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In vitro activity of linezolid, quinupristin-dalfopristin, vancomycin, teicoplanin, moxifloxacin and mupirocin against methicillin-resistant Staphylococcus aureus: comparative evaluation by the E test and a broth microdilution method
Diagnostic Microbiology and Infectious Disease 43 (2002) 319 –321
www.elsevier.com/locate/diagmicrobio
In vitro activity of linezolid, quinupristin-dalfopristin, vancomycin, teicoplanin, moxifloxacin and mupirocin against methicillin-resistant Staphylococcus aureus: comparative evaluation by the E test and a broth microdilution method Jochen Abb Institute of Microbiology, Klinikum Ludwigsburg, Posilipostrasse 4, D-71640 Ludwigsburg, Germany Received 3 January 2002; accepted 21 April 2002
Abstract The E test and broth microdilution showed comparable accuracy for the susceptibility testing of methicillin-resistant S. aureus (MRSA). All of the 109 primary clinical MRSA isolates were fully susceptible to the glycopeptides vancomycin and teicoplanin, the oxazolidinone linezolid, and the streptogramin quinupristin-dalfopristin. Nine out of the 109 MRSA isolates (8.3 percent) demonstrated resistance to moxifloxacin and 5 out of the 109 strains (4.6 percent) were resistant to the topical agent mupirocin. Linezolid and quinupristin-dalfopristin may prove useful alternatives for the treatment of patients with MRSA infections. MRSA isolates should be screened for in vitro susceptibility against mupirocin prior to the topical application.
Nosocomial infections with methicillin-resistant strains of Staphylococcus aureus (MRSA) have shown a steady world-wide increase over the last decade (Levy, 1998). Recently S. aureus isolates with reduced susceptibility to glycopeptides have also been reported (Hiramatsu et al., 1997). Since current options for the treatment of patients with MRSA infections are limited, the development of new compounds with anti-staphylococcal activity is urgently needed. Promising preliminary results have been obtained with the oxazolidinone linezolid (Diekema & Jones, 2001) and the streptogramin quinupristin-dalfopristin (Brumfitt et al., 1992). We have studied 109 non-repeat clinical MRSA isolates for their susceptibility against linezolid, quinupristin-dalfopristin, vancomycin, teicoplanin, moxifloxacin, and the topical anti-staphylococcal agent mupirocin. The minimum inhibitory concentration (MIC) of MRSA strains was evaluated by two different techniques for quantitative antimicrobial susceptibility testing. The performance of the E test was compared with a conventional broth microdilution method. One hundred nine primary clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) were used.
Tel.: ⫹07141-996663; fax: ⫹07141-997273.
The MRSA strains were collected from hospitalized patients of a large Southwest German community hospital between 1998 and 2001 and were selected to represent unique pulsed-field gel-electrophoresis types (Tenover et al., 1995). Methicillin resistance of S. aureus isolates was detected by MIC determination with the E test and broth microdilution and by testing with a latex agglutination kit for the presence of penicillin-binding protein 2 a (Van Griethuysen et al., 1999). S. aureus ATCC 29213 and the German MRSA reference isolates 131 and 134 (kindly provided by Prof. Witte, Robert Koch Institute, Wernigerode, Germany) were employed as control strains. Mueller-Hinton agar plates supplemented with two percent NaCl were inoculated by swabbing of the surface with a suspension of organisms adjusted to equal the turbidity of a 0.5 McFarland opacity standard. Inoculated plates were allowed to dry before E test strips (AB-Biodisk, Solna, Sweden) containing linezolid, quinupristin-dalfopristin, vancomycin, teicoplanin, moxifloxacin, and mupirocin were applied to the surface of the agar. After incubation for 22 to 24 h at 37°C in ambient air the MIC was read directly from the intersection of the inhibition ellipse with the test strip MIC scale. Antimicrobial susceptibility tests with the broth microdilution method were performed with commercially available kits (Micronaut, Merlin Diagnostika, Bornheim-
0732-8893/02/$ – see front matter © 2002 Elsevier Science Inc. All rights reserved. PII: S 0 7 3 2 - 8 8 9 3 ( 0 2 ) 0 0 4 0 7 - 8
320
J. Abb / Diagnostic Microbiology and Infectious Disease 43 (2002) 319 –321
Table 1 Distribution of differences with 6 antimicrobial agents for 109 MRSA strains: E test versus broth microdilution Antimicrobial agent
Vancomycin Teicoplanin Quinupristin-Dalfopristin Linezolid Moxifloxacin Mupirocin All agents
No. of strains
