scholarly journals Evaluation of Oxacillin and Cefoxitin Disk Diffusion and Microbroth Dilution Methods for Detecting mecA-Mediated β-Lactam Resistance in Contemporary Staphylococcus epidermidis Isolates

2019 ◽  
Vol 57 (12) ◽  
Author(s):  
Samia N. Naccache ◽  
Katrina Callan ◽  
Carey-Ann D. Burnham ◽  
Meghan A. Wallace ◽  
Lars F. Westblade ◽  
...  
Keyword(s):  
Sensitivity And Specificity ◽  
Staphylococcus Epidermidis ◽  
Latex Agglutination ◽  
Disk Diffusion ◽  
Content Type ◽  
Test Kit ◽  
Thermo Fisher Scientific ◽  
Microbroth Dilution ◽  
Cefoxitin Disk ◽  
Cefoxitin Disk Diffusion

ABSTRACT Methicillin (β-lactam) resistance in Staphylococcus epidermidis is mediated by the mecA gene, with resistance reported to be as high as 90%. The goal of this study was to evaluate oxacillin and cefoxitin disk diffusion (DD) and broth microdilution (BMD) methods for the detection of mecA-mediated β-lactam resistance in 100 human isolates of S. epidermidis (48 mecA-positive isolates and 52 mecA negative isolates). Oxacillin DD tests using the Clinical and Laboratory Standards Institute (CLSI) M100-S28 breakpoints for S. pseudintermedius/S. schleiferi accurately differentiated mecA-positive and -negative S. epidermidis isolates, with categorical agreement (CA) of 100% and no very major errors (VMEs) or major errors (MEs) identified. Likewise, oxacillin BMD and cefoxitin DD tests using the coagulase-negative Staphylococcus species (CoNS) breakpoints were highly reliable for detecting mecA-mediated β-lactam resistance in S. epidermidis isolates. For cefoxitin DD and BMD results interpreted using S. aureus/S. lugdunensis breakpoints, the CA was 97.6% and 96.2%, respectively. There were 4.9% VMEs for cefoxitin DD with 0% MEs, and 3.6% VMEs and 3.9% MEs for cefoxitin BMD. Oxacillin BMD using S. aureus/S. lugdunensis breakpoints yielded the highest VMEs at 17.4% and 90% CA. Our findings demonstrate that oxacillin DD tests using the CLSI M100-S28 breakpoints for S. pseudintermedius/S. schleiferi and oxacillin BMD and cefoxitin DD tests using the CoNS breakpoints reliably identified mecA-mediated β-lactam resistance in S. epidermidis. Using mecA PCR as the gold standard, the PBP2a SA culture colony test (Abbott Diagnostics) exhibited 100% sensitivity and specificity whereas 2 false negatives were identified using the PBP2ʹ latex agglutination test kit (Thermo Fisher Scientific) with sensitivity and specificity of 95.8% and 100%, respectively.

scholarly journals Evaluation of different phenotypic methods for the detection of methicillin resistant Staphylococcus aureus and antimicrobial susceptibility pattern of MRSA

2017 ◽  
Vol 4 (9) ◽  
pp. 3297 ◽  
Author(s):  
Sheetal Sharma ◽  
Preeti Srivastava ◽  
Anjali Kulshrestha ◽  
Ameer Abbas
Keyword(s):  
Staphylococcus Aureus ◽  
Sensitivity And Specificity ◽  
Antimicrobial Susceptibility ◽  
Methicillin Resistant Staphylococcus Aureus ◽  
Disk Diffusion ◽  
Diffusion Method ◽  
Disk Diffusion Method ◽  
Phenotypic Methods ◽  
Cefoxitin Disk ◽  
Cefoxitin Disk Diffusion

Background: Rapid and accurate detection of methicillin resistant Staphylococcus aureus (MRSA) is an important role of clinical microbiology laboratories to avoid treatment failure. The aim of this study was to compare conventional methods against the cefoxitin disc diffusion method to determine the best phenotypic method. Methods: Study was carried out in the Department of Microbiology, National Institute of Medical Sciences & Research, Jaipur (India), between July 2016 – December 2016. The methods included were Oxacillin E-test MIC, Oxacillin screen agar, Oxacillin disk diffusion, Cefoxitin disk diffusion and CHROMagar- MRSA methods. Antimicrobial susceptibility performed as per CLSI guidelines.Results: Out of 142 isolates of S. aureus, fifty three (37.32%) strains of MRSA were isolated from clinical specimen. E-MIC test was selected as gold standard method. The sensitivity and specificity of Oxacillin screen agar and CHROMagar-MRSA were same 98.07% and 97.80%, respectively. The sensitivity and specificity of oxacillin disk diffusion were 94.23% and 98.89%. Fifty three strains of S. aureus were MRSA by cefoxitin disk diffusion method and Oxacillin Ezy MIC test. The sensitivity and specificity of cefoxitin disk diffusion method and Oxacillin Ezy MIC method was 100% and 100% respectively. All isolates including MRSA were susceptible to Vancomycin and Linezolid. Conclusions: All phenotypic methods had high sensitivity and specificity for detection of MRSA. However, cefoxitin disk diffusion method in comparison to other methods had higher sensitivity and specificity. 

