Search PubMed⌕ Search

Biomedical subjects

H H Martin

Publications and source records attributed to H H Martin.

At least 19 recordsLinked to original sources
PubMed2000

A search for beta-lactamase in chlamydiae, mycoplasmas, planctomycetes, and cyanelles: bacteria and bacterial descendants at different phylogenetic positions and stages of cell wall development.

Bacteria from different phylogenetic positions such as chlamydiae, mycoplasmas, planctomycetes and also endosymbiotic murein-containing cyanelles were investigated for the production of beta-lactamases. No beta-lactamase activity was found in bacteria lacking murein such as Chlamydia pneumoniae, Mycoplasma pneumoniae, Pirellula marina and Planctomyces maris. In the murein-containing cyanelles of Cyanophora paradoxa no beta-lactamase activity could be detected.

Bacteria↗
PubMed1998

Contribution of overproduced chromosomal beta-lactamase and defective outer membrane porins to resistance to extended-spectrum beta-lactam antibiotics in Serratia marcescens.

Using clinical strains of Serratia marcescens with low and high resistance to extended-spectrum beta-lactam antibiotics, the relative contribution of chromosomal beta-lactamase and defective outer membrane porins to resistance was determined. Low-level resistance was caused by overproduced beta-lactamase alone. High-level resistance was due to beta-lactamase overproduction and defects of porin OmpF or OmpF and OmpC. Overproduction of beta-lactamase in bacteria with both degrees of resistance was eliminated by transformation with cloned ampD+, the gene (from Escherichia coli) for negative modulation of beta-lactamase induction. In transformants of highly resistant bacteria with normally low and inducible beta-lactamase production, the remaining porin defects alone imparted only minimal resistance to extended-spectrum beta-lactam antibiotics.

Bacterial Proteins↗
PubMed1996

beta-Lactamases are absent from Archaea (archaebacteria).

beta-Lactamases, enzymes that hydrolyze and inactive beta-lactam antibiotics, are of widespread occurrence in Bacteria and are related to the metabolism of bacterial cell wall murein. So far, no information exists on beta-lactamases in Archaea, a separate domain of prokaryotes with diverse types of unique cell wall polymers. Different mesophilic methanogenic and extremely halophilic Archaea containing methanochondroitin, pseudomurein, or S-layer protein or glycoprotein cell walls, were tested for beta-lactamase activity with the chromogenic beta-lactam nitrocefin as substrate. Also tested were representative microbial Eucarya from algae, yeasts, and protozoa. No beta-lactamase activity was detected in any of the archaeal and eukaryotic organisms. This supports the view that beta-lactamases are restricted to the domain of Bacteria.

Archaea↗
PubMed1994

A common system controls the induction of very different genes. The class-A beta-lactamase of Proteus vulgaris and the enterobacterial class-C beta-lactamase.

Among the Enterobacteriaceae, Proteus vulgaris is exceptional in the inducible production of a 29-kDa beta-lactamase (cefuroximase) with an unusually high activity towards the beta-lactamase-stable oximino-cephalosporins (e.g. cefuroxime and cefotaxime). Sequencing of the corresponding gene, cumA, showed that the derived CumA beta-lactamase belonged to the molecular class A. The structural gene was under the direct control of gene cumR, which was transcribed backwards and whose initiation codon was 165 bp away from that of the beta-lactamase gene. This resembled the arrangement of structural and regulator genes ampC and ampR of the 39-kDa molecular-class-C beta-lactamase AmpC present in many enterobacteria. Moreover, cloned genes ampD and ampG for negative modulation and signal transduction of AmpC beta-lactamase induction, respectively, were also able to restore constitutively CumA overproducing and non-inducible P. vulgaris mutants to the inducible, wild-type phenotype. The results indicate that controls of the induction phenomena are equivalent for the CumA and AmpC beta-lactamase. Very different structural genes can thus be under the control of identical systems.

Amino Acid Sequence↗
PubMed1993

Dependence of induction of enterobacterial AmpC beta-lactamase on cell-wall peptidoglycan, as demonstrated in Proteus mirabilis and its wall-less protoplast L-form.

The mobilizable plasmid pMD101 (ampR, ampC) was constructed by inserting cloned ampC, the structural gene for the chromosomal AmpC beta-lactamase of Citrobacter freundii, and the closely linked ampR encoding the transcriptional regulator essential for enzyme induction, into the broad host-range plasmid pKT231. Plasmid pMD101 was transconjugated into Proteus mirabilis VI and its isogenic, cell-wall-less protoplast L-form LVI. AmpC beta-lactamase was expressed constitutively from cloned ampR and ampC in bacteria and in some L-form protoplasts. However, induction of the enzyme by beta-lactam antibiotics occurred only in bacterial cells and not in the cell-wall- and peptidoglycan-deficient L-form. In agreement with current models, induction of AmpC beta-lactamase is thought to be initiated by an induction signal arising from the metabolic disturbance of cell-wall peptidoglycan.