109 109 109 109 109 109 654
No. of strains with indicated log2 dilution step differences between MIC values as obtained by the E test versus broth microdilution ⬍⫺2
⫺2
⫺1
0
⫹1
⫹2
⬎⫹2
0 0 0 0 1 0 1
0 0 0 0 6 0 6
2 7 2 7 20 3 41
91 72 102 98 82 105 550
15 25 5 4 0 1 50
1 5 0 0 0 0 6
0 0 0 0 0 0 0
Hersel, Germany) according to National Committee for Clinical Laboratory Standards (NCCLS) guidelines (NCCLS, 2000). Correlations between results of the E test and broth microdilution for the susceptibility testing of MRSA strains with the 6 antimicrobial agents are shown in Table 1. Overall 98.0 percent of the results demonstrated agreement within one log 2 dilution step. When the E test was used, there was a tendency for the MICs to be marginally higher for vancomycin and teicoplanin and the MICs to be lower when testing moxifloxacin (Table 1). The MICs of the E test
% agreement within 1 log2 dilution
Categorical discrepancies
99.1 95.4 100.0 100.0 94.5 100.0 98.0
0 0 0 0 5 0 5
and broth microdilution were converted to categories of susceptibility by using the definitions of the NCCLS standard M100-S8 (NCCLS, 1998). A categorical discrepancy was defined as a more than two-dilution step difference that resulted in a change of interpretation from susceptible to resistant or vice versa. Only 5 of the 654 tests (0.8 percent) demonstrated an interpretative discrepancy (Table 1). These 5 MRSA strains were classified as susceptible to moxifloxacin by the E test (MICs 0.5 to 1.0 mg/L), but determined as resistant by broth microdilution (MIC 4.0 mg/L). Fig. 1 demonstrates the distribution of MIC determina-
Fig. 1. Distribution of MIC values for 6 antimicrobial agents against MRSA isolates.
J. Abb / Diagnostic Microbiology and Infectious Disease 43 (2002) 319 –321
tions in primary clinical MRSA isolates. MRSA strains with a reduced susceptibility to the glycopeptides vancomycin or teicoplanin were not observed. All isolates were further fully susceptible to the oxazolidinone linezolid and the streptogramin quinupristin-dalfopristin. MIC values to quinupristin-dalfopristin generally were about twofold lower than those to linezolid. Nine of the 109 MRSA strains (8.3 percent) showed resistance to moxifloxacin (MIC 3.0 to 4.0 mg/L). Five of the 109 MRSA isolates (4.6 percent) demonstrated resistance to mupirocin (MIC 8 to 12 mg/L). The present study has confirmed the potential of the E test for antimicrobial susceptibility testing of methicillin– resistant S. aureus (Baker et al., 1994, Bignardi et al., 1993). Comparisons of the E test with a standard broth microdilution technique yielded excellent agreement (98.0 percent of the results were within one log 2 dilution step). Major categorical discrepancies between both methods were observed rarely only (0.8 percent). Categorical discrepancies were found exclusively with moxifloxacin; E test MICs for the quinolone tended to be lower than those determined by broth microdilution. Previous studies on the performance of the E test have shown that following the addition of two percent NaCl to Mueller-Hinton agar major error rates decreased from 20 to less than one percent (Baker et al., 1994). Other comparisons of the E test and agar dilution for susceptibility testing of staphylococci and/or enterococci showed a quantitative accuracy of the E test between 95 and 98% (Huang et al., 1992; Sanchez et al., 1992; Jansen et al., 1995). More recently, using the E test with a 2.0 Mc Farland inoculum on Brain Heart Infusion agar yielded the highest sensitivity and specificity values for the detection of staphylococci with reduced susceptibility to glycopeptides (Walsh et al., 2001). The ease of handling and the documented reliability prompted us to use the E test for studying the in vitro activity of glycopeptides, linezolid, quinupristin-dalfopristin, moxifloxacin, and mupirocin against clinical MRSA isolates. Our results demonstrated that the oxazolidinone linezolid and the streptogramin quinupristin-dalfopristin possess an in vitro activity against MRSA which is comparable or even better than that of the glycopeptides vancomycin and teicoplanin (Auckenthaler et al., 2000; Cuny & Witte, 2000; Jones et al., 1999). MIC values of MRSA strains to quinupristin-dalfopristin generally were about two-fold lower than those to linezolid. The new compounds may prove useful alternatives for the treatment of patients with MRSA infections. The high rate of resistance to mupirocin in primary MRSA isolates underlines the need for the determination of in vitro susceptibility before topical application of mupirocin for MRSA eradication (Wise & Johnson, 1991).
