Abstract
Background
Faster respiratory pathogen detection and antibiotic resistance identification is particularly important in critical care due to the severity of illness, significant prior antibiotic exposure and infection control implications.
The Unyvero P55 Pneumonia Cartridge (Curetis AG) is a new molecular assay which can detect 21 respiratory pathogen species and genera alongside 17 key antibiotic resistance genes. The test has minimal hands-on time and takes approximately 5 hours.
Aim
To compare the performance of the Unyvero P55 Pneumonia Cartridge (Curetis AG) with standard culture-based methods and our in-house bacterial molecular diagnostic assays, on bronchoalveolar lavage fluids (BALs) from critical care patients.
Methods
Specimens: 74 BAL fluids from patients admitted to the Royal Infirmary Edinburgh ICU between 01/01/13–30/09/15
Routine testing: Standard microbiological culture, biochemical and/or MALDI-TOF (Bruker) identification and automated antibiotic sensitivity testing (VITEK2, bioMérieux). In-house respiratory viral and atypical bacteria real-time multiplex PCR panel. Residual specimens were diluted approximately 1/10 in viral transport medium and stored at
-80°C for retrospective anonymised molecular testing.
Unyvero P55 pneumonia assay: 180µl specimen was added to the sample tube and placed into the lysator for 30 minutes. The sample tube was placed into the test cartridge and loaded into the analyser. Two specimens were processed simultaneously. Results were available in 4 hours.
In-house multiplex real-time PCR: 200 µl specimen was treated with lysozyme at 37°C for 1 hour then proteinase K at 56°C for 1 hour, followed by extraction with the nucliSENS easyMAG (bioMérieux). Extracts were tested with fast real-time qPCR multiplex assays for 8 respiratory bacteria [1]
Results
At least one bacterial species was isolated by routine culture in 48 (65%) cases.
Unyvero P55 and in-house PCR assay results were concordant with bacterial culture in 54% and 60% instances respectively.
Additional organisms were detected by Unyvero P55 and in-house PCR assay in 20% and 19% instances respectively.
Cultured bacteria were not detected by the Unyvero P55 and in-house PCR assay in 26% and 22% instances respectively.
Antibiotic resistance genes were detected in 26 instances by the Unyvero assay, these were in-keeping with phenotypic testing in 8/15 (53%) instances where the antibiotic sensitivity was known for a cultured isolate. In the remaining cases, an organism did not grow so phenotypic testing could not be carried out, or the relevant antibiotic was not in the battery tested.
Conclusions
Molecular testing identified a number of respiratory pathogens in this patient cohort that were not grown in culture. In their current configuration however, molecular tests are likely only to have benefit as additional tests in the critical care setting.
Faster respiratory pathogen detection and antibiotic resistance identification is particularly important in critical care due to the severity of illness, significant prior antibiotic exposure and infection control implications.
The Unyvero P55 Pneumonia Cartridge (Curetis AG) is a new molecular assay which can detect 21 respiratory pathogen species and genera alongside 17 key antibiotic resistance genes. The test has minimal hands-on time and takes approximately 5 hours.
Aim
To compare the performance of the Unyvero P55 Pneumonia Cartridge (Curetis AG) with standard culture-based methods and our in-house bacterial molecular diagnostic assays, on bronchoalveolar lavage fluids (BALs) from critical care patients.
Methods
Specimens: 74 BAL fluids from patients admitted to the Royal Infirmary Edinburgh ICU between 01/01/13–30/09/15
Routine testing: Standard microbiological culture, biochemical and/or MALDI-TOF (Bruker) identification and automated antibiotic sensitivity testing (VITEK2, bioMérieux). In-house respiratory viral and atypical bacteria real-time multiplex PCR panel. Residual specimens were diluted approximately 1/10 in viral transport medium and stored at
-80°C for retrospective anonymised molecular testing.
Unyvero P55 pneumonia assay: 180µl specimen was added to the sample tube and placed into the lysator for 30 minutes. The sample tube was placed into the test cartridge and loaded into the analyser. Two specimens were processed simultaneously. Results were available in 4 hours.
In-house multiplex real-time PCR: 200 µl specimen was treated with lysozyme at 37°C for 1 hour then proteinase K at 56°C for 1 hour, followed by extraction with the nucliSENS easyMAG (bioMérieux). Extracts were tested with fast real-time qPCR multiplex assays for 8 respiratory bacteria [1]
Results
At least one bacterial species was isolated by routine culture in 48 (65%) cases.
Unyvero P55 and in-house PCR assay results were concordant with bacterial culture in 54% and 60% instances respectively.
Additional organisms were detected by Unyvero P55 and in-house PCR assay in 20% and 19% instances respectively.
Cultured bacteria were not detected by the Unyvero P55 and in-house PCR assay in 26% and 22% instances respectively.
Antibiotic resistance genes were detected in 26 instances by the Unyvero assay, these were in-keeping with phenotypic testing in 8/15 (53%) instances where the antibiotic sensitivity was known for a cultured isolate. In the remaining cases, an organism did not grow so phenotypic testing could not be carried out, or the relevant antibiotic was not in the battery tested.
Conclusions
Molecular testing identified a number of respiratory pathogens in this patient cohort that were not grown in culture. In their current configuration however, molecular tests are likely only to have benefit as additional tests in the critical care setting.
| Original language | English |
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| Publication status | Published - 6 Nov 2016 |