An experimental study of ototoxicity induced by deferoxamine mesilate

The radiation resistance and ability of Listeria monocytogenes ATCC 7644, 15313, 43256, and 49594 to multiply on irradiated, air-packed, refrigerated raw or cooked turkey breast meat nuggets (ca. 25 g) and ground turkey breast meat was investigated. Gamma-radiation D values for L. monocytogenes were significantly different on raw and cooked nuggets, 0.56 +/- 0.03 kGy and 0.69 +/- 0.03 kGy, respectively; but they were not significantly different (P < or = 0.05) on raw and cooked ground turkey meat. High populations (approximately 10(9) CFU/g) of L. monocytogenes declined during 14 days of storage at 4 degrees C in both irradiated and nonirradiated samples of raw but not of cooked ground turkey breast meat. A moderate inoculum (approximately 10(3) CFU/g) did not survive a radiation dose of 3 kGy. The population increased in cooked but not in raw samples of irradiated ground turkey meat stored at either 2 or 7 degrees C for 21 days. The D value changed significantly from 0.70 +/- 0.04 to 0.60 +/- 0.02 kGy when the product was cooked to an internal temperature of 80 degrees C before irradiation. Growth on either raw or cooked turkey meat did not alter the radiation resistance of L. monocytogenes. Analyses were performed for pH, aw, moisture, and reducing potential of raw and cooked turkey meat and for pH, amino acid profile, thiamine, and riboflavin contents of aqueous extracts of raw and cooked turkey meats without identifying the factor or factors involved in differences in the survival and multiplication of L. monocytogenes on raw and cooked meat.     

Shelf life of ground beef patties treated by gamma radiation

The effects of irradiation on microbial populations in ground beef patties vacuum package and irradiated frozen at target doses of 0.0, 1.0, 3.0, 5.0, and 7.0 kGy were determined. Irradiated samples were stored at 4 or -18 degrees C for 42 days, and mesophilic aerobic plate counts (APCs) were periodically determined. Fresh ground beef (initial APC of 10(2) CFU/g) treated with 3.0, 5.0, and 7.0 kGy was acceptable (< 10(7) CFU/g) for 42 days at 4 degrees C. The 1.0 kGy-treated beef samples were acceptable microbiologically (< 10(7) CFU/g) after 42 days but developed an unacceptable off-odor after 21 days. Shelf life diminished in fresh ground beef patties with an initial APC of 10(4) CFU/g. Only beef patties treated with 7.0 kGy were found to be acceptable at 42 days. Beef patties treated at 1.0 and 3.0 kGy reached spoilage APC levels (> 10(7) CFU/g) by day 14 and 21, respectively, whereas patties treated at 5.0 kGy did not spoil until 42 days. The nonirradiated control samples for both batches of ground beef spoiled within 7 days. Microbial counts in ground beef patties stored at -18 degrees C did not change over the 42-day period. Shelf life of ground beef patties stored at 4 degrees C may be extended with gamma radiation, especially at 5.0 and 7.0 kGy. Initial microbial load in ground beef samples was an important shelf life factor.     

Combined effect of gamma radiation and heating on the destruction of Listeria monocytogenes and Salmonella typhimurium in cook-chill roast beef and gravy

The effect of heating alone (60, 65 or 70 degrees C), heating after irradiation (0.8 kGy) and heating after irradiation and storage for 14 days at 2-3 degrees C on the destruction of Listeria monocytogenes and Salmonella typhimurium in artifically inoculated minced cook-chill roast beef and gravy was investigated. Inoculated minced roast beef samples (5 g) were heated in Stomacher bags completely immersed in a water bath at each of the test temperatures. Survivors were enumerated and D and z values were determined for each of the pathogens. Observed thermal D values for two strains of L. monocytogenes at 60, 65 and 70 degrees C in the absence of pre-irradiation were 90.0-97.5 s, 34.0-53.0 s and 22.4-28.0 s, respectively, whereas thermal D values after pre-irradiation were 44.0-46.4 s, 15.3-16.8 s and 5.5-7.8 s at 60, 65 and 70 degrees C, respectively. This reduction in D values provides evidence for radiation-induced heat-sensitisation in L. monocytogenes. There was some evidence of heat-sensitisation of S. typhimurium at 60 degrees C, but not at either 65 or 70 degrees C. The z value also decreased as a consequence of pre-irradiation to a dose of 0.8 kGy (11.0-12.7 degrees C). The radiation-induced heat-sensitivity in L. monocytogenes was found to persist for up to 2 weeks storage at 2-3 degrees C prior to heating. As cook-chill products are intended to be reheated prior to consumption the results of the present study suggest that any L. monocytogenes present in a cook-chill product would be more easily killed during reheating if it were to be treated with a low dose of gamma radiation during manufacture.     

