The in vitro activity of gentamicin, tobramycin, and netilmicin ?against 500 clinical isolates of bacteria. A comparative study using three different test media. Acta path. microbiol. immunol. s a n d . Sect. B, 91: [135][136][137][138][139] 1983.The in v i m activities of the three aminoglycoside antibiotics, gentamicin, netilmicin and tobramycin have been compared against 500 isolates of Enterobacteriaceae, Pseudomonas aeruginosa and Staphylococcus aureus. An agar dilution method was employed with three sensitivity media: Iso-Sensitest Agar, Mueller-Minton Agar and PDM-Antibiotic Sensitivity Medium. All three aminoglycosides were highly active against S. aureus (MICS0.5 mg/l) and the majority of Enterobacteriaceae (MIC90 approx. 1 mg/l). Tobramycin showed the highest activity against P. aeruginosa ( M I C I I mg/l).No major difference in measured MIC were found on the three media. Gentamicin and netilmicin were somewhat less active against P. aeruginosa on Mueller-Hinton Agar. MICs for tobramycin against Enterobacteriaceue were a little higher on PDM than on the other two agars. Our results show that measured MIC varied very little on the three sensitivity media. All media are suitable for routine use. provided that control strains are employed.

Netilmicin, a semisynthetic derivative of sisomicin, was tested against 327 isolates of Staphylococcus aureus, Pseudomonas aeruginosa and Gram-negative enteric bacilli. Seventy-two per cent of the isolates were inhibited at a concentration of 0.5 microgram netilmicin per ml, and 93% of the isolates were susceptible to 4 microgram per ml or less. The MICs of netilmicin and gentamicin for 24 Providencia and 38 Pseudomonas isolates were compared. The activity of netilmicin closely paralleled that of gentamicin, 46% of the Providencia isolates and 32% of the Pseudomonas isolates not being inhibited by 4 microgram per ml of either drug.

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The minimal inhibitory concentrations (MICs) of norfloxacin, nalidixic acid, ampicillin, amoxycillin/clavulanic acid (4:1), mecillinam, cefaclor, sulphamethoxazole/trimethoprim (20:1) and netilmicin against 435 clinical isolates of bacterial urinary tract pathogens have been determined. An agar dilution method was employed. Norfloxacin was the most active agent in the study on a weight‐for‐weight basis. The drug was highly active against Enterobacteriaceae. Norfloxacin was more active than netilmicin against Pseudomonas aeruginosa (MICs ≤2 mg/l and ≤4 mg/l, respectively). Norfloxacin was also active against Gram‐positive bacteria including enterococci and Staphylococcus saprophyticus (MICs ≤ 4 mg/l). Norfloxacin may well become a useful agent for the oral treatment of urinary tract infection, particularly as a drug for the treatment of infections caused by multiresistant organisms.

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