[Detection of heterogeneous MRSA by using the PCR method and population analysis].
To assess the clinical usefulness of the PCR method for the detection of methicillin-resistant Staphylococcus aureus (MRSA) by targetting the mecA gene, we surveyed 150 clinical isolates of Staphylococcus aureus and compared the results of the PCR method with those of the standard broth microdilution method. Fifty-four isolates (36%) were positive for the mecA gene and two of them, presenting coagulase type IV, were recognized as susceptible strains by microdilution method, while all the other mecA positive strains were drug-resistant. Population analysis revealed that these two strains were heterogeneous in terms of drug-resistance and composed of two populations of cells; i.e., relatively susceptible cells and highly resistant cells. The discrepancy between the phenotypic expression (drug-resistance) and the genotype (mecA gene) seems to be due to the small percentage of highly resistant cells. Drug-resistant colonies could be induced in these strains by the contact with methicillin, indicating the selective increase of the population of resistant cells by a passage in the drug. These observations suggest that it is clinically important to detect the resistance-inducible strains (prototype MRSA) by using the PCR method and population analysis.
Moriki
S
S
Central Clinical Laboratory, Shimane Medical University, Izumo.
Iwata
Y
Y
Ishikura
H
H
Endo
J
J
D001431:Bacteriological Techniques; D004269:DNA, Bacterial / Q000032:analysis; D004351:Drug Resistance / Q000235:genetics; D006801:Humans; D007231:Infant, Newborn; D016106:Methicillin Resistance / Q000235:genetics*; D016133:Polymerase Chain Reaction; D013211:Staphylococcus aureus / Q000235:genetics / Q000302:isolation & purification*
D004269:DNA, Bacterial