Butterfield's Phosphate Buffer Research Articles

Growth Kinetics of Listeria monocytogenes on Cut Red Cabbage

Listeria monocytogenes is a foodborne pathogen associated with fresh produce vectors such as leafy greens. Recent outbreaks and recalls associated with red cabbage-containing salads have brought attention to this food commodity. Although data on the proliferation of L. monocytogenes are available for different varieties of whole and cut white cabbage, no information is available on the fate of this pathogen on red cabbage. The aim of this study was therefore to explore the survival of L. monocytogenes on cut red cabbage (Brassica oleracea L. var. capitata f. rubra) during storage at different temperatures. Red cabbage was cut into pieces (5 by 4 cm) and spot inoculated with a six-strain cocktail of rifampin-resistant L. monocytogenes, resulting in an initial inoculation level of 4 log CFU/g. Samples were stored at 5 or 10°C for 14 days or at 25°C for 7 days. At intervals during storage, L. monocytogenes was enumerated by homogenization of cabbage with Butterfield's phosphate buffer, and serial dilutions were plated onto brain heart infusion agar supplemented with rifampin. No growth of L. monocytogenes was observed on cut red cabbage during storage at 5°C, and only minimal proliferation was observed at the higher temperatures. Significant population increases of 0.58 and 1.07 log CFU/g were determined after 3 days of storage at 10 and 25°C, respectively; however, a significant decrease of 0.77 log CFU/g from 3 to 14 days was also observed at 10°C. The modeled growth rates for L. monocytogenes on cut red cabbage stored at 5 and 10°C were 0.11 ± 0.03 and 0.27 ± 0.07 log CFU/g/day, with calculated times to a 1-log CFU/g increase of 9.51 and 3.70 days, respectively; however, L. monocytogenes did not achieve a 1-log increase at either temperature in this study. At 25°C, the modeled growth rate of L. monocytogenes on cut red cabbage was 1.15 ± 0.36 log CFU/g, leading to a calculated and an observed 1-log increase in 0.87 and 3.00 days, respectively. Results from this study aid in understanding the fate of L. monocytogenes on cut red cabbage during storage at different temperatures.

Effect of Time, Temperature, and Transport Media on the Recovery of Listeria monocytogenes from Environmental Swabs

Environmental monitoring for Listeria monocytogenes in food processing environments is key for ensuring the safety of ready-to-eat foods. For sampling, swabs are often hydrated with a wetting or transport medium that may contain neutralizers and other ingredients. After swabbing the environment, the swabs may then be transported or shipped cold to an off-site laboratory for testing, ideally within 48 h. Extended shipping times may subject the pathogen to increased temperatures in the presence of the wetting medium, organics, and other chemicals from the processing facility that could confound detection. This study evaluated growth and detection of L. monocytogenes on stainless steel exposed to either buffer or sodium hypochlorite before drying. Swabs were rehydrated with Butterfield's phosphate buffer, neutralizing buffer, Letheen broth, or Dey-Engley neutralizing broth before swabbing. Swabs were stored in the presence of no added food, cheese whey, or ice cream under both optimal (4°C) and suboptimal (15°C) temperatures for up to 72 h. Overall, there was no growth of L. monocytogenes at 4°C through 72 h of storage, although enrichment from these swabs was dependent on the presence and type of food matrix. Pathogen growth during storage at 15°C was more variable and depended on both the food matrix and transport media used, with Dey-Engley and Letheen broths allowing for the highest population increases. Overall, more enrichments resulting in L. monocytogenes detections were observed when using Letheen broth and neutralizing buffer than Dey-Engley broth, which resulted in fewer detections at 15°C. Logistic regression and Cochran-Mantel-Haenszel analyses determined that storage temperature, transport media, and food matrix all significantly affected detection of L. monocytogenes, whereas storage time did not have a clear effect on recovery from swabs.

