Characterization of a beta-lactamase produced in Mycobacterium fortuitum D316

A Tyrosine Residue Along with a Glutamic Acid of the Omega-Like Loop Governs the Beta-Lactamase Activity of MSMEG_4455 in Mycobacterium smegmatis

Mycobacterial beta-lactamases are involved in exerting beta-lactam resistance, though many of these proteins remain uncharacterized. Here, we have characterized MSMEG_4455 of Mycobacterium smegmatis as a beta-lactamase using molecular, biochemical and mutational techniques. To elucidate its nature in vivo and in vitro, and to predict its structure-function relationship in silico analysis is done. The MSMEG_4455 is cloned and expressed ectopically in a beta-lactamase deficient Escherichia coli mutant to establish the in vivo beta-lactamase like nature via minimum inhibitory concentration (MIC) determination. Likewise the in vivo results, purified soluble form of MSMEG_4455 showed beta-lactam hydrolysis pattern similar to group 2a penicillinase. In silico analyses of MSMEG_4455 reveal glutamic acid (E)193 and tyrosine (Y)194 of omega-like loop might have importance in strengthening hydrogen bond network around the active-site, though involvement of tyrosine is rare for beta-lactamase activity. Accordingly, these residues are mutated to alanine (A) and phenylalanine (F), respectively. The mutated proteins have partially lost their ability to exert beta-lactamase activity both in vivo and in vitro. The Y194F mutation had more prominent effect on the enzymatic activity. Therefore, we infer that Y194 is the key for beta-lactamase activity of MSMEG_4455.

Biochemical Characterization of β-Lactamases from Mycobacterium abscessus Complex and Genetic Environment of the β-Lactamase-Encoding Gene

The objectives of this study were to determine the kinetic parameters of purified recombinant Bla_Mab and Bla_Mmas by spectrophotometry, analyze the genetic environment of the bla_Mab and bla_Mmas genes in both species by polymerase chain reaction and sequencing, furthermore, in silico models of both enzymes in complex with imipenem were obtained by modeling tools. Our results showed that Bla_Mab and Bla_Mmas have a similar hydrolysis behavior, displaying high catalytic efficiencies toward penams, cephalothin, and nitrocefin; none of the enzymes are well inhibited by clavulanate. Bla_Mmas hydrolyzes imipenem at higher efficiency than cefotaxime and aztreonam. Bla_Mab and Bla_Mmas showed that their closest structural homologs are KPC-2 and SFC-1, which correlate to the mild carbapenemase activity toward imipenem observed at least for BlaMmas. They also seem to differ from other class A β-lactamases by the presence of a more flexible Ω loop, which could impact in the hydrolysis efficiency against some antibiotics. A -35 consensus sequence (TCGACA) and embedded at the 3' end of MAB_2874, which may constitute the bla_Mab and bla_Mmas promoter. Our results suggest that the resistance mechanisms in fast-growing mycobacteria could be probably evolving toward the production of β-lactamases that have improved catalytic efficiencies against some of the drugs commonly used for the treatment of mycobacterial infections, endangering the use of important drugs like the carbapenems.

Crystal structure of the Mycobacterium fortuitum class A beta-lactamase: structural basis for broad substrate specificity

beta-Lactamases are the main cause of bacterial resistance to penicillins and cephalosporins. Class A beta-lactamases, the largest group of beta-lactamases, have been found in many bacterial strains, including mycobacteria, for which no beta-lactamase structure has been previously reported. The crystal structure of the class A beta-lactamase from Mycobacterium fortuitum (MFO) has been solved at 2.13-A resolution. The enzyme is a chromosomally encoded broad-spectrum beta-lactamase with low specific activity on cefotaxime. Specific features of the active site of the class A beta-lactamase from M. fortuitum are consistent with its specificity profile. Arg278 and Ser237 favor cephalosporinase activity and could explain its broad substrate activity. The MFO active site presents similarities with the CTX-M type extended-spectrum beta-lactamases but lacks a specific feature of these enzymes, the VNYN motif (residues 103 to 106), which confers on CTX-M-type extended-spectrum beta-lactamases a more efficient cefotaximase activity.

