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Biomedical subjects

P Stevenson

Publications and source records attributed to P Stevenson.

At least 73 records · Page 4Linked to original sources
PubMed1986

Iron regulated outer membrane proteins of Escherichia coli: variations in expression due to the chelator used to restrict the availability of iron.

Iron restriction was induced in Escherichia coli O 111, E. coli O 164 and E. coli C by growing the organisms in trypticase soy broth containing ovotransferrin, desferal, EDDA (ethylenediamine-dihydroxyphenylacetic acid) or alpha,alpha'-dipyridyl. There were marked qualitative and quantitative differences in the iron regulated outer membrane proteins expressed in the presence of the various iron chelators. Differences in the kinetics of growth were also noted. E. coli C was devoid of a ferric enterobactin iron uptake system.

2,2'-Dipyridyl↗
PubMed1985

Hydatid disease in the Turkana District of Kenya, IV. The prevalence of Echinococcus granulosus infections in dogs, and observations on the role of the dog in the lifestyle of the Turkana.

The prevalence of Echinococcus granulosus in dogs in the Turkana District of Kenya was 39.4% of 695 examined. Of these, 98 (35.8%) had heavy Echinococcus worm burdens (10(3)-5 X 10(4) ), while 54 (19.7%) and 122 (44.5%) had medium (201-1000) and light (1-200) burdens. The possible sources of these infections are discussed. The prevalence rate differed in various parts of the district, ranging from 63.5% in the northwest, where the highest incidence of human hydatidosis also occurs, to nil along the shores of Lake Turkana. Infection rates of 32.0% and 16.7% were recorded at Lokitaung (north-east) and Lodwar (central), while in the south 48.9% of dogs harboured Echinococcus. This latter figure is surprising as the area has a low incidence of human hydatidosis. The Turkana keep a large number of dogs, and the reasons for this and the social role of the dog in the district is discussed. No difference in susceptibility was found between Turkana-type dogs and those of mixed breeds from Nairobi when they were experimentally infected with hydatid protoscolices from man, camels, cattle, sheep and goats. However, it proved difficult to infect the Turkana-type of dogs with viable protoscolices of cattle origin. The reasons for this and its epidemiological implications remain unclear. It is suggested that droughts, which affect Turkana every six to ten years, may play an important role in the perpetuation of hydatid disease in the area.

Animals↗
PubMed1985

Naturally occurring antibodies in human sera that react with the iron-regulated outer membrane proteins of Escherichia coli.

Sera from normal healthy human adults and infants, as well as sera from mice, rabbits, and guinea pigs, were examined by immunoblotting for naturally occurring antibodies reacting with outer membrane proteins of two Escherichia coli strains, O111 and O18. Some individuals had antibodies reacting very strongly with the iron-regulated outer membrane proteins, including the ferric-enterochelin receptor protein (Mr, 81,000), as well as with ompA. However, sera from infants contained predominantly antibodies to ompA; antibodies recognizing the iron-regulated outer membrane proteins were either absent or barely detectable. In human serum the antibodies were mainly of the immunoglobulin G class. No serotype-specific antibodies to the lipopolysaccharide of E. coli O111 or O18 were found in the sera tested.

Antibodies, Bacterial↗
PubMed1985

Synthesis of aerobactin and a 76,000-dalton iron-regulated outer membrane protein by Escherichia coli K-12-Shigella flexneri hybrids and by enteroinvasive strains of Escherichia coli.

One of the chromosomal segments associated with the virulence of Shigella flexneri and transferred to Escherichia coli K-12 by conjugation has been shown to code for the production of aerobactin and for the synthesis of an iron-regulated 76,000-dalton (76K) outer membrane protein. Analysis of various E. coli K-12-S. flexneri transconjugants showed that the genes involved with the synthesis of aerobactin and with the production of the 76K protein were linked to the mtl region of the S. flexneri chromosome. S. flexneri itself synthesized a 76K protein in its outer membrane under iron restriction as well as traces of 81K and 74K proteins. An examination of four enteroinvasive strains of E. coli showed that each produced aerobactin and a 76K outer membrane protein during iron-restricted growth. The profile of the iron-regulated proteins expressed by the enteroinvasive strains of E. coli was virtually identical to that expressed by the laboratory-constructed E. coli K-12-S. flexneri hybrids under the same growth conditions.

Animals↗
PubMed1983

Observations on the hatching and activation of fresh Taenia saginata eggs.