321
References Auckenthaler, R., Courvalin, P., Feger, C., & Roche, G. (2000). In vitro activity of quinupristin-dalfopristin in comparison with five antibiotics against worldwide clinical isolates of staphylococci. Clinical Microbiology Infection, 6, 608 – 612. Baker, C. N., Huang, M. B., & Tenover, F. C. (1994). Optimizing testing of methicillin-resistant Staphylococcus species. Diagnostic Microbiology and Infectious Disease, 19, 167–170. Bignardi, G. E., Riley, U., & Easmon, C. S. F. (1993). Use of the E test for methicillin sensitivity testing. Journal of Antimicrobial Chemotherapy, 32, 37– 43. Brumfitt, W., Hamilton-Miller, J., & Shah, S. (1992). In vitro activity of RP 59500, a new semisynthetic streptogramin antibiotic against Grampositive bacteria. Journal of Antimicrobial Therapy, 30, 122–177. Cuny, C., & Witte, W. (2000). In vitro activity of linezolid against staphylococci. Clinical Microbiology Infection, 6, 328 –333. Diekema, D. J., & Jones, R. N. (2001). Oxazolidinone antibiotics. Lancet, 358, 1975–1982. Hiramatsu, K., Hanaki, H., Into, T., Yabata, K., Oguri, T., & Tenover, F. C. (1997). Methicillin-resistant Staphylococcus aureus clinical strain with reduced vancomycin susceptibility. Journal of Antimicrobial Therapy, 40, 135–136. Huang, M. B., Baker, C. N., Banerjee, S., & Tenover, F. C. (1992). Accuracy of the E test for determining antimicrobial susceptibilities of staphylococci, enterococci, campylobacter jejuni, and Gram-negative bacteria resistant to antimicrobial agents. Journal of Clinical Microbiology, 30, 3243–3248. Jansen, F., Schumacher-Perdreau, F., & Pulverer, G. (1995). Susceptibility of staphylococci and enterococci to glycopeptides. Comparison of 3 test methods. Zbl Bakteriology, 282, 402– 408. Jones, M. E., Visser, M. R., Klootwijk, M., Heisig, P., Verhoef, J., & Schmitz, F. J. (1999). Comparative activities of clinafloxacin, grepafloxacin, levofloxacin, moxifloxacin, ofloxacin, sparfloxacin, and trovafloxacin and nonquinolones linezolid, quinupristin-dalfopristin, gentamicin, and vancomycin against clinical isolates of ciprofloxacinresistant and -susceptible Staphylococcus aureus strains. Antimicrobial Agents and Chemotherapy, 43, 421– 423. Levy, S. (1998). Multidrug resistance—a sign of the times. New England Journal of Medicine, 338, 1376 –1378. National Committee for Clinical Laboratory Standards. (1998). Performance standards for antimicrobial susceptibility testing: eighth informational supplement. NCCLS document M100 –S8. NCCLS, Villanova, PA. National Committee for Clinical Laboratory Standards. (2000). Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically. Approved standard M7–A5. NCCLS, Villanova, PA. Sanchez, M. L., Barrett, M. S., & Jones, R. N. (1992). The E test applied to susceptibility tests of gonococci, multiply resistant enterococci, and enterobacteriaceae producing potent -lactamases. Diagnostic Microbiology and Infectious Disease, 15, 459 – 463. Tenover, F. C., Arbeit, R. D., Goering, R. V., Mickelsen, P. A., Murray, B. E., Persing, D. K., & Swaminathan, B. (1995). Interpreting chromosomal DNA restriction patterns produced by pulsed-field gel electrophoresis: criteria for bacterial strain typing. Journal of Clinical Microbiology, 33, 2233–2239. Van Griethuysen, A., Pouw, M., van Leeuwen, N., Heck, M., Willemse, P., Buiting, A., & Kluytmans, J. (1999). Rapid slide agglutination test for detection of methicillin-resistance in Staphylococcus aureus. Journal of Clinical Microbiology, 37, 2789 –2792. Walsh, T. R., Bolmstro¨ m, A., Qua¨ rnstro¨ m, A., Ho, P., Wooton, M., Howe, R. A., MacGowan, A. P., & Diekema, D. (2001). Evaluation of current methods for detection of staphylococci with reduced susceptibility to glycopeptides. Journal of Clinical Microbiology, 39, 2439 –2444. Wise, R., & Johnson, J. (1991). Mupirocin resistance. Lancet, 338, 578.
