Airborne Salmonella and Listeria associated with Irish commercial beef, sheep and pig plants.

Air samples from lairage, hide/fleece pulling or dehairing/scraping, evisceration and chilling areas in commercial beef, sheep and pig plants were examined for Salmonella spp. and Listeria monocytogenes, by impaction or sedimentation onto selective (Brilliant Green Agar, BSA; Listeria Selective Agar, LSA) and non-selective (Plate Count Agar, PCA) media. Both pathogens were frequently detected in all three plants. Improved recoveries were achieved by combining sedimentation, and broth based resuscitation, suggesting cell injury. Salmonella were recovered from all three plants, with the highest counts on BGA in the pig plant. The most common serotypes were S. Typhimurium in the beef/sheep plants and S. Derby in the pig plant. Very low counts of L. monocytogenes (e.g. 2.6CFUm(2)) were detected at hide removal on LSA sedimentation plates in the beef plant. These included serogroup 1/2a-3a and 1/2b-3b-7. Pathogen counts in the three plants were generally very low, suggesting that air is unlikely to be a significant source of carcass or plant surface contamination.

Comparison of aerial counts at different sites in beef and sheep abattoirs and the relationship between aerial and beef carcass contamination.

The study examined and compared levels of aerial contamination in commercial beef and sheep plants at four sites, i.e. lairage, hide/fleece pulling, evisceration and chilling. Aerial contamination was determined by impaction and sedimentation onto Plate Count Agar to enumerate Total Viable Counts, MacConkey Agar to enumerate coliforms and Violate Red Bile Glucose Agar to enumerate Enterobacteriaceae. AS I cannot see any difference in the text here - I am not sure what the change is?. The levels of aerial contamination were similar at equivalent sites in beef and sheep plants, irrespective of the sampling method or the type of organisms recovered. Mean log counts recovered on each medium in the chillers were generally significantly lower (P < .05) than the corresponding mean log numbers recovered at the other three sites. The relationship between impaction (air) and sedimentation (surface) counts could be described by the surface to air ratio (SAR) which in this study had an R(2) of 0.77. Further studies in an experimental plant compared counts recovered from the neck of beef carcasses with aerial counts determined by impaction and sedimentation onto agar and irradiated meat pieces. A relationship between counts on beef carcasses and in the air could not be established, irrespective of the method used to compare counts.

Diversity of culturable psychrophilic and psychrotrophic anaerobic bacteria isolated from beef abattoirs and their environments.

This study identified 431 psychrophilic or psychrotrophic isolates from commercial Irish beef abattoir environments and "blown packs" of vacuum-packed beef, using PCR and 16S rRNA sequencing, and estimated their intraspecies genetic diversity using restriction fragment length polymorphism (RFLP) analysis and spacer region PCR (SR-PCR). Twenty-five species were identified in the 431 isolates, with the most frequently recovered species being Clostridium gasigenes (n=315), Clostridium estertheticum (n=17), and a potentially novel species designated strain TC1 (n=52). These species were previously found to be associated with a particular type of spoilage known as blown-pack spoilage (BPS), which occurs in chilled-stored (i.e., -1.5°C to 4°C) vacuum-packaged meat within 2 to 4 weeks and involves the production of large volumes of gas. Overall, the study demonstrates the considerable and not previously reported diversity of the anaerobic microflora in abattoirs and the presence of a wide range of organisms capable of causing BPS at chilled temperatures.

The influence of storing beef aerobically or in vacuum packs on the shelf life of mince.

