TY - JOUR

T1 - Semi-selective broth improves screening for methicillin-resistant Staphylococcus aureus

AU - Böcher, S

AU - Middendorf, B

AU - Westh, H

AU - Mellmann, A

AU - Becker, K

AU - Skov, R

AU - Friedrich, A W

PY - 2010/4

Y1 - 2010/4

N2 - OBJECTIVES: To evaluate two enrichment broths for methicillin-resistant Staphylococcus aureus (MRSA) detection and compare results with direct plating.METHODS: Swabs from 1224 patients were re-analysed for MRSA in a central laboratory (Münster) using six methods. Swabs were suspended in 0.5 mL of non-selective enrichment broth (NB) and vortexed. Aliquots of 100 microL were inoculated on/into: (I) ChromID MRSA agar; (II) Columbia sheep blood (5%) agar (BA) and ChromID MRSA; (III, IV) NB incubated overnight followed by plating on BA and ChromID MRSA; and (V, VI) a semi-selective broth containing cefoxitin and aztreonam (TSB-SSI) incubated overnight followed by plating on BA and ChromID MRSA. In III-VI, 100 microL of the enriched broth was plated on each agar.RESULTS: The combined MRSA-positive rate was 21.5%. MRSA isolates detected by each method were: TSB-SSI, n = 223; NB, n = 205; BA and ChromID MRSA, n = 203; ChromID MRSA alone, n = 183. TSB-SSI detected more positive throat samples than the comparators and significantly reduced methicillin-susceptible S. aureus (MSSA) growth. The maximum sensitivity obtained was only 85%, possibly due to the study design using pre-used swabs and dilution of swab material. For 997 samples, results from Münster were compared with initial results. Peripheral laboratories identified 172 MRSA compared with Münster where 186, 186 and 204 MRSA were found for direct plating, NB and TSB-SSI broth, respectively.CONCLUSIONS: TSB-SSI was superior to both NB and direct plating on ChromID MRSA and BA. Despite re-using swabs for the study, we showed that routine diagnostic screening could be significantly improved, using a semi-selective enrichment broth.

AB - OBJECTIVES: To evaluate two enrichment broths for methicillin-resistant Staphylococcus aureus (MRSA) detection and compare results with direct plating.METHODS: Swabs from 1224 patients were re-analysed for MRSA in a central laboratory (Münster) using six methods. Swabs were suspended in 0.5 mL of non-selective enrichment broth (NB) and vortexed. Aliquots of 100 microL were inoculated on/into: (I) ChromID MRSA agar; (II) Columbia sheep blood (5%) agar (BA) and ChromID MRSA; (III, IV) NB incubated overnight followed by plating on BA and ChromID MRSA; and (V, VI) a semi-selective broth containing cefoxitin and aztreonam (TSB-SSI) incubated overnight followed by plating on BA and ChromID MRSA. In III-VI, 100 microL of the enriched broth was plated on each agar.RESULTS: The combined MRSA-positive rate was 21.5%. MRSA isolates detected by each method were: TSB-SSI, n = 223; NB, n = 205; BA and ChromID MRSA, n = 203; ChromID MRSA alone, n = 183. TSB-SSI detected more positive throat samples than the comparators and significantly reduced methicillin-susceptible S. aureus (MSSA) growth. The maximum sensitivity obtained was only 85%, possibly due to the study design using pre-used swabs and dilution of swab material. For 997 samples, results from Münster were compared with initial results. Peripheral laboratories identified 172 MRSA compared with Münster where 186, 186 and 204 MRSA were found for direct plating, NB and TSB-SSI broth, respectively.CONCLUSIONS: TSB-SSI was superior to both NB and direct plating on ChromID MRSA and BA. Despite re-using swabs for the study, we showed that routine diagnostic screening could be significantly improved, using a semi-selective enrichment broth.

KW - Bacteriological Techniques/methods

KW - Culture Media/chemistry

KW - Humans

KW - Mass Screening/methods

KW - Methicillin-Resistant Staphylococcus aureus/isolation & purification

KW - Sensitivity and Specificity

KW - Staphylococcal Infections/diagnosis

U2 - 10.1093/jac/dkq001

DO - 10.1093/jac/dkq001

M3 - Journal article

C2 - 20130023

VL - 65

SP - 717

EP - 720

JO - Journal of Antimicrobial Chemotherapy

JF - Journal of Antimicrobial Chemotherapy

SN - 0305-7453

IS - 4

ER -