An evaluation of different methods to recover methicillin-resistant Staphylococcus aureus from hospital environmental surfaces

Abstract number: P611

Objective: Due to the increased costs and clinical importance of healthcare-associated infections (HCAI), there is a need for evidence-based approaches to environmental sampling and its evaluation. We compared the recovery of MRSA from two hospital surfaces using different sampling methods, with a wild-type patient strain of methicillin-resistant Staphylococcus aureus (MRSA).

Methods: One-hundred cm2 sections of mattress cover and laboratory bench surface were contaminated with known inocula of MRSA. Bacteria were recovered at three different time intervals (0 h, 24 h and 72 h) using either saline moistened cotton swabs, neutralising buffer swabs (Technical Service Consultants, U.K.), eSwabs (Copan, Italy), or direct contact plates (MRSA Brilliance, Oxoid, U.K.). Swabs were enriched in tryptone soya broth (Oxoid), nutrient broth (Oxoid), Amies solution (Copan) or brain heart infusion (Oxoid) at 37°C. Ten microlitres of enrichment media were transferred to MRSASelect chromogenic agar plates (BIO-RAD, France) after 18 h and incubated along with the contact plates for 24 h at 37°C. The sensitivity of each method cm-2 was determined for all time intervals and surfaces.

Results: The most sensitive method was eSwabs enriched in Amies solution, which required 1.1 bacteria cm-2 to generate a positive result. The least sensitive method was saline moistened cotton swabs, which required 8.0×104 bacteria cm-2. MRSA Brilliance contact plates were the quickest (24 h for a presumptive positive) and least labour intensive method, and were highly sensitive, requiring 2.4 bacteria cm-2 to generate a positive result. All sampling methods required less bacteria cm-2 from the laboratory bench surface (flat) than the mattress cover surface (highly undulated) to generate a positive result. All sampling methods showed a significant reduction in sensitivity at the 72 h time interval.

Conclusions: The recovery of bacteria from environmental samples varies with the swabs, methodology used and the surface. Negative culture results may not exclude a pathogen-free environment. Greater standardisation in environmental sampling is required to facilitate the assessment of and monitor improvements in the cleanliness of healthcare institutions.

Session Details

Date: 10/04/2010
Time: 00:00-00:00
Session name: Abstracts 20th European Congress of Clinical Microbiology and Infectious Diseases
Location: Vienna, Austria, 10 - 13 April 2010
Presentation type:
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