Evaluation of enumeration and MPN prediction methods for Staphylococcus aureus

AbstractStaphylococcal food poisoning is among the most prevalent causes of foodborne intoxication. To monitor the safety and quality of food, rapid and reliable enumeration procedures for Staphylococcus aureus are essential. Here, we assess culture‐based methods for the isolation and enumeration of S. aureus, testing different pre‐enrichment broths, plated media, and the automated TEMPO instrument. We evaluated enumeration of S. aureus in seven different food commodities, including two naturally contaminated foods, at levels ranging between 100 and 1,500 cfu/g of inoculated target and nontarget organisms. Sixty‐four food samples were analyzed. Duplicate test portions of 25 g each were homogenized with 225 ml of Butterfield's phosphate buffer (1:10). Five tube most probable number (MPN) predictions comparing two pre‐enrichment broths, tryptic soy broth containing 10% NaCl and 1% sodium pyruvate (PTSBS) and modified Giolitti and Cantoni (GC) were assessed alongside the TEMPO STA card and the direct plate count method. The direct plate count method using Baird Parker agar and BP with Rabbit Plasma Fibrinogen versus TEMPO STA demonstrated the highest proportion of agreement at 89.19%. The two different pre‐enrichment broths assessed, PTSBS versus GC exhibited the lowest proportion of agreement at 47.5%. The TEMPO STA yielded results in 24 hr versus the current 4‐day PTSBS MPN method for S. aureus, with an 84.62% agreement.Practical applicationsOverall food quality, recalls, and other regulatory decisions are often contingent upon enumeration results. A prompt turnaround time can assist in expediting the release of unadulterated foods, and the swift removal of adulterated foods out of the food supply chain. This is paramount to the microbiology and food safety community who must consider which methods will provide more accurate and timely assessments of food contamination.

Delmopinol hydrochloride reduces Salmonella on cantaloupe surfaces.

Since the surfaces of cantaloupes are highly rough or irregular, bacteria can easily attach and become difficult to remove. Appropriate postharvest washing and sanitizing procedures can help control Salmonella and other pathogens on cantaloupe or other melons during postharvest operations. Delmopinol hydrochloride (delmopinol) is a cationic surfactant that is effective for treating and preventing gingivitis and periodontitis. The application of delmopinol to two cantaloupe cultivars was evaluated for reducing the level of inoculated Salmonella. Athena and Hale's Best Jumbo (HBJ) cantaloupe rind plugs (2.5 cm. dia.) were inoculated with nalidixic acid‐resistant Salmonella Michigan (approx. 1.0 × 109 CFU/ml). After 15 min, rind plugs were sprayed with 10 ml of a delmopinol spray solution (0% or 1.0% vol/vol) and held at 35°C for 1 hr or 24 hr. Rind plugs were diluted with Butterfield's phosphate buffer, shaken and sonicated, and solutions were enumerated on 50 ppm nalidixic acid‐tryptic soy agar. The texture quality and color of additional cantaloupes were evaluated, after 1% delmopinol spray treatment, over 14‐day storage at 4°C. A 1.0% application of delmopinol after 1 hr reduced Salmonella concentration by ~3.1 log CFU/ml for both “HBJ” skin rind plugs and “Athena” stem scar rind plugs in comparison to the control (p < .05). No differences were observed in the texture and color (L*, a*, b* values) of 1% delmopinol‐treated cantaloupes as compared to control. Storage of cantaloupes treated with 1.0% delmopinol solution for 1 hr had a greater effect on reducing concentration of Salmonella compared to 24‐hr treatment. A surface spray application of 1% delmopinol on cantaloupes could be an alternative antimicrobial postharvest treatment that could make surface bacteria more susceptible to sanitizers or physical removal.

