[Evaluation of the impact of different lengths of pre-enrichment in a nutritive broth and prolonged incubation of MRSA-ID, a chromogenic agar medium, on its performances for identifying methicillin-resistant Staphylococcus aureus in screening samples].
MRSA-carrier screening is recommended to prevent MRSA dissemination in hospitals. Rapid and specific detection of MRSA in the laboratory is a key element in enabling control measures. Our objective was to evaluate the impact of different lengths of pre-incubation in a nutritive broth and prolonged incubation of MRSA-ID, a chromogenic agar medium, on its performances for identifying MRSA in screening samples. According to our results, short-length pre-enrichments only provided a weak increase of sensitivity as compared to the absence of pre-enrichment. On the contrary, the sensitivity increase provided by an overnight pre-enrichment was significant. The prolongation of incubation in the chromogenic agar medium (48 hours instead of 24 hours) did not provide any significant increase of sensitivity but was associated with a strong and significant loss of specificity. Therefore, it seems relevant to reject prolonged incubation of selective agar media and to make a choice between the absence of pre-enrichment (faster results) and an overnight pre-enrichment (higher sensitivity), according to local epidemiology and local practices implemented for prevention.
Grandin
S
S
Service de Microbiologie-Hygiène, Hôpital Louis-Mourier (AP-HP), 178 Rue des Renouillers, 92700 Colombes, France.
Deschamps
C
C
Magdoud
F
F
Zihoune
N
N
Branger
C
C
Eveillard
M
M
D000362:Agar; D002353:Carrier State / Q000382:microbiology; D003470:Culture Media; D006761:Hospitals / Q000592:standards; D006801:Humans; D007297:Inpatients; D007700:Kinetics; D008403:Mass Screening / Q000379:methods* / Q000592:standards; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects / Q000254:growth & development* / Q000302:isolation & purification; D012680:Sensitivity and Specificity; D013203:Staphylococcal Infections / Q000382:microbiology* / Q000635:transmission; D013997:Time Factors
D003470:Culture Media; D000362:Agar