A method is described for the hatching and activation of Taenia saginata eggs. All proglottids collected from eight naturally-infected people in Kenya contained a high proportion of eggs with oncospheres that could be activated. A mean activation rate of 82.7% was recorded in eggs aged ten hours to ten days. Bile, in the absence of pancreatic enzymes, stimulated activation of T. saginata oncospheres but trypsin was necessary to achieve hatching from the oncospheral membrane.

Animals↗
PubMed1983

Hydatid disease in the Turkana District of Kenya. III. The significance of wild animals in the transmission of Echinococcus granulosus, with particular reference to Turkana and Masailand in Kenya.

The results are given of a study on the role of wildlife in the transmission of Echinococcus granulosus in the Turkana and Narok Districts of Kenya. A total of 76 wild carnivores belonging to three separate species was examined from Turkana District. Echinococcus adults were found in 11 of 38 silver-backed jackals (Canis mesomelas) and in six of 22 golden jackals (Canis aureus). This is the first record of golden jackals being infected with this parasite in Kenya. None of 16 spotted hyaenas (Crocuta crocuta) harboured the parasite. Morphological features of the parasites obtained from the jackals were compared with material obtained from dogs in the same area. No morphological differences were recorded when this material was compared with data reported by others, hence the Turkana material belonged to the single species E. granulosus. Three silver-backed jackals and three puppies (Canis familiaris) were successfully infected with protoscolices obtained from a hydatid cyst surgically removed from a Turkana patient. Three spotted hyaenas fed the same material failed to become infected. None of 152 wild herbivores of five species examined in Turkana harboured hydatid cysts. The natural jackal infections in this District are thought to be incidental and dependent on the continuance of the domestic cycle. The role of the Turkana themselves in the perpetuation of the cycle is discussed. Twenty-six wild herbivores of six species were examined for hydatid cysts, in Narok District; hydatids were found in three wildebeest (Connochaetes taurinus) and a single topi (Damaliscus korrigum). The discovery of fertile cysts in wildebeest and the reported infections in lions (Panthera leo), Cape hunting dogs (Lycaon pictus) and silver-backed jackals, support previous evidence of the existence of a wildlife cycle in the Masailand and Serengeti regions of East Africa. The relationship of this cycle to the domestic cycle operating in the same area is unclear and requires further investigation.

Animals↗
PubMed1979

Toxocara and ascaris infection in British pigs: a serological survey.

A serological survey of growing pigs from farms throughout Great Britain revealed that antibodies to toxocara and ascaris larval antigens were present in 4.5 per cent and 39.3 per cent respectively. Heavy infection with toxocara occurred only rarely and it is considered that this parasite is unlikely to be an important cause of chronic focal interstitial hepatitis. Antibodies to both nematodes were detected more frequently in heavy hogs than in pigs of lighter weight. Reginal differences in the prevalence of antibodies were also observed.

Animals↗
PubMed1979

The influence of environmental temperature on the rate of development of Ascaris suum eggs in Great Britain.

The rate of development of Ascaris suum eggs was recorded during 18 months in England. Every second or third week unembryonated eggs were placed in an unheated animal house and their development was observed at weekly intervals. Eggs underwent no development during November to May. Embryonation was most rapid during June, July and August. The shortest time for eggs to reach the infective stage was two weeks in 1976 and four weeks in 1977. A relationship was apparent between the rate of development of eggs and the seasonal occurrence of pigs in chronic focal interstitial hepatitis, a condition associated with infection by A suum larvae.

Animals↗
PubMed1977

Toxocara infection in pigs. The use of indirect fluorescent antibody tests and an in vitro larval precipitate test for detecting specific antibodies.

An in vitro larval precipitate test using second-stage Toxocara canis larvae and an indirect fluorescent antibody (IFA) test employing cuticles of T. canis larvae as antigen were evaluated using antisera produced in pigs experimentally infected with T. canis, T. cati, Ascaris suum, Toxascaris leonina and Parascaris equorum. The former test was both specific and sensitive and is suggested as a reliable and simple method of detecting Toxocara antibodies in pigs. The latter test was considered unsuitable because of cross-reactions that occurred when sera from pigs infected with other ascarids were tested. An IFA test for Ascaris antibodies, employing cuticles of A. suum larvae as antigen, is described. The degree of specificity of this test suggests that it may be of value in the detection of antibodies to Ascaris in pigs under natural conditions.

Animals↗