Transfer of verocytotoxigenic Escherichia coli O157, O26, O111, O103 and O145 from fleece to carcass during sheep slaughter in an Irish export abattoir.

The purpose of this study was to investigate carriage and transfer of verocytotoxigenic Escherichia coli (VTEC) O157, O26, O111, O103 and O145 from fleece to dressed carcasses of 500 sheep, and to establish the virulence potential of recovered VTEC. Individual sheep were tracked and sampled (10 g fleece, full carcass swab) through the slaughter process. Samples were examined for the presence of verotoxin (vt1 and vt2) genes using a duplex real-time PCR assay and positive samples were further screened for the presence of the above five serogroups by real-time PCR. VTEC cells were recovered from PCR positive samples by serogroup specific immunomagnetic separation and confirmed by serogroup specific latex agglutination and PCR. Isolates were subject to a virulence screen (vt1, vt2, eaeA and hlyA) by PCR and isolates carrying vt genes were examined by Pulsed-Field Gel Electrophoresis (PFGE). VTEC O26 was recovered from 5/500 (1.0%) fleece and 2/500 (0.4%) carcass samples. VTEC O157 was isolated from 4/500 (0.8%) fleece samples and 3/500 (0.6%) carcass samples. E. coli O103 was recovered from 84/500 (16.8%) fleece and 68/500 (13.6%) carcasses, but only one E. coli O103 isolate (0.2%) carried vt genes. E. coli O145 was recovered from one fleece sample, but did not carry vt genes. E. coli O111 was not detected in any samples. For the four serogroups recovered, the direct transfer from fleece to carcass was not observed with PFGE showing that VTEC O26 isolates from a matched fleece/carcass "pair" were not identical. This study shows that while VTEC O157 are being carried by sheep presented for slaughter in Ireland, other potentially clinically significant verotoxin producing strains (particularly VTEC O26) are emerging.

Tracking verocytotoxigenic Escherichia coli O157, O26, O111, O103 and O145 in Irish cattle.

The purpose of this study was to investigate carriage and transfer of verocytotoxigenic Escherichia coli (VTEC) O157, O26, O111, O103 and O145 from faeces and hide to dressed carcasses of Irish cattle as well as establishing the virulence potential of VTEC carried by these cattle. Individual cattle was tracked and faecal samples, hide and carcass (pre-evisceration and post-wash) swabs were analysed for verotoxin (vt1 and vt2) genes using a duplex real-time PCR assay. Positive samples were screened for the five serogroups of interest by real-time PCR. Isolates were recovered from PCR positive samples using immunomagnetic separation and confirmed by latex agglutination and PCR. Isolates were subject to a virulence screen (vt1, vt2, eaeA and hlyA) by PCR. Isolates carrying vt genes were examined by Pulsed-Field Gel Electrophoresis (PFGE). Of the VTEC isolated, E. coli O157 was the most frequently recovered from hide (17.6%), faeces (2.3%) and pre-evisceration/post-wash carcass (0.7%) samples. VTEC O26 was isolated from 0.2% of hide swabs and 1.5% of faeces samples. VTEC O145 was isolated from 0.7% of faeces samples. VTEC O26 and VTEC O145 were not recovered from carcass swabs. Non-VTEC O103 was recovered from all sample types (27.1% hide, 8.5% faeces, 5.5% pre-evisceration carcass, 2.2% post-wash carcass), with 0.2% of hide swabs and 1.0% of faeces samples found to be positive for VTEC O103 isolates. E. coli O111 was not detected in any samples. For the four serogroups recovered, the direct transfer from hide to carcass was not observed. This study shows that while VTEC O157 are being carried by cattle presented for slaughter in Ireland, a number of other verotoxin producing strains are beginning to emerge.

Effects of reduction in beef surface water activity on the survival of Salmonella Typhimurium DT104 during heating.

AIM: To investigate the influence of reducing beef surface water activity (a(w)) on the survival of Salmonella Typhimurium DT104 during heating. METHODS AND RESULTS: Beef discs were surface inoculated with S. Typhimurium DT104 and either untreated or dried to achieve surface a(w) values of 0.95, 0.85 and 0.70. The samples were vacuum packed, heat-treated at 60 degrees C and removed at predetermined times. The inactivation curves were influenced by a(w) and treatment time. Biphasic inactivation curves were observed for S. Typhimurium DT104 heat-treated on beef samples with altered a(w) values, which were characterized by an initial decline in cell numbers at commencement of heating followed by a much slower rate of inactivation during the remaining treatment period. Point estimates of the heating time required to achieve a 1 log reduction on beef surfaces with a(w) of 0.99, 0.95, 0.85 and 0.70 were 0.5, 1.55, 11.25 and 17.79 min, respectively. CONCLUSIONS: A decrease in beef surface a(w) can substantially enhance the survival of S. Typhimurium DT104 after heating. SIGNIFICANCE AND IMPACT OF THE STUDY: Caution needs to be taken using dry air as a decontamination method as this may rapidly decrease product surface and pathogen a(w) values resulting in enhanced survival.

The survival of Salmonella enterica serovar Typhimurium DT104 and total viable counts on beef surfaces at different relative humidities and temperatures.

