Clonal outbreaks of extended-spectrum beta-lactamase-producing strains of Klebsiella pneumoniae demonstrated by antibiotic susceptibility testing, beta-lactamase typing, and multilocus enzyme electrophoresis.

Nineteen extended-spectrum beta-lactamase (ESBla)-producing Klebsiella pneumoniae isolates from Rouen Hospital were investigated for their implication in nosocomial outbreaks: in addition to antibiotic susceptibility testing, the ESBlas were characterized by isoelectric focusing, and the genetic relationships between the strains were analyzed by multilocus enzyme electrophoresis using a combined polyacrylamide electrophoresis-electrophoretic transfer technique. Four isoelectric focusing beta-lactamase patterns and 11 enzyme electrophoretic types (ETs) among the strains tested were described. Three strains isolated in the same neurological unit over a 7-day period exhibited an SHV 3 beta-lactamase (pI 7.0) and were assigned to a common ET. Three of five strains isolated from patients in a rehabilitation center over a 6-week period harbored an SHV 4 beta-lactamase (pI 7.8) and exhibited the same ET. These results differentiate nosocomial transmission from sporadic cases and provide evidence that multilocus enzyme electrophoresis is a potential tool for studying genetic relationships between strains harboring a common ESBla.