CMT-Type β-Lactamase TEM-125, an Emerging Problem for Extended-Spectrum β-Lactamase Detection

Abstract

The clinical strain Escherichia coli TO799 was resistant to penicillin-clavulanate combinations and ceftazidime and was not reproducibly detected as an extended-spectrum ␤-lactamase (ESBL) according to the standards of the Clinical Laboratory Standards Institute (CLSI; formerly NCCLS) and the national guidelines of the French Society for Microbiology (Comité de l'Antibiogramme de la Société Française de Microbiologie). A novel ␤-lactamase, designated TEM-125, was responsible for this phenotype. TEM-125 harbors a complex association of mutations previously described in the ESBL TEM-12 and in the inhibitor-resistant ␤-lactamase TEM-39. TEM-125 is the first complex mutant TEM to present hydrolytic activity against ceftazidime (k cat , 3.7 s ؊1 ) together with a high level of resistance to clavulanate (50% inhibitory concentration, 13.6 M). The discovery of such an ESBL, which is difficult to detect by the usual ESBL detection methods, confirms the emergence of a complex mutant TEM subgroup and highlights the need to evaluate detection methods so as to avoid possible therapeutic failures.Among Enterobacteriaceae, the most prevalent mechanism of acquired resistance to ␤-lactams is the production of ␤-lactamases such as the penicillinases TEM-1 and SHV-1, which hydrolyze penicillins and narrow-spectrum cephalosporins. In order to thwart these ␤-lactamases, two types of ␤-lactams were developed: ␤-lactam antibiotics resistant to the hydrolysis, such as expanded-spectrum cephalosporins (ceftazidime), and inhibitors of TEM and SHV penicillinases (clavulanic acid and tazobactam). However, the intensive use of these molecules was quickly followed by an evolution of TEM-and SHVtype ␤-lactamases.The first TEM-type extended-spectrum ␤-lactamases (ESBLs) were characterized in 1987 (28). They differ from the SHV and TEM penicillinases by a few amino acid substitutions which confer hydrolytic activity against expanded-spectrum cephalosporins. These ESBLs are susceptible to ␤-lactamase inhibitors. Clinical laboratories are urged by the CLSI (formerly NCCLS) (8) and the Comité de l'Antibiogramme de la Société Française de Microbiologie (CA-SFM) (9) to use the association of hydrolytic activity against expanded-spectrum cephalosporins and susceptibility to inhibitors as a specific means of detecting this type of enzyme.As the use of expanded-spectrum cephalosporins led to the selection of ESBLs, the clinical use of penicillin-␤-lactamase inhibitor combinations led from 1990 onwards to the selection of point mutants of TEM penicillinases resistant to inhibitors (3). However, the strains producing these enzymes, designated inhibitor-resistant TEMs (IRTs), are generally susceptible to cephalosporins (5).A few enzymes that combine ESBL and IRT mutations have recently emerged among the TEM ␤-lactamases. These new enzymes, designated complex mutant TEMs (CMTs), have been identified in different species of Enterobacteriaceae such as Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, and Enterobacter aerogenes (10,19,22,24,27). De...

Evolution of TEM-Type Enzymes: Biochemical and Genetic Characterization of Two New Complex Mutant TEM Enzymes, TEM-151 and TEM-152, from a Single Patient

“…As previously observed for other complex mutants belonging to the TEM subgroup (11,(21)(22)(23)(24)27), TEM-151 and TEM-152 were slightly less efficient against oxyimino-␤-lactams than the corresponding ESBLs TEM-28 and TEM-29 (k cat , 1 to 16 versus 2.1 to 64 s Ϫ1 ). However, they both significantly hydrolyzed ceftazidime, especially TEM-152, as assessed by their hydrolytic activities (k cat , 5 to 16 s Ϫ1 ).…”

“…Such a loss of resistance to inhibitors was previously observed for all CMT-type ␤-lactamases that presented ESBL hydrolytic activity (11,(22)(23)(24)27). However, they were both more resistant to clavulanic acid and tazobactam than TEM-28 and TEM-29 and even the parental enzyme TEM-1.…”

“…These new ␤-lactamases, called complex mutant TEM (CMT) enzymes, have been identified in different species of Enterobacteriaceae, including Escherichia coli, Proteus mirabilis, Klebsiella pneumoniae, and Enterobacter aerogenes (11,(21)(22)(23)(24)27). These enzymes confer different levels of resistance to clavulanic acid and to oxyimino cephalosporins, depending on the harbored mutations.…”

TEM-187, a New Extended-Spectrum β-Lactamase with Weak Activity in a Proteus mirabilis Clinical Strain

“…Different expert systems revealed only a penicillinase pattern, without any alert on expanded-spectrum cephalosporin MICs. This difficulty was previously observed with other TEMtype ESBL such as the TEM-24 or CMT type, especially TEM-125 (23)(24)(25). As with the clinical TEM-125-producing strain TO799, TEM-187 was not easy to detect following either the American (26,27).…”

Virulence Factors and TEM-Type β-Lactamases Produced by Two Isolates of an Epidemic Klebsiella pneumoniae Strain

“…However, another subgroup of enzymes has appeared that combine the substitutions observed in the ESBLs and in the inhibitor-resistant TEM (IRT): its members were designated complex mutant TEMs (CMTs). They have been observed mainly in Escherichia coli and mostly in France (16,29,31,[34][35][36][37]39). The enzyme TEM-68 (CMT-2) was identified by Fiett et al in an epidemic strain of K. pneumoniae and appeared to have emerged from the ESBL TEM-47 (16).…”