Synergistic Effects of Lactic Acid and Sodium Dodecyl Sulfate to Decontaminate Escherichia coli O157:H7 on Cattle Hide Sections

The objective of this study was to investigate the antibacterial properties of chitosan acetate (CA), sodium dodecyl sulfate (SDS), lactic acid (LA) and their synergism when combined against a nontoxigenic strain of Escherichia coli O157:H7. Treatments that significantly reduced the concentration of E. coli O157:H7 in vitro by more than two logs were further investigated using a cattle hide decontamination model. In vitro treatments included CA (1% chitosan in 1% acetic acid vol/vol), SDS (1% vol/vol), SDS (2% vol/vol), LA (1% vol/vol), CA-SDS combination (1% chitosan in 1% acetic acid vol/vol mixed with 1% SDS vol/vol), and LA-SDS combination in two different concentrations (1% LA mixed with 1% SDS vol/vol, and 1% LA mixed with 2% SDS vol/vol). Butterfield's Phosphate Buffer water was used as a control. The antibacterial effect of 1% CA solution alone and in combination with 1% SDS in vitro resulted in a 1.8 and 1.7 log colony-forming units (CFU)/mL reduction, respectively (p<0.05). Only 1% LA, 1% SDS, 2% SDS and their combinations resulted in a >2 log reduction in E. coli O157:H7. On hide sections, both 1% LA-1% SDS and 1% LA-2% SDS combinations significantly (p<0.05) reduced E. coli O157:H7 concentration by 4.6 and 4.7 log CFU/ cm(2) greater than the control, respectively. There was no significant difference in the antibacterial effect of 1% LA compared to the control, 2% SDS compared to the control, or 1% LA compared to 2% SDS. Hence, the antibacterial efficacy of 1% LA against E. coli O157:H7 on hide sections was significantly enhanced when combined with 1% SDS. Results of this study support the use of low concentration LA-SDS combination as a hide wash to reduce the risk of E. coli O157:H7 contamination.

Observation of Injured E. coli Population Resulting from the Application of High‐Pressure Throttling Treatments

This study used flow cytometry (FC), epifluorescent microscopy (EM), and conventional culture media (PC) to evaluate the potential for high-pressure throttling (HPT) to produce injury in E. coli. E. coli cells suspended at a concentration of approximately 8 log (CFU/mL) in Butterfield's phosphate buffer and UHT skimmed milk, were treated with HPT at pressures ranging from 35 to 283 MPa. Cells were stained with SYTO 9 and propidium iodide (Live/Dead Baclight kit) to assess their membrane integrity. MacConkey and Tryptone Soy agars and a modification of the thin agar layer method were used to determine injured and non-injured cells. PC results indicated a reduction in E. coli counts as pressure increased but no significant injured population was detected in either matrix. However, FC and EM observations indicated that the membrane integrity of a portion of the bacterial population was affected by HPT, producing different degrees of cell injury that could be sublethal. The percentage of this heterogeneous population increased with applied pressure. These results reassert the importance of understanding the potential of new processing treatments to produce sublethally-injured bacteria, and developing appropriate detection techniques.

Validation of a lactic acid- and citric acid-based antimicrobial product for the reduction of Escherichia coli O157: H7 and Salmonella on beef tips and whole chicken carcasses.

The objectives of this study were to determine the effects of a lactic acid- and citric acid-based antimicrobial product on the reduction of Salmonella on whole broiler carcasses during processing and the reduction of Salmonella and Escherichia coli O157:H7 on beef trim. Freshly harvested broiler carcasses were inoculated with an inoculum of Salmonella strains to yield a 10(5) CFU/ml pathogen load on the surface of the carcass. The beef tips were inoculated as well with an inoculum of either E. coli O157:H7 or Salmonella to yield 10(4) CFU/100 cm(2). After 30 min for attachment, the broiler carcasses were treated with Chicxide applied for 5 s via a spray or immersed in Chicxide for 5, 10, or 20 s. Broiler carcasses were rinsed in poultry rinse bags with 400 ml of Butterfield's phosphate buffer in which Salmonella was enumerated from the diluents and Butterfield's phosphate. Chicxide significantly reduced Salmonella by 1.3 log CFU/ml with spray treatment and 2.3 log CFU/ml for all dip treatments. Following 30 min of attachment, the beef tips were placed into a spray cabinet with either Beefxide or sterilized water (control) and sprayed at 1 ft/2.5 s chain speed at 40 lb/in(2). The external surface of each beef tip was swabbed (100 cm(2)) to determine pathogen loads. Beefxide significantly reduced E. coli O157:H7 by 1.4 log CFU/100 cm(2) and Salmonella by 1.1 log CFU/100 cm(2) (P < 0.05) compared with the control samples.

