Comparison of the Vitek Gram-Positive Susceptibility 106 Card, the MRSA-Screen Latex Agglutination Test, and mecA Analysis for Detecting Oxacillin Resistance in a Geographically Diverse Collection of Clinical Isolates of Coagulase-Negative Staphylococci

Abstract

The Vitek automated susceptibility testing system with a modified gram-positive susceptibility (GPS) 106 card (bioMerieux Vitek, Inc., Hazelwood. Mo.) and a rapid slide latex agglutination test (MRSA-Screen test; Denka Seiken Co., Ltd., Tokyo, Japan) were evaluated for their abilities to detect oxacillin resistance in coagulase-negative staphylococci (CoNS). The reference broth microdilution method and the detection of the mecA gene by PCR ("gold standard" reference result) were used to compare the results obtained with the commercial products. A total of 123 clinical isolates consisting of eight species were selected from U.S. surveillance collections. Among the mecA-positive isolates (95 strains), 30 isolates were initially negative on the MRSA-Screen test read at 3 min. When the agglutination reaction was extended for 10 min, 26 of the 30 isolates became positive. For a different four isolates, the oxacillin MIC was <0.25 g/ml on the Vitek GPS 106 card. Among the mecA-negative isolates (28 strains), for two Staphylococcus warneri, two S. lugdunensis, and two S. saprophyticus strains MICs were >0.5 g/ml by the reference broth microdilution method. Four of these isolates were also categorized as resistant with the Vitek GPS 106 card and two isolates were positive by the MRSA-Screen test. Overall, the MRSA-Screen test, GPS 106 card, and reference broth microdilution method had sensitivities of 95.7 (result at 10 min), 95.7, and 100%, respectively, and specificities of 92.8, 85.7, and 78.5%, respectively. Although the MRSA-Screen test required a slight procedural modification, both commercial methods achieved a sensitivity and specificity at detecting oxacillin resistance in CoNS at a level that was acceptable for clinical laboratory use.

Automated systems in the identification and determination of methicillin resistance among coagulase negative staphylococci

“…In Brazil, a multicenter study showed that methicillin resistance was observed in 87.7% of CoNS isolated from bloodstream infections (Sader et al 1999). The accurate detection of methicillin resistance among CoNS isolates in the clinical laboratory is important to guide therapy and to promote the correct use of glycopeptides (Hussain et al 1998, Yamazumi et al 2001.…”

“…In Brazil, a multicenter study showed that methicillin resistance was observed in 87.7% of CoNS isolated from bloodstream infections (Sader et al 1999). The accurate detection of methicillin resistance among CoNS isolates in the clinical laboratory is important to guide therapy and to promote the correct use of glycopeptides (Hussain et al 1998, Yamazumi et al 2001.This work was performed to evaluate the accuracy of two automated systems in the identification of species and determination of methicillin resistance, considering as gold standard the conventional biochemical tests and the characterization of mecA gene by polymerase chain reaction (PCR), respectively. …”

A Study on Antimicrobial Sensitivity and Cost Analysis of Antibiotics in Pediatric Unit at a Tertiary Care Hospital.

“…A second function of antibiotic susceptibility tests is to monitor the effectiveness of therapy is compromised by the potential development of tolerance or resistance to that component [1][2][3][4][5]. It is true for all agents used in the treatment of bacterial, fungal, parasitic, and viral infections.…”

Molecular diagnostics and genotyping of MRSA: an update

“…These methods have been superseded by the introduction of selective agar cultivation methods and latex agglutination tests for the specific detection of the product of the mecA gene, penicillin-binding protein 2a. Most of these tests have been evaluated in different studies [13][14][15][16][17][18][19][20][21][22][23][24][25][26]. Sensitivity and specificity for agar cultivation ranged from 40 to 98% and 80 to 100%, respectively.…”