www.elsevier.com/locate/diagmicrobio
In vitro activity of linezolid, quinupristin-dalfopristin, vancomycin, teicoplanin, moxifloxacin and mupirocin against methicillin-resistant Staphylococcus aureus: comparative evaluation by the E test and a broth microdilution method Jochen Abb Institute of Microbiology, Klinikum Ludwigsburg, Posilipostrasse 4, D-71640 Ludwigsburg, Germany Received 3 January 2002; accepted 21 April 2002
Abstract The E test and broth microdilution showed comparable accuracy for the susceptibility testing of methicillin-resistant S. aureus (MRSA). All of the 109 primary clinical MRSA isolates were fully susceptible to the glycopeptides vancomycin and teicoplanin, the oxazolidinone linezolid, and the streptogramin quinupristin-dalfopristin. Nine out of the 109 MRSA isolates (8.3 percent) demonstrated resistance to moxifloxacin and 5 out of the 109 strains (4.6 percent) were resistant to the topical agent mupirocin. Linezolid and quinupristin-dalfopristin may prove useful alternatives for the treatment of patients with MRSA infections. MRSA isolates should be screened for in vitro susceptibility against mupirocin prior to the topical application.
Nosocomial infections with methicillin-resistant strains of Staphylococcus aureus (MRSA) have shown a steady world-wide increase over the last decade (Levy, 1998). Recently S. aureus isolates with reduced susceptibility to glycopeptides have also been reported (Hiramatsu et al., 1997). Since current options for the treatment of patients with MRSA infections are limited, the development of new compounds with anti-staphylococcal activity is urgently needed. Promising preliminary results have been obtained with the oxazolidinone linezolid (Diekema & Jones, 2001) and the streptogramin quinupristin-dalfopristin (Brumfitt et al., 1992). We have studied 109 non-repeat clinical MRSA isolates for their susceptibility against linezolid, quinupristin-dalfopristin, vancomycin, teicoplanin, moxifloxacin, and the topical anti-staphylococcal agent mupirocin. The minimum inhibitory concentration (MIC) of MRSA strains was evaluated by two different techniques for quantitative antimicrobial susceptibility testing. The performance of the E test was compared with a conventional broth microdilution method. One hundred nine primary clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) were used.
Tel.: ⫹07141-996663; fax: ⫹07141-997273.
The MRSA strains were collected from hospitalized patients of a large Southwest German community hospital between 1998 and 2001 and were selected to represent unique pulsed-field gel-electrophoresis types (Tenover et al., 1995). Methicillin resistance of S. aureus isolates was detected by MIC determination with the E test and broth microdilution and by testing with a latex agglutination kit for the presence of penicillin-binding protein 2 a (Van Griethuysen et al., 1999). S. aureus ATCC 29213 and the German MRSA reference isolates 131 and 134 (kindly provided by Prof. Witte, Robert Koch Institute, Wernigerode, Germany) were employed as control strains. Mueller-Hinton agar plates supplemented with two percent NaCl were inoculated by swabbing of the surface with a suspension of organisms adjusted to equal the turbidity of a 0.5 McFarland opacity standard. Inoculated plates were allowed to dry before E test strips (AB-Biodisk, Solna, Sweden) containing linezolid, quinupristin-dalfopristin, vancomycin, teicoplanin, moxifloxacin, and mupirocin were applied to the surface of the agar. After incubation for 22 to 24 h at 37°C in ambient air the MIC was read directly from the intersection of the inhibition ellipse with the test strip MIC scale. Antimicrobial susceptibility tests with the broth microdilution method were performed with commercially available kits (Micronaut, Merlin Diagnostika, Bornheim-
0732-8893/02/$ – see front matter © 2002 Elsevier Science Inc. All rights reserved. PII: S 0 7 3 2 - 8 8 9 3 ( 0 2 ) 0 0 4 0 7 - 8
320
J. Abb / Diagnostic Microbiology and Infectious Disease 43 (2002) 319 –321
Table 1 Distribution of differences with 6 antimicrobial agents for 109 MRSA strains: E test versus broth microdilution Antimicrobial agent
Vancomycin Teicoplanin Quinupristin-Dalfopristin Linezolid Moxifloxacin Mupirocin All agents
No. of strains
109 109 109 109 109 109 654
No. of strains with indicated log2 dilution step differences between MIC values as obtained by the E test versus broth microdilution ⬍⫺2
⫺2
⫺1
0
⫹1
