[Resistance of blood culture isolates in vitro to 4 aminoglycoside antibiotics in Austria--1982/83].

Over the period September 1982 to February 1983 268 blood culture isolates were consecutively collected in 4 microbiological laboratories in Austria (Linz, Vienna, Graz, Feldkirch) and 251 of these strains (streptococci excluded) were tested for resistance to Gentamicin (G), Tobramycin (T), Netilmicin (N) and Amikacin (A) using a microtitre broth dilution method. This investigation was part of an international study. Of the bacterial strains examined 57% were staphylococci (34% Staphylococcus aureus) and 43% gram-negative rods (18% E. coli, 17% other enterobacteriaceae and 5% Pseudomonas aeruginosa etc.). 25% of all strains tested were resistant to Gentamicin (MIC greater than 4 mg/l), 27% to Tobramycin (MIC greater than 4 mg/l), 6% to Netilmicin (MIC greater than 4 mg/ml) and 5% to Amikacin (MIC greater than 8 mg/l). The resistance rate of staphylococci was markedly greater towards Gentamicin (35%) and Tobramycin (39%) than Netilmicin (4%) and Amikacin (6%). The respective percentages of resistant gram-negative rods were considerably smaller, except in the case of Netilmicin (G 13%, T 11%, N 8%, A 4%). Regional differences were observed between Linz and Vienna in the resistance of staphylococci to Gentamicin (24% versus 49%) and Tobramycin (33% versus 53%). On a weight basis Netilmicin was the most active substance in combating nearly all groups of bacteria. Also in strains sensitive to the other aminoglycosides the MIC values of Netilmicin were considerably lower than for the other substances. A noteworthy feature in comparison with the results of other countries participating in this international study was the distinctly higher incidence of staphylococci among the blood culture isolates and the considerably higher percentage of aminoglycoside-resistant strains in Austria. Analysis of the data suggests that the high resistance rates among staphylococci are a consequence of selection by frequently used antibiotics. Hence, it appears essential to observe the development of aminoglycoside resistance in Austria closely and to recommend that these substances, of extreme value in the treatment of severe infections, should be used solely for the most stringent indications.