AIMS: The aim of this study was to investigate changes in Salmonella and total viable count (TVC) survival on beef carcass surfaces stored for 72 h under different combinations of relative humidity (i.e. RH 75% or 96%) and temperature (5 degrees C or 10 degrees C). METHODS AND RESULTS: The influence of low water activity (a(w)) and temperature on the survival and growth of Salmonella enterica serovar Typhimurium DT104 and the aerobic mesophilic flora on meat pieces from different sites on beef carcasses was investigated, under controlled conditions (75% or 96% RH; 5 or 10 degrees C) in an environmental cabinet. Salmonella counts declined during storage at low a(w) (75% RH) conditions at 5 degrees C or 10 degrees C. Salmonella counts increased during storage at high a(w) (96% RH) at 10 degrees C only. At 5 degrees C, TVCs increased during storage at high a(w), but not at low a(w). TVCs increased on all samples from carcasses stored at high or low a(w) at 10 degrees C, except those samples taken from areas of surface fat. CONCLUSIONS: This suggests that substrate composition dictates growth rates under low a(w) conditions. The results are discussed in terms of the possible protective effects of substrate osmolyte accumulation in bacterial survival and/or growth. SIGNIFICANCE AND IMPACT OF THE STUDY: The data obtained in this study provides useful insights on the influence of a(w) and temperature on pathogen survival on meat surfaces at chill temperature.

Effects of storage and the presence of a beef microflora on the thermal resistance of Salmonella Typhimurium DT104 in beef and broth systems.

AIMS: To investigate the effects of storage and the presence of a beef microflora on the thermal resistance of Salmonella serotype Typhimurium DT104 on beef surfaces and in a broth system during subsequent heat treatments after extended low-temperature storage (4 degrees C for 14 days) or mild temperature abuse (10 degrees C for 7 days). METHODS AND RESULTS: Surviving Salm. Typhimurium DT104 cells were estimated after heating in a water bath (55 degrees C) by plating beef and broth samples on tryptone soya agar and overlaying with xylose-lysine-deoxycholate agar. In beef and broth systems, D(55) values for Salm. Typhimurium DT104 stored at 4 degrees C or 10 degrees C in the presence or absence of a beef microflora were significantly lower (P < 0.01) than the D values for this organism heat-treated immediately after inoculation. In beef systems, the D(55) values were significantly lower (P < 0.05) in the presence of a beef microflora than the D(55) values obtained in 'pure' culture under all temperature/storage combinations. However, in broth systems, there was no significant difference between the D(55) values obtained in 'pure' culture and the D(55) values obtained from systems containing beef microflora. CONCLUSIONS: Storage of Salm. Typhimurium DT104 significantly reduced the thermal resistance of the pathogen in beef and broth systems. In the presence of high numbers of a Gram-negative beef microflora, the heat sensitivity of the pathogen was further increased on beef surfaces but not in broth. SIGNIFICANCE AND IMPACT OF THE STUDY: Studies investigating the survival of Salm. Typhimurium DT104 in different food systems will help define safe food preservation processes and will aid in the elimination this pathogen from the food production environments.

Surface decontamination of beef inoculated with Salmonella Typhimurium DT104 or Escherichia coli O157:H7 using dry air in a novel heat treatment apparatus.

AIMS: To determine the effectiveness of a novel dry air decontamination apparatus in the deactivation of Salmonella serotype Typhimurium DT104 or Escherichia coli O157:H7 on beef surfaces. METHODS AND RESULTS: A laboratory scale dry air decontamination apparatus, capable of producing repeatable and known heating time-temperature cycles on food surfaces was used in decontamination trials. Beef samples were surface inoculated with 7-8 log10CFU cm(-2) of S. Typhimurium DT104 or E. coli O157:H7 and heated at 60, 75, 90 and 100 degrees C using fast and slow heating rates and subsequently held at these temperatures for up to 600 s. A substantial reduction in pathogen numbers was achieved at higher temperatures (90 and 100 degrees C, 4.18-6.06 log10CFU cm(-2)) using both heating rates, but cell survival at these temperatures was also observed. At the lower temperatures, deactivation was small at 60 degrees C in particular it was less than one log unit after 3 min heating. No significant differences were observed when total reductions in pathogen counts were compared for all the temperature/heat up time combinations tested. During slow heating at 90 degrees C, and both heating rates at 100 degrees C, the pattern of deactivation of S. Typhimurium DT104 or E. coli O157:H7 was triphasic. CONCLUSIONS: This study has shown that heating meat surfaces with dry air can achieve substantial reductions in S. Typhimurium DT104 or E. coli O157:H7. As surface decontamination of beef surfaces with dry air had a negative effect on beef colour and appearance, such a decontamination apparatus would be unsuitable for producing meat for retail sale but it could be used to produce safer meat for use in the catering trade. SIGNIFICANCE AND IMPACT OF THE STUDY: This study provides researchers and food processors with data on the dynamic changes in S. Typhimurium DT104 and E. coli O157:H7 counts on intact beef surfaces during heating with dry air under realistic (time-varying) temperature conditions.