AIMS: To investigate the influence of aerobic or vacuum pack storage of beef trimmings on the microbiology, colour and odour of subsequently produced mince. METHODS AND RESULTS: Trimmings stored aerobically for 7 or 10 days and in vacuum packs for 7, 10, 14 or 22 days at 0 or 5°C were minced, stored aerobically at 0 or 5°C for up to 7 days and examined daily to determine Total viable, Pseudomonas, Lactic acid bacteria, Brochothrix thermosphacta, and Enterobacteriaceae counts, colour and odour. Mincing reduced counts, particularly of Pseudomonas, B. thermosphacta and Enterobacteriaceae, probably because of the action free radicals released from muscle and bacterial cells. Storage of vacuum-packed trimmings for 22 days resulted in improved mince colour and inhibition of the growth of Pseudomonas. CONCLUSIONS: The shelf life of mince from trimmings is directly influenced by the trimmings storage conditions, and longer-term vacuum storage of trimmings produced improvements in mince quality. SIGNIFICANCE AND IMPACT OF THE STUDY: There appears to be no scientific rationale for limiting the storage of vacuum packaging beef trimmings to 15 days, prior to mince production, as stated in EU 835/2004. This study identifies advantages in storing trimmings in vacuum packs for at least 21 days prior to mincing, in terms of improved mince quality.

Survival of Pseudomonas fluorescens on beef carcass surfaces in a commercial abattoir.

The influence of a commercial chilling process (18 h at 10 degrees C followed by up to 78 h at 2 degrees C) on Pseudomonas fluorescens inoculated on beef carcass surfaces at four sites, neck (NE), outside round (OR), brisket (BR) and foreshank/brisket (FB) before chilling ("hot inoculated") or after chilling for 24h ("cold inoculated") was investigated. Pseudomonas counts increased significantly at all sites on "hot inoculated" carcasses during storage, but on "cold inoculated" carcasses, counts declined or remained unchanged. On hot and cold inoculated carcasses, differences in Pseudomonas growth or survival were demonstrated between sites. No clear relationships were observed between Pseudomonas growth or survival and chiller relative humidity (RH) or surface water activity (a(w)) at the different sites. These results were unexpected, and are discussed in relation to environmental factors that affect the growth/survival of P. fluorescens on carcass surfaces during chilling i.e. temperature, RH, and the relationship of these parameters to surface water activity (a(w)).

The effect of storage temperature and inoculum level on the time of onset of 'blown pack' spoilage.

AIMS: To examine the effect of storage temperature and inoculum level on the time of onset of 'blown pack' spoilage (BPS) caused by psychrotolerant bacteria in vacuum-packed (VP) meats. METHODS AND RESULTS: Gas-producing species and strains (n = 11), recovered in our laboratory or reported as associated with BPS, were inoculated onto beef or lamb meat pieces at final levels of <10, 10, 10(2) and 10(3) CFU cm(-2), VP and stored at -1.5, 1 or 4 degrees C. Six strains produced observable amounts of gas within 42 days and a further four strains produced gas within 100 days. BPS was observed earliest in VP meats inoculated with Clostridium estertheticum ssp. estertheticum at all inoculum levels/storage temperature combinations examined. Storage temperature and inoculum level significantly affected (P < 0.001 and P < 0.05 respectively) the onset of BPS in all cases. CONCLUSIONS: Controlling contamination levels and lowering the storage temperature delay the onset of BPS. SIGNIFICANCE AND IMPACT OF THE STUDY: The study demonstrates the positive effects of low contamination-low temperature as control interventions preventing/delaying BPS in VP chilled meats and identifies some of the contaminants most likely to cause BPS in chilled stored VP meat products.

Molecular characterization of Irish E. coli O157:H7 isolates of human, bovine, ovine and porcine origin.

AIMS: To determine the degree of relatedness between isolates of Escherichia coli O157:H7 of human, bovine, ovine and porcine origin. METHODS AND RESULTS: Escherichia coli O157:H7 isolates were compared using (i) PFGE XbaI patterns, (ii) PCR profiles of virulence genes and (iii) the DNA sequences of genes reported to play a role in pathogenicity. The 77 E. coli O157:H7 isolates demonstrated 49 different PFGE patterns of which, eight were common to multiple isolates, and the remaining 41 were distinct. Isolates of different origin did not correlate, except for one cluster consisting of two human and two beef isolates. The majority of animal isolates had the same PCR profiles of virulence genes as those isolated from clinical patients. Single nucleotide polymorphisms (SNPs) were identified in the sequence of a 255-bp region of the vtx2 subunit A gene. CONCLUSIONS: Six SNPs were detected in the vtx2A gene, defining four different haplotypes. One nonsynonymous substitution encoded for an amino acid change from glutamic to aspartic acid. SIGNIFICANCE AND IMPACT OF THE STUDY: Results indicate that although E. coli O157:H7 isolates of differing origin were distinct by PFGE, the DNA sequences of the main virulence genes associated with human clinical illness were conserved.

