Acinetobacter in Denmark: I. Taxonomy, antibiotic susceptibility, and pathogenicity of 112 clinical strains

One hundred and twelve clinical strains of Acinetobacter were collected during a 7-month period in 1990-1991 from Danish clinical microbiology departments. According to the old notation, 37 strains were biovar anitratus and 75 b.lwoffii. Using the newest terminology, 35 strains were unambiguously identified as the species A. haemolyticus, A. johnsonii, A. radioresistens, and as the unnamed phenons 6, 10, and 14, by a numerical approach using a simplified phenotypical identification scheme. Most of the remaining strains were identified to the genotypically heterogeneous A. calcoaceticus-A. baumannii complex and the A. lwoffii phenotype. Sixteen strains (14%) were left unidentified. Eight A. lwoffii strains were glucose-oxidizing and were thus classified as b. anitratus using the old terminology. The strains were tested for susceptibility to ampicillin, piperacillin, ticarcillin, cefotaxime, ceftazidime, imipenem, gentamicin, tetracycline, sulphonamide, and nalidixic acid. All strains were susceptible to imipenem. The susceptibility to the remaining beta-lactams was variable, the A. lwoffii isolates being the most and the A. calcoaceticus-A. baumannii complex strains the least susceptible. All non-A. calcoaceticus-A. baumannii complex strains were susceptible to all other antibiotics tested, except for one A. lwoffii strain that was sulphonamide resistant. Twenty-two percent of the strains in the A. calcoaceticus-A. baumannii complex showed reduced susceptibility or resistance to gentamicin, but only sporadic resistance to sulphonamides, tetracyclines, and nalidixic acid. Eight infections were recorded: three cases of septicaemia, three cases of peritonitis related to continuous ambulatory peritoneal dialysis, and two cases of recurrent urinary tract infection. No epidemics were detected.