⫹2
⬎⫹2
0 0 0 0 1 0 1
0 0 0 0 6 0 6
2 7 2 7 20 3 41
91 72 102 98 82 105 550
15 25 5 4 0 1 50
1 5 0 0 0 0 6
0 0 0 0 0 0 0
Hersel, Germany) according to National Committee for Clinical Laboratory Standards (NCCLS) guidelines (NCCLS, 2000). Correlations between results of the E test and broth microdilution for the susceptibility testing of MRSA strains with the 6 antimicrobial agents are shown in Table 1. Overall 98.0 percent of the results demonstrated agreement within one log 2 dilution step. When the E test was used, there was a tendency for the MICs to be marginally higher for vancomycin and teicoplanin and the MICs to be lower when testing moxifloxacin (Table 1). The MICs of the E test
% agreement within 1 log2 dilution
Categorical discrepancies
99.1 95.4 100.0 100.0 94.5 100.0 98.0
0 0 0 0 5 0 5
and broth microdilution were converted to categories of susceptibility by using the definitions of the NCCLS standard M100-S8 (NCCLS, 1998). A categorical discrepancy was defined as a more than two-dilution step difference that resulted in a change of interpretation from susceptible to resistant or vice versa. Only 5 of the 654 tests (0.8 percent) demonstrated an interpretative discrepancy (Table 1). These 5 MRSA strains were classified as susceptible to moxifloxacin by the E test (MICs 0.5 to 1.0 mg/L), but determined as resistant by broth microdilution (MIC 4.0 mg/L). Fig. 1 demonstrates the distribution of MIC determina-
Fig. 1. Distribution of MIC values for 6 antimicrobial agents against MRSA isolates.
J. Abb / Diagnostic Microbiology and Infectious Disease 43 (2002) 319 –321
tions in primary clinical MRSA isolates. MRSA strains with a reduced susceptibility to the glycopeptides vancomycin or teicoplanin were not observed. All isolates were further fully susceptible to the oxazolidinone linezolid and the streptogramin quinupristin-dalfopristin. MIC values to quinupristin-dalfopristin generally were about twofold lower than those to linezolid. Nine of the 109 MRSA strains (8.3 percent) showed resistance to moxifloxacin (MIC 3.0 to 4.0 mg/L). Five of the 109 MRSA isolates (4.6 percent) demonstrated resistance to mupirocin (MIC 8 to 12 mg/L). The present study has confirmed the potential of the E test for antimicrobial susceptibility testing of methicillin– resistant S. aureus (Baker et al., 1994, Bignardi et al., 1993). Comparisons of the E test with a standard broth microdilution technique yielded excellent agreement (98.0 percent of the results were within one log 2 dilution step). Major categorical discrepancies between both methods were observed rarely only (0.8 percent). Categorical discrepancies were found exclusively with moxifloxacin; E test MICs for the quinolone tended to be lower than those determined by broth microdilution. Previous studies on the performance of the E test have shown that following the addition of two percent NaCl to Mueller-Hinton agar major error rates decreased from 20 to less than one percent (Baker et al., 1994). Other comparisons of the E test and agar dilution for susceptibility testing of staphylococci and/or enterococci showed a quantitative accuracy of the E test between 95 and 98% (Huang et al., 1992; Sanchez et al., 1992; Jansen et al., 1995). More recently, using the E test with a 2.0 Mc Farland inoculum on Brain Heart Infusion agar yielded the highest sensitivity and specificity values for the detection of staphylococci with reduced susceptibility to glycopeptides (Walsh et al., 2001). The ease of handling and the documented reliability prompted us to use the E test for studying the in vitro activity of glycopeptides, linezolid, quinupristin-dalfopristin, moxifloxacin, and mupirocin against clinical MRSA isolates. Our results demonstrated that the oxazolidinone linezolid and the streptogramin quinupristin-dalfopristin possess an in vitro activity against MRSA which is comparable or even better than that of the glycopeptides vancomycin and teicoplanin (Auckenthaler et al., 2000; Cuny & Witte, 2000; Jones et al., 1999). MIC values of MRSA strains to quinupristin-dalfopristin generally were about two-fold lower than those to linezolid. The new compounds may prove useful alternatives for the treatment of patients with MRSA infections. The high rate of resistance to mupirocin in primary MRSA isolates underlines the need for the determination of in vitro susceptibility before topical application of mupirocin for MRSA eradication (Wise & Johnson, 1991).
