Pyrolysis-gas-liquid chromatography (PGLC) of whole cells and cell fragments was used to differentiate 10 Salmonella serotypes. Lyophilized samples (200 ,ug) of whole cells, cell walls, flagella, and deoxyribonucleic acid from each serotype were analyzed in duplicate by PGLC. Pyrochromatograms recorded as pyrolytic elution patterns represented thermal fragmentation products of the samples. Mathematical expressions of percent similarity and percent conformity were calculated for all possible pair combinations of the 10 serotypes. Stepwise discriminant analysis of the PGLC data showed that 100% correct classification of the 10 serotypes was possible from the flagella or deoxyribonucleic acid pyrochromatograms. The classification matrix of the whole-cell data showed a 90% correct classification. PGLC of cell fragments may provide useful information for taxonomic studies of Salmonella and other microorganisms.
The bacteriological quality of unfrozen raw ground beef was evaluated after 0, 3, 6, 9, 12, 15, and 18 days of storage at 29 +/- 1 F (-1.7 +/- 0.6 C). At the time of fabrication, all of the ground beef samples contained 10(6) or fewer total aerobic and psychrotrophic bacteria/g; 81% contained 100 or fewer coliforms/g; 94% contained 100 or fewer Escherichia coli/g; and all of the samples contained 100 or fewer coagulase-positive Staphylococcus aureus and Clostridium perfringens/g. Total aerobic and psychrotrophic bacteria increased by 1 log between 3 and 18 days of storage. Coliform and E. coli counts decreased during storage, whereas coagulase-positive S. aureus and C. perfringens counts did not change significantly. These data indicate that meat processors, wholesalers, and retailers could improve the bacteriological quality and prolong the shelf life of ground beef packaged in oxygen-impermeable film if the temperature of product never exceeded 29 +/- 1 F (-1.7 +/- 0.6 C).
When Vibrio parahaemolyticus ATCC 17802 was heated at 41°C for 30 min in 100 mM phosphate-3% NaCl buffer (pH 7.0), the plate counts obtained when using Trypticase soy agar containing 0.25% added NaCl (0.25 TSAS) were nearly 99.9% higher than plate counts using Trypticase soy agar containing 5.5% added NaCl (5.5 TSAS). A similar result was obtained when cells of V. parahaemolyticus were grown in a glucose salts medium (GSM) and heated at 45°C. The injured cells recovered salt tolerance within 3 h when placed in either 2.5 TSBS or GSM at 30°C. The addition of chloramphenicol, actinomycin D, or nalidixic acid to 2.5 TSBS during recovery of cells grown in 2.5 TSBS indicated that recovery was dependent upon protein, ribonucleic acid (RNA), and deoxyribonucleic acid (DNA) synthesis. Penicillin did not inhibit the recovery process. Heatinjured, GSM-grown cells required RNA synthesis but not DNA synthesis during recovery in GSM. Chemical analyses showed that total cellular RNA decreased and total cellular DNA remained constant during heat injury. The addition of [6-3H]uracil, L-[U-_4C]leucine, and [methyl-3Hlthymidine to the recovery media confirmed the results of the antibiotic experiments.
The bacteriological quality of ground beef chub packs prepared from beef sides at 2 h postmortem (hot-boned) and opposite sides conventionally chilled for 24 h at 3 C (cold-boned) were compared at the time of preparation and at 3-day intervals up to 45 days of storage at 0 C. Aerobic plate counts (APCs) in ground beef from hot-boned beef were either significantly lower or not significantly different from APCs in ground beef from cold-boned carcasses. There were no significant differences of any practical importance in Most Probable Numbers (MPNs) of coliforms and Escherichia coli between hot-boned and cold-boned ground beef stored at 0 C. Ground beef prepared from hot-boned beef offers great potential to the meat industry for energy conservation. The bacteriological quality of ground beef from hot-boned carcasses does not limit and might enhance the feasibility of boning carcasses before chilling.
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