scholarly journals Phenotypic Detection of Methicillin Resistance in Staphylococcus aureus by Disk Diffusion Testing and Etest on Mueller-Hinton Agar

2006 ◽  
Vol 44 (12) ◽  
pp. 4395-4399 ◽  
Author(s):  
R. Skov ◽  
R. Smyth ◽  
A. R. Larsen ◽  
A. Bolmstrom ◽  
A. Karlsson ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Methicillin Resistance ◽  
Disk Diffusion ◽  
Mueller Hinton ◽  
Disk Diffusion Testing ◽  
Mueller Hinton Agar

scholarly journals Vancomycin intermediate and high level vancomycin resistant Staphylococcus aureus clinical isolates in Osogbo, Nigeria

2011 ◽  
Vol 2 (1) ◽  
pp. 6
Author(s):  
Samuel Sunday Taiwo ◽  
Titilope Bosede Bamigboye ◽  
Osatohanmwen Odaro ◽  
Olusegun Adelowo Adefioye ◽  
Solomon Olufemi Fadiora
Keyword(s):  
Staphylococcus Aureus ◽  
Public Health Problem ◽  
Disk Diffusion ◽  
Major Public Health Problem ◽  
Disk Diffusion Test ◽  
Mueller Hinton ◽  
Mueller Hinton Agar ◽  
Vancomycin Resistant ◽  
High Level ◽  
Broth Dilution

<p>The decreased vancomycin susceptibility and subsequent emergence of vancomycin resistant <em>Staphylococcus aureus </em>(VRSA) strains already multi-resistant to antibiotics is a major public health problem. In 2009, the Clinical and Laboratory Standards Institute (CLSI) altered its guidelines for vancomycin susceptibility testing in <em>S. aureus</em> and recent data suggests the possibility that VRSA may emerge more frequently than previously expected. Against this background, we conducted a study to ascertain the susceptibility status of clinical <em>S. aureus</em> isolates to vancomycin in our environment using vancomycin agar screen, disk diffusion and broth dilution methods. Of the total 49 <em>S. aureus </em>invasive strains isolated, 25 (51.0%) had vancomycin MIC of ≤2µg/ml by the CLSI standard broth dilution method and are classed as vancomycin susceptible; 18 (36.7%) had MIC of 4-8µg/ml (vancomycin intermediate resistant) and 6 (12.2%) had MIC of &gt;256µg/ml (high level vancomycin resistant). Vancomycin agar screen with Mueller-Hinton agar containing 3µg/ml vancomycin (MHA-V3) correctly identified 20 of 25 (80%) vancomycin susceptible isolates; detected all 6 vancomycin resistant isolates and 16 of 18 (88.9%) vancomycin intermediate strains. Similarly, Mueller-Hinton agar containing 6µg/ml vancomycin (MHA-V6) correctly identified 23 of 25 (92%) vancomycin susceptible isolates and all 6 vancomycin resistant isolates but detected 14 (77.8%) of 18 vancomycin intermediate strains. Vancomycin disk diffusion test correctly identified all the 25 vancomycin susceptible <em>S. aureus</em> isolates giving 100% specificity but detected only 1 of 18 (5.6%) vancomycin intermediate and none (0%) of vancomycin resistant isolates. This result shows the occurrence of VISA and high level VRSA isolates in our environment, which contrary to current belief, may indicate widespread dissemination of VRSA. MHA-V3 agar is a useful alternative screening medium for vancomycin non-susceptibility detection in clinical <em>S. aureus</em> isolates but vancomycin disk diffusion is not useful in this regard.</p>

scholarly journals Disk Diffusion Testing for Detection of Methicillin-Resistant Staphylococci: Does Moxalactam Improve upon Cefoxitin?

2016 ◽  
Vol 54 (12) ◽  
pp. 2905-2909 ◽  
Author(s):  
Marie Bonjean ◽  
Elisabeth Hodille ◽  
Oana Dumitrescu ◽  
Céline Dupieux ◽  
Christina Nkoud Mongo ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Operating Characteristic ◽  
Methicillin Resistance ◽  
Inhibition Zone ◽  
Disk Diffusion ◽  
Large Collection ◽  
Coagulase Negative Staphylococci ◽  
Content Type ◽  
High Inoculum ◽  
Disk Diffusion Testing

