Involvement of SHV-12 and SHV-2a Encoding Plasmids in Outbreaks of Extended-Spectrum β-Lactamase-Producing Klebsiella pneumoniae in a Tunisian Neonatal Ward

Previous genotypic investigations of extended-spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae recovered in a Tunisian neonatal ward revealed the spread of two epidemic strains and a high number of genetically unrelated isolates. The aim of the present study was to determine the role of the dissemination of self-transferrable plasmids harboring bla genes in the outbreaks experienced by the ward. The 49 previously identified clinical isolates of ESBL-producing K. pneumoniae were examined for relationships between their enzymes and plasmids. Analysis of crude extracts by isoelectric focusing showed four β-lactamase-activities at pI 8.2, 7.6, 6, and 5.4. Clinical isolates contained large plasmids that could be transferred by conjugation and transformation conferring resistance to expanded-spectrum cephalosporins. DNA amplification and sequencing were performed to confirm the identities of transferred β-lactamases. Nucleotide sequence analysis of SHV-specific PCR products from six isolates identifi...