[Susceptibility of methicillin-sensitive and methicillin-resistant staphylococci to ciprofloxacin]

Investigations were carried on 352 strains of Staphylococcus aureus and 105 strains of coagulase-negative staphylococci, isolated from various clinical materials and derived from some regions of the country. Methicillin-resistance was tested by an antibiotic dilution method in solid Mueller-Hinton medium with addition of 2% NaCl. Staphylococci with MIC higher than 4 micrograms/ml were considered as resistant. The same method for testing resistance to ciprofloxacin was used. Only one strain (S. aureus) was resistant to both ciprofloxacin and methicillin. All remaining strains of staphylococci were ciprofloxacin-susceptible. The MIC for all of them was not higher than 2 micrograms/ml, regardless of resistance to methicillin. Some slight differences in MIC50 and MIC90 values were found between MRSA and MSSA and they were, respectively, 1 microgram/ml and 0.25 microgram/ml, and 2 micrograms/ml and 1 microgram/ml. Mean MIC of ciprofloxacin for MRSA was 1.1 microgram/ml and for MSSA it amounted to 0.4 microgram/ml. Range of MIC was following: MRSA--0.12 microgram/ml--16 micrograms/ml and MSSA--0.12-2 micrograms/ml. Coagulase-negative staphylococci, both methicillin-resistant and methicillin-sensitive, exhibited same value for MIC50, MIC90 and MIC range and they were following: 0.5 microgram/ml, 1 microgram/ml and 0.12-1 micrograms/ml. Both groups differed slightly in mean MIC values which was 0.6 microgram/ml for methicillin-resistant strains and 0.47 microgram/ml for methicillin-sensitive staphylococci. It seems that within staphylococci isolated in Poland there is no correlation between resistance to methicillin and ciprofloxacin, which is frequently pointed out by other authors.