Novel SHV-Derived Extended-Spectrum β-Lactamase, SHV-57, That Confers Resistance to Ceftazidime but Not Cefazolin

Abstract

A new SHV-derived extended-spectrum ␤-lactamase, SHV-57, that confers high-level resistance to ceftazidime but not cefotaxime or cefazolin was identified from a national surveillance study conducted in Taiwan in 1998. An Escherichia coli isolate resistant to ampicillin, cephalothin, and ceftazidime but sensitive to cefoxitin, ceftriaxone, cefotaxime, imipenem, and a narrow-spectrum cephem (cefazolin) was isolated from the urine of a patient treated with ␤-lactam antibiotics. Resistance to ␤-lactams was conjugatively transferred with a plasmid of about 50 kbp. The pI of this enzyme was 8.3. The sequence of the gene was determined, and the open reading frame of the gene was found to consist of 861 bases (GenBank accession number AY223863). Kinetic parameters showed that SHV-57 had a poor affinity to cefazolin. The K m value toward cefazolin (5.57 ؋ 10 3 M) was extremely high in comparison to those toward ceftazidime (30.9 M) and penicillin G (67 M), indicating its low affinity to cefazolin. Although the K m value of the ␤-lactamase inhibitor was too high for the study of catalytic activity (k cat ), indicating the low k cat of SHV-57, the SHV-57 carrier was highly susceptible to a ␤-lactam-␤-lactamase inhibitor combination. Comparison of the three-dimensional molecular model of SHV-57 with that of the SHV-1 ␤-lactamase suggests that the substitution of arginine for leucine-169 in the ⍀ loop is important for the substrate specificity.Since the first extended-spectrum ␤-lactamase (ESBL) was isolated in Germany in 1983 (11), TEM-, SHV-, CTX-, and OXA-type ESBLs have been described in various members of the family Enterobacteriaceae (G. A. Jacoby and K. Bush, http://www.lahey.org/studies/webt.htm). Most of the ESBLs have altered hydrolytic activities compared with those of the classical enzymes TEM-1, TEM-2, and SHV-1 as a result of amino acid changes in different specific positions (10, 17). SHV-1 is a narrow-spectrum ␤-lactamase with activity against penicillins. The first extended-spectrum SHV enzyme was described in 1985 and was named SHV-2 (10). The serine at amino acid position 238 was found to be replaced by glycine in SHV-1 and was found to cause resistance to extended-spectrum ␤-lactams. Since then, many SHV-type ESBLs have been reported. Most of the substitutions are at Ambler position 179 or 238, alone or in combination with alterations at positions 35 and 240, which are important for substrate extension (G. A. Jacoby and K. Bush, http://www.lahey.org/studies/webt.htm). X-ray crystallography shows that mutations which cause amino acid changes on or close to the ⍀ loop of the enzyme are highly correlated to resistance to extended-spectrum ␤-lactams (12). The mutation at Gly238 has frequently been reported in SHVtype ESBLs. It causes resistance to various antibiotics, ranging from narrow-spectrum cephalosporins (cefazolin) to extendedspectrum cephalosporins (ceftazidime and cefotaxime). However, resistance only to extended-spectrum cephalosporins with susceptibility to narrow-spectrum cephalosporins is rarely...

Dissemination of Extended-Spectrumβ-Lactamase-Producing Enterobacteriaceae in Intensive Care Units of a Medical Center in Taiwan

“…22,23,28,31,32,34 Rare ESBLs, such as SHV-57, TEM-10, and CTX-M-9 also have been reported. 21,32,34 Our results were similar to these reports in that a disseminating plasmid carried with the respective resistant genes was responsible for the prevalence of ESBL-producing E. coli. 23,31,32 In contrast, clonal spread of two epidemic strains in RICU (80%), MICU1 (60%), and MICU2 (62%) has resulted in the higher prevalence of ESBL-producing K. pneumoniae in the three ICUs.…”

Prediction of the Evolution of Ceftazidime Resistance in Extended-Spectrum β-Lactamase CTX-M-9

“…Residue 169 is highly conserved in ␤-lactamases. In vitro mutagenesis experiments with the TEM-1 enzyme and the recent characterization of the ESBL SHV-57 showed that substitutions Leu169Pro and Leu169Arg resulted in activity against ceftazidime with a concomitantly significant compromise in the resistance to penicillins (25,40). Two different substitutions were obtained at position 169 in our CTX-M mutants, Leu169Gln and Leu169Met, which seem to confer similar behavior against penicillins and ceftazidime.…”

Kinetics Study of KPC-3, a Plasmid-Encoded Class A Carbapenem-Hydrolyzing β-Lactamase

“…The periplasmic content was extracted as described previously (12). Purification was achieved using a HiPrep 16/10 SP XL column (Amersham Biosciences AB, Uppsala, Sweden) equilibrated in 10 mM acetate buffer (pH 5.0).…”