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Biomedical subjects

C Wray

Publications and source records attributed to C Wray.

At least 19 recordsLinked to original sources
PubMed1997

Studies on the development and use of a monoclonal sandwich ELISA for the detection of verotoxic Escherichia coli in animal faeces.

A sandwich ELISA using monoclonal antibodies to Escherichia coli verocytotoxins 1 and 2 for capture and detection was developed for detection of verocytotoxin-producing Escherichia coli (VTEC) in animal faeces. For optimal toxin detection, the faeces were cultured in MacConkey broth before subculture on to trypticase soy agar containing mitomycin C. It was possible to detect between 10 and 10(3) VTI-producing and 1 to 10 VT2-producing E coli/g faeces, and overall the sensitivity and specificity of the ELISA for VTEC in faeces were 80.5 per cent and 91.2 per cent, respectively, when compared with a verocell assay. A limited survey of faeces from healthy animals (89 cattle, 16 sheep, 22 pigs, 11 goats and six domestic fowl) and faeces from 144 cattle with enteric disease detected VTEC in 64 per cent, 63 per cent, 5 per cent, 45 per cent, none and 16 per cent of the samples, respectively.

Animals↗
PubMed1997

Immunomagnetic separation for enhanced flagellar antigen phase inversion in salmonella.

Immunomagnetic separation (IMS) was used to reduce delays in serotyping caused by slow flagellar phase inversion of diphasic salmonellas. Some 375 strains of 11 salmonella serotypes were examined using IMS. The mean time for successful flagellar phase inversion was reduced from 4.3 (range 1-18) d to 1.0 (range 1-3) d using the IMS method, and in a further experiment phase inversion was achieved within 8 h in 112 of a further 117 strains representing four salmonella serotypes.

Animals↗
PubMed1997

Attaching and effacing E. coli. Microscopic and ultrastructural observation of intestinal infections in pigs.

Pigs aged from neonate to 8 weeks with naturally occurring diarrhoea were submitted to a Veterinary Investigation Centre for routine diagnosis. They were retrospectively found to be infected with "attaching and effacing" E. coli (AEEC) on histological and ultrastructural examination of the intestinal tract. Subcultures of E. coli isolated from some of the affected pigs were tested against standard anti-sera and probed for the presence of verotoxin (VT) and "cae" genes. One strain of E. coli was positive for the VT gene and three VT-negative strains possessed the "cae" gene. This preliminary report suggests that in naturally occurring diarrhoea of suckling and weaned pigs, AEEC infection can be identified by histological examination of the intestinal mucosa and confirmed by electron microscopy, in the abscence of infection by recognised enteric pathogens on microbiological examination.

Adhesins, Bacterial↗
PubMed1996

Determination of an effective sampling regime to detect salmonella enteritidis in the environment of poultry units.

A study of the dissemination of Salmonella enteritidis in the poultry breeder industry in the UK showed that the choice of sites for sampling the environment of occupied houses and empty houses which had been disinfected after depopulation had a significant influence on the outcome. Increased isolation rates could be achieved by sampling nest box floors and dust in open slave feed hoppers in occupied poultry houses. Nest box floors were the most sensitive sites for detection of residual environmental contamination in poultry houses where enrofloxacin treatment had been used. Floor sweepings, nest box floors, slave feed hoppers, hydrated wall fabric junctions and high beams and pipes were the most sensitive sample sites in cleansed and disinfected poultry houses. The use of universal disinfectant neutralisers gave good results in laboratory trials but appeared to reduce the isolation rate from field samples.

Animals↗
PubMed1996

World Health Organisation--supervised interlaboratory comparison of ELISAs for the serological detection of Salmonella enterica serotype Enteritidis in chickens.