Different effects of phorbol ester derivates on human immunodeficiency virus 1 replication in lymphocytic and monocytic human cells

The objective of the present study was to analyze iron and zinc in major lean meat cuts in order to estimate the contribution of the average lean meat consumption in Switzerland (1995) for these trace elements. Iron, heme iron and zinc contents were analyzed in following muscles: pork (longissimus dorsi muscle and shoulder), beef (longissimus dorsi muscle and shoulder), veal (longissimus dorsi muscle) and chicken (breast and thigh). Beef and pork shoulder were the best sources of iron, heme iron and zinc. Pork and veal longissimus dorsi muscle and chicken were relatively poor in these trace elements. With an average daily lean meat consumption of 105 g, iron and zinc intake were about 1.1 mg/d and 3.8 mg/d, respectively. Recommendations for daily iron intake were met to 11% (men) and 7% (women) and for zinc to 25% (men) and 32% (women). Applying a modified Monsen model, the requirements for absorbed iron were met in the range of 10-30% and 7-20% for men and women, respectively. Taking into account a zinc absorption rate from meat of about 20-36%, the daily requirements for absorbed zinc were covered to 32-56%. In conclusion, the average amount of lean meat as consumed in Switzerland was high enough to be an important source of available iron and zinc, particularly for people with low iron and zinc status.     

Effect of ex vivo storage on human peripheral blood neutrophil expression of CD11b and the stabilizing effects of Cyto-Chex

Enterobacteriaceae were found in high numbers after storage at 7 degrees C in 6% of consumers packs of pasteurised milk or cream, in 31% of retailed fish and in 100% of retail packs of minced meat. Seventy two fresh-water fishes, 40 packs of minced meat and 430 milk packs were sampled. One hundred and eighty four isolates were randomly picked from Tryptone glucose extract (TGE) agar (30 degrees C for 3d) or Violet red bile glucose (VRBG) agar (37 degrees C for 1d). In minced meat, Serratia liquefaciens, Hafnia alvei, Rahnella aquatilis were frequently encountered. On fish, the most frequently found species were R. aquatilis, and in milk, the dominating species were S. liquefaciens, H. alvei and R. aquatilis. One to three isolates of Citrobacter freundii were found in all three food categories. Using a polymerase chain reaction (PCR) technique, the gene of Escherichia coli heat-labile toxin (lt) was indicated in one fish isolate of R. aquatilis whereas heat-stable toxin genes (s.t.) were indicated in four H. alvei isolates, two originating from fish and two from minced meat. Positive PCR-reaction for vero cytotoxin genes were found in one H. alvei strain originating from fish (vt1), in two S. liquefaciens strains from minced meat (vt2), and in a C. freundii reference strain. One of the st-positive H. alvei strains from meat harboured the eaeA gene involved in the attaching phenotype of enteropathogenic E. coli.     

Atopic sensitization during the first year of life in relation to long chain polyunsaturated fatty acid levels in human milk

The influence of low (0.39-1.1%), medium (4.25%) and high (7.1-32.5%) fat levels in fish on radiation inactivation of four food-borne pathogens was investigated. Cells of Listeria monocytogenes 036, Yersinia enterocolitica F5692, Bacillus cereus and Salmonella typhimurium at logarithmic phase were inoculated in 10% fish homogenates and subjected to gamma irradiation at ice temperature (0-1 degree C) with doses ranging from 0.05 to 0.8 kGy. The radiation survival curves of L. monocytogenes and B. cereus were characterized by shoulders, while a tailing effect was depicted by cells of Y. enterocolitica and B. cereus. The D10 values in kGy calculated on the exponential part of the curve ranged from 0.2 to 0.3, 0.15 to 0.25, 0.1 to 0.15 and 0.09 to 0.1 for L. monocytogenes 036, B. cereus, Salm. typhimurium and Y. enterocolitica F5692, respectively. This order (D10) of radiation resistance of each organism was not affected by the fat content of the fish. Inoculated pack studies carried out separately with each pathogen in fatty (Indian sardine, 7.1%) and lean (Golden anchovy, 0.39%) fish showed no difference in their survival after exposure to 1 kGy and 3 kGy doses, which corroborated the above observation. The practical significance of these results in the application of the technology is discussed.     