Bacterial Proteins↗
PubMed1993

AmpG, a signal transducer in chromosomal beta-lactamase induction.

The chromosomal ampC beta-lactamase in Citrobacter freundii and Enterobacter cloacae is inducible by beta-lactam antibiotics. When an inducible ampC gene is introduced on a plasmid into Escherichia coli together with its transcriptional regulator ampR, the plasmid-borne beta-lactamase is still inducible. We have isolated mutants, containing alterations in a novel E. coli gene, ampG, in which a cloned C. freundii ampC gene is unable to respond to beta-lactam inducers. The ampG gene was cloned, sequenced and mapped to minute 9.6 on the E. coli chromosome. The deduced amino acid sequence predicted AmpG to be a 53 kDa, transmembrane protein, which we propose acts as a signal transducer or permease in the beta-lactamase induction system. Immediately upstream of ampG there is another 579-base-pair-long open reading frame (ORF) encoding a putative lipoprotein shown to be non-essential for beta-lactamase induction. We have found that ampG and this ORF form an operon, whose promoter is located in front of the ORF. Located closely upstream of the putative promoter is the morphogene bolA, which is transcribed in the opposite orientation. However, using transcription fusions, we have found that the ampG transcription is not regulated by bolA. In addition, we show that transcription is probably not regulated by either the starvation specific sigma factor RpoS, which controls bolA, or by AmpD the negative regulator for ampC transcription.

Amino Acid Sequence↗
PubMed1991

Composition of the outer membrane of Proteus mirabilis in relation to serum sensitivity in progressive stages of cell form defectiveness.

A serum-resistant strain of Proteus mirabilis was used to determine whether changes in the composition of surface components could be detected following induction of progressive stages of cell form defectiveness by beta-lactam antibiotics. The critical stage was the conversion from filaments to the spheroplast form, which was accompanied by increased susceptibility to the bactericidal action of human serum. Inner and outer membranes of the bacterium, its filament form and its spheroplast form were separated by sucrose density-gradient centrifugation after digestion of peptidoglycan, followed by osmotic lysis of the cells. Outer membranes of the bacterial and the filament forms sedimented at the same density, whilst the outer membrane fraction of the spheroplast form sedimented in a region of lesser density. In addition, the amounts of two major outer-membrane proteins as well as the O-polysaccharide content of the lipopolysaccharide were reduced in the spheroplast form. These results indicate a general disorganization in structure and assembly of components in regard to their interactions with one another in the outer membrane of the spheroplast form.

Anti-Bacterial Agents↗
PubMed1991

State of penicillin-binding proteins and requirements for their bactericidal interaction with beta-lactam antibiotics in Serratia marcescens highly resistant to extended-spectrum beta-lactams.

The quantities of penicillin-binding proteins (PBPs), and sensitivity to extended-spectrum beta-lactams, were measured in isogenic strains of Serratia marcescens with high (HR) and low (LR) resistance to extended-spectrum beta-lactam antibiotics and with constitutively overproduced chromosomal beta-lactamase in the periplasm. The binding of structurally different beta-lactams to PBPs in growing resistant bacteria was determined quantitatively. In S. marcescens HR, the amounts of PBPs 3 and 6 were, respectively, 1.5 and 2 times those in strain LR and in sensitive reference strains. Sensitivities of the essential PBPs in S. marcescens LR and HR to the tested beta-lactams were identical. Only a single target, PBP 3, was highly sensitive to cefotaxime, ceftazidime and aztreonam. In contrast, three PBPs (2, 1A and 3) were highly sensitive to imipenem. In growing S. marcescens HR and LR, all antibiotics, even at fractions of their minimal growth inhibitory concentrations (MICs), bound extensively to those PBPs which were highly sensitive to them. Thus, overproduced beta-lactamase did not prevent PBP-beta-lactam interaction. Only at or above their (high) MICs did cefotaxime, ceftazidime and aztreonam bind to multiple targets. Growth inhibition of the otherwise highly resistant S. marcescens HR at the lower MIC of imipenem was correlated with the binding of this antibiotic to multiple, highly sensitive targets in the bacteria. Killing of the bacteria by inactivation of multiple targets was suggested. This assumption was supported by the synergistic killing of HR bacteria by combinations of the PBP-2-specific mecillinam with PBP-3-specific beta-lactams.

