Comparative in vitro activity of netilmicin, amikacin, tobramycin and sisomicin against gentamicin highly-resistant enterobacteriaceae.

Netilmicin was compared with sisomicin, tobramycin and amikacin against 65 recent clinical enterobacterial isolates found to be highly resistant to gentamicin (MIC larger than or equal to 80 microgram/ml). Netilmicin showed a high activity against 20 out of 65 strains tested. Most of the sensitive strains (60%) to netilmicin required a concentration of gentamicin equal or lower than 160 microgram/ml for inhibition. Amikacin proved to be extremely effective in all the organisms tested. Tobramycin was consistently less active than either netilmicin or amikacin and the same was the case with sisomicin. The MIC was determined in both solid and liquid media for 24 strains. Depending upon which aminoglycoside was used, we found that 10-30% of the enterobacteriaceae exhibited a twofold diminution of MIC when tested in broth as compared to agar, while the greater proportion of strains was characterized by a higher MIC tested in broth as compared to agar.

Differentiation of Serratia marcescens and Serratia liquefaciens by tests for lipase and phospholipase production.

The production of lipase and phospolipase by certain members of the Enterobacteriaceae was examined by thin-layer chromatography of resting-cell suspensions incubated with triolein or lecithin. Most strains of Serratia marcescens produced both enzymes while most strains of Serratia liquefaciens exhibited strong lipase but only a minor phospholipase activity. Enterobacter spp. (25 strains), Klebsiella pneumoniae (20 strains), Escherichia coli (15 strains), Citrobacter freundii (7 strains) and Proteus spp. (20 strains) lacked both types of enzymic activity except for the following: three strains of Enterobacter cloacae, two of Proteus mirabilis and three of Proteus vulgaris possessed slight lipase activity; about one-half of the Enterobacter aerogenes and Enterobacter hafniae strains examined produced slight phospholipase activity. It is suggested that tests for lipase and phospholipase should be used in conjunction with those for DNAase production and sugar fermentation for the differentiation of S. marcescens and S. liquefaciens.