Antibiotic resistance patterns of enterococci and occurrence of vancomycin-resistant enterococci in raw minced beef and pork in Germany

The food chain, especially raw minced meat, is thought to be responsible for an increase in the incidence of vancomycin-resistant enterococci (VRE) in human nosocomial infections. Therefore, 555 samples from 115 batches of minced beef and pork from a European Union-licensed meat-processing plant were screened for the occurrence of VRE. The processed meat came from 45 different slaughterhouses in Germany. Enterococci were isolated directly from Enterococcosel selective agar plates and also from Enterococcosel selective agar plates supplemented with 32 mg of vancomycin per liter. In addition, peptone broth was used in a preenrichment procedure, and samples were subsequently plated onto Enterococcosel agar containing vancomycin. To determine resistance, 209 isolates from 275 samples were tested with the glycopeptides vancomycin, teicoplanin, and avoparcin and 19 other antimicrobial substances by using a broth microdilution test. When the direct method was used, VRE were found in 3 of 555 samples (0.5%) at a concentration of 1.0 log CFU/g of minced meat. When the preenrichment procedure was used, 8% of the samples were VRE positive. Our findings indicate that there is a low incidence of VRE in minced meat in Germany. In addition, the resistance patterns of the VRE isolates obtained were different from the resistance patterns of clinical isolates. A connection between the occurrence of VRE in minced meat and nosocomial infections could not be demonstrated on the basis of our findings.     

Cultured human ankle and knee cartilage differ in susceptibility to damage mediated by fibronectin fragments

A culture of the psychotrophic strain FloraCarn L-2 of Lactobacillus alimentarius was added to ground beef (pH 5.4) inoculated with two isolates of Listeria monocytogenes able to grow in refrigerated ground beef. The ground beef was vacuum-packaged and stored for 9 weeks at 4 degrees C. Populations of inoculated L. monocytogenes initially were 6.3 to 6.4 log10 CFU/g and increased to 7.4 log10 CFU/g in ground beef with no added lactobacilli. Addition of L. alimentarius L-2 or its antibiotic-resistant mutant SRL-2 reduced the final populations of L. monocytogenes to 4.3 or 4.1 log10 CFU/g, respectively. L. alimentarius L-2 did not produce bacteriocins or hydrogen peroxide in vitro. The antilisterial effect of L. alimentarius observed in laboratory media and ground beef is attributed to lactic acid (ca. 50 mM) produced by growing cultures.     

Studies on Chrysomyia albiceps (Wiedemann) one of the most important carrion flies in Egypt

Chrysomyia albiceps often feeds to repletion and then regurgitates a portion of the food, a behaviour that heightens its importance as a mechanical vector of enteric pathogens. Pupae of this fly are susceptible to the attack of the parasitic wasp, Nasonia vitripennis in the laboratory as well as in nature at different underground depths where they pupate. The fly needs to feed on proteinaceous meals to start and complete its ovarian development. Liver, beef, camel, chicken, rabbit and fish meat were tested. Of the 6 tested diets, liver proved to be the most advantageous as 98% pupation was obtained, while with beef, camel, chicken, rabbit and fish 95.2%, 95.9%, 90.9%, 89.1% and 86% pupation, respectively, were obtained. Field observations revealed that Chrysomyia albiceps prefers to breed in big carcasses over small ones as the latter contain less moisture or amount of food and are subjected to desiccation and consumption before the full growth of larvae especially during the hot and dry months. Anatomical studies of the females attracted to a piece of meat in laboratory and outdoors experiments showed that the degree of ovarian development is variable including completely undeveloped ovaries, sexually mature ones and different stages of ovarian development. So, attraction to meat fulfill to important functions: nutrition and oviposition. Feeding visits are short in duration (6.2 +/- 2.1 min) and behaviourally simple. The oviposition visits last from 40-60 min with more complex behaviour which can be divided into the time before, during and after oviposition. Females in selecting a place for oviposition, preferred the softer places of the fresh meat; round its lower moist edge where much liquid food is present and where the females oviposit in groups at one location. When a female began to oviposit, it was joined by others that located the eggs with their ovipositors and started to oviposit where a clumped irregular egg masses are deposited.     