Anti-Bacterial Agents↗
PubMed1989

Quantitative relationship between sensitivity to beta-lactam antibiotics and beta-lactamase production in gram-negative bacteria--II. Non-steady-state treatment and progress curves.

A non-steady-state model is discussed for the study of the interplay between beta-lactamase activity and outer membrane permeability with slowly hydrolysed beta-lactams. The analysis shows: (1) that the simple, steady-state model presented in the accompanying paper remains valid as long as kcat (i.e. k3 with chromosome-encoded class C beta-lactamases) is larger than 10(-3)/sec (generation time = 20 min or more); (2) that among the beta-lactam antibiotics studied here, the complete, non-steady-state model needs only be used in the case of aztreonam; (3) that the term "trapping" should be replaced by "formation of a covalent acyl-enzyme" and that such a phenomenon only contributes significantly to the resistance when penetration and hydrolysis are very slow and the periplasmic beta-lactamase concentration is very high. Aztreonam seems to be the only compound which fulfils the first two conditions.

Anti-Bacterial Agents↗
PubMed1989

Overproduced beta-lactamase and the outer-membrane barrier as resistance factors in Serratia marcescens highly resistant to beta-lactamase-stable beta-lactam antibiotics.

In a clinical isolate of Serratia marcescens different states of low and high resistance to different beta-lactam antibiotics considered to be beta-lactamase-stable, viz. cefotaxime, ceftizoxime, ceftazidime, aztreonam, cefoxitin and imipenem, were found to be connected with the presence of constitutively overproduced, chromosomally encoded beta-lactamase at concentrations in the bacterial periplasm of 0.4 and 0.9 mM, respectively. All the antibiotics were degraded by the beta-lactamase. However, kinetic constants varied widely: k(m) from 92 to 0.012 microM and k(cat) from 3.4 to 2x10(-4)s(-1). The relative contributions to resistance by the functioning of periplasmic beta-lactamase, resynthesis of this enzyme, and limitation of antibiotic penetration by the bacterial outer membrane were analysed by computer simulations according to steady-state and non-steady-state models of interactions in the periplasm. Results for cefotaxime, ceftizomime, ceftazidime, aztreonam and latamoxef revealed overproduced beta-lactamase as the sole cause of the state of low resistance while antibiotic permeability was the same as in non-resistant S. marcescens strains. In contrast, high resistance was due to beta-lactamase action and decreased permeability of antibiotics. For resistance to aztreonam, only, immobilization of the antibiotic as covalent acyl-enzyme by newly synthesized beta-lactamase was essential. For cefoxitin, ampicillin and imipenem the analyses indicated that additional resistance factors may play a role, e.g. induction of beta-lactamase.

Anti-Bacterial Agents↗
PubMed1984

In vitro synthesis of peptidoglycan by spheroplasts of Proteus mirabilis grown in the presence of penicillin.

Spheroplasts of the unstable L-form of Proteus mirabilis with fragile, shape defective cell walls grown in medium containing 120 mg/l penicillin G and then killed and permeabilized by ether treatment, were capable of in vitro synthesis of peptidoglycan from the precursors UDP-GlcNAc and UDP-MurNAc-L-Ala-D-Glu(ms-A2pm-D-Ala-D-Ala). The in vitro peptidoglycan was extensively peptide-crosslinked, indicating a continuing function of peptidoglycan transpeptidase in the spheroplasts. The seven penicillin-binding proteins (PBPs) of P. mirabilis with their functions as multiple peptidoglycan transpeptidases were shown to be saturated in the spheroplasts and thereby functionally inactivated by the penicillin of the growth medium to a very different degree. Complete or almost complete saturation occurred with the PBPs 1A, 1B, and 3, for which functions as indispensable transpeptidases in Escherichia coli have been postulated. In contrast, PBPs 5 and 6 were not saturated in the L-form spheroplasts. Transpeptidase function has been described previously in PBP 5 of P. mirabilis. The working hypothesis is proposed that synthesis of the functionally defective peptidoglycan of L-form spheroplasts in the presence of penicillin takes place with transpeptidase function of PBP 5.

Acetylation↗
PubMed1982

Murein and lipopolysaccharide biosynthesis in synchronized cells of Escherichia coli K 12 and the effect of penicillin G, mecillinam and nalidixic acid.