Inactivation of Escherichia coli ATCC 25922 and Escherichia coil O157:H7 in apple juice and apple cider, using pulsed light treatment.

The main objective of this work was to evaluate the effectiveness of pulsed light (PL) treatment for the inactivation of Escherichia coli in liquids with different levels of clarity. Nonpathogenic E. coli ATCC 25922 and pathogenic E. coli O157: H7 were used as challenge organisms. Butterfield's phosphate buffer (BPB), tryptic soy broth (TSB), apple juice, and apple cider were used as substrates. The inoculated liquids were placed in a thin layer (1.3 mm) into glass chambers (23 by 53 by 11 mm) and exposed to PL doses of up to 13.1 J/cm2. PL treatments were performed in a Xenon RS-3000C PL unit, both in static mode and under turbulence. Survivors were determined by standard plate counting or the most-probable-number technique. For static treatments, reduction levels exceeding 8.5 log were obtained in BPB for all strains and reduction levels of about 3.5 log were obtained in TSB. For apple juice, inactivation levels of 2.66 +/- 0.10 log were obtained for E. coli ATCC 25922 and 2.52 +/- 0.19 log for E. coli O157:H7. In cider, inactivation levels of 2.32 +/- 0.16 log and 3.22 +/- 0.29 log were obtained for the nonpathogenic and pathogenic strains, respectively. Inactivation kinetics was characterized using the Weibull model. Turbulent treatments resulted in 5.76 +/- 0.06 log reduction in cider and 7.15 +/- 0.22 log reduction in juice, which satisfies the U.S. Food and Drug Administration requirement of 5-log reduction of E. coli. These results show promise for the use of PL for the effective reduction of E. coli in apple juice and cider.

Inactivation of avirulent Yersinia pestis in Butterfield's phosphate buffer and frankfurters by UVC (254 nm) and gamma radiation.

Yersinia pestis is the causative agent of plague. Although rare, pharyngeal plague in humans has been associated with consumption or handling of meat prepared from infected animals. The risks of contracting plague from consumption of deliberately contaminated food are currently unknown. Gamma radiation is a penetrating form of electromagnetic radiation, and UVC radiation is used for decontamination of liquids or food surfaces. Gamma radiation D10-values (the radiation dose needed to inactivate 1 log unit pathogen) were 0.23 (+/-0.01) and 0.31 (+/-0.03) kGy for avirulent Y. pestis inoculated into Butterfield's phosphate buffer and onto frankfurter surfaces, respectively, at 0 degree C. A UVC radiation dose of 0.25 J/cm2 inactivated avirulent Y. pestis suspended in Butterfield's phosphate buffer. UVC radiation doses of 0.5 to 4.0 J/cm2 inactivated 0.97 to 1.20 log units of the Y. pestis surface inoculated onto frankfurters. A low gamma radiation dose of 1.6 kGy could provide a 5-log reduction and a UVC radiation dose of 1 to 4 J/cm2 would provide a 1-log reduction of Y. pestis surface inoculated onto frankfurters. Y. pestis was capable of growth on frankfurters during refrigerated storage (10 degrees C). Gamma radiation of frankfurters inhibited the growth of Y. pestis during refrigerated storage, and UVC radiation delayed the growth of Y. pestis.

