I. McLaren

Faecal carriage of verocytotoxin-producing Escherichia coli O157 in cattle and sheep at slaughter in Great Britain.

A 12-month abattoir survey was conducted between January 1999 and January 2000, to determine the prevalence of faecal carriage of verocytotoxin-producing Escherichia coli 0157 (VTEC 0157) in cattle and sheep slaughtered for human consumption in Great Britain. Samples of rectum containing faeces were collected from 3939 cattle and 4171 sheep at 118 abattoirs, in numbers proportional to the throughput of the premises. The annual prevalence of faecal carriage of VTEC 0157 was 4.7 per cent (95 per cent confidence interval 4.1 to 5.4) for cattle and 1.7 per cent (1.3 to 2.1) for sheep, values which were statistically significantly different from each other (P<0.001). The organisms were recovered from both cattle and sheep slaughtered throughout the year and at abattoirs in all regions of the country, but the highest prevalence was in the summer. The most frequency recovered VTEC 0157 isolates were phage types 2, 8 and 21/28 in cattle and 4 and 32 in sheep, the five most frequently isolated phage types associated with illness in people in Great Britain during the same period.

Persistence and clearance of different Salmonella serovars in buildings housing laying hens

We investigated factors associated with persistence of different Salmonella serovars in buildings housing laying hens in Great Britain using survival analysis. A total of 264 incidents of Salmonella detection occurring between July 1998 and August 2007 in 152 houses were recorded. For incidents involving Salmonella Enteritidis (SE), both the rodent score of the house and the type of house were positively associated with persistence. For non-SE serovars, only the type of house was associated with persistence. Persistence of SE in the houses was longest (>15 months) in step-cage and cage-scraper houses when high levels of rodents were present, and lowest in non-cage and cage-belt houses. We estimated that 42% (95% CI 23.3-63.1) of SE incidents may be cleared during the lay period, and this was related to elimination of rodents from the houses. From January 2009, EU legislation will ban the sale of fresh eggs from SE-positive and S. Typhimurium-positive flocks over their remaining lifespan. If infection is eliminated from such flocks, they would cease to represent a public health risk.

Bacteriological and serological investigation of persistent Salmonella enteritidis infection in an integrated poultry organisation

Bacteriological monitoring of broiler breeder farms, the hatchery, rendering plant and animal feed mill during 1991 identified a number of potential cross-contamination hazards, such as the use of processed poultry proteins in the company feed mill and contamination of egg trolleys and trays, which may have led to widespread dissemination of Salmonella enteritidis within an integrated poultry organisation. Serological monitoring of the flocks suggested that, in most cases, substantial exposure to S. enteritidis infection occurred during the mid-rearing stage whereas routine bacteriological monitoring of poultry house litter and dust samples, and meconium samples taken in the hatchery identified infection only after the onset of the laying period. At least 10 phage types and six plasmid profile types of S. enteritidis were identified in historic submissions from the organisation including one apparently specific plasmid profile type that was distributed throughout the various parts of the company. During sampling for this investigation, most of these strains were not identified, and the number of plasmid profile types was reduced to a single common UK type.

Antimicrobial resistance in Salmonella isolated from animals and their environment in England and Wales from 1988 to 1999

Resistance to 16 antimicrobial agents was monitored in 109,125 Salmonella cultures isolated from animals, their environment and feedstuffs between 1988 and 1999. The sensitivity of the 6512 isolates of Salmonella enterica enterica serotype Dublin to all the antimicrobial agents tested varied from 98.2 per cent in 1997 to 99.7 per cent in 1990 and 1996. In contrast, among 28,053 isolates of Salmonella enterica enterica serotype Typhimurium, there was a marked decrease in their sensitivity to all the antimicrobial agents tested, from 57.4 per cent in 1992 to 7.6 per cent in 1995, owing to the widespread occurrence in farm animals of S Typhimurium isolates of the definitive type DT104, resistant to ampicillin, sulphonamides, streptomycin, chloramphenicol and tetracyclines, although the percentage of sensitive isolates increased to 18.4 per cent in 1999, when the incidence of DT104 had decreased. Some isolates of DT104 also showed an increase in resistance to potentiated sulphonamides (2.4 per cent in 1989 to 19.2 per cent in 1999) and nalidixic acid (0 per cent in 1992, 3.8 per cent in 1995 to a peak of 16.9 per cent in 1998). In 1996, 5.1 per cent of 1086 isolates of S Typhimurium from cattle and 35.9 per cent of 192 isolates of S Typhimurium from poultry showed resistance to nalidixic acid. Of the other 74,528 Salmonella isolates, the percentage of strains sensitive to all the antimicrobials tested decreased slightly from 88.2 per cent in 1988 to 70.6 per cent in 1996 and then increased slightly to 73.7 per cent in 1999. The commonest of these other Salmonella serotypes was Salmonella Enteritidis (20,982), which remained predominantly susceptible (ranging from 81.4 to 97.4 per cent) during the study period. Few isolates were resistant to commonly used veterinary antimicrobials, for example, furazolidone, the use of which was banned in 1990, and the aminoglycoside, apramycin.

