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 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 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. 

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