Disk diffusion testing is widely used to detect methicillin resistance in staphylococci, and cefoxitin is currently considered the best marker formecA-mediated methicillin resistance. In low-inoculum diffusion testing (colony suspension at 106CFU/ml), the addition of moxalactam in combination with cefoxitin has been reported to improve on cefoxitin alone for the detection of methicillin-heteroresistant staphylococci. However, moxalactam is absent from EUCAST and CLSI guidelines, which use high-inoculum diffusion testing (colony suspension at 108CFU/ml), calling into question the potential interest of including moxalactam in their recommendations. The inhibition zone diameters of cefoxitin and moxalactam, alone and in combination, were evaluated for concordance withmecAandmecCpositivity in a large collection of clinicalStaphylococcusisolates (611Staphylococcus aureus,Staphylococcuslugdunensis, andStaphylococcus saprophyticusisolates and 307 coagulase-negative staphylococci other thanS. lugdunensisandS. saprophyticusisolates, of which 22% and 53% weremecA-positive, respectively) and in 25mecC-positiveS. aureusisolates using high-inoculum diffusion testing. Receiver operating characteristic, sensitivity, and specificity analyses indicated that the detection ofmecA- andmecC-positive and negative isolates did not improve with moxalactam, either alone or in combination with cefoxitin, compared to cefoxitin alone. These findings were similar in both theS. aureus/S. lugdunensis/S. saprophyticusgroup and in the coagulase-negative staphylococci group. Our results do not support the use of moxalactam as an additional marker of methicillin resistance when testing with high-inoculum disk diffusion.

scholarly journals Disk Diffusion-Based Methods for Determining Candida parapsilosis Susceptibility to Anidulafungin

2003 ◽  
Vol 47 (9) ◽  
pp. 3018-3020 ◽  
Author(s):  
Zekaver Odabasi ◽  
Victor Paetznick ◽  
Beth P. Goldstein ◽  
John H. Rex ◽  
Luis Ostrosky-Zeichner
Keyword(s):  
Methylene Blue ◽  
Dimethyl Sulfoxide ◽  
Candida Parapsilosis ◽  
Tween 80 ◽  
Disk Diffusion ◽  
Broth Microdilution ◽  
Mueller Hinton ◽  
Mueller Hinton Agar

ABSTRACT Zone diameters for anidulafungin by disk diffusion for 139 isolates of C. parapsilosis were compared with MICs by NCCLS M27-A2 broth microdilution. The comparison was poor unless the disks were prepared by dissolving anidulafungin in 1% dimethyl sulfoxide plus 0.1% Tween 80 and testing on Mueller-Hinton agar flooded with glucose and methylene blue.

scholarly journals Synergy of Daptomycin with Oxacillin and Other β-Lactams against Methicillin-Resistant Staphylococcus aureus

2004 ◽  
Vol 48 (8) ◽  
pp. 2871-2875 ◽  
Author(s):  
Kenneth H. Rand ◽  
Herbert J. Houck
Keyword(s):  
Staphylococcus Aureus ◽  
Bactericidal Activity ◽  
Screening Method ◽  
Methicillin Resistant ◽  
Drug Concentrations ◽  
Mueller Hinton ◽  
Mueller Hinton Agar ◽  
High Level ◽  
Time Kill

ABSTRACT We previously observed marked synergy between daptomycin and both rifampin and ampicillin against vancomycin-resistant enterococci (VRE). Because the synergy between daptomycin and ampicillin was observed for 100% of VRE strains with high-level ampicillin resistance (ampicillin MIC of ≥128 μg/ml), we looked for synergy between daptomycin and other β-lactams against 18 strains of methicillin-resistant Staphylococcus aureus (MRSA) by employing a time-kill method using Mueller-Hinton broth supplemented to 50 mg of Ca2+/liter. All strains were resistant to oxacillin (16 of 18 strains were resistant at drug concentrations of ≥256 μg/ml), and all strains were susceptible to daptomycin (the MIC at which 90% of the tested isolates were inhibited was 1 μg/ml). Daptomycin was tested at concentrations of 2, 1, 0.5, 0.25, 0.125, and 0.0625 μg/ml alone or in combination with oxacillin at a fixed concentration of 32 μg/ml. Synergy was found for all 18 strains with daptomycin at one-half the MIC in combination with 32 μg of oxacillin/ml, and synergy was found for 11 of 18 strains (61%) with daptomycin at one-fourth the MIC or less in combination with oxacillin. At 24 h, the daptomycin-oxacillin combination with daptomycin at one-half the MIC showed bactericidal activity against all 18 strains, and the combination with one-fourth the daptomycin MIC showed bactericidal activity against 9 of 18 strains. We also used a novel screening method to look for synergy between daptomycin and other β-lactams. In this approach, daptomycin was incorporated into Ca2+-supplemented Mueller-Hinton agar at subinhibitory concentrations, and synergy was screened by comparing test antibiotic Kirby-Bauer disks on agar with and without daptomycin. By this method, daptomycin with ampicillin-sulbactam, ticarcillin-clavulanate, or piperacillin-tazobactam showed synergy comparable to or greater than daptomycin with oxacillin. For seven of the eight strains tested, time-kill studies confirmed synergy between daptomycin and ampicillin-sulbactam with ampicillin in the range of 2 to 8 μg/ml. The combination of daptomycin and β-lactams may be useful for the treatment of MRSA infection, but further studies are needed to elucidate the mechanisms and to determine the in vivo efficacy of the combination.

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