Rapid detection of meticillin-resistant Staphylococcus aureus bacteraemia using combined three-hour short-incubation matrix-assisted laser desorption/ionization time-of-flight MS identification and Alere Culture Colony PBP2a detection test

Abstract

Meticillin-resistant Staphylococcus aureus (MRSA) bloodstream infection is responsible for significant morbidity, with mortality rates as high as 60 % if not treated appropriately. We describe a rapid method to detect MRSA in blood cultures using a combined three-hour shortincubation BRUKER matrix-assisted laser desorption/ionization time-of-flight MS BioTyper protocol and a qualitative immunochromatographic assay, the Alere Culture Colony Test PBP2a detection test. We compared this combined method with a molecular method detecting the nuc and mecA genes currently performed in our laboratory. One hundred and seventeen S. aureus blood cultures were tested of which 35 were MRSA and 82 were meticillin-sensitive S. aureus (MSSA). The rapid combined test correctly identified 100 % (82/82) of the MSSA and 85.7 % (30/35) of the MRSA after 3 h. There were five false negative results where the isolates were correctly identified as S. aureus, but PBP2a was not detected by the Culture Colony Test. The combined method has a sensitivity of 87.5 %, specificity of 100 %, a positive predictive value of 100 % and a negative predictive value of 94.3 % with the prevalence of MRSA in our S. aureus blood cultures. The combined rapid method offers a significant benefit to early detection of MRSA in positive blood cultures. INTRODUCTIONStaphylococcus aureus is a clinically important pathogen that causes a wide variety of diseases and accounts for more than 50 % of nosocomial infections in intensive care units (NNIS System, 1999). S. aureus bacteraemia (SAB) is an infection of the blood associated with a mortality rate in excess of 20 % (Klevens et al., 2006;Lowy, 1998) while meticillin-resistant S. aureus (MRSA) bacteraemia is associated with mortality rates as high as 60 % (Cluff et al., 1968;Julander, 1985).Until the 1980s, MRSA was almost exclusively limited to nosocomial settings and community strains were largely considered meticillin susceptible (Thompson et al., 1982). However, a decade later there was a measurable increase in community-acquired meticillin-resistant S. aureus (CA-MRSA) infections in people with no known risk factors and an overall increase in CA-MRSA infections in general (Layton et al., 1995). In Canada, there was a 17-fold increase in CA-MRSA infections from 1995 to (Simor et al., 2010. In London, Ontario, the all-cause mortality Abbreviations: BAP, blood agar plate; CA-MRSA, community-acquired meticillin-resistant Staphylococcus aureus; CCT, Alere PBP2a Culture Colony Test; CI, confidence interval; MALDI-ToF, matrix-assisted laser desorption/ionization time-of-flight; MRSA, meticillin-resistant S. aureus; MSSA, meticillin-sensitive S. aureus; OR, odds ratio; SAB, S. aureus bacteraemia; SIMI, short-incubation MALDI-ToF MS identification. Cavassini et al., 1999). Some of these methods depend on well-defined colony morphology and can be very time and labour intensive. To the best of our knowledge, a combined rapid, 3 h procedure, using a shortincubationThe objective of this study was to determine the ability t...

An Automated Sample Preparation Instrument to Accelerate Positive Blood Cultures Microbial Identification by MALDI-TOF Mass Spectrometry (Vitek®MS)

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Molecular Detection of Methicillin-Resistant Staphylococcus aureus by Non-Protein Coding RNA-Mediated Monoplex Polymerase Chain Reaction

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The management and outcomes of Staphylococcus aureus bacteraemia at a South African referral hospital: A prospective observational study

“…This delay in definitive treatment reflects a delay in the identification and susceptibility profiling of S. aureus from positive blood cultures. The use of novel tools to identify S. aureus directly from blood cultures, such as fluorescence in situ hybridization (FISH), PCR, immunochromatographic assays for PBP2a, and other methods, has been shown to quickly and reliably identify S. aureus (Buchan et al, 2015;Delport et al, 2016;Felsenstein et al, 2016;Oliveira et al, 2002;Thomas et al, 2007). The use of such tools in the present setting could be valuable in encouraging prompt antimicrobial treatment of SAB and an improvement in patient outcomes, although cost may be an important limiting factor.…”