Production of Amidase and -Lactamase by Bacteria

Strategies to Name Metallo-β-Lactamases and Number Their Amino Acid Residues

Metallo-β-lactamases (MBLs), also known as class B β-lactamases (BBLs), are Zn(II)-containing enzymes able to inactivate a broad range of β-lactams, the most commonly used antibiotics, including life-saving carbapenems. They have been known for about six decades, yet they have only gained much attention as a clinical problem for about three decades. The naming conventions of these enzymes have changed over time and followed various strategies, sometimes leading to confusion. We are summarizing the naming strategies of the currently known MBLs. These enzymes are quite diverse on the amino acid sequence level but structurally similar. Problems trying to describe conserved residues, such as Zn(II) ligands and other catalytically important residues, which have different numbers in different sequences, have led to the establishment of a standard numbering scheme for BBLs. While well intended, the standard numbering scheme is not trivial and has not been applied consistently. We revisit this standard numbering scheme and suggest some strategies for how its implementation could be made more accessible to researchers. Standard numbering facilitates the comparison of different enzymes as well as their interaction with novel antibiotics and BBL inhibitors.

Infection microenvironment-related antibacterial nanotherapeutic strategies

The emergence and spread of antibiotic resistance is one of the biggest challenges in public health. There is an urgent need to discover novel agents against the occurrence of multidrug-resistant bacteria, such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci. The drug-resistant pathogens are able to grow and persist in infected sites, including biofilms, phagosomes, or phagolysosomes, which are more difficult to eradicate than planktonic ones and also foster the development of drug resistance. For years, various nano-antibacterial agents have been developed in the forms of antibiotic nanocarriers. Inorganic nanoparticles with intrinsic antibacterial activity and inert nanoparticles assisted by external stimuli, including heat, photon, magnetism, or sound, have also been discovered. Many of these strategies are designed to target the unique microenvironment of bacterial infections, which have shown potent antibacterial effects in vitro and in vivo. This review summarizes ongoing efforts on antibacterial nanotherapeutic strategies related to bacterial infection microenvironments, including targeted antibacterial therapy and responsive antibiotic delivery systems. Several grand challenges and future directions for the development and translation of effective nano-antibacterial agents are also discussed. The development of innovative nano-antibacterial agents could provide powerful weapons against drug-resistant bacteria in systemic or local bacterial infections in the foreseeable future.

A review of the interactions between acrylamide, microorganisms and food components

Acrylamide (AA) and its metabolites have been recognized as potential carcinogens, but also they can cause other negative symptoms in human or animal organisms and therefore this class of chemical compounds has attracted a lot of attention.

Autonomously Sensing Hydrogels for the Rapid and Selective Detection of Pathogenic Bacteria

The development of a versatile approach for the rapid and sensitive detection of relevant pathogenic bacteria and autonomous signaling of the detection events in reporter hydrogel film coatings is reported. Exploiting chitosan hydrogel films equipped with chromogenic or fluorogenic reporter moieties, the presence of the Gram-negative bacterium Pseudomonas aeruginosa and the Gram-positive bacterium Staphylococcus aureus is sensed within 1 h by detecting the characteristic enzymes α-glucosidase and elastase with limits of detection (LOD) <45 × 10(-9) M and <20 × 10(-9) M, respectively, for this observation time. The values for the LOD are two to three orders of magnitude smaller than the concentrations of the enzymes detected in the corresponding bacterial supernatants. The results show that the covalently conjugated reporter moieties are exclusively and efficiently reacted by the associated enzyme, allowing in principle for discrimination among different types of bacteria. Since high enzyme concentrations are a result of proliferating bacteria, e.g., in wounds or food, and since the selectivity of the reporting function is easily adapted to bacteria of choice, these reporter hydrogels comprise an interesting platform for the rapid detection of bacteria.

Metabolism of oral cephalothin and related cephalosporins in the rat

The fate of orally administered [(14)C]cephalothin has been studied in the rat. This antibiotic undergoes degradation in the gut followed by the subsequent absorption of a portion of the degradation products. About 50% of the administered radioactivity appears in the urine as a mixture of thienylacetylglycine, thienylacetamidoethanol and an unidentified polar metabolite. Evidence is presented indicating that thienylacetamidoethanol arises by the enzymic reduction of a metabolic intermediate, thienylacetamidoacetaldehyde. The metabolic fate of cephalothin is very similar to that of cephaloram reported earlier. The fate of [(14)C]cephaloridine and 7-phenoxy[1-(14)C]acetamidocephalosporin was also investigated. In addition to the expected metabolites, about 5% of the cephaloridine dose is absorbed unchanged. With 7-phenoxy[1-(14)C]acetamidocephalosporin, 15% of the dose is recovered in urine as deacetyl-7-phenoxy[1-(14)C]acetamidocephalosporin.

Co-existence of beta-lactamase and penicillin acylase in bacteria; detection and quantitative determination of enzyme activities

Twenty-six bacteria were examined for the presence of penicillin acylase and beta-lactamase. A copper reducing assay, which was sensitive in the analytical range 2-20 micrograms/ml, was used for determination of penicilloates and a fluorescamine assay was used to determine 6-aminopenicillanic acid concentrations when both substances were produced by the action of the enzymes on a single substrate. Seventeen bacteria contained beta-lactamases, six contained penicillin acylases and four contained both enzymes. Two bacteria contained a Type 1 penicillin acylase and four bacteria contained a Type II enzyme. No ampicillin acylases were detected. All beta-lactamases were constitutive enzymes in those organisms where both enzymes co-existed. Bacillus subtilis and B. cereus produced inducible and extracellular beta-lactamases. Acinetobacter calcoaceticus ATCC 21288 produced a constitutive beta-lactamase which was detected extracellularly.

