Complexity and diversity of Klebsiella pneumoniae strains with extended-spectrum beta-lactamases isolated in 1994 and 1996 at a teaching hospital in Durban, South Africa

beta -Lactamase production was investigated in cultures of 25 Klebsiella pn eumoniae isolates isolated at a hospital in Durban, South Africa, in 1994 a nd 1996. Twenty of these isolates gave ceftazidime MIC/ceftazidime plus cla vulanate MIC ratios of greater than or equal to8, implying production of ex tended-spectrum beta -lactamases (ESBLs), and DNA sequencing identified an ESBL gene (bla(TEM-53)) in a further two isolates. Pulsed-field gel electro phoresis (PFGE) defined 4 distinct strains among the 12 isolates collected in 1994 and 9 distinct strains among the 13 isolates collected in 1996. In three cases, multiple isolates from single patients varied in their PFGE pr ofiles and antibiograms, implying mixed colonization or infection. Isoelect ric focusing and DNA hybridization found both TEM and SHV enzymes and their genes in all 25 isolates. Many isolates had multiple identical or differen t beta -lactamase gene variants, with at least 84 bla(SHV) and bla(TEM) gen e copies among the 25 organisms. Sequencing identified the genes for the SH V-1, -2, and -5 enzymes and for four new SHV types (SHV-19, -20, -21, and - 22). These new SHV variants had novel mutations remote from sites known to affect catalytic activity. Sequencing also found the genes for TEM-1, TEM-5 3, and one novel type, TEM-63. All the isolates had multiple and diverse pl asmids. These complex and diverse patterns of ESBL production and strain ep idemiology are far removed from the concept of an ESBL outbreak and suggest a situation in which ESBL production has become endemic and in which evolu tion is generating a wide range of enzyme combinations. This complexity and diversity complicates patient management and the design of antibiotic use policies.