Shiga toxin-producing Escherichia coli in healthy young beef steers from Argentina: prevalence and virulence properties.

Between July 1999 and December 2000, the prevalence of Shiga toxin-producing Escherichia coli (STEC) was established in 200 Argentine healthy young beef steers (14-16 months old) grown under local production systems with a feed grain period of 3-4 months, and the STEC strains isolated were examined in regard to their phenotypic and genotypic characteristics. Stool samples (n = 70) and rectal swabs (n = 130) were taken at the slaughterhouse level. By polymerase chain reaction (PCR), Shiga toxin (stx) gene sequences were detected in 69% of the samples. Eighty-six STEC strains were isolated from 39% of the animals. Serogroups identified, in order of frequency, were: O8 (16 strains), O113 (14), O103 (5), O91 (4), O171 (3), O174 (3), O25 (2), O112 (2), O145 (2), O2, O11, O104, O121, O128, O143, O146, O157. The most frequent serotype isolated was O8:H19 (12.9%). A total of 17 serotypes, including E. coli O157:H7 found in one animal (0.5%), have been previously associated with hemolytic uremic syndrome (HUS), bloody and non-bloody diarrhea in different countries, including Argentina. The prevalent genotype isolated was stx2 (51 of 86, 59.3%). Subtyping of stx2 variants showed the prevalence of stx2vh-b (25.6%) and stx2vh-a types (24.4%), and revealed the presence of an atypical stx2-v. Only 7.0% of STEC strains carried eae, and 33.7% harbored EHEC-hlyA gene. The full virulent genotype (stx/eae/EHEC-hlyA) was found to be present in 4 of the 86 (4.7%) STEC strains isolated. This research indicates that young steers from the main beef-producing area of Argentina are an important reservoir of STEC strains; however, its importance as agents of human diseases in our country has still to be established.

Sodium Propionate To Control Clostridium botulinum Toxigenesis in a Shelf-Stable Beef Product Prepared by Using Combined Processes Including Irradiation.

The antibotulinal effect of sodium propionate was evaluated by a factorial-design experiment and by an inoculated-pack study on a shelf-stable beef product. Processing of samples involved curing, cooking, vacuum packing, and gamma irradiation. The factorial-design experiment involved 240 samples treated with 0, 0.8, 2.0, and 3.3% sodium propionate, challenged with 101 to 105 spores of type A Clostridium botulinum per package, irradiated with 2.5, 5, 7.5, and 10 kGy, and stored at 28°C for up to 4 months. In the pack study, 110 samples with 2% added sodium propionate were challenged with 108 spores of C. botulinum per package, irradiated with 12.5 kGy, and stored (28°C) for 8 months. Addition of 0.8% sodium propionate resulted in a delay (compared to control samples) in toxigenesis of 18 (5 kGy), 34 (2.5 kGy), and 34 (7.5 kGy) days, while no toxin was detected in samples irradiated with 10 kGy. Samples containing 2 and 3.3% sodium propionate were not toxic at any irradiation dose assayed. A safety level, expressed as the number of decimal reductions (DR = log 1/P) for the combination 0.8% sodium propionate and 10 kGy, was estimated to be >4.4. In the inoculated pack study, 2 of 107 samples became toxic, and the safety level treatment resulted in 10.7 DR. Sodium propionate in combination with other processing factors was very effective in preventing C. botulinum toxigenesis: it can be used as a further safety hurdle in the development of shelf-stable meat products.

Foot-and-Mouth Disease Virus Inactivation in Miniburgers by a Continuous Dry-Moist Heat Cooking System.

Several thermal processes were tested to inactivate foot-and-mouth disease virus in beef miniburgers using a dry oven to grill and a steam oven to finish the cooking. A satisfactory product free of foot-and-mouth disease virus was obtained by grilling the contaminated miniburgers in the dry oven for 299 s at 208°C, followed by steam cooking in the moist oven for 190 s with a minimum average exit temperature of 99.4°C. It was found that a temperature indicator device is a reliable tool to verify the thermal process.

Effect of Low-Temperature Long-Time Thermal Processing of Beef-Cuts on the Survival of Foot-and-Mouth Disease Virus.

We determined the virucidal effectiveness against foot-and-mouth disease virus of the low-temperature long-time cooking of virus-contaminated semitendinosus muscle (ST). Of the 11 time and temperature combinations examined, over a range of 63°C to 75°C for extended periods, the respective processing conditions of 71°C for 10.66 h and 75°C for 5.75 h were virucidal. Samples cooked under these temperature-time combinations were more tender (P<0.01) and had better overall acceptability (P<0.05) than beef cuts cooked by conventional commercial processes currently used in Argentina for meat to be exported. Product yields were increased from 60% for the commercial process to 67.8% or 68.6%, respectively, for the two virucidal thermal processes.

Low-Dose Gamma Irradiation and Refrigeration to Extend Shelf Life of Aerobically Packed Fresh Beef Round.

A 2-kGy gamma (low-dose) irradiation was applied to fresh top round from beef animals slaughtered and fabricated at commercial facilities. Cuts were packed in polyethylene film and stored at 1°C. Temperature abuse (9°C/24h) was simulated during storage. Psychrotroph counts on nonirradiated samples reached 107 CFU/cm2 between 8 and 11 d of storage, while similar counts were found after 28 d of storage on low-dose irradiated samples. Pseudomonads, Enterobacteriaceae , and Brochotrix thermosphacta were strongly inhibited on irradiated samples. No changes in organoleptic attributes were observed by a trained panel on treated samples. Low-dose irradiated samples had an average of 17 more shelf life days than the nonirradiated counterparts based on psychrotroph counts status and under the experimental condition being tested in this study.