scholarly journals Multicenter Evaluation of a Modified Cefoxitin Disk Diffusion Method and PBP2a Testing To PredictmecA-Mediated Oxacillin Resistance in Atypical Staphylococcus aureus

2016 ◽  
Vol 55 (2) ◽  
pp. 485-494 ◽  
Author(s):  
Shelley A. Miller ◽  
James Karichu ◽  
Peggy Kohner ◽  
Nicolynn Cole ◽  
Janet A. Hindler ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Clinical Laboratory ◽  
Disk Diffusion ◽  
Diffusion Method ◽  
Disk Diffusion Method ◽  
Content Type ◽  
Oxacillin Resistance ◽  
Mueller Hinton ◽  
Cefoxitin Disk ◽  
Cefoxitin Disk Diffusion

ABSTRACTPhenotypic variants ofStaphylococcus aureusthat display small colonies, reduced pigmentation, and decreased hemolysis and/or coagulase activity are periodically isolated by the clinical laboratory. Antimicrobial susceptibility testing (AST) of these isolates is complicated, because many do not grow on routine AST media, including Mueller-Hinton agar (MHA) and cation-adjusted Mueller-Hinton broth. This multicenter study evaluated cefoxitin disk diffusion for 37 atypicalS. aureusisolates (156 readings) with MHA supplemented with 5% sheep's blood (BMHA), usingmecAPCR as the reference standard. The correlation of two commercial PBP2a assays withmecAPCR was also assessed. Ten isolates were negative and 27 positive formecA. No major errors for cefoxitin were observed, but 19.5% very major errors (VMEs) were observed at 24 h of incubation, and 17.2% VMEs were observed at 48 h. The proportions of VMEs ranged from 14.7 to 23.0% at 24 h, and from 13.3 to 17.6% at 48 h, across three testing laboratories. PBP2a tests were performed from growth on BMHA and blood agar plates (BAP), with and without cefoxitin disk induction. The Alere PBP2a SA culture colony test sensitivities formecAwere 90.0% with uninduced growth and 97.4% with induced growth from BMHA. On BAP, sensitivity was 96.0% with induced growth. The sensitivities of the Oxoid PBP2′ latex agglutination test were 85.7% with uninduced growth and 93.9% with induced growth from BMHA and 95.9% with induced growth on BAP. On the basis of these data, we recommend that laboratories perform onlymecAPCR and/or PBP2a tests when requested to perform AST on atypical isolates ofS. aureus.

scholarly journals Comparison of Different Phenotypic Approaches To Screen and Detect mecC-Harboring Methicillin-Resistant Staphylococcus aureus

2017 ◽  
Vol 56 (1) ◽  
Author(s):  
André Kriegeskorte ◽  
Evgeny A. Idelevich ◽  
Andreas Schlattmann ◽  
Franziska Layer ◽  
Birgit Strommenger ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Susceptibility Testing ◽  
Disk Diffusion ◽  
Broth Microdilution ◽  
Disk Diffusion Test ◽  
Methicillin Resistant ◽  
Content Type ◽  
Vitek 2 ◽  
Cefoxitin Disk ◽  
Cefoxitin Disk Diffusion

ABSTRACT Similar to mecA, mecC confers resistance against beta-lactams, leading to the phenotype of methicillin-resistant Staphylococcus aureus (MRSA). However, mecC-harboring MRSA strains pose special difficulties in their detection. The aim of this study was to assess and compare different phenotypic systems for screening, identification, and susceptibility testing of mecC-positive MRSA isolates. A well-characterized collection of mecC-positive S. aureus isolates (n = 111) was used for evaluation. Routinely used approaches were studied to determine their suitability to correctly identify mecC-harboring MRSA, including three (semi)automated antimicrobial susceptibility testing (AST) systems and five selective chromogenic agar plates. Additionally, a cefoxitin disk diffusion test and an oxacillin broth microdilution assay were examined. All mecC-harboring MRSA isolates were able to grow on all chromogenic MRSA screening plates tested. Detection of these isolates in AST systems based on cefoxitin and/or oxacillin testing yielded overall positive agreements with the mecC genotype of 97.3% (MicroScan WalkAway; Siemens), 91.9% (Vitek 2; bioMérieux), and 64.9% (Phoenix, BD). The phenotypic resistance pattern most frequently observed by AST devices was “cefoxitin resistance/oxacillin susceptibility,” ranging from 54.1% (Phoenix) and 83.8% (Vitek 2) to 92.8% (WalkAway). The cefoxitin disk diffusion and oxacillin broth microdilution assays categorized 100% and 61.3% of isolates to be MRSA, respectively. The chromogenic media tested confirmed their suitability to reliably screen for mecC-harboring MRSA. The AST systems showed false-negative results with varying numbers, misidentifying mecC-harboring MRSA as methicillin-susceptible S. aureus. This study underlines cefoxitin's status as the superior surrogate mecC-positive MRSA marker.

