Development of resistance to aminoglycosides among coagulase-negative staphylococci and enterobacteriaceae in a neonatal intensive care unit

Abstract

A prospective study of the development of resistance to aminoglycosides among coagulase-negative staphylococci (CNS) and Enterobacteriaceae (ENT) was conducted for all patients admitted to a neonatal intensive care unit (NICU) from October 1985 to January 1990. A change in antibiotic regimen from gentamicin to amikacin occurred in January 1986, due to widespread gentamicin resistance among CNS, the most important cause of nosocomial infections in this NICU. From 657 patients, 884 faecal cultures, 1505 cultures from the respiratory tract and 152 blood cultures were included in the study. After its introduction, susceptibility to amikacin decreased rapidly in faecal and respiratory CNS isolates (from 62% to 28% and from 58% to 23% respectively). During the first half year, resistance to amikacin in faecal CNS isolates developed more rapidly among antibiotic-treated patients than among patients not treated with antibiotics. Susceptibility to amikacin in CNS blood isolates decreased more slowly, from 94% to 58% in 1987, while subsequently an increase in susceptibility was observed to about 80% in 1989. The same difference in development of resistance in faecal and respiratory CNS isolates compared to CNS blood isolates was noticed for gentamicin and tobramycin. In contrast, ENT remained highly (85–100%) susceptible to amikacin, gentamicin and tobramycin throughout the study period. It was concluded that four years after its introduction amikacin still appeared to be a valuable antibiotic in combination treatment of the vast majority of clinically important infections occurring in our NICU, since both Enterobacteriaceae and the majority of CNS blood isolates proved to be susceptible to this agent. However, no substantial advantage in terms of susceptibility was found in the use of amikacin over gentamicin or tobramycin.