Abstract
We describe two false-negative results in the detection of meticillin-resistant Staphylococcus aureus (MRSA) of sequence type 398 and spa type t011 using the Cepheid Xpert MRSA NxG assay. The isolates were recovered in late February and early March 2021 from two patients in different hospitals in the northern Netherlands. Variations between the two isolate genomes indicate that this MRSA strain might have been spreading for some time and could have disseminated to other regions of the Netherlands and other European countries.
Highlights
We describe two false-negative results in the detection of meticillin-resistant Staphylococcus aureus (MRSA) of sequence type 398 and spa type t011 using the Cepheid Xpert MRSA NxG assay
The minimum inhibitory concentration (MIC) values of 22 antibiotics were determined by Etest and the results were interpreted according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines [1]
The gene encoding a putative Ig domaincontaining protein differed between isolates by a number of 267 nt repeats, and at least four transpositions of IS256 had occurred. These alterations suggest that the ST398 strain bearing the SCC-like element between orfX and SCCmec IVa has circulated for a longer time in the northern Netherlands, as it had already undergone microevolution. We alert that this ‘false-negative’ MRSA strain could have already spread to other regions of the Netherlands and to other neighbouring countries
Summary
We describe two false-negative results in the detection of meticillin-resistant Staphylococcus aureus (MRSA) of sequence type 398 and spa type t011 using the Cepheid Xpert MRSA NxG assay. The second MRSA isolate (designated UMCG578) was recovered from a sinus pus sample from a male patient in his early 70s with chronic purulent sinusitis at the beginning of March 2021 in a hospital in Groningen, the Netherlands. The isolates were identified as S. aureus by matrixassisted laser desorption/ionization–time of flight mass spectrometry (MALDI-TOF MS) (Bruker Daltonics, Billerica, Massachusetts, US). In both cases, the Xpert MRSA NxG assay was performed on pure colonies cultured and taken for testing from blood agar plates.
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