Studies of the presence of verocytotoxic Escherichia coli O157 in bovine faeces submitted for diagnostic purposes in England and Wales and on beef carcases in abattoirs in the United Kingdom.

A survey of beef carcases in abattoirs in the UK was carried out in order to estimate the prevalence of contamination with verocytotoxin-producing Escherichia coli (VTEC) serogroup O157. Contamination with verocytotoxin-producing E. coli (VTEC) O157 was confirmed in 0.47% of the 4067 (95% confidence limits 0.22-1.00%) of neck muscle samples. A significant tendency for carcases present in the same abattoir on the same day to have similar results was found, thus suggesting cross contamination. VTEC O157 was found in 0.83% of 6495 bovine faeces samples routinely submitted for diagnostic purposes to Veterinary Investigation Centres in England and Wales. Of the samples from cattle less than 6 months old, 3.7% of 68 samples from animals without gastrointestinal disease were positive for E. coli O157, in contrast to 0.75% of 2321 samples from cases of gastrointestinal disease. No association with season or herd type (beef or dairy) was found.

A comparison of the efficacy of cleaning and disinfection methods in eliminating Salmonella spp. from commercial egg laying houses

Effective terminal cleaning and disinfection (C&D) is regarded as a necessary step for the elimination of Salmonella spp. from laying houses. A total of 60 commercial laying houses that had housed laying flocks infected with Salmonella enterica serovar Enteritidis or Salmonella enterica serovar Typhimurium that were representative of all production systems (cage, barn, free-range) were intensively sampled immediately after C&D as well as in the follow-on flock. The procedures investigated were: (1) a compound disinfectant consisting of a mixture of formaldehyde, glutaraldehyde and quarternary ammonium applied at the recommended concentration; (2) a 10% (vol/vol) dilution of the standard 37% commercial formalin, applied by a contractor; and (3) other disinfection procedures selected and applied by the farmer. The recovery of Salmonella in the cleaned and disinfected houses was variable, with samples from floor and dropping boards/belts (cage houses) and scratching areas (non-cage houses) being the most likely to remain contaminated. In cage houses, the use of the 10% formalin dilution led to a statistically greater reduction in the sample prevalence than using any of the other C&D methods. A negative post-C&D result predicted clearance of Salmonella in 52% of cases, although the isolation of Salmonella from the houses immediately after C&D was not a perfect predictor of carry-over of infection.

Longitudinal survey of the occurrence of Salmonella in pigs and the environment of nucleus breeder and multiplier pig herds in England

Eight pig breeding units previously associated with Salmonella Typhimurium were visited during a period of up to seven years. Samples from voided faeces, surfaces, fomites and wildlife were cultured. Certain serovars (Derby, Stanley, Give, Bredeney, Mbandaka and Manhattan) were isolated repeatedly on certain units, while others (Agona, Ajiobo, Heidelberg, Meleagridis, Muenchen, Montevideo, Rissen and Senftenberg) were detected only once or intermittently. Serovars Kedougou, Newport and Typhimurium were isolated consistently on some units but only intermittently on others. There was an association between the Salmonella serovar in pens and in the immediate environment of the pens. Pens holding breeding stock destined for production herds were frequently positive for Salmonella. Herds under common ownership showed similar serovar combinations. Serovars from wildlife were typical of the associated premises. Cleaning and disinfection was frequently ineffective. On one unit, a low level of Salmonella was attributed to a small herd size, good cleaning and disinfection, and good rodent control. Breeding herds are therefore susceptible to endemic infections with multiple Salmonella serovars, and cleaning, disinfection and vector control may be inadequate in many cases. The prevalence of S Typhimurium was greater in youngstock, which may have important implications for public health.

