Antimicrobial resistance among gram-negative bacilli to newer aminoglycosides and beta-lactams.

Two hundred and fifty nine i.e. 30.72% of 843 strains of gram negative bacilli were resistant to gentamicin. When tested against newer aminoglycosides, 48.9% were resistant to tobramycin, 4.1% to amikacin and 20.5% to netilmicin. Marked cross-resistance between gentamicin and tobramycin was seen. All these strains were resistant to ampicillin, amoxycillin and co- trimoxazole. However, a high level of antimicrobial activity was seen with third generation cephalosporins, cefotaxime and ceftriaxone. Minimum inhibitory concentrations of gentamicin and tobramycin were of significant level. Gentamicin resistance could be transferred directly in 20 of 45 strains of S. typhimurium where conjugation experiments were done.