Search

The EVIGENE MRSA Detection Kit was evaluated on coagulase-negative staphylococci (CoNS) from agar plates and on staphylococci directly from positive spiked blood cultures. For the CoNS study, a total of 242 isolates were tested, and of these 237 gave valid test results. For the 237 valid tests, all gave correct mecA classification. For the blood culture procedure, a collection of 51 mecA-positive Staphylococcus aureus, 21 mecA-negative S. aureus, 31 mecA-positive CoNS and 28 mecA-negative CoNS were used for the simulated blood cultures. For the S. aureus strains, all gave valid test results and correct mecA classification. One of the MRSA isolates gave a very faint nuc signal, and another four isolates gave results close to the cut-off of the kit; however, these were still clearly positive when read by the naked eye. For the CoNS isolates, 51 of the 59 strains gave valid results. All of these 51 strains gave correct mecA status. Thus the EVIGENE MRSA Detection Kit can provide fast and accurate determination of methicillin resistance in CoNS. This preliminary study of the blood culture procedure indicates that it is possible to achieve determination of methicillin resistance in staphylococci 8 h after positivity of the blood culture, making same-day detection of methicillin resistance possible.

We were delighted to see the recent article by Felten et al. on the detection of low-level methicillin-resistant Staphylococcus aureus (MRSA) (1). The study is, to our knowledge, the first to specifically test the MRSA-screen test on low-level MRSA strains. However, Felten et al. concluded that the MRSA-screen test is the best commercially available test for distinguishing very-low-level class 1 MRSA from methicillin-susceptible S. aureus. We would therefore like to point the authors' attention to the EVIGENE MRSA Detection Kit (Statens Serum Institut, Copenhagen, Denmark), which is also a commercially available product for detecting methicillin resistance in staphylococci. This kit is a DNA probe-based hybridization assay for detecting the mecA gene in staphylococci. Each test also detects the nuc gene for differentiating between S. aureus and coagulase-negative staphylococci as well as internal positive and negative controls. The kit uses no amplification steps; thus, the issues of contamination applicable to PCR do not apply to this kit. The kit result, which is obtained in 3.5 h, is visually read as yellow or blank. We have evaluated the EVIGENE MRSA Detection Kit with 275 S. aureus isolates, including 18 borderline-resistant strains; the results showed both the sensitivity and the specificity to be 100% for the entire collection (3). For coagulase-negative staphylococci, 242 strains have been evaluated (128 mecA-positive and 114-mecA negative strains). Of these 242 strains, 5 (2%) produced a positive control signal below the cutoff defined for the kit, thus rendering the five tests invalid. For the remaining 239 strains, the sensitivity and specificity were as for S. aureus: both 100% (2).

The functionally uncharacterised N-terminal of translation initiation factor IF2 has been found to be extremely variable when comparing different bacterial species. In order to study the intraspecies variability of IF2 the 2670 basepairs nucleotide sequence of the infB gene (encoding IF2) was determined in 10 clinical isolates of E. coli. The N-terminal domains (I, II and III) were completely conserved indicating a specific function of this region of IF2. Only one polymorphic position was found in the deduced 890 amino acid sequence. This Gln/Gly490 is located within the central GTP/GDP-binding domain IV of IF2. The results are further evidence that IF2 from E. coli has reached a highly defined level of structural and functional development.