Physiopathology of bedsores

Listeria monocytogenes is a food-borne pathogenic bacterium that can be found in soft cheese. At the beginning of cheese ripening, the pH is about 4.85-4.90. The aim of this work was to study the influence of temperature, preincubation temperature (temperature at which the inoculum was cultivated) and initial bacterial concentration on the survival of L. monocytogenes (strain Scott A) at pH 4.8. It was demonstrated in an earlier study that these factors did influence growth kinetics. Survival studies of L. monocytogenes were done in a laboratory broth simulating cheese composition. Four test temperatures (2, 6, 10 and 14 degrees C) and two preincubation temperatures were studied (30 degrees C or the test temperature). Listeria monocytogenes (strain Scott A) was unable to grow at pH 4.8 under all conditions tested. The time for 10% survival was about 11 and 2 d, at 2 degrees C with preincubation at 2 degrees C and 30 degrees C, respectively; 9 d at 6 degrees C with preincubation at 6 degrees C; 4 d at 6 degrees C with preincubation at 30 degrees C; and 1 d at 14 degrees C with preincubation at 14 degrees C or at 30 degrees C. The results show that survival of L. monocytogenes (strain Scott A) at pH 4.8 is not dependent on initial bacterial concentration but on both the test and preincubation temperatures.     

Estimation of the absorbed dose in radiation-processed food--3: The effect of time of evaluation on the accuracy of the estimate

Electron paramagnetic resonance (EPR) spectrometry is evaluated as a method to retrospectively assess the absorbed dose to radiation-processed chicken (containing bone). Decay of the hydroxyapatite paramagnetic center EPR signal intensity was monitored at three different dose levels (0.5, 3.0, 7.0 kGy) up to 20 days, and the dose was assessed for each level at 1, 8, and 20 days after irradiation. It was determined that the time of evaluation (up to 20 days post-irradiation) did not adversely affect the estimate for 0.5 and 3.0 kGy bone, and only moderately affected the 7.0 kGy estimates.     

Gamma irradiation and ozone treatment for inactivation of Escherichia coli O157:H7 in culture media

A study was conducted to investigate the reduction and elimination of Escherichia coli O157:H7 by the effects of gamma irradiation and ozone treatment. Log phase cells were found to be more sensitive to gamma irradiation than stationary phase cells. E. coli O157:H7 was found to be considerably more resistant to irradiation at -18 degrees C than at 20 degrees C. The D values for this organism for treatment with ozone in tryptic soy agar were higher than those for treatment with ozone in phosphate buffer. Gamma irradiation at a dose of 1.5 kGy or ozone treatment at a concentration of 3 to 18 ppm for 20 to 50 min was required to assure the elimination of E. coli O157:H7.     

Management of treatment-resistant schizophrenia with olanzapine

BACKGROUND: The term oral allergy syndrome (OAS) describes an IgE-mediated reaction that takes place minutes after ingestion of some food to which the organism is previously sensitised. The clinical manifestations are typically localized to the mouth and throat. Oral allergy syndrome is commonly elicited by fresh fruits and vegetables, especially in subjects with hypersensitivity to pollens. METHODS: We report a patient with OAS following intake of chicken meat. We performed (1) skin prick test to chicken meat, egg, milk, and wheat and to common inhalants, (2) determination of serum specific IgE, (3) histamine release test, and (4) in vitro antigen-specific production of sulphidoleukotrienes and challenge test with chicken meat. RESULTS: Skin prick test was positive only for chicken meat. The patient had serum specific IgE, positive histamine release test, and specific production of sulphidoleukotrienes to chicken meat. We confirmed these findings by means of the challenge test.     

