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

OBJECTIVES: To analyse all extended-spectrum-beta-lactamase (ESBL)-producing Klebsiella pneumoniae isolates recovered from 2001 to 2004 in our institution and to compare this period with that of 1989 to 2000.

METHODS: All K. pneumoniae isolates recovered during the studied period were screened for ESBL production. 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 increment in resistance to trimethoprim (41.5% versus 10.3%), sulphonamide (54.7% versus 29.3%) and nalidixic 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 epidemiology. The main features were a few outbreaks with persistence of specific plasmids, emergence of new enzymes and an increment in community isolates. These results should be taken into account for the implementation of epidemiological containment measures.