Comparative in vitro Activity of Cef epime and Four Extended-Spectrum Beta-Lactams on 1,251 Aminoglycoside-Resistant Gram-Negative Hospital Strains

Cefepime was the most active compound on the Enterobacte-riaceae with a MIC90 of 0.26 µg/ml and a resistance rate of 0.1%. Ceftazidime was the most active drug on the non-fermeting bacilli (MIC90 9.65 µg/ml; resistance rate 3%). Amikacin- and gentamicin-resistant strains showed a decreased susceptibility to the Β-lactams, though the Enterobacteriaceae and the non-fermenters remained fairly sensitive to cefepime and ceftazidime, respectively. Aminoglycoside-3-N-acetyltransferase was the most prevalent enzyme and was often associated with intermediate resistance or resistance to Β-lactams. Non-fermenters showing aminoglycoside impermeability were very often intermediately resistant or resistant to Β-lactams.