Changes in Escherichia coli O157:H7 numbers during holding on excised lean, fascia and fat beef surfaces at different temperatures.

AIM: To investigate changes in Escherichia coli O157:H7 numbers on excised beef carcass surfaces over 72 h at different temperatures. METHODS AND RESULTS: Excised lean meat, fascia and fat were inoculated with E. coli O157:H7 and held in an environmental chamber for 72 h, at air speed 0.5 m s(-1), relative humidity (RH) 90%, and temperatures 4, 8 and 12 degrees C. On lean, pathogen counts increased significantly at 12 degrees C. On fascia, significant reductions in counts occurred at 4 and 8 degrees C. Pathogen numbers were significantly reduced on fat at 4, 8 and 12 degrees C (64 h). Counts on fat were significantly less at all temperatures, compared to lean or fascia and surface water activity, a(w), decreased significantly over time on fat at 4 degrees C. Significant decreases in surface pH values were recorded on all meat substrates. CONCLUSIONS: The survival of E. coli O157:H7 varied in relation to the meat substrate and the holding temperature. Reductions in counts on fat surfaces appeared to be related to low surface a(w) values. No relationship between pathogen survival and surface pH was established. SIGNIFICANCE AND IMPACT OF THE STUDY: The use of excised meat pieces in an environmental cabinet offers a more flexible approach to determining the use of different chilling regimes in the production of safe meat.

Isolation and sources of 'blown pack' spoilage clostridia in beef abattoirs.

AIMS: (i) To evaluate methods for isolation and molecular detection of blown pack spoilage (BPS) clostridia and (ii) to survey beef abattoirs for sources and distributions of Clostridium estertheticum and Cl. gasigenes. METHODS AND RESULTS: Molecular detection and conventional isolation methods were used to detect and recover BPS associated clostridia (Cl. estertheticum and Cl. gasigenes), from four commercial Irish beef abattoirs and their environments, during a one year study. DNA-based methods detected 218 Cl. estertheticum and 300 Cl. gasigenes, from 1680 samples, whereas culture-methods only yielded 17 Cl. estertheticum and 176 Cl. gasigenes isolates. BPS Clostridia were frequently detected in beef abattoirs and their environments, especially at areas prior to hide removal. The study noted a higher percentage of positive samples during the month of May (38.6%). CONCLUSIONS: (i) DNA-based techniques are the most reliable ways to determine the presence of these organisms in various samples and (ii) hides and faeces are the main reservoirs of BPS clostridia in the abattoirs. SIGNIFICANCE AND IMPACT OF THE STUDY: This paper provides useful information to detect BPS organisms, as well as to develop a science-based control strategy of the problem.

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 potential use of chilling to control the growth of Enterobacteriaceae on porcine carcasses and the incidence of E. coli O157:H7 in pigs.

AIMS: To (i) monitor the presence of Enterobacteriaceae as indicators of faecal contamination on pig carcasses, (ii) examine the potential use of chilling as a critical control point (CCP) and establish its influence on pig carcass categorization by Decision 471/EC and (iii) determine the incidence of E. coli O157:H7 in pigs. METHODS AND RESULTS: Porcine faecal samples and carcass swabs were collected before and after chilling at four Irish pig abattoirs and examined for Enterobacteriaceae and E. coli O157:H7. Chilling generally reduced Enterobacteriaceae counts on carcasses, but increases were also observed, particularly in one abattoir. E. coli O157:H7 was absent from carcasses before chilling, present on 0.21% after chilling and was recovered from 0.63% of faecal samples. All of the isolates were found to contain virulence genes associated with clinical illness in humans. CONCLUSIONS: The data show that overall chilling had the capacity to reduce the numbers of carcasses positive for the presence of Enterobacteriaceae. SIGNIFICANCE AND IMPACT OF STUDY: The influence of chilling on the categorization of pig carcasses suggests that it has the potential to improve the numbers of acceptable carcasses and the process could be used as a CCP within a HACCP plan.