The incorporation of radioactive N-acetyl-glucosamine into murein and lipopolysaccharide of synchronized cells of Escherichia coli K 12 was followed over 100 min in the presence of antibiotics. At 20 min intervals cell walls were prepared. Lipopolysaccharide and murein sacculi were isolated and the radioactivity was quantified in both polymers. Labelled, newly synthesized murein was characterized according to murein subunits linked to lipoprotein, and the degree of crosslinkage. Furthermore, murein subunits containing anhydromuramic acid were determined, permitting the calculation of the average glycan chain length. The results indicated that penicillin G at 30 micrograms/ml stimulated the incorporation of new murein subunits into sacculi followed by a sudden increase in lipopolysaccharide incorporation into the outer membrane. The degree of crosslinkage in murein synthesized in the presence of 30 micrograms/ml penicillin G was higher than in the control, and almost twice as high as in murein synthesized in the presence of 20 micrograms/ml nalidixic acid. Both antibiotics inhibited cell division at the concentrations indicated. Murein synthesized in the presence of 2 micrograms/ml mecillinam also showed higher crosslinkage. However, about twice as much anhydromuramic acid-containing subunits were observed as in the control. At the same time lipopolysaccharide incorporation into the outer membrane was stimulated two- to three-fold.

Amdinocillin↗
PubMed1981

[Bacterial penicillin-binding proteins as specific targets of beta-lactam-antibiotics and as factors of resistance to antibiotics (author's transl)].

Bacteria contain several isofunctional, beta-lactam sensitive membrane enzymes engaged in the synthesis of cell wall peptidoglycan (peptidoglycan-DD-carboxypeptidases, -transpeptidases, -endopeptidases) as members of sets of even more numerous membrane proteins with specific, high binding-affinity for beta-lactam antibiotics (penicillin-binding proteins, PBPs). Effective inhibition of bacterial growth by beta-lactam antibiotics requires simultaneous inactivation of the essential functions of several PBPs by formation of stable enzyme-antibiotic complexes. Failure to achieve permanent inactivation of all essential targets by a given beta-lactam appears to be another cause of bacterial beta-lactam resistance, in addition to known resistance mechanisms based on action of beta-lactamases and on screening off targets from antibiotic by a penetration barrier. Different groups of beta-lactam antibiotics vary characteristically in their affinity for specific essential PBPs. Combined application of two beta-lactams which complement each other in the inactivation to essential targets is a possibility to overcome resistance of single antibiotics.

Anti-Bacterial Agents↗
PubMed1980

Membranes of the protoplast L-form of Proteus mirabilis.

Isolated membranes of the cell wall-less stable protoplast L-form of Proteus mirabilis were characterized by density gradient centrifugation and by assay for their major chemical constituents, proteins, phospholipids and lipopolysacchartide, and for some specific marker enzymes of the cytoplasmic membrane. In most of the analyzed properties the L-form protoplast membrane resembled the bacterial cytoplasmic membrane, with some notable modifications. Considerable amounts of lipopolysaccharide, normally an exclusive constituent of the outer membrane, were found. Furthermore, the L-form membranes contained the functions of the reduced nicotinamide adenine dinucleotide oxidase system, of D-lactate dehydrogenase (EC 1.1.1.28) and of succinate dehydrogenase (EC 1.3.99.1) at specific activities comparable to, or in some cases considerably higher than, those present in cytoplasmic membranes of the bacterial form. Of two peptidoglycan DD-carboxypeptidase/transpeptidases (EC 3.4.17.8 and EC 2.3.2.10). which are normally present in the cytoplasmic membrane of the bacterial form of P. mirabilis, the membrane of the protoplast L-form contained only one. Electron microscopy of thin sectioned L-form protoplasts showed extensive heterogeneity of membraneous structures. In addition to the single membraneous integument, internal membrane-bounded vesicles and multiple stacks of membranes were present, as the result of unbalanced growth and membrane synthesis in the L-form state.

Bacterial Proteins↗
PubMed1980

Differentiation of mycoplasmatales from bacterial protoplast L-forms by assay for penicillin binding proteins.

Membrane proteins with the specific ability for binding penicillin with high affinity (penicillin binding proteins) were found to be present in two strains of the cell wall-less protoplast L-form of P. Mirabilis and were absent from different species of Mycoplasma and from Acholeplasma laidlawii. Thus, the assay for penicillin binding proteins appeared to be suitable for the differentiation of the cell wall-less procaryotes. The absence of penicillin binding proteins from the mycoplasmatales further confirmed the unrelatedness of this group to the bacteria.

Acholeplasma laidlawii↗