Inhibition of Bacillus subtilis aminopeptidase D by beta-lactam antibiotics

Penicillins and cephalosporins inhibit the hydrolysis of D-alanyl-beta-naphthylamide by aminopeptidase D (EC 3.4.11.-) from Bacillus subtilis. The inhibition is predominantly non-competitive, although the more effective inhibitors, i.e., those with the lower Ki values, seem to exhibit a tendency toward competitive kinetics, while penicillin V, the antibiotic with the largest Ki, exhibits a strong tendency toward uncompetitive kinetics. The removal of antibiotic from the enzyme by gel filtration on Sephadex G-25 restores 100% activity to the enzyme, and suggests that the inhibition does not derive from a covalent antibiotic-enzyme complex. The antibiotics which have been studied, with their respective Ki values (mM) and inhibition type are: methicillin (1.01 +/- 0.34, mixed non-competitive-competitive); cephaloridine (2.43 +/- 0.17, non-competitive); cloxacillin (3.19 +/- 1.29, mixed non-competitive-competitive); oxacillin (6.88 +/- 0.77, non-competitive); cephalothin (8.12 +/- 0.99, non-competitive); penicillin G (20.0 +/- 3.21, non-competitive) and penicillin V (32.1 +/- 4.90, mixed non-competitive-uncompetitive). An empirical correlation exists between the Ki value and the freedom of rotation about the bond between the phenyl ring and the atom alpha to the ring in the variable side chain portion of the penicillin molecule.

Penicillinase (beta-lactamase) formation by blue-green algae

Beta-Lactamase (penicillinase) activity was found in a number of strains of blue-green algea. In some cases, this enzyme permitted algae to overcome the inhibitory effects of penicillin. Production and localization of beta-lactamase were studied in a unicellular species, Coccochloris elabens (strain 7003), and in a filamentous, nitrogen-fixing Anabaena species (strain 7120). When cells were grown in a neutral medium with NaNO3 as N source, the pH rose during growth; at a pH of about 10, most of the enzyme was expressed equally well in intact or disrupted cells. If the pH was kept near neutrality during growth by gassing with CO2 in N2 or by growth under conditions of N2 fixation, the enzyme remained cell-bound and cryptic for most of the growth phase, being measurable only after cells were disrupted. The enzymes from strains 7003 and 7120 had greater activity on benzyl penicillin and other penicillins than on cephalosporins. Some differences were observed in the "substrate proliles" of penicillinases from the two strains against different penicillins.

Beta-lactamase activity in anaerobic bacteria

A diverse group of anaerobic bacteria representing a spectrum of resistance to beta-lactam antibiotics was studied to characterize their beta-lactamase activity and relate it to resistance. The Bacteroides fragilis organisms had moderate resistance and produced a cephalosporinase with low activity. The Clostridium ramosum was intermediate in resistance and had intermediate, inducible beta-lactamase activity. The B. clostridiiformis organism was highly resistant, produced a potent inducible penicillinase, and had a barrier to the penicillin substrates. Only the beta-lactamase of C. ramosum fit Richmond's classification (class IV). Although there was a rough correlation between beta-lactamase activity and antibiotic resistance, other mechanisms are undoubtedly involved in determining resistance levels.

In vivo protection of Fusobacterium necrophorum from penicillin by Bacteroides fragilis

A mixed infection of Bacteroides fragilis and Fusobacterium necrophorum was resistant to treatment with penicillin even though a pure F. necrophorum infection could be successfully treated with penicillin. Since B. fragilis alone did not produce infection, these results indicate that B. fragilis can protect F. necrophorum from penicillin in vivo. The extent of protection afforded by a strain of B. fragilis was related to its level of resistance to penicillin. Only a few cells of B. fragilis were required in the initial bacterial injection. Moreover, protection was demonstrated when B. fragilis cells were injected as late as 24 h after the F. necrophorum cells. Protection of F. necrophorum from penicillin by B. fragilis was also demonstrated in vitro.

Cephalosporinase activity in Bacteroides fragilis

Cephalosporinase activity was demonstrated in all of 10 strains of Bacteroides fragilis investigated. Low rates of hydrolysis of cephalosporins (0.25 to 3.5 mumol of cephaloridine per h per 10(9) cells) were found, but no activity against penicillin substrates was detected. In two strains the cephalosporinase activity was increased 40-and 80-fold by growing cells in the presence of penicillin. No permeability barrier for these antibiotics was demonstrated. In most cases the substrate profile showed decreasing activity in the following order: cephaloridine > cephalothin > cephaloglycin > cephalexin. The cephalosporinase from these organisms differed from that found in facultative and aerobic gram-negative bacilli in that it was inhibited by both cloxacillin and p-chloromercuribenzoate. Among nine strains of Bacteroides fragilis subspecies fragilis, correlation was found between in vitro resistance to cephaloridine and amount of beta-lactamase activity in sonically disrupted cells.

Beta-lactamase and penicillinacylase coexistence in Escherichia coli

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