[Problem of the in vitro sensitivity to cefamandole of methicillin-resistant Staphylococcus aureus]

In work involving 127 strains of methicillin resistant Staphylococcus aureus, belonging to two resistance categories, homogeneous or RO and heterogeneous or RH and using five cephalosporins, cefalotin, cefazolin, cefamandole, cefotaxime and latamoxef, the authors compared the results of their in vitro sensitivity measurements with two methods: agar disk diffusion and growth inhibition in liquid medium (Autobac). They also compared the MIC values with a significant fraction (19 strains). In order to detect heterogeneous resistance experiments were carried out in duplicate, with one series grown in hypertonic medium and incubated for 48 heures at 37 degrees C, or grown on normal medium with lower incubation at 30 degrees C. In both defined techniques and in vitro, it was observed that the 127 methicillin resistant Staphylococcus aureus strains except one were sensitive to cefamandole and that 26 were also sensitive to cefalotin. Considerable caution is necessary in the in vivo transposition of these findings. May be present media are not able to allow growth of resistant strains to cefamandole.