S. Haeggman et al., AN ALLELIC VARIANT OF THE CHROMOSOMAL GENE FOR CLASS-A BETA-LACTAMASEK2, SPECIFIC FOR KLEBSIELLA-PNEUMONIAE, IS THE ANCESTOR OF SHV-1, Antimicrobial agents and chemotherapy, 41(12), 1997, pp. 2705-2709
Fecal Klebsiella isolates from neonates in 22 Swedish special care uni
ts were examined by a PCR we developed for detection of the SHV-1 beta
-lactamase gene. All 105 K. pneumoniae isolates and all 11 K. pneumoni
ae reference strains (including the K. pneumoniae subsp. pneumoniae, o
zaenae, and rhinoscleromatis type strains) tested were positive, where
as all 67 K. oxytoca isolates and the K. oxytoca, K. planticola, and K
. terrigena type strains tested were negative. Resistance to beta-lact
ams in K. pneumoniae was not transferable by conjugation, and the beta
-lactamase gene was never found on a plasmid. Southern blot analysis s
howed that the gene had a defined chromosomal location. Isoelectric fo
cusing and sequencing of 231-bp PCR amplicons from different isolates
revealed many variants of the enzyme, with the two main groups being S
HV-1 like (pI 7.6; 68 isolates) and LEN-1 like (pI 7.1; 14 isolates).
Clavulanic acid markedly reduced the MICs of ampicillin for all the K.
pneumoniae isolates tested, This fact, MIC profiles (penicillin rathe
r than cephalosporin resistance), pIs, and sequence data showed that t
he chromosomal beta-lactamase of K. pneumoniae is a class A, group 2 e
nzyme distinct from the chromosomal AmpC enzymes found in several othe
r gram-negative bacteria and from the chromosomal beta-lactamase K1 of
K. oxytoca. We propose that the chromosomal beta-lactamase of K. pneu
moniae be designated K2 and suggest that an allelic pI 7.6 variant of
this enzyme is the ancestor of the SHV family of plasmid-mediated beta
-lactamases.