Increased resistance to β-lactams in a Klebsiella pneumoniae strain: role of a deletion downstream of the Pribnow box in the blaSHV-1 promoter

Two hundred and five isolates of Klebsiella pneumoniae were collected from Nantes University Hospital in 2002. A new 30 bp deletion was detected downstream of the –10 box of the SHV-1 promoter in a clinical K. pneumoniae isolate with a high amoxicillin/clavulanic acid minimum inhibitory concentration. Reverse transcription polymerase chain reaction revealed increased transcription of blaSHV-1 mRNA. All conjugation mating assays failed. This new promoter was cloned upstream of the cat gene of the reporter plasmid pKK232-8 and compared with previously described blaSHV-1 promoters. The deletion induced a 15-fold increase in promoter strength compared with the usual weak promoter. This study reports a new genetic event that increases blaSHV-1 chromosomal gene expression, which may be of clinical relevance when associated with porin deficiency.