogenes means that it is not possible to design a probe to distinguish the subclasses of mef. A probe is able to target only a small portion of the whole mef gene, and with the kind of variation found in S. pyogenes, this can lead to misclassification. Interestingly, the organisms containing the mosaic mef variant are from one clonal complex whose predicted founder was ST39 and were all isolated from regions within the Far East. In contrast, isolates containing mef(E) were from seven unrelated STs and emm types, although the majority belonged to ST36 and emm type 12.0. The isolate showing low identity to mef(E) (MB56Spyo001) was ST317, which was a new ST for S. pyogenes, while the isolate that contained the novel subclass of mef was a singleton in the MLST database.

S. pyogenes containing the mef(A) gene had erythromycin MIC₅₀ values greater than that of S. pyogenes that was found to contain mef(E). This reflects the scenario found in S. pneumoniae, where isolates with mef(A) have higher median macrolide MICs than those with mef(E) (1). Mac^r phenotype M and tetracycline resistance in S. pneumoniae have been characterized by the mef(E)- and tet(M)-containing element Tn2009, which consists of a Tn916-like element with the mega element inserted into it (7). In S. pyogenes, the Mac^r phenotype M and tetracycline resistance have been characterized by an element containing mef(A) and tet(O), where mef(A) is present on a Tn1207.1-like transposon inserted into unique elements containing tet(O) (3). The isolates found to contain the mosaic variant of mef also contained tet(O) (J. Blackman Northwood, L. R. Cossins and D. J. Farrell, unpublished data), suggesting that the mosaic mef variant is present on an element similar to that of mef(A)-tet(O) previously described in S. pyogenes.

The characterization of mef(E) in S. pyogenes has highlighted the need to distinguish mef(A), mef(E), and the variations of mef separately. The macrolide MICs between mef(A) and mef(E), shown here and in other studies, vary (1).

Therefore, the subclasses of mef would be better described by the genetic element they are present on, with mef(A) and the mosaic variant being present on Tn1207.1-like transposons (3), mef(E) being present on mega (6), and mef(I) being present on the IQ element (11). With respect to the novel mef subclass found in this study, it will be necessary to determine the transposable element it is associated with before adding a further subclass to mef nomenclature.

 
These investigations formed part of the DRESP2 study, which was funded by the 6th Framework Programme of the European Commission under the reference LSHM-CT-2005-518226.

We acknowledge our colleagues within the molecular biology department at Quotient Bioresearch (formerly GR Micro Ltd.).

 
* Corresponding author. Mailing address: Quotient Bioresearch Limited, Newmarket Road, Fordham CB7 5WW, United Kingdom. Phone: 44 (0)1638 720 500. Fax: 44 (0)1638 724 200. E-mail: John.BlackmanNorthwood{at}quotientbioresearch.com

Published ahead of print on 2 March 2009.

