Ca. Resende et Ams. Figueiredo, DISCRIMINATION OF METHICILLIN-RESISTANT STAPHYLOCOCCUS-AUREUS FROM BORDERLINE-RESISTANT AND SUSCEPTIBLE ISOLATES BY DIFFERENT METHODS, Journal of Medical Microbiology, 46(2), 1997, pp. 145-149
Methicillin-resistant Staphylococcus aureus (MRSA) are important nosoc
omial pathogens, Diseases caused by these resistant bacteria frequentl
y are serious and there is a need to control the spread of epidemic MR
SA clones in hospitals. However, detection is complicated by the fact
that expression of the resistance is variable and, commonly, heterogen
eous within strains. The reliability of several tests recommended to d
iscriminate heterogeneous MRSA isolates from borderline-resistant and
susceptible strains was evaluated. Screening for growth on agar with m
ethicillin 25 mg/L was the only method that detected all MRSA strains
tested, but screening on agar with methicillin 10 mg/L or oxacillin 6
mg/L detected all but one of 10 heterogeneously resistant strains test
ed. None of the borderline-resistant nor any truly susceptible staphyl
ococci tested grew on any of these screening plates.