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

Susceptibility study of aerobic gram-negative urinary bacilli to sixteen antimicrobial agents

The susceptibility of 316 fully identified urinary tract isolates was studied in parallel to 16 antimicrobial agents using a modified Kirby-Bauer method. In addition to commonly encountered organisms, less common isolates which are resistance problem organism [Serratia spp., Enterobacter spp., Morganella morganii and Acinetobacter calcoaceticus] were included. The frequency of antimicrobial resistance was high, especially to sulphamethoxazole, tetracycline, ampicillin and carbenicillin. A high sensitivity frequency was found to cefotaxime [> 99%], amikacin [100%] and gentamicin [80-100%] for Escherichia coli, Klebsiella spp., Proteus spp. and M. morganii isolates. Cephalosporin sensitivity frequencies were very low for Pseudomonas spp., and A. calcoaceticus. All Serratia spp. were resistant to sulphamethoxazole, trimethoprim, cephalothin, cefuroxime and ampicillin, and only 17% were sensitive to gentamicin and 50% to amikacin. Overall the frequencies of antimicrobial resistance in this study are higher than those reported from most other countries