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Biomedical subjects

J R Saunders

Publications and source records attributed to J R Saunders.

At least 145 records · Page 8Linked to original sources
PubMed1979

Liposarcomas of the head and neck: a review of the literature and addition of four cases.

Liposarcomas of the head and neck are rare. There have been 25 previously reported patients in the literature. Four patients with head and neck liposarcomas, recently treated by the Head and Neck Surgery Service, Walter Reed Army Medical Center, are presented. Less than half of reported patients were noted to be living without evidence of disease. Prognosis generally corresponds to the cell type of the tumor. Intraoral, cheek and orbital tumors seem to have a worse prognosis compared to neck tumors. Wide local excision remains the treatment of choice. Advances in surgical techniques have allowed adequate therapy for most head and neck liposarcomas. Advanced lesions should be managed by conservative surgery and radical radiation therapy.

Adolescent↗
PubMed1978

New transposons.

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Bacteria↗
PubMed1978

beta-lactamases and R-plasmids of Haemophilus influenzae.

The emergence of resistance to ampicillin and other antibiotics in Haemophilus influenzae has been a relatively recent event. In contrast, drug resistance has been rampant in the Enterobacteriaceae for many years. Ampicillin-resistance in H. influenzae is almost invariably attributable to possession of the TEM (Type III a)beta-lactamase. As is common in other bacteria the gene specifying this enzyme is plasmid-borne in Haemophilus. Some ampicillin-resistant strains of H. influenzae can transfer the TEM beta-lactamase gene to other strains of Haemophilus, to Escherichia coli and to Pseudomonas aeruginosa. The features of such transfer are unusual and lead for example, to the induction of adenine requirement in recipient strains of P. aeruginosa. Crypticity measurements of beta-lactamase activity show that in comparison to P. aeruginosa or E. coli, the outer membrane of H. influenzae affords only a weak penetration barrier to beta-lactam antibiotics. This may have consequences for the stability and distribution of beta-lactamase production in Haemophilus spp. which are discussed. A comparison of the molecular properties of R-plasmids determining a variety of resistances and carried by strains of H. influenzae isolated in diverse geographical locations has revealed unexpected homologies. A series of such plasmids of similar molecular weights (about 30 X 10(6)) differ substantially only in the transposable resistance genes that they carry. A model based on these findings is presented to explain the acquisition of ampicillin- and other resistances by Haemophilus.

Amidohydrolases↗
PubMed1977

Transfer of a plasmid-specified beta-lactamase gene from Haemophilus influenzae.

A number of ampicillin-resistant strains of Haemophilus influenzae could donate a gene specifying the type IIIa (TEM) beta-lactamase to Haemophilus parainfluenzae, Escherichia coli, and Pseudomonas aeruginosa. Donor strains rapidly lost their ability to transfer ampicillin resistance on storage or subculture. Such strains also apparently contained a single species of covalently closed circular deoxyribonucleic acid of contour length 1.2 mum, equivalent to about 2.5 x 10(6) daltons. No species of plasmid deoxyribonucleic acid large enough to encode sex factor activity was detected. Despite this, transfer occurred to several bacterial genera in the presence of deoxyribonuclease, suggesting that transmissibility was by conjugation. The beta-lactamase gene was generally unstable after transfer and was lost in the absence of selection. Where stable transcipients were found, this was evidently by insertion of the beta-lactamase gene into the host chromosome. In P. aeruginosa insertion was always accompanied by induction of auxotrophy for adenine, suggesting insertion at a specific site. It is believed that insertion also occurred at one site on the chromosome of Escherichia coli. Crypticity measurements for beta-lactamase activity showed that there was little or no penetration barrier to beta-lactam drugs in Haemophilus. This may explain the long delay in the acquisition of ampicillin resistance by this organism.

Ampicillin↗
PubMed1977

Relationships among some R plasmids found in Haemophilus influenzae.

Tetracycline resistance in a strain of Haemophilus influenzae isolated in the United Kingdom was found to be determined by an apparently non-selftransmissible plasmid of 31 X 10(6) daltons (31 MDal), designated pUB701. Deoxyribonucleic acid hybridization studies indicated that pUB701 shares about 70% base sequence homology with the 30-MDal ampicillin resistance R plasmid RSF007 isolated in the United States from H. influenzae, and 64% sequence homology with the 38-MDal tetracycline and chloramphenicol resistance R plasmid pRI234, isolated in the Netherlands. Heteroduplex studies between RSF007 and pUB701 confirmed the fact that these plasmids were largely homologous, except that pUB701 contained the tetracycline resistance transposon TnD, whereas RSF007 contained the ampicillin resistance transposon TnA. A strain of H. parainfluenzae resistant to both chloramphenicol and tetracycline carried two species of plasmid deoxyribonucleic acid of 2.7 and 0.75 MDal. We were unable to prove that either resistance was plasmid-borne in this strain. Hybridization studies with a [3H]thymine-labeled tetracycline resistance enteric plasmid suggested that the tetracycline transposon was integrated into the chromosome of H. parainfluenzae UB2832. We conclude either that the strains we studied received R factors of the same incompatibility group bearing different resistance genes, or that different resistance genes were translocated to a commom resident plasmid of H. influenzae.

