Evaluation of BacLite Rapid MRSA, a rapid culture based screening test for the detection of ciprofloxacin and methicillin resistant S. aureus (MRSA) from screening swabs

Gemma Johnson,Peter Marsh,Michael R Millar,Margaret Skyrme,Emma Barringer,Stuart Matthews,Mark Wilks,Stephen O'Hara

doi:10.1186/1471-2180-6-83

Abstract

BackgroundMethicillin-resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen worldwide. The need for accurate and rapid screening methods to detect MRSA carriers has been clearly established. The performance of a novel assay, BacLite Rapid MRSA (Acolyte Biomedica, UK) for the rapid detection (5 h) and identification of hospital associated ciprofloxacin resistant strains of MRSA directly from nasal swab specimens was compared to that obtained by culture on Mannitol salt agar containing Oxacillin (MSAO) after 48 h incubation.ResultsA total of 1382 nasal screening swabs were tested by multiple operators. The BacLite Rapid MRSA test detected 142 out of the 157 confirmed MRSA that were detected on MSAO giving a diagnostic sensitivity of 90.4, diagnostic specificity of 95.7% and a negative predictive value of 98.7%. Of the 15 false negatives obtained by the BacLite Rapid MRSA test, seven grew small amounts (< 10 colonies of MRSA) on the MSAO culture plate and five isolates were ciprofloxacin sensitive. However there were 13 confirmed BacLite MRSA positive samples, which were negative by the direct culture method, probably due to overgrowth on the MSAO plate. There were 53 false positive results obtained by the BacLite Rapid MRSA test at 5 h and 115 cases where MRSA colonies were tentatively identified on the MSAO plate when read at 48 h, and which subsequently proved not to be MRSA.ConclusionThe Baclite MRSA test is easy to use and provides a similar level of sensitivity to conventional culture for the detection of nasal carriage of MRSA with the advantage that the results are obtained much more rapidly.

Highlights

Methicillin-resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen worldwide
This study describes the evaluation of the BacLite MRSA, a rapid culture based test which has been developed to detect ciprofloxacin resistant MRSA strains that have been associated with hospital acquired infections within the UK
The BacLite Rapid MRSA test detected 142 out of the 157 confirmed MRSA that were detected on Mannitol salt agar containing Oxacillin (MSAO) giving a diagnostic sensitivity of 90.4 and a diagnostic specificity of 95.7% (Table)

Summary

Introduction

Methicillin-resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen worldwide. The use of screening cultures to identify MRSA-colonised patients so that infection control measures can be implemented and prevent transmission to other patients, is well established [1]. The use of chromogenic media may reduce the time significantly, but there are few published studies on their efficacy [3]. During this time period, infection control measures, such as isolation, or cohorting of patients and prophylactic decontamination may be applied unnecessarily, or if not applied, unidentified MRSA-positive individuals may remain a hidden reservoir for cross infection. A rapid negative result should allow more effective use of hospital isolation resources, whilst a rapid positive result should help reduce the spread of the infection and MRSA infection rates

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