Biomedical subjects

Z Parsell

Publications and source records attributed to Z Parsell.

5 recordsLinked to original sources

PubMed1978

Thermosensitive antibiotic resistance plasmids in enterobacteria.

Of 775 conjugative plasmids found in enterobacteria mediating antibiotic resistance, 24 (3.1%) were thermosensitive (ts); they were most common in Klebsiella pneumoniae. Ts plasmids were also found in all the samples of sewage and river water examined. Over half of 73 ts plasmids from unrelated sources mediated resistance to chloramphenicol in addition to several other antibiotics. Many of them mediated resistance to mercury (53.4%), arsenite (38.4%) and tellurite (79.5%) but not to copper, cobalt and silver. Fifty-eight belonged to incompatibility group H2 and 12 belonged to the H1 group. Resistance to mercury, arsenite and tellurite was common in strains containing H2 plasmids but not in H1 plasmids. The 73 plasmids transferred at high rates at 22 and 28 degrees C and at lower rates at 15 degrees C; they transferred at very low rates or not at all at 37 degrees C. They could be divided into two sets according to whether they transferred at a high or at a low rate at 33 degrees C. Unlike the prototype plasmid, Rts 1, they were solely or mainly ts for transfer and not for replication and only one of them brought about a marked reduction in growth rate of its host organism at 42 degrees C. None of the 73 plasmids mediated colicin or haemolysin production. Three plasmids, all from K. pneumoniae, mediated utilization of lactose, two of sucrose and raffinose and three, all belonging to group H1, of citrate. None of the plasmids increased the pathogenicity of Salmonella typhimurium for chicks or Escherichia coli K12 for mice.

Animals↗

PubMed1978

Thermosensitive H1 plasmids determining citrate utilization.

Twelve thermosensitive H1 plasmids from strains of Salmonella typhi that had caused outbreaks of chloramphenicol-resistant typhoid fever in Vietnam, Thailand and India mediated citrate utilization (Cit+) in a prototrophic Escherichia coli K12 strain but not in the S. typhi strains from which they were derived. Four H1 plasmids from a similar outbreak in Mexico differed from the Far Eastern plasmids in not mediating citrate utlization but in mediating mercury resistance. H1 plasmids resembling the Far Eastern and the Mexican plasmids in regard to citrate utilization and mercury resistance were found in sewage in Britain. Citrate utilization was transferred to eight pathogenic strains of E. coli and to one strain each of Shigella flexneri and Shigella sonnei. Cultures of Cit+ bacteria grew more rapidly in citrate media at 28 degrees C than at 37 degrees C. Plasmid mutants that were more efficient at utilizing citrate were present in all such cultures--they grew equally well or better at 37 degrees C than at 28 degrees C. None of 222 strains of E. coli or Shigella that contained a variety of different plasmids were able to utilize citrate. This property was not transferred to the prototrophic E. coli K12 strain from Citrobacter (3 strains), Salmonella (39 strains), Proteus (44 strains), Klebsiella pneumoniae (33 strains) or Pseudomonas aeruginosa (44 strains).

Anti-Bacterial Agents↗

PubMed1977

Temperature-sensitive and other mutants of the Essex 70 strain of Newcastle disease virus as vaccines.

The most reliable method of distinguishing strains of low virulence amongst a collection of stock strains of Newcastle disease virus (NDV) was by their failure to produce a good c.p.e. in monolayers of baby hamster kidney cells and of chick embryo cells. This method was of no help in identifying avirulent mutants that emerged in the Essex 70 strain of NDV following ultraviolet light, nitrous acid, hydroxylamine or N-methyl-N'-nitro-N-nitrosoguanidine (NTG) treatment. A marked reduction in the ability to kill developing chick embryos at 41 degrees C was a much more reliable indicator. Several of these temperature-sensitive mutants, most of which had been isolated from NTG-treated virus, were non-lethal for young chicks but they did have a depressive effect on their growth rate. The immunity produced by three of these mutants in chicks free of NDV antibody, but not in chicks possessing appreciable amounts of antibody, was probably even better than that produced by Hitchner B1 strain. All three mutants reverted to virulence during passage in chicks, although in no case were the revertants as virulent as the original Essex 70 strain. The virulent revertants obtained from one of the mutants had lost their temperature-sensitivity and proliferated in large numbers in the tissues of infected chicks. Those obtained from the other two had either not lost, or only partly lost, their temperature-sensitivity; they were found only in low concentrations in the tissues of infected chicks, their concentrations being little different from that found in the tissues of chicks infected with the mutants from which they were derived.

Animals↗

PubMed1976

A transmissible plasmid determining lactose fermentation and multiple antibiotic resistance in a strain of Klebsiella pneumoniae.

In a wild strain of Klebsiella pneumoniae the plasmid that determined lactose fermentation also determined resistance to chloramphenicol, ampicillin, tetracyclines, streptomycin, spectinomycin, and sulphonamides. The plasmid transferred at a very low rate to Escherichia coli K12 and Salmonella typhi. By implanting other transfer factors in the strain the rate of transfer and the recipient range were increased. Plasmid transfer from the modified strain to Salm. typhimurium and Salm. gallinarum was detected in the alimentary tract of experimentally infected chicks fed diets containing ampicillin.

Ampicillin↗

PubMed1975

Transmissible substrate-utilizing ability in enterobacteria.

Three of 152 strains of Escherichia coli transmitted their ability to utilize sucrose (Sac+) to other strains by conjugation. The transfer factor of one of them and of a Sac+ Salmonella thompson strain was thermosensitive. The raffinose-utilizing ability of 27 of 163 E. coli strains was also transmissible. Transmissible raffinose-utilizing ability was a feature of porcine enterpathogenic strains possessing the K88 antigen. The determinants controlling raffinose utilization (Raf) and K88 antigen production were commonly transmitted together from these strains; so also was the determinant controlling enterotoxin production, but to a lesser extent. It was not possible to transfer lactose-utilizing ability from 320 strains of E. coli, salicin-utilizing ability from 12 strains of E. coli or dulcitol-utilizing ability from 99 strains of E. coli and 88 strains of salmonellae. Sucrose- and raffinose-utilizing ability were transmitted separately to several Salmonella sp., including Salm. typhi, to Shigella flexneri and Sh. sonnei and to a variety of strains of E. coli. A strain of Salm. typhimurium in which Sac had been established and a strain of E. coli in which Raf had been established survived less well in the alimentary tract of chickens than their Sac minus or Raf minus parent strains.

Animals↗