Inactivation of Escherichia coli JM109, DH5α, and O157:H7 Suspended in Butterfield's Phosphate Buffer by Gamma Irradiation

Food irradiation is a safe and effective method for inactivation of pathogenic bacteria, including Escherichia coli O157:H7, in meat, leafy greens, and complex ready-to-eat foods without affecting food product quality. Determining the radiation dose needed to inactivate E. coli O157:H7 in foods and the validation of new irradiation technologies are often performed through inoculation of model systems or food products with cocktails of the target bacterium, or use of single well-characterized isolates. In this study, the radiation resistance of 4 E. coli strains, 2 DNA repair deficient strains used for cloning and recombinant DNA technology (JM109 and DH5alpha) and 2 strains of serotype O157:H7 (C9490 and ATCC 35150), were determined. The D-10 values for C9490, ATCC 35150, JM109, and DH5alpha stationary phase cells suspended in Butterfield's Phosphate Buffer and irradiated at 4 degrees C were 229 (+/- 9.00), 257 (+/- 7.00), 61.2 (+/- 10.4), and 51.2 (+/- 8.82) Gy, respectively. The results of this study indicate that the extreme radiation sensitivity of JM109 and DH5alpha makes them unsuitable for use as surrogate microorganisms for pathogenic E. coli in the field of food irradiation research. Use of E. coli JM109 and DH5alpha, which carry mutations of the recA and gyrA genes required for efficient DNA repair and replication, is not appropriate for determination of radiation inactivation kinetics and validation of radiation processing equipment.

Changes in the Bacterial Flora of Skin of Processed Broiler Chickens Washed in Solutions of Salicylic Acid

Changes in the number of bacteria recovered from the skin of processed broilers after each of five consecutive washings in salicylic acid (SA) solutions was examined. Skin samples from commercially processed broiler carcasses were divided into 3 groups and washed in distilled water (control), 10% SA, or 20% SA by agitating skin in wash solutions in a Stomacher laboratory blender. After each wash, skin was transferred to fresh solutions and washing was repeated to provide samples washed 1 to 5 times in each solution. Washed skin was stomached in Butter field's Phosphate Buffer to recover bacteria on the skin. Bacterial flora of the rinsates was enumerated on Plate Count (PC) Agar, Staphylococcus (STA) Agar, Levine Eosin Methylene Blue (EMB) Agar, Lactic Acid Bacteria (LAB) Agar, and Perfringens (PER) Agar with TSC supplement; and then bacterial isolates from each medium were identified. Results indicated that after each of 5 consecutive washes in water, there was no significant difference in the number of bacteria recovered from skin on any of the agar media. Significantly fewer bacteria were recovered on LAB Agar from skin after 5 washes in 10% SA than after 1 wash, but there was no significant decrease in the number of bacteria recovered on any other media after skin was washed in this solution. However, washing skin 4 or 5 times in 20% SA significantly reduced the number of bacteria recovered on PC and STA Agar, while no bacteria were recovered on EMB or LAB Agars from rinsates of skin washed 4 or 5 times in 20% SA or on PER Agar from skin washed 3 or more in the 20% solution. In vitro studies indicated that SA is bactericidal towards bacterial isolates recovered from skin and that resistance to the bactericidal activity of SA in descending order is Staphylococcus simulans > Lactobacillus > Escherichia coli > Clostridium perfringens. Findings indicate that successive washing of skin in SA may significantly reduce the number of bacteria recovered from the poultry skin and that the bactericidal activity SA can kill bacteria in vitro.

Electron Beam and Gamma Irradiation Effectively Reduce Listeria monocytogenes Populations on Chopped Romaine Lettuce

Fresh, chopped romaine lettuce contaminated with a seven-strain cocktail of Listeria monocytogenes (in a solution containing approximately 108 organisms per ml) that had attained a level of contamination of between 7 and 8 log CFU/g was packaged in 15-g samples. The lettuce was irradiated with a Co60 source at 1.15 or 0.51 kGy and then stored at 4°C. In addition, samples contaminated with isolated strains 16397, 0733, and 1992 were subjected to either electron beam irradiation at doses ranging from 0.3 to 1.2 kGy or gamma irradiation at 0.56 kGy without subsequent refrigerated storage. All postir-radiation and control samples were diluted with Butterfield's phosphate buffer and plated in duplicate on modified Oxford media. Samples that received electron beam or gamma irradiation without subsequent refrigerated storage were also plated in duplicate on modified Oxford media plates coated with two 7-ml layers of basal yeast extract agar. Electron beam irradiation yielded D10-values (the dose required to eliminate 90% of the microbial population) of 0.16, 0.17, and 0.19 kGy for strains 16397, 0733, and 1992, respectively. The corresponding log reductions obtained for these same three strains at 0.56 kGy of gamma irradiation were 2.91, 2.62, and 2.66 log, respectively. Gamma irradiation at 1.15 and 0.51 kGy with subsequent refrigerated storage (4°C) reduced populations by >5 and >2 log, respectively, compared with controls. Neither the irradiated samples nor the control samples showed increases in population during the storage periods. Our results indicate that low-dose irradiation can effectively reduce or eliminate L. monocytogenes on chopped romaine lettuce, improving the safety of ready-to-eat salads.

