Natural antibiotic susceptibility of strains of the Enterobacter cloacae complex

The natural susceptibility to 70 antibiotics of 104 strains of the Enterobacter cloacae complex was examined using a microdilution procedure in Isosensitest broth. One hundred and one clinical strains designated as 'E. cloacae' were identified as E. hormaechei (n=65), E. asburiae (n=20) and E. cloacae genospecies 1 or 2 (n=16). Apart from fosfomycin susceptibility, there were only minor differences in natural antibiotic susceptibility patterns. All species were naturally sensitive or naturally sensitive and intermediate to numerous beta-lactams (e.g. carbapenems, aztreonam, acylaminopenicillins, ticarcillin, and some 'modern' cephalosporins), quinolones, aminoglycosides, tetracyclines, antifolates, chloramphenicol, and nitrofurantoin. Uniform natural resistance was found in benzylpenicillin, oxacillin, amoxycillin, amoxycillin/clavulanate, cefoxitin, rifampicin, lincosamides, glycopeptides, streptogramins and fusidic acid. Enterobacter hormaechei was the species most susceptible to fosfomycin. beta-Lactam susceptibility patterns pointed to the presence of chromosomally-encoded AmpC enzymes in all taxa of the E. cloacae complex.