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Biomedical subjects

L G Burman

Publications and source records attributed to L G Burman.

At least 109 records · Page 6Linked to original sources
PubMed1983

Changes in the composition of Escherichia coli murein as it ages during exponential growth.

Escherichia coli murein was specifically labeled with [14C]diaminopimelic acid in the mutant strains W7 (dap lysA) and BUG6. Pulse-labeled heat-denatured E. coli cells were digested with 2 mg of egg-white lysozyme per ml to degrade the murein completely and free any lipoprotein-bound muropeptide trimers, dimers, and monomers. Pulse-chase experiments showed that the relative percentage of trimers and dimers found in the newly synthesized murein increased somewhat with time at the expense of monomers. The increase in cross-links indicated that the radioactive monomers served as acceptors in multisite transpeptidations occurring after the labeling period. The content of nonreducing monomers (C7 and C8) remained unaltered, indicating that the oligosaccharide chain length did not change with time. A gradual conversion of the reducing disaccharide tetrapeptide monomer to its tripeptide analog occurred during chasing. Braun lipoprotein was linked to about 2% of the murein subunits within 30 s of the incorporation of subunits into insoluble murein, and after one-half a generation of chase, lipoprotein-associated muropeptides had approached the maximum (16% of the total murein subunits). The distribution of muropeptides was similar in lipoprotein-linked and lipoprotein-free murein, showing that the enzyme that links Braun lipoprotein to murein does not discriminate between monomers, dimers, and trimers. No evidence for a chasable, soluble polymer of murein was found in our experiments. Hence, our data support the idea that new murein is incorporated directly into the sacculus without first existing as a soluble intermediate.

Escherichia coli↗
PubMed1983

Evidence for diffuse growth of the cylindrical portion of the Escherichia coli murein sacculus.

High-resolution autoradiography of thin sections of Escherichia coli cells whose murein was pulse-labeled with [3H]diaminopimelic acid after a period of diaminopimelic acid deprivation indicated that elongation of the murein sacculus occurs by a multisite (diffuse) process. Upon chasing, radioactivity in polar murein was stable, whereas radioactivity in cylindrical murein was reduced, indicating that diffuse intercalation of new murein occurred during cell elongation. Elongation and septation were shown to be overlapping processes.

Cell Wall↗
PubMed1983

Evidence for multisite growth of Escherichia coli murein involving concomitant endopeptidase and transpeptidase activities.

During diaminopimelic acid starvation of Escherichia coli W7, a large fraction of the preexisting murein cross-links are opened by murein endopeptidase and the resulting uncross-linked material is degraded. This is reflected morphologically in a general loss of rigidity of the murein sacculus long before lysis occurs. In growing cells, a dynamic situation is demonstrable. When cells whose murein sacculi are uniformly labeled with [14C]diaminopimelic acid were chased with unlabeled DAP, a significant, rapid shift of [14C]diaminopimelic acid from the donor to the acceptor half of dimers was observed. The shift can be explained by the presence of about 100 separate sites where new murein strands were being inserted between old radioactive strands of murein. Thus, the gradual loss of rigidity of the murein sacculus as endopeptidase continues to function during starvation of E. coli W7 suggests an even distribution of the active endopeptidases. This is consistent with the kinetic data which suggest that endopeptidase, along with murein synthetase and transpeptidase, acts at about 100 distinct sites to elongate the murein sacculus.

Acyltransferases↗
PubMed1982

Streptococcus pneumoniae and three species of anaerobic bacteria in experimental otitis media in guniea pigs.

Three species of anaerobic bacteria commonly isolated in upper respiratory tract infections in humans were studied in an animal model of otitis media. The ability of Propionibacterium acnes to induce acute otitis media was comparable with that of streptococcus pneumoniae, the classic middle ear pathogen. The response to Peptostreptococcus micros was weak and irregular, and no effects of Bacteroides asaccharolyticus were observed despite the use of high doses (10(8) colony-forming unite per ear). The results of this study support the contention that anaerobic bacteria such as P. acnes may be true pathogens in middle ear infections.

Animals↗
PubMed1981

Molecular cloning in streptococci: physical mapping of the vehicle plasmid pSM10 and demonstration of intergroup DNA transfer.

The streptococcal resistance plasmid pSM10 (8.3 kb), a deletion derivative of pSM10419 (22.9 kb) determining constitutive erythromycin and lincomycin resistance, was physically mapped with the restriction endonucleases AvaI, AvaII, EcoRI, HpaI, KpnI, PvuII (one site each), HindIII, HaeII (three sites each), HincII (four sites), and HhaI (five sites). Using the cryptic plasmid pVA318 as cloning vehicle, the largest HindIII fragment of pSM10 (3.3 kb) was shown to contain the erythromycin/lincomycin resistance gene(s) of the plasmid. The AvaII site of pSM10 proved to be suitable as a site for cloning AvaII-generated chromosomal DNA fragments from a group C streptococcal strain in the Challis strain of Streptococcus sanguis (group) H). A detailed physical map of the chimeric plasmid pSM10221 (12.8 kb), a fusion product of pSM10 and the staphylococcal chloramphenicol resistance plasmid pC221 (4.5 kb), is also presented. The plasmid chimera has properties making it potentially useful in development of a doubly selective streptococcal cloning vehicle by searching for insertional inactivation.

Chromosome Mapping↗
PubMed1980

Collecting and banking human milk: to heat or not to heat?

Data on human breast milk and its handling when fed to babies who cannot be breast-fed were reviewed to determine whether the method of processing and storage affected the properties of the milk. Breast milk is normally contaminated by potential pathogens, which seem to produce no ill effects, but it also contains antimicrobial properties which protect against infection. The evidence suggests that pasteurisation not only eliminates pathogenic bacteria but also damages bacteriostatic mechanisms, so making the milk more susceptible to later contamination. Pasteurisation also affects the nutritional properties of milk. Freezing has little effect on milk proteins, while a study on the effect of refrigeration showed that there was little bacterial growth at temperatures below 8 degrees C. Several years' experience of feeding donated raw milk to newborn infants has confirmed that it produces no ill effects. These findings suggest that pasteurisation of donated breastmilk is unnecessary, and it is not recommended, while the decision whether or not to freeze the milk may be made on practical grounds. Raw breast milk can be safely stored at 4-6 degrees C for 72 hours.

Bacteria↗
PubMed1979

Recurrent pneumonia and encephalitis due to Mycoplasma pneumoniae.

Recurrent Mycoplasma pneumoniae encephalitis in a young man is reported. The patient appeared not to be immunodeficient and despite the presence of a focal inflammatory brain lesion with a predominance of polymorphonuclear cells no direct evidence of inent in M. pneumoniae respiratory tract infection still is unknown the case strongly indicates that certain individuals are somehow predisposed to such complications. The case also illustrates that CNS complications may occur even during a mild mycoplasma respiratory tract infection and that the radiological findings can mimic cerebral haemorrhage or abscess necessitating neurosurgical exploration.

Adult↗
PubMed1979

Prophylaxis of neurosurgical infections by improved preoperative disinfection of the scalp.

The heads of neurosurgical patients were subject to 2 scrubbings with hexachlorophene detergent, performed in the ward prior to operation. After this single change of routines the frequency of wound infections after craniotomy dropped 4-fold, from 2% to 0.5%. The result indicates that the scalp of the patient is the major source of the staphylococci that cause neurosurgical infections.

Administration, Topical↗