Effect of antibiotics on fnb A and fnb B mRNA levels. Exponentially growing cultures of S. aureus 8325-4 were treated for 2 h with no antibiotics or with 1/2 the MIC of oxacillin, gentamicin, vancomycin, moxifloxacin, clindamycin, linezolid or rifampicin. Samples of each culture were taken and adjusted to an OD600 of 1 and then used for total RNA extraction and subsequent reverse transcription with random primers, as described above. The cDNA obtained was used as the template for LightCycler PCR with specific fnbA, fnbB and gyrB primers. Relative quantification was performed by reporting it relative to gyrB expression, as described elsewhere . The results are expressed as the n-fold variation of fnbA (white bars) and fnbB (black bars) mRNA levels in the presence of each antibiotic relative to the growth of no antibiotic control levels. The values are the means ± standard deviations (four different experiments). A change in mRNA level was interpreted as significant if greater than 2-fold variation.