A PCR method for the identification of methicillin-resistant Staphylococcus aureus (MRSA) from screening swabs.
OBJECTIVE
The aim of this study was to assess the discriminatory power and potential turn around time (TAT) of a PCR-based method for the detection of methicillin-resistant Staphylococcus aureus (MRSA) from screening swabs.


METHODS
Screening swabs were examined using the current laboratory protocol of direct culture on mannitol salt agar supplemented with oxacillin (MSAO-direct). The PCR method involved pre-incubation in broth for 4 hours followed by a multiplex PCR with primers directed to mecA and nuc genes of MRSA. The reference standard was determined by pre-incubation in broth for 4 hours followed by culture on MSAO (MSAO-broth).


RESULTS
A total of 256 swabs was analysed. The rates of detection of MRSA using MSAO-direct, MSAO-broth and PCR were 10.2, 13.3 and 10.2%, respectively. For PCR, the sensitivity, specificity, positive predictive value and negative predictive values were 66.7% (95%CI 51.9-83.3%), 98.6% (95%CI 97.1-100%), 84.6% (95%CI 76.2-100%) and 95.2% (95%CI 92.4-98.0%), respectively, and these results were almost identical to those obtained from MSAO-direct. The agreement between MSAO-direct and PCR was 61.5% (95%CI 42.8-80.2%) for positive results, 95.6% (95%CI 93.0-98.2%) for negative results and overall was 92.2% (95%CI 88.9-95.5%).


CONCLUSIONS
(1) The discriminatory power of PCR and MSAO-direct is similar but the level of agreement, especially for true positive results, is low. (2) The potential TAT for the PCR method provides a marked advantage over conventional methods. (3) Further modifications to the PCR method such as increased broth incubation time, use of selective broth and adaptation to real-time PCR may lead to improvement in sensitivity and TAT.
Hope
William W
WW
Microbiology Department, Queensland Health Pathology Service, Princess Alexandra Hospital, Brisbane, Queensland, Australia.
Morton
Anthony P
AP
Looke
David F M
DF
Schooneveldt
Jacqueline M
JM
Nimmo
Graeme R
GR
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics; D015373:Bacterial Typing Techniques; D003470:Culture Media; D017931:DNA Primers; D004720:Endonucleases / Q000235:genetics; D006801:Humans; D008403:Mass Screening; D016106:Methicillin Resistance / Q000235:genetics*; D008836:Micrococcal Nuclease / Q000235:genetics; D046915:Penicillin-Binding Proteins; D016133:Polymerase Chain Reaction / Q000379:methods*; D012680:Sensitivity and Specificity; D013203:Staphylococcal Infections / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000302:isolation & purification*
D001426:Bacterial Proteins; D003470:Culture Media; D017931:DNA Primers; D046915:Penicillin-Binding Proteins; C487789:mecA protein, Staphylococcus aureus; C074002:nuc protein, staphylococcus; D004720:Endonucleases; D008836:Micrococcal Nuclease