Complex molecular epidemiology of extended-spectrum-lactamases in Klebsiella pneumoniae: a long-term perspective from a single institution in

Methods: All K. pneumoniae isolates recovered during the studied period were screened for ESBL pro-duction. One isolate per patient was selected for ESBL characterization and for population structure, including phylogenetic groups, and plasmid analysis. Results: Ninety-three (3.2 % mean) ESBL-producing K. pneumoniae isolates recovered from 61 patients (26%, medical wards; 18%, surgical wards; 25%, ICU; and 31%, outpatients) were identified. Outpatients significantly increased (P < 0.01) when compared with 1989–2000 (7%). The number of different ESBLs increased with persistence of previously identified enzymes (TEM-4, SHV-2, CTX-M-9 and CTX-M-10) and emergence of new ESBLs (TEM-110, SHV-11, SHV-12, CTX-M-14 and CTX-M-15). A polyclonal structure, including epidemic clones with specific ESBLs (TEM-4, SHV-12 and CTX-M-15), was observed. Phylogenetic analysis showed that most isolates (74.6%) belonged to KpI-type with a clear relationship between KpIII-type and CTX-M-10 producers. Persistence of specific plasmids associated with specific ESBLs (TEM-4, SHV-12, CTX-M-10 and CTX-M-15) was observed. Co-resistance analysis revealed an incre-ment in resistance to trimethoprim (41.5 % versus 10.3%), sulphonamide (54.7 % versus 29.3%) and nali-dixic acid (34.0 % versus 6.9%) when compared with 1989–2000. Conclusions: K. pneumoniae is still an important ESBL producer in our institution with a complex epide