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Biomedical subjects

C Wray

Publications and source records attributed to C Wray.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1994

An approach to reduction of Salmonella infection in broiler chicken flocks through intensive sampling and identification of cross-contamination hazards in commercial hatcheries.

A comparative study of salmonella contamination in eleven commercial hatcheries in the UK was carried out during 1992/93. The sampling protocol involved individual swabbing and culture from surfaces and items of equipment within each premises. This allowed the identification of many areas where salmonella control measures were not successful resulting in a cross-contamination hazard for eggs and chicks. Egg sanitisation and handling methods, design of incubator and whole building ventilation systems, control of dust, fluff and aerosol production, disinfection of surfaces and equipment and handling of waste were areas where improvements could be made. There were examples of successful reduction of salmonella in all key areas and these could be extended to provide general practical protocols for salmonella control. The sampling and culture techniques used in this study required less labour and were more rapid and sensitive than traditional methods so could be used in comparative investigations of other complex high throughput livestock and food processing operations.

Animal Husbandry↗
PubMed1994

Evaluation of a rapid cultural method for identification of salmonellas in naturally contaminated veterinary samples.

Three thousand and forty-two samples of post-mortem tissues, environmental swabs, animal feed ingredients and eggs were examined by conventional methods and by a simple rapid culture method. The rapid method gave reliable presumptive identification of salmonella contamination within 48 h of the start of culture. The rapid method also showed enhanced sensitivity for detection of salmonellas, in most types of sample, particularly those taken in poultry houses and hatcheries where high levels of competitive faecal bacteria are present.

Animal Feed↗
PubMed1993

Escherichia coli isolated from farm animals in England and Wales between 1986 and 1991.

Escherichia coli isolated from farm animals in England and Wales between 1986 and 1991 were examined for their serogroup, fimbrial adhesin and toxin production, and resistance to antimicrobial drugs. Among the 3595 porcine isolates the more common serogroups were O149, O8, O138, O147 and O157. The F4(K88) adhesin was detected in 21 per cent of the cultures, whereas the other adhesins were never present in more than 3 per cent during any year, although there was an upward trend in the prevalence of the F6(987P) antigen. The heat labile enterotoxin was produced by more than 17 per cent of the cultures usually in association with the F4 antigen. The other toxins, heat stable (STa), verocytotoxin (VT) and cytotoxic necrotising factor (CNF) were produced by 5.3, 4.7 and 6.8 per cent of the cultures, respectively. Among the 1383 bovine cultures the more common serogroups were O8, O101 and O17. The F5(K99) adhesin was detected in 9.1 per cent of the cultures, usually in association with STa production. The toxins STa, VT and CNF were produced by 4.4, 2.8 and 8.3 per cent of the cultures, respectively. Among the 407 ovine isolates the more common serogroups were O8, O101 and O78, and 11 per cent of the cultures produced the F5(K99) antigen. The toxins STa, VT and CNF were produced by 1.5, 6.1 and 9.1 per cent of the cultures, respectively. In the case of the 402 poultry isolates the more common serogroups were O78, O2 and O8, which are usually associated with colisepticaemia. Resistance to antibiotics was common, particularly among the bovine isolates.

Animals↗
PubMed1993

PCR jumping in clones of 30-million-year-old DNA fragments from amber preserved termites (Mastotermes electrodominicus).

DNA from 30-million-year-old amber preserved termites (Mastotermes electrodominicus) was PCR amplified with nuclear ribosomal RNA small subunit primers and cloned into the TA vector (INVITROGEN). We obtained several classes of recombinant clones as a result. Authentic Mastotermes electrodominicus clones were identified. The source of other classes of clones was identified as contaminants of the ancient DNA template. Several of the clones appeared to be chimeric in structure with half of the clone identical to the termite sequence and the other half identical to contaminant sequences. The phenomenon of PCR jumping was identified as a possible source for the chimeric clones.

Animals↗
PubMed1993

Experimental infection of neonatal pigs with CNF toxin-producing strains of Escherichia coli.

To examine and compare the pathogenicity of cytotoxic necrotising factor (CNF)-producing Escherichia coli, two litters of piglets were infected orally with 10(10) E coli O88 or 10(10) E coli O32 strains. Of the six piglets infected with E coli O88, two died within 24 hours and three developed blood-stained diarrhoea. The other piglets were killed one, five, six and eight days after infection, when bacterial cultures indicated an overwhelming bacteraemic infection with E coli O88 in the early stages followed by clearance through the large intestine. The pathological changes consisted of an early enteritis, progressing to enterocolitis and a bacteraemic spread to the lungs. The histopathological changes were characteristic of toxaemic effects in brain, heart, liver and kidney, and characterised by congestion, oedema and exudation. Infection with E coli O32 produced a milder but similar enterocolitis, also with bacterial colonisation in the lungs. The histopathological findings again reflected a toxaemia. The enteritis was more persistent after E coli O32 infection and the strain persisted in large numbers in the intestine. No evidence of bacterial adherence to the intestinal mucosa was found with either strain. Enteroinvasion was only evident in one E coli O88-infected piglet, but the consistent occurrence of interstitial pneumonia showed the predilection of these organisms for the lung. The results confirm the toxigenic properties of CNF+ E coli and suggest an important role for this organism in enteric infection of young pigs.

Animals↗
PubMed1993

Bacterial resistance monitoring of salmonellas isolated from animals, national experience of surveillance schemes in the United Kingdom.

Antimicrobial resistance has been monitored in salmonellas isolated from animals in England and Wales since 1970. The current trends are indicated by comparing the results for the years 1981, 1989 and 1990. Seventy-six per cent of all salmonella isolations are still sensitive to all 16 antimicrobials used for testing. Most antimicrobial resistance is encountered in bovine isolations of Salmonella typhimurium especially phage type DT204C. This phage type, which was initially resistant to at least seven antimicrobials, has however become more susceptible in recent years. Ninety-eight per cent of S. dublin strains from cattle are still sensitive to all the antimicrobials used for testing. Although the number of porcine salmonella isolations is small, many show antimicrobial resistance especially to tetracyclines. A large increase in the number of salmonellas isolated from poultry has occurred in recent years and 75% of these strains are sensitive to all the antibiotics used for testing. Although there has been a slight decrease in the percentage of S. enteritidis strains showing susceptibility 87% of isolations are still sensitive. The emergence of resistance to the newer antimicrobials trimethoprim, apramycin and fluorquinolones has been studied and data presented. The results are discussed with regards to the choice of techniques, bacteria monitored and future surveillance programmes in relation to the veterinary use of antimicrobials.

Animals↗