A comparison of wet-dry swabbing and excision sampling methods for microbiological testing of bovine, porcine, and ovine carcasses at red meat slaughterhouses.

A comparison of wet-dry swabbing and surface tissue excision of carcasses by coring was undertaken. Samples from 1,352 bovine, 188 ovine, and 176 porcine carcasses were collected from 70 separate visits to commercial slaughterhouses operating under normal conditions. The mean total aerobic viable bacterial counts (TVCs) for all species sampled by excision was 5.36 log units, which was significantly greater than the 4.35 log units measured for swabbing. Poorly correlated linear relationships between swab- and excision-derived bacterial numbers from near-adjacent carcasses were observed for all three animal species. R2 values for least squares regressions for bovine, ovine, and porcine carcasses were 0.09, 0.27, and 0.21, respectively. The reasons why it was not possible to calculate a factor that allowed the interconversion of bacterial numbers between samples collected by each sampling method were investigated. Uncertainty associated with laboratory analyses was a contributing factor because the geometric relative standard deviations measured for TVCs were 0.174 and 0.414 for excision and swabbing, respectively. Uneven distribution of bacteria at identical sampling sites on near-adjacent carcasses on processing lines was also a contributory factor. The implications of these findings for process control verification were investigated by intensive sampling for 13 weeks in three commercial slaughterhouses. As many as 4 log units of difference in TVCs were observed in duplicate samples collected within a narrow timeframe from near-adjacent carcasses on the processing line. We conclude that it might not be appropriate to institute corrective actions in slaughterhouses on the basis of a single week's test results.

Fate of pathogens present in livestock wastes spread onto fescue plots.

Fecal wastes from a variety of farmed livestock were inoculated with livestock isolates of Escherichia coli O157, Listeria monocytogenes, Salmonella, Campylobacter jejuni, and Cryptosporidium parvum oocysts at levels representative of the levels found in naturally contaminated wastes. The wastes were subsequently spread onto a grass pasture, and the decline of each of the zoonotic agents was monitored over time. There were no significant differences among the decimal reduction times for the bacterial pathogens. The mean bacterial decimal reduction time was 1.94 days. A range of times between 8 and 31 days for a 1-log reduction in C. parvum levels was obtained, demonstrating that the protozoans were significantly more hardy than the bacteria. Oocyst recovery was more efficient from wastes with lower dry matter contents. The levels of most of the zoonotic agents had declined to below detectable levels by 64 days. However, for some waste types, 128 days was required for the complete decline of L. monocytogenes levels. We were unable to find significant differences between the rates of pathogen decline in liquid (slurry) and solid (farmyard manure) wastes, although concerns have been raised that increased slurry generation as a consequence of more intensive farming practices could lead to increased survival of zoonotic agents in the environment.

Antilisterial Effects of a Sorbate-Nisin Combination In Vitro and on Packaged Beef at Refrigeration Temperature.

The antilisterial effects of a sorbate-nisin combination were assessed in vitro and on beef at refrigeration temperature. Three hemolytic pathogenic strains of Listeria monocytogenes , reference strain NCTC 7973, food strain L70, and clinical strain L94, were stored at 4°C in phosphate-buffered saline, pH 5.5, containing a combination of sorbate (0.2% wt/vol) and nisin (40 IU/ml). After 4 weeks, hemolysin production by the strains had ceased, their subsequent lag phases at 37°C were extended from an initial 1.23 to 1.32 h to a final 7.13 to 8.06 h and their pathogenicity for chick embryos had decreased from an initial 93.3 to 95.5% to a final 43.3 to 60.0%. Sterile beef steaks of normal pH (5.4 to 5.5) were inoculated with a cocktail of the three strains at approximately 5 log CFU/cm2 and the surface of half the steaks was treated with the antimicrobial solution 1.0% sorbate plus 1,000 IU of nisin per ml. The meat was packaged under vacuum or 100% carbon dioxide and stored at 4°C for 4 weeks. On untreated meat, L. monocytogenes grew by 1.79 log cycles in vacuum packages, but in CO2 packages the initial population decreased by 0.54 log cycle. On treated vacuum-packaged meat, L. monocytogenes decreased during storage to the extent that 96.5% of the initial pathogen load was eliminated, but the lag phase of the remaining cells at 37°C was unaffected. On treated CO2-packaged meat L. monocytogenes decreased during storage to the extent that 89.3% of the initial pathogen load was eliminated, and for surviving cells the lag phase at 37°C was extended. Treatment with the sorbate-nisin combination did not significantly affect pathogenicity of the L. monocytogenes cocktail recovered from vacuum- or carbon dioxide-packages after storage, in contrast to the in vitro study, where pathogenicity was clearly attenuated. The reason for this difference is unknown.

Inhibition of Listeria monocytogenes on Normal Ultímate pH Beef (pH 5.3-5.5) at Abusive Storage Temperatures by Saturated Carbon Dioxide Controlled Atmosphere Packaging.

Beef striploin steaks (each weighing between 60 and 100 g) of normal ultimate pH (average 5.45) were inoculated with a mixture of two food isolates of Listeria monocytogenes , packaged under saturated carbon dioxide controlled atmosphere or vacuum, and stored at either 5 or 10°C. Saturated carbon dioxide packaging but not vacuum packaging inhibited growth of L. monocytogenes . During storage under vacuum at 5°C, numbers increased from 6.2-logl0 CFU per sample to 9.0-log10 CFU per sample in 23 days, and at 10°C numbers increased from 6.3-log10 CFU per sample to 9.5-log10 CFU per sample in 11 days. During storage under saturated carbon dioxide at 5°C, numbers decreased from 5.6-log10 CFU per sample to 5.0-log10 CFU per sample in 18 days, and at 10°C numbers decreased from 6.7-log10 CFU per sample to 5.2- logl0 CFU per sample in 44 days. The use of saturated carbon dioxide controlled atmosphere packaging to extend the storage life of fresh beef results in apparent destruction of L monocytogenes even at abuse temperatures.