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 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 Evaluation of cefoxitin disk diffusion breakpoint for detection of methicillin resistance in Staphylococcus pseudintermedius isolates from dogs

2012 ◽  
Vol 24 (5) ◽  
pp. 964-967 ◽  
Author(s):  
David A. Bemis ◽  
Rebekah D. Jones ◽  
Ricardo Videla ◽  
Stephen A. Kania
Keyword(s):  
Methicillin Resistance ◽  
Screening Method ◽  
Inhibition Zone ◽  
Disk Diffusion ◽  
Coagulase Negative Staphylococci ◽  
Staphylococcus Pseudintermedius ◽  
Growth Inhibition Zone ◽  
Disk Method ◽  
Cefoxitin Disk ◽  
Cefoxitin Disk Diffusion

Cefoxitin disk diffusion susceptibility testing is a recommended screening method for the detection of methicillin resistance in human isolates of Staphylococcus aureus and coagulase-negative staphylococci. A retrospective analysis of 1,146 clinical isolates of Staphylococcus pseudintermedius from dogs was conducted to determine if screening by the cefoxitin disk method can be similarly useful with S. pseudintermedius. The distribution of cefoxitin growth inhibition zone diameters within this collection was bimodal and correlated well with the results of methicillin resistance gene ( mecA) detection by polymerase chain reaction. Of the isolates, 5% had discordant results and, when retested, 84% of these were in agreement. While a greater diversity of isolates and interlaboratory comparisons must be tested, the current study suggests that an epidemiological breakpoint (of approximately ≤30 mm = resistant; ≥31 = susceptible) can be established to predict methicillin resistance in S. pseudintermedius.

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 Current status of oxacillin-susceptible mecA-positive Staphylococcus aureus infection in Shanghai, China: A multicenter study

2019 ◽  
Author(s):  
Junlan Liu ◽  
Tianming Li ◽  
Ni Zhong ◽  
Xing Wang ◽  
Jie Jiang ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Multicenter Study ◽  
Multidrug Resistant ◽  
Disk Diffusion ◽  
Current Status ◽  
Oxacillin Resistance ◽  
Important Challenge ◽  
Underlying Mechanisms ◽  
Cefoxitin Disk ◽  
Cefoxitin Disk Diffusion

Abstract The worldwide reported oxacillin-susceptible mecA -positive Staphylococcus aureus (OS-MRSA) represents a distinctly important challenge to detection and treatment of MRSA, but finite data on current status of OS-MRSA infection in Chinese hospitals are available. The present multicenter study carried out a battery of phenotypic susceptibility tests as well as diagnostic tests (PBP2a detection, mecA , and mecC PCR) for a collection of 956 clinical S. aureus isolates from 10 hospitals in Shanghai, molecular typing was performed for all identified OS-MRSA strains. OS-MRSA represented 1.8% (17/956) of total isolates and were commonly borderline oxacillin-susceptible (Oxacillin-MIC of 1 or 2 mg/L). 10 of 17 OS-MRSA were ST59 lineages, followed by ST965 (3/17). Unlike oxacillin-resistant MRSA that commonly exhibit a multidrug resistant (MDR) phenotype, OS-MRSA were less likely to be MDR and displayed MIC pattern remarkably differential from OR-MRSA. OS-MRSA showed oxacillin-inducible oxacillin resistance and the majority of them (15/17) were cefoxitin-resistant by cefoxitin disk diffusion. S. aureus with borderline susceptible oxacillin MICs (1 or 2 mg/L) should be confirmed by cefoxitin disk diffusion in clinical practice, whereas susceptible isolates reclassified by cefoxitin disk diffusion should still be subjected to PBP2a testing and (or) mecA (mecC) PCR. The presented study has characterized phenotypically and molecularly an atypical type of MRSA showing cryptic but inducible resistance to oxacillin, but its underlying mechanisms warrant further elucidation.

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 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 Is a New Standard Needed for Diffusion Methods forIn VitroSusceptibility Testing of Fosfomycin against Pseudomonas aeruginosa?

2015 ◽  
Vol 60 (2) ◽  
pp. 1158-1161 ◽  
Author(s):  
María Díez-Aguilar ◽  
Laura Martínez-García ◽  
Rafael Cantón ◽  
María Isabel Morosini
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Reference Method ◽  
Inhibition Zone ◽  
Clinical Isolates ◽  
Disk Diffusion ◽  
Content Type ◽  
Agar Dilution

ABSTRACTWe analyzed fosfomycin susceptibility results inPseudomonas aeruginosaclinical isolates obtained by MIC gradient strips and disk diffusion methods using two different inocula, 108and 106CFU/ml, and compared them to the agar dilution reference method. Essential and categorical agreements were 93.6% and 95%, respectively, for the 106CFU/ml alternative inoculum, and they were 67.6% and 78.2%, respectively, for the standard inoculum (108CFU/ml). The use of the 106CFU/ml inoculum improves the agreement values and inhibition zone readings.

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