Synergistic enhancement of in vitro antimicrobial activity of cefmetazole and cefazolin, cefotiam, cefamandole or cefoperazone in combination against methicillin-sensitive and -resistant Staphylococcus aureus. I. Effect of NaCl

The in vitro antimicrobial activity of cephamycin, e.g. cefmetazole and cephalosporin, such as cefazolin, cefotiam, cefamandole and cefoperazone, alone and in combination, was studied employing 9 strains of methicillin-sensitive Staphylococcus aureus (MSSA) and 30 strains of methicillin-resistant Staphylococcus aureus (MRSA). Using the checkerboard agar dilution method, strong synergism was demonstrable in a majority of MSSA and MRSA strains for cefmetazole combined with these cephalosporins, with the minimum fractional inhibitory concentration index < or = 0.5. In the presence of a concentration < or = 6.25 micrograms/ml of these cephalosporins in Mueller-Hinton agar medium, the activity of cefmetazole against MRSA was most prominently potentiated by cefotiam, followed by cefamandole, cefazolin and cefoperazone. At a concentration of 12.5 micrograms/ml, cefotiam and cefamandole showed a similar effect in potentiation of cefmetazole activity. In hypertonic agar medium containing 4% NaCl, these synergistic combination effects were reduced. However, the activity of cefmetazole and cefamandole in combination under these conditions was influenced to a lesser extent and more potent than that of other combinations.