Characterization of an inhibitor-resistant TEM (IRT) beta-lactamase in a novel strain of Klebsiella pneumoniae

Molecular and biochemical characterization of SHV-56, a novel inhibitor-resistant beta-lactamase from Klebsiella pneumoniae

A clinical strain of Klebsiella pneumoniae was found to possess the chromosomal gene bla(SHV-56), encoding a new inhibitor-resistant beta-lactamase with a pI of 7.6. SHV-56 is derived from SHV-11 by the single substitution K234R. This mutation therefore evidences a new critical site for inhibitor resistance among SHV enzymes.

SHV-49, a novel inhibitor-resistant beta-lactamase in a clinical isolate of Klebsiella pneumoniae

A clinical strain of Klebsiella pneumoniae carried the bla(SHV-49) gene, encoding a novel inhibitor-resistant beta-lactamase of pI 7.6, derived from SHV-1 by the single substitution M69I. It also harbored a gene differing from bla(SHV-11) by four silent mutations and coding for a penicillinase. Both genes were chromosome located and might represent either a species-specific gene or an acquired resistance gene.

TEM-80, a novel inhibitor-resistant beta-lactamase in a clinical isolate of Enterobacter cloacae

Enterobacter cloacae Ecl261 was isolated with Escherichia coli Ec257 from the urine of a patient living in a nursing home. Both isolates were resistant to ticarcillin (MICs, 1,024 microg/ml), without significant potentiation of its activity by 2 microg of clavulanate per ml (MICs, 512 microg/ml), and susceptible to naturally active cephalosporins. This inhibitor-resistant phenotype was conferred in both strains by similar conjugative plasmids of 40 kb (Ecl261) and 30 kb (Ec257), which also conveyed resistance to sulfonamides and trimethoprim. Clinical and transconjugant strains produced a beta-lactamase with a pI of 5.2 which belonged to the TEM family, as indicated by specific PCR amplification. Compared with TEM-1, this enzyme exhibited lower catalytic efficiencies (14- and 120-fold less for amoxicillin and ticarcillin, respectively), and higher concentrations of beta-lactamase inhibitors were required to yield a 50% reduction in benzylpenicillin hydrolysis (750-, 82-, and 50-fold higher concentrations for clavulanate, sulbactam, and tazobactam, respectively). Gene sequencing revealed four nucleotide differences with the nucleotide sequence of bla(TEM-1A). The first replacement (T32C), located in the promoter region, was described as being responsible for the increase in the level of beta-lactamase production. The three other changes led to amino acid substitutions that define a new inhibitor-resistant TEM (IRT) beta-lactamase, TEM-80 (alternate name, IRT-24). Two of them, Met69Leu and Asn276Asp, have previously been related to inhibitor resistance. The additional mutation, Ile127Val, was demonstrated by site-directed mutagenesis to have a very weak effect, at least alone, on the IRT phenotype. This is the first description of an IRT beta-lactamase in E. cloacae. The horizontal transfer of bla(TEM-80) may have occurred either from Ec257 to Ecl261 or in the reverse order.

TEM-89 beta-lactamase produced by a Proteus mirabilis clinical isolate: new complex mutant (CMT 3) with mutations in both TEM-59 (IRT-17) and TEM-3

TEM-89 (CMT-3) is the first complex mutant beta-lactamase produced by a clinical strain of Proteus mirabilis (strain Pm 631). This new enzyme, which has a pI of 6.28, is derived from TEM-3 and has a single amino acid substitution also encountered in TEM-59 (inhibitor-resistant TEM beta-lactamase IRT-17): Ser-130 to Gly. TEM-89 hydrolyzed penicillins to the same extent that TEM-3 did but lost almost all hydrolytic activity for cephalosporins and, like TEM-59, was highly resistant to inhibitors.

Multiple antibiotic-resistant bacteria in long-term-care facilities: An emerging problem in the practice of infectious diseases

Long-term-care facilities (LTCFs) are becoming a major component of the health care delivery system. The management of infections with antibiotic-resistant bacteria in elderly patients in LTCFs is presenting new challenges to our current therapeutic armamentarium. Among the enteric bacilli, resistance to ceftazidime, beta-lactam/beta-lactamase-inhibitor combinations, and trimethoprim-sulfamethoxazole present the foremost problems. Quinolone-resistant gram-negative and gram-positive bacteria are increasing in frequency because of the widespread use of these agents in empirical treatment. Among the resistant gram-positive organisms, methicillin-resistant Staphylococcus aureus, penicillin-resistant pneumococci, and vancomycin-resistant enterococci are the most feared pathogens. Education, antibiotic control measures, and fundamental epidemiological and scientific research are advocated as important preventive measures.