Evaluation of commonly-used farm disinfectants in wet and dry models of Salmonella farm contamination

Two experimental models of Salmonella contamination were used in an attempt to mimic the conditions of disinfectant use on farms. A wet model, for conditions such as boot dips, used disinfectant application to a slurry of poultry faeces inoculated with Salmonella Enteritidis or Salmonella Typhimurium. A dry model, for disinfectant application to surfaces and equipment with adherent or residual organic material, used Salmonella-inoculated poultry faeces that were air-dried onto wooden dowels, immersed in disinfectant solution then left in air at room temperature overnight. All samples were subjected to a disinfectant neutralization step and resuscitation in broth, followed by Salmonella culture on semi-solid then indicator media. Disinfectants were tested at 0.5x, 1x and 2x the concentrations specified for the general control of bacterial pathogens on livestock premises in the UK (Defra General Orders rates). Chlorocresol-based disinfectants provided consistently high rates of Salmonella killing in both wet and dry tests. Formaldehyde-containing disinfectants showed very high efficacy in the dry test but were less effective in the shorter wet test, whereas the efficacy of glutaraldehyde without formaldehyde was variable between products. Other chemical classes tested (quaternary ammonium compounds, amphoteric surfactants, iodine preparations, peroxygens and a substituted phenol blend) were only moderately effective. They often required concentrations above General Orders rates to eliminate the test salmonellas, and frequently elimination was not achieved even under maximal conditions of concentration and exposure.

Detection of antibiotic residues and association of cefquinome residues with the occurrence of Extended-Spectrum β-Lactamase (ESBL)-producing bacteria in waste milk samples from dairy farms in England and Wales in 2011

Waste milk samples from 103 farms in England and Wales were examined for the presence of β-lactam antibiotics and ESBL-producing Enterobacteriaceae. Approximately 10 months after the initial sampling, further waste milk, environmental and faecal samples from farms shown to be positive for CTX-M Escherichia coli were investigated further. Isolates with an ESBL phenotype were tested by PCR for the presence of blaCTX-M, blaOXA, blaSHV and blaTEM genes. Isolates positive for blaCTX-M were sequenced to determine CTX-M type. Representative isolates were further examined by PFGE, plasmid replicon typing and serotyping. Of particular interest, 21.4% of waste milk samples contained residues of the cephalosporin cefquinome, which was significantly associated with CTX-M bacteria. Such bacteria occurred in 5.8% of the waste milk samples (including 3.9% CTX-M E. coli). CTX-M types identified were 1, 14, 14b and 15, but none of the E. coli were serotype O25, the serotype of the human pandemic strain.

Estimation of the Rate of Egg Contamination from Salmonella-Infected Chickens

Salmonella enterica serovar Enteritidis (S. Enteritidis) is one of the most prevalent causes for human gastroenteritis and is by far the predominant Salmonella serovar among human cases, followed by Salmonella Typhimurium. Contaminated eggs produced by infected laying hens are thought to be the main source of human infection with S. Enteritidis throughout the world. Although previous studies have looked at the proportion of infected eggs from infected flocks, there is still uncertainty over the rate at which infected birds produce contaminated eggs. The aim of this study was to estimate the rate at which infected birds produce contaminated egg shells and egg contents. Data were collected from two studies, consisting of 15 and 20 flocks, respectively. Faecal and environmental sampling and testing of ovaries/caeca from laying hens were carried out in parallel with (i) for the first study, testing 300 individual eggs, contents and shells together and (ii) for the second study, testing 4000 eggs in pools of six, with shells and contents tested separately. Bayesian methods were used to estimate the within‐flock prevalence of infection from the faecal and hen post‐mortem data, and this was related to the proportion of positive eggs. Results indicated a linear relationship between the rate of contamination of egg contents and the prevalence of infected chickens, but a nonlinear (quadratic) relationship between infection prevalence and the rate of egg shell contamination, with egg shell contamination occurring at a much higher rate than that of egg contents. There was also a significant difference in the rate of egg contamination between serovars, with S. Enteritidis causing a higher rate of contamination of egg contents and a lower rate of contamination of egg shells compared to non‐S. Enteritidis serovars. These results will be useful for risk assessments of human exposure to Salmonella‐contaminated eggs.