A collaborative exercise, supervised by the World Health Organisation, was set up to compare ELISAs used for the serological detection of Salmonella enteritica serotype Enteritidis in chickens. The aim was to ascertain how far agreement could be reached on the interpretation of optical density readings for high titre, intermediate titre and low titre sera. Two sets of sera were sent to 14 participants. The first set compared high, medium and low titre sera raised in specified-pathogen-free and commercial broiler breeder chickens. The second set comprised 20 sera of different antibody titres raised in commercial birds reared under laboratory conditions and sent blind. Both indirect and double-antibody sandwich blocking ELISAs were used with a number of different detecting antigens. With a few exceptions good agreement was reached on the interpretation of results obtained from high and low titre sera from the optical density obtained with a single serum dilution. Differences were observed in the interpretation of medium titre sera. The results suggested that most ELISAs produce reasonably comparable results and that practical problems may arise from interpretation of the results mainly as a result of the choice of the criteria used for differentiating sera obtained from infected and uninfected chickens. These problems are discussed.

Animals↗
PubMed1996

Persistence of Salmonella enteritidis in poultry units and poultry food.

1. Studies on the survival of Salmonella enteritidis in poultry units and food were carried out over a two-year period. 2. The organism persisted for at least one year in an empty trial house at the laboratory in which naturally-infected broiler breeder birds had previously been housed. A similar survival period was seen in a building which had housed an infected layer breeder flock, although infection was not detected in a subsequent pullet flock. 3. Salmonella enteritidis was also frequently found surviving outside poultry houses in small pockets of litter and fan dust which had been left after cleansing and disinfection of the site. On some poultry units S. enteritidis was also found in wild bird droppings. 4. Salmonella contamination appeared to persist preferentially in association with dust particles swept from the floor and in food troughs and S. enteritidis survived at least 26 months in artificially contaminated poultry food.

Animal Feed↗
PubMed1996

Seasonal variations in the isolation of Salmonella typhimurium, Salmonella enteritidis, Bacillus cereus and Clostridium perfringens from environmental samples.

Calf carcasses contaminated with S. typhimurium, B. cereus and Cl. Perfringens were placed in either a decomposition pit or in a deep burial pit. Salmonella was isolated from the soil around the decomposition pit for 27 weeks and for 15 weeks around the burial site. Salmonella re-appeared in soil samples during cold winter weather after an apparent 9-week absence from the decomposition pit and after 68 weeks in the burial site (a total of 88 weeks after the start of the experiment). There was also an annual rise in the isolation rate of B. cereus from the soil during the colder winter months, but Cl. perfringens appeared to be more prevalent in samples taken during spring of the second year of the study. A similar apparent rise in the prevalence of S. enteritidis during a cold winter period occurred in an empty poultry house that had previously held a naturally infected broiler-breeder flock.

Animals↗
PubMed1996

Development and evaluation of a simple, one-step salmonella isolation test.

A one-step test unit was developed which allowed migration of salmonellas to selective medium and indicated the presence of salmonella by motility inhibition using polyvalent flagella antiserum. Evaluation of the method using 1038 naturally contaminated samples led to identification of more contaminated samples than a standard method within 24 h as opposed to 96 h.

Animal Feed↗
PubMed1995

Mice as carriers of Salmonella enteritidis on persistently infected poultry units.

Evidence of the possible role of wild mice in the epidemiology of Salmonella enteritidis infection on broiler breeder and layer breeder units was obtained by a bacteriological examination of local mice. Persistent S enteritidis infection in birds on these units had been a problem and a high proportion of the mice were found to carry salmonella. S enteritidis was isolated from the liver and the intestine of most of the mice, indicating a systemic infection. Three-week-old chicks were infected by contact with droppings from mice which had been infected experimentally with S enteritidis two and five months previously. Wild mice infected artificially or naturally excreted S enteritidis intermittently, with up to 10(4) organisms in some individual droppings. A naturally infected mouse which died after intermittently excreting small numbers of S enteritidis in its droppings for 19 weeks had 10(4) organisms/g of liver and 10(3)/g of macerated intestine and contents. S enteritidis was also found in fetal tissue in a naturally infected mouse suggesting the possibility that the organism might be transmitted vertically.

Animal Husbandry↗
PubMed1995

Diversity and molecular variation among plasmids in Salmonella enterica serotype Dublin based on restriction enzyme fragmentation pattern analysis.