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.

Detection of numerous verotoxigenic E. coli serotypes, with multiple antibiotic resistance from cattle faeces and soil.

Verotoxigenic E. coli (VTEC) belong to a diverse range of serotypes. Serotypes O157 and O26 are predominately identified in VTEC-associated disease in Europe, however due to difficulty in detection little is known about the epidemiology of non-O157 serotypes. This study reports the identification of 7 VTEC serotypes from cattle faeces and soil. Cattle faeces samples (n=128) were taken from animals in 6 different farms, with soil samples (n=20) obtained from 1 farm. After sample incubation in modified tryptone soy broth (mTSB) supplemented with streptomycin sulphate samples were plated onto sorbitol MacConkey (SMAC) also supplemented with streptomycin sulphate. Bacteria detected on the plates were subjected to biochemical testing, antibiotic resistance profiling, and PCR to detect typical virulence genes, beta-lactamase and class 1 integron associated genes. Serotyping was performed on isolates positive for virulence genes. E. coli was identified from 103 samples, with verotoxin genes present in 7 E. coli isolates. Of these 7 isolates, 5 were resistant to 5 or more antibiotics. The isolate resistant to 9 antimicrobials contained a class 1 integron structure. Serotyping identified 7 separate VTEC, O2:H27, O26:H11, O63:H(-), O148:H8, O149:H1, O174:H21 and ONT:H25. Six of these VTEC have been previously associated with human disease, however with the exception of O26:H11, these serotypes have been rarely reported worldwide. Increased surveillance is required to determine the prevalence of these and other non-O157 VTEC. The presence of multi-antibiotic resistance in these isolates is of concern, and the overall implications for public health must be ascertained.

Survival of Escherichia coli O157:H7 and non-pathogenic E. coli on irradiated and non-irradiated beef surfaces.

This study examined changes in numbers of pathogenic (PEC) and non-pathogenic (NPEC) Escherichia coli during storage at 10°C on the surfaces of irradiated (IR) and non-irradiated (NIR) meat pieces excised from the neck, brisket and rump of beef carcasses and in Brain Heart Infusion Broth (BHI) and Maximum Recovery Diluent (MRD). On irradiated meat pieces, there were significant differences between mean PEC and NPEC counts at all sites. Differences in counts were also observed between IR and NIR surfaces and among the three meat sites for both E. coli types. These differences occurred only on IR samples, suggesting that the irradiation associated reductions in normal beef surface flora influenced survival of both E. coli types. PEC and NPEC counts increased during storage in BHI, but only NPEC counts increased in MRD. The results of this study highlight the impact of meat surface type and the presence/absence of the normal beef carcass surface flora on E. coli survival and/or growth during meat storage. Such previously unreported effects, and their precise mechanisms, have direct implications in the development and application of accurate models for the prediction of the safety and shelf life of stored meat.

Prevalence and molecular characterization of Escherichia coli O157:H7 on Irish lamb carcasses, fleece and in faeces samples.