Crystal structures of the Bacillus licheniformis BS3 class A beta-lactamase and of the acyl-enzyme adduct formed with cefoxitin

The Bacillus licheniformis BS3 beta-lactamase catalyzes the hydrolysis of the beta-lactam ring of penicillins, cephalosporins, and related compounds. The production of beta-lactamases is the most common and thoroughly studied cause of antibiotic resistance. Although they escape the hydrolytic activity of the prototypical Staphylococcus aureus beta-lactamase, many cephems are good substrates for a large number of beta-lactamases. However, the introduction of a 7alpha-methoxy substituent, as in cefoxitin, extends their antibacterial spectrum to many cephalosporin-resistant Gram-negative bacteria. The 7alpha-methoxy group selectively reduces the hydrolytic action of many beta-lactamases without having a significant effect on the affinity for the target enzymes, the membrane penicillin-binding proteins. We report here the crystallographic structures of the BS3 enzyme and its acyl-enzyme adduct with cefoxitin at 1.7 A resolution. The comparison of the two structures reveals a covalent acyl-enzyme adduct with perturbed active site geometry, involving a different conformation of the omega-loop that bears the essential catalytic Glu166 residue. This deformation is induced by the cefoxitin side chain whose position is constrained by the presence of the alpha-methoxy group. The hydrolytic water molecule is also removed from the active site by the 7beta-carbonyl of the acyl intermediate. In light of the interactions and steric hindrances in the active site of the structure of the BS3-cefoxitin acyl-enzyme adduct, the crucial role of the conserved Asn132 residue is confirmed and a better understanding of the kinetic results emerges.

Molecular and biochemical analysis of AST-1, a class A beta-lactamase from Nocardia asteroides sensu stricto

A beta-lactamase gene was cloned from a Nocardia asteroides sensu stricto clinical isolate. A recombinant plasmid, pAST-1, expressed the beta-lactamase AST-1 in Escherichia coli JM109. Its pI was 4.8, and its relative molecular mass was 31 kDa. E. coli JM109(pAST-1) was resistant to penicillins and narrow-spectrum cephalosporins. The beta-lactamase AST-1 had a restricted hydrolytic activity spectrum. Its activity was partially inhibited by clavulanic acid but not by sulbactam and tazobactam. AST-1 is an Ambler class A beta-lactamase sharing 65% amino acid identity with beta-lactamase FAR-1, the most closely related enzyme.

Biochemical-genetic analysis and distribution of FAR-1, a class A beta-lactamase from Nocardia farcinica

From genomic DNA of the clinical isolate Nocardia farcinica VIC, a 1. 6-kb Sau3AI fragment was cloned and expressed in Escherichia coli JM109. The recombinant strain expressed a beta-lactamase (pI, 4.6), FAR-1, which conferred high levels of resistance to amoxicillin, piperacillin, ticarcillin, and cephalothin. The hydrolysis constants (kcat, Km, Ki, and 50% inhibitory concentration) confirmed the MIC results and showed that FAR-1 activity is inhibited by clavulanic acid and at a low level by tazobactam and sulbactam. Moreover, FAR-1 beta-lactamase hydrolyzes aztreonam (at a low level) without significant activity against ceftazidime, cefotaxime and imipenem. FAR-1 mature protein of molecular mass ca 32 kDa, has less than 60% amino acid identity with any other class A beta-lactamases, being most closely related to PEN-A from Burkholderia cepacia (52%). A blaFAR-1-like gene was found in all studied N. farcinica strains, underlining the constitutive origin of this gene.

Contribution of beta-lactamases to beta-lactam susceptibilities of susceptible and multidrug-resistant Mycobacterium tuberculosis clinical isolates

The beta-lactamases in 154 clinical Mycobacterium tuberculosis strains were studied. Susceptibilities to beta-lactam antibiotics, their combination with clavulanate (2:1), and two fluoroquinolones were determined in 24 M. tuberculosis strains susceptible to antimycobacterial drugs and in nine multiresistant strains. All 154 M. tuberculosis isolates showed a single chromosomal beta-lactamase pattern (pI 4.9 and 5.1). M. tuberculosis beta-lactamase hydrolyzes cefotaxime with a maximum rate of 22.5 +/- 2.19 IU/liter (strain 1382). Neither amoxicillin, carbenicillin, cefotaxime, ceftriaxone, nor aztreonam was active alone. Except for aztreonam, beta-lactam combinations with clavulanate produced better antimycobacterial activity.

