Improved Sensitivity and Reduction in MRSA Surveillance Costs by Using MRSA-B Enrichment Broth

J. Korver*1, C. Rutherford1, C. Lee1,2 1Hamilton Regional Laboratory Medicine Program- & St. Joseph’s Healthcare, 2Department of Pathology and Molecular Medicine, McMaster University, Hamilton, , Canada.

INTRODUCTION: RESULTS: CONCLUSIONS: Multiple body sites are swabbed when screening a patient for MRSA • Using direct plate inoculation of the swab (standard lab method), This study shows that using MRSA-B colonization. Each swab is directly inoculated onto a selective and 11.05% (21/190 patients) were identified as MRSA carriers enrichment broth and pooling multiple differential agar plate, usually a Chromogenic-based plate, specific for • The MRSA-B broth method identified 31.6% (61/190 patients) as body-site samples from the same MRSA. A significant portion of the laboratory budget is utilized for this MRSA carriers patient results in a statistically purpose, yet the sensitivity of direct plate inoculation is suboptimal compared to the broth culture method. • The MRSA-B broth detected all 21 patients detected by the significant improvement in sensitivity standard method and an additional 40 patients. 11.05% vs. 32.1% (P = .000001). STUDY OBJECTIVES: • MRSA results using the MRSA-B broth method were reported on Pooling samples also results in • To determine whether MRSA-B broth [Copan Italia SpA, Brescia, the same day as the direct plate inoculation method. reduction of laboratory cost. Italy], has superior sensitivity to the conventional direct plate inoculation method for isolation of MRSA. • Pooling the swabs in MRSA-B broth resulted in a 50% reduction The improved sensitivity will in chromogenic MRSA plate use. • To reduce laboratory costs by pooling multiple body site swabs into 1 significantly enhance patient care by tube of MRSA-B broth and inoculating 1 MRSA Select plate [Bio-Rad, identifying more colonized patients Marnes-la-Coquette, France]per patient. and reducing nosocomial transmission. METHODS:

1. Van horn KG, Audette CD, Sebeck D et al. Comparison of the Copan Eswab system • 372 swabs (Amies ®Transport Swabs with charcoal [Copan, Italia SpA, with two Amies agar swab transport systems for maintenance of microogranism mec viability. J Clin Microbiol 2008; 46(5): 1655-8. Brescia Italy]), were received from 190 patients 2. Saegeman V, Flamaing J, Muller J et al. Clinical evaluation of the Copan Eswab for PVL methicillin-resistant Sta[hylococcus aureus detection and culture of wounds. Eur J • Body sites swabbed included nares, groin and rectum nuc Clin Microbiol Infect Dis ; accepted Jan 2011. 3. Fontana C, Favaro M, Limongi D et al. Comparison of the eSwab collection and transportation system to an amies gel transystem for Gram stain of clinical • Each swab was directly inoculated onto MRSA Select® agar [BD specimens. BMC Res Notes 2009; 2: 244. Microbiology, Paris, France] and incubated at 35-37oC for 24 hours

• All swabs from the same patient were then pooled and inoculated Acknowledgements: o Copan for providing MRSA- B Broth into a single tube of MRSA-B broth and incubated for 5 hours at 37 C Fig. 1MRSA on CHROMagar Fig. 2PCR for mec, nuc, PVL No conflict of interest to disclose • Tubes were vortexed and 50 µL of broth was plated onto a MRSA Mr. John Korver ([email protected]) Select plate. Plates were incubated at 37oC for 24 hours. Ms. Candy Rutherford ([email protected]) • Presumptive MRSA colonies from all plates were confirmed by PCR Dr. Christine Lee ([email protected]) for nuclease, PVL and mecA.