N. Brenwald

Evaluation of Diagnostic Tests for Clostridium difficile Infection

ABSTRACT We evaluated toxigenic Clostridium difficile detection by a lateral flow assay for antigen and toxin, an enzyme immunoassay, and two commercial PCR methods. Compared to the cell cytotoxicity neutralization assay and toxigenic culture, both toxin detection methods lacked sensitivity. PCR following combined antigen and toxin detection provided the most useful diagnostic information.

Molecular and Kinetic Comparison of the Novel Extended-Spectrum β-Lactamases CTX-M-25 and CTX-M-26

ABSTRACT CTX-M-25 is a novel extended-spectrum β-lactamase isolated from a single Canadian Escherichia coli isolate. Susceptibility testing demonstrated that this enzyme confers resistance to both cefotaxime and ceftazidime, but the level of resistance was reduced with the addition of β-lactamase inhibitors. The blaCTX-M-25 gene was detected on a 111-kb plasmid. It is a member of the CTX-M-8 group and has the closest amino acid identity (99%; three amino acid substitutions) with CTX-M-26. The blaCTX-M-26 gene was detected on a 100-kb plasmid isolated from a Klebsiella pneumoniae strain from the United Kingdom, and plasmid profiling revealed that it showed some homology to the blaCTX-M-25-harboring plasmid. Both CTX-M genes were located downstream of ISEcp1, although the copy upstream of blaCTX-M-25 was disrupted by IS50-A. Comparative kinetic studies of recombinant CTX-M-25 and CTX-M-26 enzymes showed that CTX-M-25 has a higher level of ceftazidime hydrolysis (kcat values, 33 and 0.005 s−1 for CTX-M-25 and CTX-M-26, respectively).

Rapid diagnosis of influenza: An evaluation of two commercially available RT-PCR assays

OBJECTIVE To evaluate the sensitivity and specificity of influenza virus detection by two commercial reverse transcriptase PCR methods compared with a reference real-time PCR. METHODS 122 clinical specimens were tested on Xpert(®) Flu and RealStar(®) Influenza Screen & Type. A reference real-time RT-PCR, at a specialist laboratory was chosen as the gold standard for comparison. RESULTS RealStar(®) Influenza Screen & Type had higher sensitivity for influenza A and influenza B respectively (92.3% and 88.2%) when compared to Xpert(®) Flu (78.8% and 76.5%). Both tests had excellent specificity. CONCLUSIONS The simplicity and speed of the Xpert(®) Flu system could allow it to be used in the near-patient setting; however in circumstances where excluding a diagnosis of influenza may be critical, negative specimens may need to be repeated using a more sensitive assay.