Recombinant expression and characterization of the major beta-lactamase of Mycobacterium tuberculosis

New antibiotic regimens are needed for the treatment of multidrug-resistant tuberculosis. Mycobacterium tuberculosis has a thick peptidoglycan layer, and the penicillin-binding proteins involved in its biosynthesis are inhibited by clinically relevant concentrations of beta-lactam antibiotics. beta-Lactamase production appears to be the major mechanism by which M. tuberculosis expresses beta-lactam resistance. beta-Lactamases from the broth supernatant of 3- to 4-week-old cultures of M. tuberculosis H37Ra were partially purified by sequential gel filtration chromatography and chromatofocusing. Three peaks of beta-lactamase activity with pI values of 5.1, 4.9, and 4.5, respectively, and which accounted for 10, 78, and 12% of the total postchromatofocusing beta-lactamase activity, respectively, were identified. The beta-lactamases with pI values of 5.1 and 4.9 were kinetically indistinguishable and exhibited predominant penicillinase activity. In contrast, the beta-lactamase with a pI value of 4.5 showed relatively greater cephalosporinase activity. An open reading frame in cosmid Y49 of the DNA library of M. tuberculosis H37Rv with homology to known class A beta-lactamases was amplified from chromosomal DNA of M. tuberculosis H37Ra by PCR and was overexpressed in Escherichia coli. The recombinant enzyme was kinetically similar to the pI 5.1 and 4.9 enzymes purified directly from M. tuberculosis. It exhibited predominant penicillinase activity and was especially active against azlocillin. It was inhibited by clavulanic acid and m-aminophenylboronic acid but not by EDTA. We conclude that the major beta-lactamase of M. tuberculosis is a class A beta-lactamase with predominant penicillinase activity. A second, minor beta-lactamase with relatively greater cephalosporinase activity is also present.

Contribution of beta-lactamase production to the resistance of mycobacteria to beta-lactam antibiotics

Mycobacterium fallax (M. fallax) is naturally sensitive to many beta-lactam antibiotics (MIC < 2 microg/ml) and devoid of beta-lactamase activity. In this paper, we show that the production of the beta-lactamase of Mycobacterium fortuitum by M. fallax significantly increased the MIC values for good substrates of the enzyme, whereas the potency of poor substrates or transient inactivators was not modified. The rates of diffusion of beta-lactams through the mycolic acid layer were low, but for all studied compounds the half-equilibration times were such that they would only marginally affect the MIC values in the absence of beta-lactamase production. These results emphasize the importance of enzymatic degradation as a major factor in the resistance of mycobacteria to penicillins.

beta-Lactamases in laboratory and clinical resistance

beta-Lactamases are the commonest single cause of bacterial resistance to beta-lactam antibiotics. Numerous chromosomal and plasmid-mediated types are known and may be classified by their sequences or phenotypic properties. The ability of a beta-lactamase to cause resistance varies with its activity, quantity, and cellular location and, for gram-negative organisms, the permeability of the producer strain. beta-Lactamases sometimes cause obvious resistance to substrate drugs in routine tests; often, however, these enzymes reduce susceptibility without causing resistance at current, pharmacologically chosen breakpoints. This review considers the ability of the prevalent beta-lactamases to cause resistance to widely used beta-lactams, whether resistance is accurately reflected in routine tests, and the extent to which the antibiogram for an organism can be used to predict the type of beta-lactamase that it produces.

