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Evaluation of an acromopeptidase based extraction method and use of the Rotor-Gene to improve the BD GeneOhm IDI MRSA assay

Abstract number: P1997

Ling C., Vanstone G., Hopkins S., James E., Smith R., Williams K., McDonald I., McHugh T., Rattenbury S., Kibbler C.

Objectives: The IDI MRSA assay was first implemented at the RFH in 2006. Its use has enabled the timely implementation of appropriate infection control measures, which have contributed to the reduction in MRSA rates within the Trust. Currently the test is only used for specific patient groups, however there is the desire to increase the number of patients screened using this methodology. Due to the hands on time required for the IDI MRSA assay, increasing the numbers would have an effect on the time required to perform each run and would impact on turnaround times. We therefore set out to evaluate the use of an acromopeptidase extraction method (ACP) which requires less hands on time, the Corbett Research CAS-1200 to automate the PCR set up and the Corbett Research Rotor-Gene platform to increase the capacity of each run.

Methods: Over a five week period a preliminary study was performed during which 511 samples were tested using the routine method (IDI extraction and the SmartCycler, method 1) and three other methods: ACP and the SmartCycler (method 2); IDI extraction and the Rotor-Gene (method 3); and ACP and the Rotor-Gene (method 4). In-house cut-off values were used to analyse the Rotor-Gene data. Samples that were from known MRSA positive patients, which were culture positive and/or positive by all four methods, were regarded as true positive samples.

Results: During the preliminary study the inhibition rates were 35 (6.8%), 37 (7.2%), 9 (1.8%) and 6 (1.2%) for methods 1–4 respectively; the false positive rates were 5 (1%), 1 (0.2%), 1 (0.2%) and 2 (0.4%) for methods 1–4 respectively and the false negative rates were 4 (0.8%), 10 (2%), 6 (1.2%) and 7 (1.4%) respectively.

Conclusions: This preliminary study has shown that an ACP extraction method and the Rotor-Gene could be used to improve the workflow of the IDI MRSA assay without compromising the sensitivity or specificity of the assay. The lower inhibition rates observed when using the Rotor-Gene were a reflection of the less stringent in-house cut-off values used. Subsequent to the study additional measures have been put in place and the inhibition rate of the routine method has now been reduced to approximately 2%. To fully validate the use of ACP and the Rotor-Gene a further 2000 samples are in the process of being tested and appropriate cut-off values are being established.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Barcelona, Spain
Presentation type:
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