Effect of magnesium and calcium supplementation on the in-vitro activity of some -lactam-aminoglycoside combinations agents staphylococcus aureus

ABSTRACT

The effect of physiological levels of Mg +2 and Ca +2 on the in vitro activity of cephradine [Cep], cefoperazone [Cef] and cefotaxime [Ctx] alone and in combination with three aminoglycoside antibiotics [gentamicin [Gm], tobramycin [Tm], and netilmicin [Nt]] was evaluated against ten strains of Staphylococcus aureus. Adding Mg +2 or Ca +2 to commercial media deficient to these cations increased the MICs and MBCs of the three cephalosporins 2 to 4-fold, while aminoglycoside antibiotics revealed 4 to 8-fold increase in their MICs and MBCs. The combined antibacterial activity of the studied cephalosporin/aminoglycoside combinations decreased by the addition of Mg +2 or Ca +2