Sensitivity patterns of gram-negative pathogens to four modern aminoglycosides

Using a modified Kirby Bauer method, we studied the susceptibility of 349 fully identified urinary tract isolates to netilmicin, tobramycin, gentamicin and amikacin. Gentamicin resistance was the most common: 40 isolates were resistant [R] and 7 intermediate [M], followed by tobramycin [31R, 5M], netilmicin [18R, 4M] and amikacin [6R, 5M]. Similar decreasing resistance frequency was found for all genera tested. The relative gentamicin resistance frequency was highest for Providencia [67%], Serratia [57%] Enterobacter and Citrobacter [33%], Pseudomonas [26%] and Morganella [20%]. It was lower for Klebsiella [5%] and Proteus [11%]. No fully gentamicin resistant E. coli were encountered. The majority of isolates resistant to amikacin [82%] and/or 2 other aminoglycosides originated from inpatients. The relative frequency of these multiresistant isolates was 16% for surgical department, 17% for medical, 7% for paediatrics and 2% for maternity, reflecting the length of hospitalization and aminoglycoside usage in these units. Part of this study was presented at the European Congress of Clinical Microbiology, Nice-1989