Susceptibilities of nontuberculosis mycobacterial species to amoxicillin-clavulanic acid alone and in combination with antimycobacterial agents

Neither amoxicillin nor clavulanic acid used alone was active at the highest level tested, i.e., 256.0 micrograms/ml, in vitro against 24 isolates of Mycobacterium fortuitum, Mycobacterium kansasii, and Mycobacterium marinum. However, the MIC of an amoxicillin-clavulanic acid combination of 2:1 was < or = 8.0/4.0 micrograms/ml for 50 percent of the isolates tested, with all isolates being inhibited in the range of 4.0/2.0 to 32.0/16.0 micrograms/ml, respectively. Titration of amoxicillin-clavulanic acid with a fixed 2-micrograms/ml concentration of ethambutol resulted in synergistic activity against 3 of 9 isolates of M. fortuitum, 10 of 10 isolates of M. kansasii, and 5 of 5 isolates of M. marinum. This observation was confirmed in a checkerboard analysis in which fractional inhibitory concentrations were < or = 0.5 for 20 of the 24 isolates. Synergistic activity was observed against the other four isolates in one of two trials. On the other hand, titration of amoxicillin-clavulanic acid in the presence of either one or two fixed concentrations of isoniazid, rifampin, cycloserine, tetracycline, or amikacin failed to result in synergism.

Interactions of biapenem with active-site serine and metallo-beta-lactamases

Biapenem, formerly LJC 10,627 or L-627, a carbapenem antibiotic, was studied in its interactions with 12 beta-lactamases belonging to the four molecular classes proposed by R. P. Ambler (Philos. Trans. R. Soc. Lond. Biol. Sci. 289:321-331, 1980). Kinetic parameters were determined. Biapenem was readily inactivated by metallo-beta-lactamases but behaved as a transient inhibitor of the active-site serine enzymes tested, although with different acylation efficiency values. Class A and class D beta-lactamases were unable to confer in vitro resistance toward this carbapenem antibiotic. Surprisingly, the same situation was found in the case of class B enzymes from Aeromonas hydrophila AE036 and Bacillus cereus 5/B/6 when expressed in Escherichia coli strains.

Distribution and characterization of beta-lactamases of mycobacteria and related organisms

SETTING

The detailed distribution and precise features of mycobacterial beta-lactamases urgently need to be elucidated.

OBJECTIVE

To study the distribution pattern of beta-lactamases among mycobacteria, their enzymatic profiles and degree of contribution to the expression of drug resistance of some mycobacteria to beta-lactam antibiotics.

DESIGN

Cell-associated beta-lactamase was measured by nitrocefin disc method. beta-lactamases obtained from some mycobacteria were studied for their substrate specificity, metal ion-dependency and isoelectric focusing (IEF) patterns. Changes in the minimum inhibitory concentrations (MICs) of beta-lactams for rapidly growing mycobacteria due to the combined use of tazobactam were measured.

RESULTS

In slow growers, Mycobacterium tuberculosis complex possessed strong and M. kansasii showed strong to intermediate beta-lactamase activity, while M. avium complex lacked such an activity. All the rapid growers possessed strong to intermediate activity. The beta-lactamases of test organisms including M. tuberculosis, M. kansasii, M. fortuitum etc, exerted both penicillinase and cephalosporinase activities and were not metalloenzymes. M. tuberculosis, M. kansasii, and M. smegmatis exhibited the species-specific IEF patterns of beta-lactamases. Tazobactam potentiated the in vitro antimicrobial activities of some beta-lactams against M. fortuitum and M. chelonae.

CONCLUSION

Many mycobacteria possessed peculiar beta-lactamases and the enzymes were partly attributable to their drug resistance to certain beta-lactam antibiotics.

Antigenic properties and immunoelectron microscopic localization of Mycobacterium fortuitum beta-lactamase

Mycobacterium fortuitum is a fast-growing Mycobacterium species which produces a beta-lactamase involved in the intrinsic resistance of the microorganism to beta-lactam antibiotics. An anti-beta-lactamase serum against the purified enzyme was raised in rabbits. Antibody binding was specific for native beta-lactamase, and enzyme activity was partially inhibited by the serum; furthermore, cross-reactions with denatured class A beta-lactamases were observed. This serum was used as a probe in immunogold labeling for the localization of the cell-bound beta-lactamase in both the low-level producer ATCC 19542 (parental strain) and the overproducer mutant D316. By the combination of preembedding immunogold labeling and replica technique, it was shown that the beta-lactamase was uniformly distributed on the whole external cell surface, where it appeared to be associated with a Tween 80-removable capsule-like material. Compared with the parental strain, a much higher level of expression of surface enzyme was observed in strain D316. Surface labeling was more intense in the stationary phase of growth than in exponentially growing cells. The data obtained are interpreted in the context of the intrinsic resistance of M. fortuitum to beta-lactam antibiotics.