scholarly journals Evaluation of Oxacillin and Cefoxitin Disk Diffusion and MIC Breakpoints Established by the Clinical and Laboratory Standards Institute for Detection of mecA-Mediated Oxacillin Resistance in Staphylococcus schleiferi

2017 ◽  
Vol 56 (2) ◽  
Author(s):  
H. K. Huse ◽  
S. A. Miller ◽  
S. Chandrasekaran ◽  
J. A. Hindler ◽  
S. D. Lawhon ◽  
...  
Keyword(s):  
Opportunistic Infections ◽  
Performance Standards ◽  
Inhibition Zone ◽  
Disk Diffusion ◽  
Testing Methods ◽  
Coagulase Negative Staphylococci ◽  
Content Type ◽  
Oxacillin Resistance ◽  
Cefoxitin Disk ◽  
Cefoxitin Disk Diffusion

ABSTRACTStaphylococcus schleiferiis a beta-hemolytic, coagulase-variable colonizer of small animals that can cause opportunistic infections in humans. In veterinary isolates, the rate ofmecA-mediated oxacillin resistance is significant, with reported resistance rates of >39%. The goal of this study was to evaluate oxacillin and cefoxitin disk diffusion (DD) and MIC breakpoints for detection ofmecA-mediated oxacillin resistance in 52 human and 38 veterinary isolates ofS. schleiferi. Isolates were tested on multiple brands of commercial media and according to Clinical and Laboratory Standards Institute (CLSI) methods. Zone diameters and MIC values were interpreted using CLSI breakpoints (CLSI,Performance Standards for Antimicrobial Susceptibility Testing. M100-S27, 2017) forStaphylococcus aureus/Staphylococcus lugdunensis, coagulase-negative staphylococci (CoNS), andStaphylococcus pseudintermedius. Results were compared to those ofmecAPCR. Twenty-nine of 90 (32%) isolates weremecApositive. Oxacillin inhibition zone sizes and MICs interpreted byS. pseudintermediusbreakpoints reliably differentiatedmecA-positive andmecA-negative isolates, with a categorical agreement (CA) of 100% and no very major errors (VMEs) or major errors (MEs) for all media. For cefoxitin DD results interpreted usingS. aureus/S. lugdunensisand CoNS breakpoints, CA values were 85% and 75%, respectively, and there were 72% and 64% VMEs, respectively, and 0 MEs. For cefoxitin MICs interpreted usingS. aureus/S. lugdunensisbreakpoints, CA was 81%, and there were 60% VMEs and no MEs. Our data demonstrate that oxacillin DD or MIC testing methods using the currentS. pseudintermediusbreakpoints reliably identifymecA-mediated oxacillin resistance inS. schleiferi, while cefoxitin DD and MIC testing methods perform poorly.

scholarly journals Effects of Pretreating Serum Samples on the Performance of a Latex Agglutination Test for Serodiagnosis of Paracoccidioidomycosis

2011 ◽  
Vol 19 (3) ◽  
pp. 386-390 ◽  
Author(s):  
Fabíola Silveira-Gomes ◽  
Silvia Helena Marques-da-Silva
Keyword(s):  
Sensitivity And Specificity ◽  
Bacterial Infections ◽  
Paracoccidioides Brasiliensis ◽  
Latex Agglutination ◽  
Agglutination Test ◽  
Latex Agglutination Test ◽  
Serum Samples ◽  
Content Type ◽  
Human Sera ◽  
Normal Human

ABSTRACTParacoccidioidomycosis (PCM) is a fungal disease caused byParacoccidioides brasiliensis, and Brazil is one of the principal countries where it is endemic. Diagnosis is based on the observation of buddingP. brasiliensisyeast in clinical specimens from patients; however, the sensitivity of the visualization of fungi is low, indicating that serological tests are used for early diagnosis. The double-immunodiffusion test (ID) is the “gold standard” test for serology in PCM, although the execution of this test requires the availability of laboratorial infrastructure. We report the improved performance of a latex agglutination test (LAT) by pretreating 30 serum samples from PCM patients and 71 controls (histoplasmosis and aspergillosis patients, patients with bacterial infections, and normal human sera) with a dilution buffer incubated at 37°C for 30 min. The sensitivity and specificity of the LAT test in the nonpretreated samples were 73% and 79%, respectively. However, when samples were pretreated, the sensitivity and specificity of the test increased to 90%. In this study, we did not observe cross-reactivity with histoplasmosis patient sera, but some reactions to sera from patients with aspergillosis and bacterial infections were noted. Normal human sera were not reactive in our tests. These results indicate the need for the elimination of heterologous reactions so that we can adequately use this method for screening cases of PCM.

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