Biomedical subjects

R W Pickup

Publications and source records attributed to R W Pickup.

40 records · Page 3Linked to original sources

PubMed1986

Antibiotic resistant bacteria in Windermere and two remote upland tarns in the English Lake District.

The incidence of antibiotic resistance was determined in over 2000 bacteria which were divided into the following groups: faecal streptococci, coliforms (excluding Escherichia coli), E. coli, Pseudomonas spp. and aquatic bacteria (i.e. bacteria predominant in the lake water which were excluded from the previous four categories). The isolates were obtained from the water of Windermere (English Lake District) and from a sewage effluent which entered the lake. With the exception of the faecal streptococci, the incidence of antibiotic resistance was higher in the bacteria isolated from the lake water than in those from the effluent, and ranked according to groups Pseudomonas spp. greater than E. coli greater than aquatic bacteria greater than coliforms greater than faecal streptococci. The highest incidence of multiple resistance was found among the pseudomonads. When corrected for the relative size of each population the pool of antibiotic resistance in the aquatic bacteria was by far the largest. The incidence of antibiotic resistance in aquatic bacteria isolated from Windermere was, however, lower than in those isolated from two remote upland tarns. This finding may have been due to differences in the species composition of the three sites except that the same results were obtained when only fluorescent pseudomonads were tested. The upland tarns were not totally isolated from man and other animals but did not receive any sewage or other effluents and therefore the results were surprising. Possible explanations include a lack of susceptibility in aquatic bacteria and increased resistance associated with growth in nutrient poor environments.

Anti-Bacterial Agents↗

PubMed1986

Factors affecting the measurement of antibiotic resistance in bacteria isolated from lake water.

It is more difficult to obtain a reliable assessment of antibiotic resistance in populations of aquatic bacteria than in those populations which are well characterized (e.g. bacteria of medical and veterinary significance). Factors which influence the results include the bacterial taxa involved, their site of origin and the methods and media used to isolate and subculture the bacteria, and to perform the sensitivity tests. Examples of these effects are provided. The resistance profiles obtained with populations of aquatic pseudomonads depend on the species composition of the population. Resistance patterns in aquatic bacteria varied with the site from which they were isolated; a higher incidence of resistance was recorded along shorelines and in sheltered bays than in the open water. The inclusion of antibiotics in the media employed for primary isolation increased the number of individual and multiple resistances recorded. A similar effect was observed with increased inoculum size in the sensitivity disc method but this could be reversed by raising the incubation temperature. The medium used to conduct the test also affected the results and many aquatic bacteria failed to grow on media such as Iso-Sensitest Agar. It is recommended that the sensitivity disc method is adopted for aquatic bacteria because it permits interpretation of a wider range of response. Comparison of the incidence of antibiotic resistance in different habitats will remain meaningless, however, until comprehensive methods for the identification of bacteria are developed and the techniques used for sensitivity testing are standardized.

Ampicillin↗

PubMed1985

Evolutionary conservation of genes coding for meta pathway enzymes within TOL plasmids pWW0 and pWW53.

Pseudomonas putida MT53 contains a TOL plasmid, pWW53, that encodes toluene-xylene catabolism. pWW53 is nonconjugative, is about 105 to 110 kilobase pairs (kbp) in size, and differs significantly in its restriction endonuclease digestion pattern and incompatibility group from the archetypal TOL plasmid pWW0. An RP4::pWW53 cointegrate plasmid, pWW53-4, containing about 35 kbp of pWW53 DNA, including the entire catabolic pathway genes, was formed, and a restriction map for KpnI, HindIII, and BamHI was derived. The entire regulated meta pathway genes for the catabolism of m-toluate were cloned into pKT230 from pWW53 on a 17.5-kbp HindIII fragment. The recombinant plasmid supported growth on m-toluate when mobilized into plasmid-free P. putida PaW130. A restriction map of the insert for 10 restriction enzymes was derived, and the locations of xylD, xylL, xylE, xylG, and xylF were determined by subcloning and assaying for their gene products in both Escherichia coli and P. putida hosts. Good induction of the enzymes by m-toluate and m-methylbenzyl alcohol but not by m-xylene was measured in P. putida, but little or no regulation was found in E. coli. The restriction map and the gene order showed strong similarities with published maps of the DNA encoding both the entire meta pathway operon (xylDLEGFJIH) and the regulatory genes xylS and xylR on the archetype TOL plasmid pWW0, suggesting a high degree of conservation in DNA structure for the catabolic operon on the two different plasmids.

Alcohol Oxidoreductases↗

PubMed1982

Spontaneous deletions in the TOL plasmid pWW20 which give rise to the B3 regulatory mutants of Pseudomonas putida MT20.

The size of the TOL plasmid pWW20 from Pseudomonas putida MT20, as measured by analysis of agarose electrophoresis gels after restriction endonuclease hydrolysis, was 270-280 kilobase pairs (kb). During growth on benzoate, MT20 segregates strains carrying mutations in the plasmid regulatory gene xylS; these so-called B3 strains retain the ability to grow on m-xylene (Mxy+) but do not grow on its metabolite m-toluate (Mtol-) and have also lost the ability to transfer the plasmid (Tra-). Analysis of restriction digests of plasmid DNA from seven such segregants, independently isolated, showed that pWW20 had undergone extensive deletions of 90-100 kb. All the deleted plasmids had lost a common core of DNA, of about 72-80 kb, but in class A mutants the deletion extended at one end of this core and in class B mutants at the other end. Class A and B mutants also differed in their rate of growth on m-xylene as a result of differences in the level of expression of their plasmid-coded catabolic enzymes. This suggests that an additional gene, involved in regulating levels of gene expression, is located in the region uniquely deleted in the class B mutants.

Chromosome Deletion↗