Ampicillin↗
PubMed1976

Ferrous sulphate.

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Child, Preschool↗
PubMed1976

Extrachromosomal deoxyribonucleic acid in wild-type and photosynthetically incompetent strains of Rhodopseudomonas spheroides.

Three covalently closed circular species of extrachromosomal deoxyribonucleic acid have been identified by electron microscopic analysis in strains of Rhodopseudomonas spheroides. The weights of these plasmids, as determined from contour length, are about 75 X 10(6), 66 X 10(6), and 28 X 10(6) daltons for both aerobically grown and photosynthetically grown R. spheroides strain 2.4.1 (NRS) and for the photosynthetically incompetent strain V-2 (obtained by N-methyl-N-nitro-N'nitrosoguanidine mutagenesis) and 74 X 10(6), 66 X 10(6) and 34 X 10(6) daltons for a second photosynthetically incompetent strain, SLS I (obtained by incubating strain 2.4.1 [NRS] in medium containing sodium lauryl sulfate). Buoyant densities uere found to be 1.717 g/cm3 (58% guanine plus cytosine) for the plasmids of 66 X 10(6), 28 X 10(6), and 34 X 10(6) daltons in weight and 1.724 g/cm3 (65% guanine plus cytosine) for those weighing about 75 X 10(6) daltons. Possible functions of these plasmids are discussed.

Aerobiosis↗
PubMed1976

Acceptance and transfer of R-factor RP1 by members of the "herbicola" group of the genus Erwinia.

The R-factor RP1 was transferred by conjugation from Pseudomonas aeruginosa PAO12r(RPI) to various strains of Erwinia herbicola and to one strain of Erwinia stewartii. The exconjugate strains had minimum inhibitory concentration values for carbenicillin, kanamycin, neomycin, and tetracycline somewhat lower than the corresponding values for the pseudomonad RP1 donor strain. The biochemical characteristics of the exconjugant strains displayed minor variation in some instances from those of the corresponding R- strains. Sensitivity of the RP1+ strains to the RP1-specific bacteriophages PRD1 and PRR1 varied from an efficiency of plating [compared with P. aeruginosa PA067(RP1)] of 0 [E. herbicola Y46(RP1)] to 133 [E. herbicola Y190(RP1)] and 148 [E. stewartii SS104R(RP1)] for PRD1, and from 0 [E. herbicola Y46(RP1)] to 0.0002 [E. herbicola Y185(RP1)] and 18.4 [E. stewartii SS104R(RP1)] for PRR1. The phage-resistant strain E. herbicola Y46(RP1), would donate, by conjugation, the R-factor to E. herbicola Y46rifr, P, aeruginosa PAT900, or Escherichia coli UB1005 only at extremely low frequencies, if at all. Transformation of E. coli JC7620 by covalently closed circular DNA from E. herbicola Y46(RP1) gave and E. coli R+ strain exhibiting the expected antibiotic resistance pattern and having the ability to donate RP1 by conjugation. It is suggested (i) that some strains of E. herbicola RP1 either do not produce RP1 pili or produce defective pili, and (ii) that sensitivity to the bacteriophages PRD1 and PRR1 is not a suitable means of diagnosing the presence RP1 in E. herbicola strains.

Bacteriophages↗
PubMed1976

Subcutaneous exposure of the Richardson's ground squirrel (Spermophilus richardsonii Sabine) to western equine encephalomyelitis virus.

Both adult and suckling Richardson's ground squirrels (Spermophilus richardsonii) were susceptible to subcutaneous exposure with western equine encephalomyelitis (WEE) virus, but the virus was more virulent for sucklings than adults. In sucklings, the incubation period was from 4 to 5 days, followed by apparent signs of central nervous system (CNS) involvement. Death occurred 10 to 13 days postexposure. In adults, infections were inapparent or acute with typical signs of CNS involvement similar to those observed in sucklings. In both age groups, brain and lymph nodes were the most frequently involved tissues. The highest titres of virus were recovered from brain, sections of which also showed the most marked histological changes. Lesions in the brain included multifocal vasculitis, perivascular edema, perivascular cuffing, focal or diffuse gliosis, parenchymal hemorrhage, meningitis with infiltration of mononuclear cells, neuronal degeneration, and occasional demyelination. For both age groups, viremias were detected for 3 to 5 days with a maximum virus titre of 4 to 6 logs, a sufficient time and magnitude to infect numerous mosquitoes, further supporting the hypothesis that S. richardsonii may serve as an amplifying host of WEE virus in the prairie provinces.

Animals↗