Antimicrobial activity of netilmicin in comparison with gentamicin, sisomicin, tobramycin, and amikacin and their resistance patterns.

The antimicrobial activity of netilmicin, gentamicin, sisomicin, tobramycin and amikacin was determined by means of the microdilution test. 1000 fresh isolates of strains of Staphylococcus aureus, Pseudomonas aeruginosa and 7 species of the Enterobacteriaceae were tested. The activities were compared and cross-resistances were analyzed which appeared among the various drugs. Against amikacin, only 0.5% of all strains (3 P. aeruginosa, 1 S. aureus, 1 P. mirabilis) were resistant. Of the other drugs, netilmicin was the most active drug against S. aureus, Klebsiella spp., Enterobacter spp. and Escherichia coli. Against E. coli, too, sisomicin showed its best activity, and further against Citrobacter spp., Proteus spp. and P. aeruginosa. A total of 12% of all pathogens was gentamicin-resistant. With one exception, these pathogens showed cross-resistance to at least one of the other drugs. In 39% of the cases a cross-resistance between gentamicin and tobramycin was noted, in 26% a gentamicin-tobramycin-sisomicin cross-resistance, in 17% gentamicin-tobramycin-sisomicin-netilmicin cross-resistance, in 11% a gentamicin-sisomicin-netilmicin cross-resistance. A complete cross-resistance was observed between gentamicin and sisomicin with S. aureus, Serratia spp. and Proteus mirabilis, between gentamicin and tobramycin with E. coli, Citrobacter spp. and Enterobacter spp.