Natural antibiotic susceptibility of Klebsiella pneumoniae, K. oxytoca, K. planticola, K. ornithinolytica and K. terrigena strains.

The natural susceptibility of 221 Klebsiella strains to 71 antibiotics was examined. The strains were isolated from clinical specimens and the environment, and belonged to K. pneumoniae subsp. pneumoniae (n = 40), K. pneumoniae subsp. ozaenae (37), K. pneumoniae subsp. rhinoscleromatis (10), K. oxytoca (44), K. planticola (40), K. ornithinolytica (25) and K. terrigena (25). MIC values were determined by a microdilution procedure in IsoSensitest broth according to the German standard (DIN). All Klebsiella spp. were naturally resistant or intermediate to amoxicillin, ticarcillin and to antibiotics to which other Enterobacteriaceae are also intrinsically resistant. Klebsiella spp. were naturally sensitive or intermediate to several penicillins, all tested cephalosporins, aminoglycosides, quinolones, tetracyclines, trimethoprim, cotrimoxazole, chloramphenicol and nitrofurantoin. K. pneumoniae subsp. ozaenae and subsp. rhinoscleromatis strains were generally more susceptible to antibiotics than strains of other Klebsiella taxa. K pneumoniae subsp. rhinoscleromatis was the most susceptible taxon, being highly susceptible to cefuroxime, anti-folates and naturally intermediate to erythromycin and clarithromycin. K. pneumoniae subsp. ozaenae was most susceptible to glycopeptides. K. oxytoca and K. terrigena strains were least susceptible to cefazoline, cefoperazone and fosfomycin, respectively. The results of the present study describe a database of the natural antimicrobial susceptibility of Klebsiella spp., which can be used for the validation of antibiotic susceptibility results of these bacteria. MIC patterns to beta-lactams indicate the expression of chromosomally encoded class A gamma-lactamases in all the species, including the subspecies of K. pneumoniae. Similar natural susceptibility patterns of K. planticola and K. ornithinolytica to all tested antibiotics support the status of K. ornithinolytica as a biovar of K. planticola.