[Detection of nasal colonization methicillin-resistant Staphylococcus aureus: a prospective study comparing real-time genic amplification assay vs selective chromogenic media].
In contrast to "classical" genic amplification, real-time genic amplification can be performed in every laboratory without the need of sophisticated isolation procedures. Moreover, real-time genic amplification allows an early detection of meticillin resistant Staphylococcus aureus colonization, 2 hours compared to 1 or 2 days for culture.


OBJECTIVE
In order to assess the feasibility on Smartcycler of the IDI-MRSA real-time genic amplification assay in comparison with chromogenic media.


METHODS
A prospective study has been initiated in July 2004: nasal swabs were taken from patients entering the ICU, vascular surgery, diabetology and geriatry wards. During a 4 months period, 682 specimens have been obtained from 508 patients.


RESULTS
Sixty-four (9.3%) patients were positive by genic amplification and selective agar culture (CHROMagar MRSA, MRSASelect and/or ORSAB), 19 (2.9%) were positive by genic amplification only (3 of these patients were under antibiotic treatment); 572 specimens remained negative by both methods. The sensitivity and specificity of this assay were 100% and 96% respectively with a positive predictive value of 70% and negative predictive value of 100%. Initially 82 nasal specimens were unresolved (12%). 38 were resolved following a freeze-thaw cycle. Thus, 44 (6.4%) were unresolved specimens. Comparison between CHROMagar MRSA and MRSASelect showed a good correlation for the detection at 24 hours (5.5% and 5.6% respectively). These two chromogenic media allowed a much better detection of MRSA than ORSAB medium within 24H.


CONCLUSIONS
The results obtained by the early real-time genic amplification for the detection of meticillin resistant Staphylococcus aureus are promising. Despite 6.4% amplification failure, we consider that IDI-MRSA real-time genic amplification assay represents a significant breakthrough in the detection of colonization.
Nguyen Van
J-C
JC
Laboratoire de microbiologie médicale, Fondation hôpital Saint-Joseph, 185, rue Raymond-Losserand 75674 Paris cedex 14, France. jcnguyen@hopital-saint-joseph.org
Kitzis
M-D
MD
Ly
A
A
Chalfine
A
A
Carlet
J
J
Ben Ali
A
A
Goldstein
F
F
D003470:Culture Media; D005784:Gene Amplification; D006801:Humans; D007362:Intensive Care Units; D016106:Methicillin Resistance; D009297:Nasal Mucosa / Q000382:microbiology*; D010297:Paris; D016133:Polymerase Chain Reaction / Q000379:methods; D012680:Sensitivity and Specificity; D013211:Staphylococcus aureus / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification*
D003470:Culture Media