Epidemiological survey of amoxicillin-clavulanate resistance and corresponding molecular mechanisms in Escherichia coli isolates in France: new genetic features of bla(TEM) genes

Amoxicillin-clavulanate resistance (MIC >16 microg/ml) and the corresponding molecular mechanisms were prospectively studied in Escherichia coli over a 3-year period (1996 to 1998) in 14 French hospitals. The overall frequency of resistant E. coli isolates remained stable at about 5% over this period. The highest frequency of resistant isolates (10 to 15%) was observed, independently of the year, among E. coli isolated from lower respiratory tract samples, and the isolation rate of resistant strains was significantly higher in surgical wards than in medical wards in 1998 (7.8 versus 2.8%). The two most frequent mechanisms of resistance for the 3 years were the hyperproduction of the chromosomal class C beta-lactamase (48, 38.4, and 39.7%) and the production of inhibitor-resistant TEM (IRT) enzymes (30.4, 37.2, and 41.2%). By using the single-strand conformational polymorphism-PCR technique and sequencing methods, we determined that 59 IRT enzymes corresponded to previously described IRT enzymes whereas 8 were new. Three of these new enzymes derived from TEM-1 by only one amino acid substitution (Ser130Gly, Arg244Gly, and Asn276Asp), whereas three others derived by two amino acid substitutions (Met69Leu and Arg244Ser, Met69Leu and Ile127Val, and Met69Val and Arg275Gln). The two remaining new IRTs showed three amino acid substitutions (Met69Val, Trp165Arg, and Asn276Asp and Met69Ile, Trp165Cys, and Arg275Gln). New genetic features were also found in bla(TEM) genes, namely, bla(TEM-1B) with either the promoters Pa and Pb, P4, or a promoter displaying a C-->G transversion at position 3 of the -35 consensus sequence and new bla(TEM) genes, notably one encoding TEM-1 but possessing the silent mutations originally described in bla(TEM-2) and then in some bla(TEM)-encoding IRT enzymes.

Molecular epidemiology of an outbreak due to IRT-2 beta-lactamase-producing strains of Klebsiella pneumoniae in a geriatric department

In February 1998, 195 patients in the geriatric department of a French hospital were screened for the presence of co-amoxiclav-resistant Klebsiella pneumoniae. Eleven co-amoxiclav-resistant isolates obtained all produced an identical IRT-2 beta-lactamase. These K. pneumoniae isolates were clonally related and harboured a c. 55 kb non-conjugative plasmid encoding a non-class-1 integron-located blaIRT-2 gene. This study underlines that geriatric departments may be a reservoir for antibiotic-resistant strains and that IRT beta-lactamase-producing strains may be nosocomial pathogens.

Molecular characterization of TEM-59 (IRT-17), a novel inhibitor-resistant TEM-derived beta-lactamase in a clinical isolate of Klebsiella oxytoca

A clinical isolate of Klebsiella oxytoca (Kox 443) was found to have a low-level resistance to broad-spectrum penicillins (MICs of amoxicillin and ticarcillin, 256 and 32 microg/ml, respectively), without substantial potentiation by 2 microg of clavulanic acid per ml (amoxicillin- and ticarcillin-clavulanate, 128 and 8 microg/ml, respectively), while being fully susceptible to cephalosporins and other beta-lactam antibiotics. These resistances were carried by a ca. 50-kb conjugative plasmid that encodes a single beta-lactamase with a pI of 5.6. Compared to TEM-2, this enzyme exhibited a 3- to 30-fold higher Km and a decreased maximal hydrolysis rate for beta-lactams; higher concentrations of suicide inactivators (5- to 500-fold higher concentrations giving a 50% reduction in hydrolysis) were required for inhibition. Nucleotide sequence analysis revealed identity between the blaTEM gene of Kox 443 and the blaTEM-2 gene, except for a single A-to-G change at position 590, leading to the amino acid change from Ser-130 Gly. This mutation has not been reported previously in the TEM type beta-lactamases produced by clinical strains, and the novel enzyme was called TEM-59 (alternative name IRT-17). This is the first description of an inhibitor-resistant TEM-derived enzyme in the species K. oxytoca.

Inhibitor-resistant TEM beta-lactamases: phenotypic, genetic and biochemical characteristics

Beta-lactamases represent the main mechanism of bacterial resistance to beta-lactam antibiotics. The recent emergence of bacterial strains producing inhibitor-resistant TEM (IRT) enzymes could be related to the frequent use of beta-lactamase inhibitors such as clavulanic acid, sulbactam and tazobactam in hospitals and in general practice. The IRT beta-lactamases differ from the parental enzymes TEM-1 or TEM-2 by one, two or three amino acid substitutions at different locations. This paper reviews the phenotypic, genetic and biochemical characteristics of IRT beta-lactamases in an attempt to shed light on the pressures that have contributed to their emergence.

Bacterial enzymatic resistance: beta-lactamases and aminoglycoside-modifying enzymes

Numerous novel beta-lactamases and aminoglycoside-modifying enzymes with altered substrate profiles continue to be identified. Plasmid-mediated transmission of many of these enzymes readily occurs due to inclusion of the encoding genes in mobile gene cassettes. Recent crystallographic determinations of the structures of metallo-beta-lactamases and aminoglycoside-modifying enzymes provide the opportunity for the rational design of inhibitors.