Plasmid-mediated resistance to antimicrobial agents among listeriae

The resistance to 14 antiseptic-disinfectant and dye compounds of 208 strains of Listeria (132 L. monocytogenes, 63 L. innocua, 8 L. seeligeri, 1 L. ivanovii, 1 L. welshimeri, and 3 Listeria spp.) was tested by the agar-dilution procedure. The Listeria strains were isolated from different varieties of foods, environments of cheese dairies, humans, and wild birds. A total of 14 (6.7%) Listeria strains (12 L. monocytogenes and 2 L. innocua) were resistant to benzalkonium chloride, hexamidine diisethionate, and ethidium bromide. This multiple resistance was observed more frequently from strains of Listeria spp. detected on carcasses of poultry (47%) than strains isolated from human listeriosis cases or carriers (11.5%), red meats (10%), cheeses (5.4%), wild birds (0.9%), and environments of cheese dairies (0%). Among resistant strains, 10 groups of strains (71.5%) were differentiated by serogroup, phage typing, and sensitivity or resistance to cadmium. Extrachromosomal DNA was found in all resistant strains and was transferred at a high frequency among Listeria spp. (8.7 x 10(-6) to 1 x 10(-3) transconjugant CFUs per one donor CFU). These resistances were also transferable between L. monocytogenes and Staphylococcus aureus with similar transfer frequencies (7.8 x 10(-6) to 1 x 10(-4) and between strains of Staphylococcus aureus with similar transfer frequencies from 8 x 10(-7) to 3.3 x 10(-6). These results suggest that emergence of this multiple resistance in Listeria spp. could be due to acquisition of a replicon originating in staphylocci.     

Intensive (pasture) beef cattle operations: the perspective of New Zealand

Beef production in New Zealand has characteristics typical of a temperate climate and pasture-based animal husbandry. The specific pathogens which may contaminate fresh beef and which are empirically considered to be of public health importance are similar to those in other countries with temperate climates, i.e. Salmonella, Campylobacter, Escherichia coli O157:H7, Listeria monocytogenes and Toxoplasma gondii. With the exception of T. gondii, it is likely that almost all transmission of these hazards through consumption of beef results from unseen microbial cross-contamination from gastrointestinal sources during slaughter, dressing and further processing. Gaining comprehensive information on carcass contamination levels is an essential first step in establishing food safety objectives for a particular beef production system, and in designing risk-based hazard analysis and critical control point (HACCP) plans. It is likely that the lower mean and maximum numbers of indicator micro-organisms on New Zealand carcasses (when compared with other countries) are in part due to the pre-slaughter cleanliness status of cattle reared under temperate, pasture conditions. Similarly, the failure to detect specific pathogens of gastrointestinal origin in a comprehensive baseline survey most probably reflects the limited pathway for faecal contamination during slaughter and dressing under processing conditions in New Zealand. The New Zealand example provides strong evidence for the need to design HACCP plans according to the specific national (or regional) situation. Reducing all pathways for faecal contamination of products to the maximum extent practicable will be the most important factor in achieving desired food safety objectives for fresh beef. Variable densities of microbial pathogens in gastrointestinal contents are also likely to have a significant effect on subsequent contamination levels of beef carcasses: however, effective controls for limiting the presence of most pathogens of concern in the live animal have yet to be identified.     

Detection of Listeria monocytogenes in humans, animals and foods

The Listeria monocytogenes-carrying rates were 100% for listeriosis patients and 1.3% for healthy humans. The L. monocytogenes contamination rates for retail sliced beef (34.2%) and pork (36.4%) were significantly higher (p < 0.05) than those for cattle (2.0%) and pigs (0.8%) and for cattle (4.9%) and swine (7.4%) carcasses. The percentages of serotypes 1/2a, 1/2b and 4b which are most dominant in human patients were high in isolates from fresh (90.0%) and processed (100%) fish and shellfish and imported natural cheese (96.7%).     

Sensory and objective characteristics of broiler meat from commercial broilers fed rendered spent hen meal

The objective of the study was to determine sensory and objective characteristics of broiler breast and thigh meat from commercial broilers fed rendered spent hen meal (RSHM) from hatch to 42 d of age. Breast and thigh muscles from 90, 6-wk-old straight-run broilers (i.e., mixed male and female broilers) fed starter and grower diets consisting of either 0, 8, or 12% RSHM were evaluated for sensory characteristics, instrumental texture, and compositional profiles. The RSHM treatments had no adverse effects (P > 0.05) on juiciness, chicken flavor intensity, tenderness, or compositional profiles for the breast or thigh meats. Off-flavor scores for all treatments were above the threshold value, indicating that the RSHM imparted no off-flavors to the breast and thigh meats. Warner-Bratzler shear measurements were similar (P > 0.05) for breast meat from broilers in all treatments. No shear measurements were conducted for the thigh meat. It was concluded that RSHM can be incorporated into the diets of broilers at levels of up to 12% without causing objectionable sensory characteristics in the cooked broiler meat.     