321
References Auckenthaler, R., Courvalin, P., Feger, C., & Roche, G. (2000). In vitro activity of quinupristin-dalfopristin in comparison with five antibiotics against worldwide clinical isolates of staphylococci. Clinical Microbiology Infection, 6, 608 – 612. Baker, C. N., Huang, M. B., & Tenover, F. C. (1994). Optimizing testing of methicillin-resistant Staphylococcus species. Diagnostic Microbiology and Infectious Disease, 19, 167–170. Bignardi, G. E., Riley, U., & Easmon, C. S. F. (1993). Use of the E test for methicillin sensitivity testing. Journal of Antimicrobial Chemotherapy, 32, 37– 43. Brumfitt, W., Hamilton-Miller, J., & Shah, S. (1992). In vitro activity of RP 59500, a new semisynthetic streptogramin antibiotic against Grampositive bacteria. Journal of Antimicrobial Therapy, 30, 122–177. Cuny, C., & Witte, W. (2000). In vitro activity of linezolid against staphylococci. Clinical Microbiology Infection, 6, 328 –333. Diekema, D. J., & Jones, R. N. (2001). Oxazolidinone antibiotics. Lancet, 358, 1975–1982. Hiramatsu, K., Hanaki, H., Into, T., Yabata, K., Oguri, T., & Tenover, F. C. (1997). Methicillin-resistant Staphylococcus aureus clinical strain with reduced vancomycin susceptibility. Journal of Antimicrobial Therapy, 40, 135–136. Huang, M. B., Baker, C. N., Banerjee, S., & Tenover, F. C. (1992). Accuracy of the E test for determining antimicrobial susceptibilities of staphylococci, enterococci, campylobacter jejuni, and Gram-negative bacteria resistant to antimicrobial agents. Journal of Clinical Microbiology, 30, 3243–3248. Jansen, F., Schumacher-Perdreau, F., & Pulverer, G. (1995). Susceptibility of staphylococci and enterococci to glycopeptides. Comparison of 3 test methods. Zbl Bakteriology, 282, 402– 408. Jones, M. E., Visser, M. R., Klootwijk, M., Heisig, P., Verhoef, J., & Schmitz, F. J. (1999). Comparative activities of clinafloxacin, grepafloxacin, levofloxacin, moxifloxacin, ofloxacin, sparfloxacin, and trovafloxacin and nonquinolones linezolid, quinupristin-dalfopristin, gentamicin, and vancomycin against clinical isolates of ciprofloxacinresistant and -susceptible Staphylococcus aureus strains. Antimicrobial Agents and Chemotherapy, 43, 421– 423. Levy, S. (1998). Multidrug resistance—a sign of the times. New England Journal of Medicine, 338, 1376 –1378. National Committee for Clinical Laboratory Standards. (1998). Performance standards for antimicrobial susceptibility testing: eighth informational supplement. NCCLS document M100 –S8. NCCLS, Villanova, PA. National Committee for Clinical Laboratory Standards. (2000). Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically. Approved standard M7–A5. NCCLS, Villanova, PA. Sanchez, M. L., Barrett, M. S., & Jones, R. N. (1992). The E test applied to susceptibility tests of gonococci, multiply resistant enterococci, and enterobacteriaceae producing potent -lactamases. Diagnostic Microbiology and Infectious Disease, 15, 459 – 463. Tenover, F. C., Arbeit, R. D., Goering, R. V., Mickelsen, P. A., Murray, B. E., Persing, D. K., & Swaminathan, B. (1995). Interpreting chromosomal DNA restriction patterns produced by pulsed-field gel electrophoresis: criteria for bacterial strain typing. Journal of Clinical Microbiology, 33, 2233–2239. Van Griethuysen, A., Pouw, M., van Leeuwen, N., Heck, M., Willemse, P., Buiting, A., & Kluytmans, J. (1999). Rapid slide agglutination test for detection of methicillin-resistance in Staphylococcus aureus. Journal of Clinical Microbiology, 37, 2789 –2792. Walsh, T. R., Bolmstro¨ m, A., Qua¨ rnstro¨ m, A., Ho, P., Wooton, M., Howe, R. A., MacGowan, A. P., & Diekema, D. (2001). Evaluation of current methods for detection of staphylococci with reduced susceptibility to glycopeptides. Journal of Clinical Microbiology, 39, 2439 –2444. Wise, R., & Johnson, J. (1991). Mupirocin resistance. Lancet, 338, 578.