AIMS: To determine the prevalence, seasonal variation and virulence characteristics of Escherichia coli O157:H7 in lambs presented for slaughter in Ireland. METHODS AND RESULTS: Over a 13-month period, pre- and postchill carcass swabs, faeces and fleece samples from 1600 lambs were examined for the presence of E. coli O157:H7. Escherichia coli O157:H7 was isolated from 5.75% (23/400) of fleece samples, 1.5% (6/400) of pre- and 1% (4/400) of postchill carcass swabs but was not isolated in faeces (0/400). The present study detected no evidence of seasonal variation. Polymerase chain reaction analysis showed that both the vt1 and vt2 genes associated with clinical illness were carried by five of the E. coli O157:H7 isolates, while 24 of the remaining isolates carried the vt2 gene only. Phage typing detected four different subtypes: PT 32 (48.48%), PT 8 (12.12%), PT 31 (12.12%) and PT 21/28 (12.12%). CONCLUSIONS: Escherichia coli O157:H7 is present in lambs at slaughter in Irish abattoirs and the virulence profiles of these isolates reveals that they are potentially harmful to humans. SIGNIFICANCE AND IMPACT OF THE STUDY: The present study provides crucial information indicating that sheep may be a significant contributing source to human E. coli O157:H7 infection.

Survival of Listeria innocua on hot and cold beef carcass surfaces.

AIMS: This study aimed to determine the survival and growth of Listeria innocua on hot and cold beef carcass surfaces. METHODS AND RESULTS: Four sites, the neck, outside round, brisket and foreshank/brisket, were inoculated with L. innocua (i) immediately after dressing while hot and (ii) when cold after chilling. After inoculation, all carcasses were stored at 4 degrees C for 72 h. Survival of L. innocua on cold surfaces declined during storage and was less than on hot carcasses at all times. Data on the survival of L. innocua in broth (maximum recovery diluent) indicated that counts could not be compared with those on carcasses, in particular on cold carcasses. CONCLUSIONS: The results indicate that L. innocua survives on hot carcass surfaces during chilling, but declines over time on cold surfaces. The decrease in L. innocua counts on cold surfaces may be related to a synergy between the combined stresses of low available water (a(w)) and low temperature. SIGNIFICANCE AND IMPACT OF THE STUDY: This study is the first to determine the effect of chilling on the survival and growth of Listeria on beef carcass surfaces. The information can potentially be used to determine the survival and growth of the pathogen, L. monocytogenes on beef surfaces.

The influence of attachment to beef surfaces on the survival of cells of Salmonella enterica serovar Typhimurium DT104, at different a(w) values and at low storage temperatures.

This study investigated the influence of attachment to beef surfaces on the survival, injury and death of stationary phase cells of Salmonella enterica serovar Typhimurium DT104, compared to cells free in solution. The effects on cells are considered at different a(w) values and low temperatures in relation to osmotic and cold temperature shock effects. Attachment of cells to meat surfaces prevented cell injury and death from hyperosmosis and low temperatures, compared to meat solutions. Storage of cells for 72h resulted in higher levels of cell death on cells attached to meat surfaces. The improved survival of cells in solutions was considered to be related to adaptation to osmotic stress as a result of exposure to a previous hyperosmotic shock and the ability of the cells to produce cold shock proteins. Pathogen cell growth at low temperatures is discussed in relation to the presence of low levels of NaCl. Finally the data is discussed in relation to pathogen survival on beef carcass surfaces during refrigeration.

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.

Assessing the hygiene of pig carcasses using whole-body carcass swabs compared with the four-site method in EC Decision 471.

An investigation was carried out in a pig abattoir to determine the microbiological status of carcasses being produced after slaughter and dressing. The carcasses were sampled in accordance with EC Decision 471 in relation to the application of hazard analysis critical control point (HACCP) criteria to the slaughter of animals. In this regard, four sites on the animals were examined on five consecutive carcasses during each of 10 visits for the presence of total viable counts and Enterobacteriaceae. A comparison of the EC four-site method, with a whole-body swab technique, as a means of measuring carcass contamination found that the two methods gave significantly different results for both groups of organisms. A comparison of the mean of the individual data from the four sites with the data from the pooled samples revealed that there was a poor relationship between the two. Samples may be taken by excision or swabbing and allocated to three categories of process control, which, in turn, are based on microbiological criteria that are different, depending on whether sampling is by excision or swabbing. The influence of these changes in microbiological criteria is discussed in relation to the categorization of samples as acceptable, marginal, or unacceptable and the influence this has on process control. Finally, the proposed introduction of Salmonella as a safety indicator in the EC HACCP system is discussed.

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.