Decontamination of chicken carcasses artificially contaminated with Salmonella

A study was conducted to evaluate the efficacy of three chemical disinfectants and of ionising radiation in reducing the level of contamination in chicken carcasses which had been artificially contaminated with Salmonella Virchow. Chicken carcasses were obtained from a local abattoir. Five carcasses and one control carcass were used to test each concentration of disinfectant and the radiation. The amount of contaminant employed was 0.5 ml of 10(4) colony-forming units per ml of S. Virchow spread over the thigh, breast and wing areas. All treatments were conducted in duplicate. The three disinfectants used were as follows: calcium hypochlorite, at concentrations of 20 ppm, 50 ppm, 100 ppm and 200 ppm of available chlorine. Lactic acid at concentrations of 0.5%, 0.75% and 1%. Hydrogen peroxide compound at concentrations of 1%, 2% and 3%. Five inoculated carcasses were immersed at a time in one disinfectant concentration for 15 min, while the control carcasses were simultaneously immersed in water free from disinfectants. Five carcasses, each in a plastic bag, were subjected to varying ascending doses (from 2 to 7 k gray [kGy]) of ionising radiation from radioactive isotopes of cobalt 60. A bacteriological examination of each carcass was conducted after the treatment to determine the presence or absence of S. Virchow. The number of carcasses which gave positive results showing the presence of Salmonella decreased after chemical treatment, but the organism was not completely eliminated. However, in those carcasses subjected to 7 kGy of radiation, Salmonella was eliminated and no changes in the appearance, colour or smell of the carcasses were observed.     

Rapid determination of Listeria monocytogenes in foods using a resuscitation/selection/kit system detection

A resuscitation medium consisting of a trypticase soy broth base supplemented with 0.5% yeast extract, 0.25% sodium pyruvate, 0.01% sodium thioglycollate, and 0.1% chicken fat was used in the resuscitation of heat-injured and freeze-injured cells of Listeria monocytogenes. After a resuscitation period of 4-h, the medium was made selective through the addition of nalidixic acid, acriflavin, and cycloheximide. The organisms were incubated in the selectivized medium at 35 degrees C for an additional 16 h. The numbers of resuscitated Listeria monocytogenes cells rose from 10(1) to 10(7) cells/mL in 20 h. Similar numbers of Staphylococcus aureus, Escherichia coli, and Salmonella bonn were grown together with Listeria monocytogenes; these organisms did not inhibit the growth of Listeria monocytogenes nor interfere with its detection by the Listeria-Tek kit system. The resuscitation/selection/kit system (RSK) was compared with the methodology in the Bacteriological Analytical Manual (BAM) for the detection of Listeria monocytogenes in 22 naturally contaminated cheese samples: 8 of these were positive by the BAM system and 12 were positive by the RSK system. The 8 Listeria positives found by the BAM system were positive by the RSK system. All 12 Listeria-presumptive positive samples by the RSK system were confirmed to be Listeria monocytogenes. The use of the RSK system enhanced the recovery of the pathogen, and detection was accomplished within 24 h.     

Effect of Pseudomonas fluorescens on beef discoloration and oxymyoglobin oxidation in vitro

The relationship between bacterial growth and oxymyoglobin oxidation in vitro and in meat was studied. In the in vitro study, oxymyoglobin was combined with Pseudomonas fluorescens or sterile nutrient broth (control) in an airtight vessel. P. fluorescens samples showed greater metmyoglobin formation and oxygen consumption than controls. The P. fluorescens population in the reaction vessels was correlated with metmyoglobin formation (r = 0.85, P < 0.05) and oxygen consumption (r = 0.91, P < 0.05). When P. fluorescens and oxymyoglobin were combined in an airtight vessel, reducing the headspace from 13 ml and 9 ml to 3 ml resulted in greater metmyoglobin formation (P < 0.05). In the meat study, beef cores prepared from longissimus lumborum were inoculated with P. fluorescens (10(7) CFU/cm2) or sterile peptone water (control), packaged under 1% O2 (+99% N2), air, or 100% O2 and stored at 4 degrees C. Inoculated beef cores showed higher bacterial loads and metmyoglobin formation than their respective controls during 10 h storage in 1% O2, 3 days in air, and 7 days in 100% O2 (P < 0.05). This finding indicated that P. fluorescens could accelerate beef discoloration. Overall, studies demonstrated that oxygen consumption concomitant with P. fluorescens growth decreased partial oxygen pressure, which accelerated oxymyoglobin oxidation.