Contribution of mutant analysis to the understanding of enzyme catalysis: the case of class A beta-lactamases

Class A beta-lactamases represent a family of well studied enzymes. They are responsible for many antibiotic resistance phenomena and thus for numerous failures in clinical chemotherapy. Despite the facts that five structures are known at high resolution and that detailed analyses of enzymes modified by site-directed mutagenesis have been performed, their exact catalytic mechanism remains controversial. This review attempts to summarize and to discuss the many available data.

Use of the chromosomal class A beta-lactamase of Mycobacterium fortuitum D316 to study potentially poor substrates and inhibitory beta-lactam compounds

Sixteen different compounds usually considered beta-lactamase stable or representing potential beta-lactam inhibitors and inactivators were tested against the beta-lactamase produced by Mycobacterium fortuitum. The compounds exhibiting the most interesting properties were BRL42715, which was by far the best inactivator, and CGP31608 and ceftazidime, which were not recognized by the enzyme. These compounds thus exhibited adequate properties for fighting mycobacterial infections. Although cloxacillin, dicloxacillin, cefoxitin, and CP65207-2 exhibited poor inhibitory efficiency against the enzyme, they were also rather poor substrates and might be considered potential antimycobacterial agents. By contrast, CGP31523A and ceftamet were good substrates.

Transcription and expression analysis, using lacZ and phoA gene fusions, of Mycobacterium fortuitum beta-lactamase genes cloned from a natural isolate and a high-level beta-lactamase producer

The gene encoding a class A beta-lactamase was cloned from a natural isolate of Mycobacterium fortuitum (blaF) and from a high-level amoxicillin-resistant mutant that produces large amounts of beta-lactamase (blaF*). The nucleotide sequences of the two genes differ at 11 positions, including two in the region upstream from the coding sequence. Gene fusions to Escherichia coli lacZ and transcription and expression analysis of the cloned genes in Mycobacterium smegmatis indicated that high-level production of the beta-lactamase in the mutant is mainly or wholly due to a single base pair difference in the promoter. These analyses also showed that transcription and translation start at the same position. A comparison of the amino acid sequence of BlaF, as predicted from the nucleotide sequence, with the determined N-terminal amino acid sequence indicated the presence of a typical signal peptide. The fusion of blaF (or blaF*) to the E. coli gene phoA resulted in the production of BlaF-PhoA hybrid proteins that had alkaline phosphatase activity. These results demonstrate that phoA can be used as a reporter gene for studying protein export in mycobacteria.

A class-A beta-lactamase from Pseudomonas stutzeri that is highly active against monobactams and cefotaxime

A beta-lactamase produced by Pseudomonas stutzeri was purified to protein homogeneity, and its physicochemical and catalytic properties were determined. Its profile was unusual since, in addition to penicillins, the enzyme hydrolysed second- and third-generation 'beta-lactamase-stable' cephalosporins and monobactams with similar efficiencies. On the basis of the characteristics of the interaction with beta-iodopenicillanic acid, the enzyme could be classified as a class-A beta-lactamase. However, when compared with most class-A beta-lactamases, it exhibited significantly lower kcat./Km values for the compounds usually considered to be the best substrates of these enzymes.

In vitro activity of cefodizime (HR-221) in combination with beta-lactamase inhibitors

Cefodizime (formerly HR221) was tested either for in vitro microbiological activity or for its stability to beta-lactamases in the presence of two beta-lactamase inhibitors (clavulanic acid, tazobactam). Cefodizime was a poor substrate of class C enzymes but hyperproducer strains were generally resistant with or without a beta-lactamase inhibitor used in combination. On the contrary, class A enzymes were able to hydrolyze cefodizime. However, strains expressing class A beta-lactamase were susceptible to cefodizime in combination with clavulanic acid.

