Diversity of beta-lactam resistance levels among related Klebsiella pneumoniae strains isolated in an intensive care unit

Seven multiresistant Klebsiella pneumoniae strains isolated in an intensive care unit were studied. Susceptibility to beta-lactams was determined with the E test. Molecular-typing of the isolates was performed by a PCR-based technique (ERIC2-PCR). Sonic cell-extracts were used as beta-lactamase prep arations. Beta-lactamase quantities were evaluated measuring nitrocefin hyd rolysis. The similarity of the ERIC2-PCR patterns indicated that the seven isolates constituted a single clone. The levels of resistance to oximino-be ta-lactams, however, were different. There were indications that the differ ences in susceptibilities were due, at least partly, to differences in the levels of expression of an extended-spectrum beta-lactamase (most likely SH V-5), Related K pneumoniae isolates may exhibit different levels of resista nce to beta-lactams, Therefore, comparison of resistance phenotypes is of l imited usefulness in epidemiological investigations of nosocomial infection s caused by resistant K. pneumoniae.