Simplified phenotypic tests for identification of Acinetobacter spp. and their antimicrobial susceptibility status

Acinetobacter spp. have been found to be responsible for an increasing number of nosocomial infections. During a 16-month period, 22 patients hospitalised mainly in the respiratory intensive care unit (RICU), paediatric and other medical wards were investigated either for infection or colonisation by Acinetobacter spp. Of the 45 isolates of Acinetobacter detected among the total of 425 non-fermenters encountered, 24 representative isolates were selected for extended phenotypic identification. Four environmental isolates were also included in the study. These 28 isolates were typed by biotyping and antibiotyping, which helped in delineating the Acinetobacter spp. into 12 phenotypes and two distinct antibiotypes respectively. A sudden increase of cases of acinetobacter infection suggested that three outbreaks during the study period were due to phenotypes 1 and 2 of A. calcoaceticus-A. baumannii complex (Acb). Strains of Acb-complex showed multiple drug resistance and were sensitive only to netilmicin. A comparatively high proportion of resistance to amikacin (48%) was also detected among these strains by the agar dilution method. The RICU environment was recognised as an important reservoir for the resistant outbreak strain (Acb-1) which was probably leading to persistent colonisation and recurrent infections.