Resistance to beta-lactams in Mycobacterium fortuitum

It is widely assumed that the high level of intrinsic resistance to beta-lactam antibiotics exhibited by mycobacteria results from the combination of factors including permeability to the drugs, beta-lactamase production, and affinity for penicillin-binding proteins (PBPs). We conducted an evaluation of the second and third factors by isolating nitrosoguanidine-induced mutants from the beta-lactamase-producing strain Mycobacterium fortuitum ATCC 19542 that displayed either elevated or reduced resistance to various beta-lactam antibiotics. The mutants studied included D1 (a beta-lactamase producer with high penicillin resistance), gamma 27 (a low-level beta-lactamase producer with low penicillin resistance), and D316 (a high-level beta-lactamase producer with high penicillin resistance). In all strains examined, four major PBPs, named 1, 2a, 2b, and 3, with apparent molecular weights of 102,000, 90,000, 87,000, and 50,000, respectively, were found. The MICs of various beta-lactams toward ATCC 19542 and its mutants were considered in the context of beta-lactamase production, the quantity of PBPs synthesized, and their affinities for beta-lactam antibiotics. The data obtained show that beta-lactamase production is likely to be an important factor in the expression of resistance by clinical isolates and that PBP alterations can contribute to resistance at least in laboratory-derived mutants.

Beta-lactamase of Mycobacterium fortuitum: kinetics of production and relationship with resistance to beta-lactam antibiotics

The kinetics of both intracellular and extracellular beta-lactamase production and the relationship between extracellular enzyme and in vitro susceptibility of Mycobacterium fortuitum to beta-lactam antibiotics have been studied. To this end we used a panel of stable nitrosoguanidine-induced mutants of M. fortuitum derived from the parental strain ATCC 19542 and differing in beta-lactamase production from 0.0001 to 278 U/liter in Mueller-Hinton broth. For overproducers of beta-lactamase (mutants A188, B180, C207, D316, and E31), MICs of benzylpenicillin, amoxicillin, ampicillin, and cephaloridine progressively increased with the amount of enzyme released into the medium, whereas MICs of imipenem and cefoxitin did not. The resistance of the mutants to amoxicillin was reduced up to 32-fold by clavulanic acid, whereas that to ampicillin was reduced 8-fold by sulbactam. These data suggest that the enzyme participated in the mechanisms of resistance to the beta-lactam antibiotics. However, for a mutant of M. fortuitum (gamma 27) with virtually nonexistent beta-lactamase production, the antibiotics still had relatively high MICs (for instance, benzylpenicillin and cephaloridine had MICs of 64 and 32 micrograms/ml, respectively). This suggests that, aside from beta-lactamase production, other mechanisms such as cell wall permeability and/or affinity for penicillin-binding proteins could coexist in M. fortuitum and explain its natural resistance to beta-lactam antibiotics.

Diversity of the mechanisms of resistance to beta-lactam antibiotics

The sensitivity of a bacterium to beta-lactam antibiotics depends upon the interplay between 3 independent factors: the sensitivity of the essential penicillin-binding enzyme(s), the quantity and properties of the beta-lactamase(s) and the diffusion barrier that the outer-membrane of Gram-negative bacteria can represent. Those three factors can be modified by mutations or by the horizontal transfer of genes or portions of genes.

Some molecular properties of Citrobacter diversus beta-lactamases

Citrobacter diversus ULA-27, a clinical isolate showing a broad resistance pattern towards both penicillins and cephalosporins, produces chromosome encoded beta-lactamases. However, the strain remains susceptible to some cephamycins, imipenem, ceftazidime and tetracyclines. Crude bacterial extracts analyzed by isoelectric focusing on polyacrylamide gels, revealed the presence of two main isoforms and some "satellite" bands focusing in the pH range 5.7-7.2. The isoform showing the pIs 6.8 and 6.2 were characterized as class "A" beta-lactamases (according to Ambler's classification) based on the rate of interaction of beta-iodopenicillanate and the amino acid sequence around the active site serine. The substrate specificity of the Citrobacter diversus beta-lactamases explains the resistance phenomenon of this bacterium to penicillins and cephalosporins.