Molecular variation within and between plasmids of Salmonella enterica serotype Dublin was analysed. Such variation has been demonstrated in the serotype-specific plasmids (SSP's) of Typhimurium and Enteritidis. The two aims of this study were to determine the plasmid diversity in a host-adapted serotype and also the incidence of molecular variation in the SSP among strains of Dublin using restriction endonuclease fragmentation pattern (REFP) analysis with Pst1, Sma1 and EcoRV. Sixty-five strains were examined from seven countries. Plasmid profile and REFP analysis showed that none of the strains was plasmid-free. Seventy-seven percent of the strains possessed the 72 kb SSP either alone or in combination with another plasmid; 23% harboured plasmids which were molecular variants of the SSP. Four of the variants were more closely related to each other than to the reference SSP and were harboured by Dublin isolated from both the USA and Europe. A further three were shown to be cointegrate plasmids and were similarly distributed. Thirty-two percent of strains possessed the SSP alone. None of the UK strains was resistant to any of the antimicrobial agents tested whereas 74% of the remaining strains were resistant to between one and five antimicrobial agents. This study corroborates previous findings concerning the high degree of stability of the SSP and confirmed the clonal nature of Dublin. Co-resident plasmids provided evidence of sub-clones within localized geographical areas.

Animals↗
PubMed1995

Observations on disinfection regimens used on Salmonella enteritidis infected poultry units.

Studies carried out at the laboratory and in the field identified many potential problems during disinfection of poultry units naturally contaminated with Salmonella enteritidis. There appeared to be variations in the efficiency of commonly used disinfectants within a disinfectant group when used in a contaminated house. It was possible for Salmonella and other coliforms to be amplified during the pressure washing or steam cleaning process. If an effective terminal disinfectant was not used after this, then high levels of Salmonella were likely to persist. The efficiency of the disinfection regimen was not directly dependent on the standard of physical cleaning if this was carried out to a reasonable standard, as a high level of elimination of Salmonella could be achieved even in the presence of substantial quantities of residual organic matter. Disinfection regimens involving formaldehyde, either as part of a terminal compound disinfectant spray or as a final fogging agent, were found to be the most effective in the field.

Animals↗
PubMed1994

Observations on a broiler breeder flock naturally infected with Salmonella enteritidis phage type 4.

Bacteriological and serological studies in a broiler breeder flock naturally infected with Salmonella enteritidis indicated that the infection had become established by about 20 to 22 weeks of age. By 35 weeks, 70 per cent of the birds were positive by ELISA and at 39 weeks, 39 per cent were estimated to be carrying the infection as judged by culture post mortem. By 50 weeks, post mortem culture showed 17 per cent to be infected and 85 per cent reacted to the ELISA. Over the period of observation at the laboratory, combined cloacal swabbing and post mortem culture showed that at least 12.5 per cent of the birds were carrying the infection and 95.7 per cent reacted serologically. As the level of infection apparently declined with age it may have been present at too low a level to detect in the unincubated eggs and newly hatched chicks which were cultured. However, maternal antibody was present in 81 per cent of the eggs and 23 per cent of the chicks and it may have affected the colonisation of the organism and the ability to isolate S enteritidis.

Animals↗
PubMed1994

Computational problems in molecular systematics.

The development of extremely powerful computer programs and the ready availability of microcomputers has revealed several computational problems with data analysis. These problems occur in the handling of systematic data in general and molecular systematic data in particular. This paper examines three areas of controversy in molecular systematics resulting from increased computer power. We start by examining the first step in DNA sequence analysis, the establishment of homology via sequence alignment. Next we examine several problems in phylogenetic analysis that have arisen in the last few years due to use of the PAUP (Swofford, 1991), HENNIG86 (Farris, 1988), and PHYLIP programs. These problems include limitations on the number of taxa examined in a given analysis and the accuracy of the parsimony trees in such analyses. The final subject is an examination of programs used for assessing tree robustness. We concentrate on certain programs (such as MALIGN (Wheeler and Gladstein, 1993), PAUP (Swofford, 1991), HENNIG86 (Farris, 1988), PHYLIP (Felsenstein, 1990), CLADOS (Nixon, 1993), MacClade (Maddison and Maddison, 1993), etc.), but similar comments about other programs could also be made.

Animals↗