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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. Beall, B., R. Facklam, and T. Thompson. 1996. Sequencing emm-specific PCR products for routine and accurate typing of group A streptococci. J. Clin. Microbiol. 34:953-958.[Abstract]
3
3. Brenciani, A., K. K. Ojo, A. Monachetti, S. Menzo, M. C. Roberts, P. E. Varaldo, and E. Giovanetti. 2004. Distribution and molecular analysis of mef(A)-containing elements in tetracycline-susceptible and -resistant Streptococcus pyogenes clinical isolates with efflux-mediated erythromycin resistance. J. Antimicrob. Chemother. 54:991-998.[Abstract/Free Full Text]
4
4. Clancy, J., J. Petitpas, F. Dib-Hajj, W. Yuan, M. Cronan, A. V. Kamath, J. Bergeron, and J. A. Retsema. 1996. Molecular cloning and functional analysis of a novel macrolide-resistance determinant, mefA, from Streptococcus pyogenes. Mol. Microbiol. 22:867-879.[CrossRef][Medline]
5
5. CLSI. 2006. Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically; approved standard M7-A7, 7th ed., vol. 26. Clinical Laboratory Standards Institute, Wayne, PA.
6
6. Del Grosso, M., F. Iannelli, C. Messina, M. Santagati, N. Petrosillo, S. Stefani, G. Pozzi, and A. Pantosti. 2002. Macrolide efflux genes mef(A) and mef(E) are carried by different genetic elements in Streptococcus pneumoniae. J. Clin. Microbiol. 40:774-778.[Abstract/Free Full Text]
7
7. Del Grosso, M., A. Scotto d'Abusco, F. Iannelli, G. Pozzi, and A. Pantosti. 2004. Tn2009, a Tn916-like element containing mef(E) in Streptococcus pneumoniae. Antimicrob. Agents Chemother. 48:2037-2042.[Abstract/Free Full Text]
8
8. Enright, M. C., B. G. Spratt, A. Kalia, J. H. Cross, and D. E. Bessen. 2001. Multilocus sequence typing of Streptococcus pyogenes and the relationships between emm type and clone. Infect. Immun. 69:2416-2427.[Abstract/Free Full Text]
9
9. Farrell, D. J., I. Morrissey, S. Bakker, and D. Felmingham. 2001. Detection of macrolide resistance mechanisms in Streptococcus pneumoniae and Streptococcus pyogenes using a multiplex rapid cycle PCR with microwell-format probe hybridization. J. Antimicrob. Chemother. 48:541-544.[Abstract/Free Full Text]
10
10. Klaassen, C. H., and J. W. Mouton. 2005. Molecular detection of the macrolide efflux gene: to discriminate or not to discriminate between mef(A) and mef(E). Antimicrob. Agents Chemother. 49:1271-1278.[Free Full Text]
11
11. Mingoia, M., M. Vecchi, I. Cochetti, E. Tili, L. A. Vitali, A. Manzin, P. E. Varaldo, and M. P. Montanari. 2007. Composite structure of Streptococcus pneumoniae containing the erythromycin efflux resistance gene mef(I) and the chloramphenicol resistance gene catQ. Antimicrob. Agents Chemother. 51:3983-3987.[Abstract/Free Full Text]
12
12. Oggioni, M. R., C. G. Dowson, J. M. Smith, R. Provvedi, and G. Pozzi. 1996. The tetracycline resistance gene tet(M) exhibits mosaic structure. Plasmid 35:156-163.[CrossRef][Medline]
13
13. Roberts, M. C., J. Sutcliffe, P. Courvalin, L. B. Jensen, J. Rood, and H. Seppala. 1999. Nomenclature for macrolide and macrolide-lincosamide-streptogramin B resistance determinants. Antimicrob. Agents Chemother. 43:2823-2830.[Free Full Text]
14
14. Roche. 2000. High Pure PCR template preparation kit: instruction manual, version 2. Roche Diagnostics, Mannheim, Germany.
15
15. Sangvik, M., P. Littauer, G. S. Simonsen, A. Sundsfjord, and K. H. Dahl. 2005. mef(A), mef(E) and a new mef allele in macrolide-resistant Streptococcus spp. isolates from Norway. J. Antimicrob. Chemother. 56:841-846.[Abstract/Free Full Text]
16
16. Sutcliffe, J., T. Grebe, A. Tait-Kamradt, and L. Wondrack. 1996. Detection of erythromycin-resistant determinants by PCR. Antimicrob. Agents Chemother. 40:2562-2566.[Abstract]
17
17. Sutcliffe, J., A. Tait-Kamradt, and L. Wondrack. 1996. Streptococcus pneumoniae and Streptococcus pyogenes resistant to macrolides but sensitive to clindamycin: a common resistance pattern mediated by an efflux system. Antimicrob. Agents Chemother. 40:1817-1824.[Abstract]
18
18. Tait-Kamradt, A., J. Clancy, M. Cronan, F. Dib-Hajj, L. Wondrack, W. Yuan, and J. Sutcliffe. 1997. mefE is necessary for the erythromycin-resistant M phenotype in Streptococcus pneumoniae. Antimicrob. Agents Chemother. 41:2251-2255.[Abstract]

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Antimicrobial Agents and Chemotherapy, May 2009, p. 1921-1925, Vol. 53, No. 5
0066-4804/09/$08.00+0     doi:10.1128/AAC.01065-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

This Article Abstract 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 Google Scholar Google Scholar Articles by Blackman Northwood, J. Articles by Farrell, D. J. Search for Related Content PubMed PubMed Citation Articles by Blackman Northwood, J. Articles by Farrell, D. J.