No abstract

Gram-negative isolates from blood and cerebrospinal fluid were monitored for 1 year before and for 1 year after the first-line aminoglycoside in a busy pediatric department was changed from gentamicin to amikacin.In the general pediatric wards, the switch to amikacin resulted in no change in resistance of nosocomial gram-negative infections to either amikacin (0%Yo before and after) or gentamicin (23.9% [before] versus 26.5% [after]). In the neonatal unit, the switch to amikacin was followed by an outbreak of Serratia spp. that were commonly resistant to amikacin but susceptible to gentamicin. This outbreak abated spontaneously. In the year after the change in aminoglycoside usage, the resistance to amikacin of nosocomially acquired gram-negative infections increased from 7.6 to 27.7% (P < 0.001), and the resistance to gentamicin decreased from 71.2 to 60.2% (P = 0.07). The increase in amikacin resistance of gram-negative bacilli other than Serratia spp. has persisted for more than a year after the introduction of amikacin as the sole aminoglycoside. The different effects observed in the two sections of the pediatric department may be related to the more intensive usage of aminoglycosides in the neonatal unit.The effect of predominant amikacin usage on susceptibility of gram-negative bacteria (GNB) to aminoglycosides is well documented (1, 5-7, 11, 13, 17, 19, 22-24, 28, 30). Those studies showed that frequent usage of amikacin usually results in no increase or only a slight increase in resistance to amikacin and a decrease in resistance to other aminoglycosides. However, in none of those studies were communityand hospital-acquired infections analyzed separately. Also, GNB isolated from all sites were included, and except in one study (6), invasive disease was not separated from colonization without invasion. Because all infections were combined, increases in amikacin resistance of nosocomial infections may have been "diluted" by the inclusion of large numbers of community-acquired isolates. Similarly, combining isolates from all sections of a hospital may mask significant changes in a specific area.Further motivation for this study was the lack of information on antimicrobial resistance levels in relation to aminoglycoside usage in developing countries, where overcrowded hospitals with very high rates of patient turnover are common.Because of increasing resistance of GNB to gentamicin, both the neonatal and general pediatric wards of our hospital changed to amikacin as the sole aminoglycoside for suspected GNB infections.The purpose of this study was to record prospectively the effect of intensive amikacin usage on the aminoglycoside resistance patterns of invasive hospital-acquired GNB in a busy pediatric department. MATERIALS AND METHODSPatient population. Baragwanath is the major hospital serving Soweto, South Africa (population of 1 to 2 million).