Survival of Salmonella Enteritidis PT 30 on Inoculated Almonds after Commercial Fumigation with Propylene Oxide

Propylene oxide (PPO) is commonly used to reduce microbial populations in U.S. bulk raw almonds, but the process has not been validated for reduction of foodborne pathogens. The reduction of Salmonella Enteritidis phage type (PT) 30 inoculated onto almonds was evaluated after exposure to a standard commercial PPO treatment. Almonds were inoculated with Salmonella Enteritidis PT 30 to approximately 8.0 log CFU/g after drying. Inoculated almonds were placed in bags designed for gaseous sterilization and positioned in the center of 900-kg bins or 22.7-kg boxes of warmed almonds. Almonds were further warmed to an initial temperature of 23 to 34°C, treated with PPO (0.5 kg/m3 for 4 h), and held for 0 or 2 days at 38 to 43°C followed by storage for 2 to 5 days at 15 to 18°C. Salmonella Enteritidis PT 30 was recovered by vigorously shaking 100 g of almonds in 100 ml of Butterfield's phosphate buffer, plating onto tryptic soy or bismuth sulfite agar, and incubating at 35°C for 24 or 48 h, respectively. Populations of Salmonella Enteritidis were consistently reduced by >5.0 log CFU/g (5.2 to >8.6 log CFU/g) when initial counts were compared with counts obtained 5 days after PPO treatment. Reductions of 1.2 to 4.4 log CFU/g occurred during post-PPO storage. Reductions were not significantly improved (P < 0.05) when almonds were held at 38 to 43°C after PPO treatment. PPO residues were >400 ppm immediately after removal from the PPO chamber and declined to <300 ppm during post-PPO storage. PPO is an effective treatment for reducing populations of Salmonella Enteritidis PT 30 on bulk almonds.

Surface Material, Temperature, and Soil Effects on the Survival of Selected Foodborne Pathogens in the Presence of Condensate

The effects of surface type (stainless steel, acetal resin, and fiberglass reinforced plastic wall paneling [FRP]), soil, and temperature on the survival of Listeria monocytogenes, Salmonella spp., and Yersinia enterocolitica, in the presence of condensate were evaluated. Surface coupons—half soiled with sterile porcine serum—were exposed to cell suspensions made from individual five-strain cocktails composed of organisms from the same genus (107 CFU/ml) in Butterfield's phosphate buffer and incubated for 2 h at 25°C allowing attachment of cells to coupon surfaces. Coupons were rinsed to remove unattached cells, incubated at either 4 or 10°C under condensate-forming conditions, and sampled at six time intervals over a 15-day period. For enumeration, cells were removed from the coupons by vigorous shaking in 100 ml of Butterfield's phosphate buffer with 3 g of glass beads and plated on tryptic soy agar with 0.6% yeast extract. Stainless steel did not support the survival of Listeria as well as acetal resin or FRP. Acetal resin and stainless steel were less supportive of Salmonella than FRP. All surfaces supported the survival of Yersinia over the 15-day trial equally. Temperature had little effect on survival of all organisms across all surfaces with one exception. However, Yersinia displayed growth on FRP at 10°C, but death at 4°C. Serum had a protective effect on L. monocytogenes on all surfaces, with populations sustained at significantly (P ≤ 0.05) higher numbers over time than unsoiled coupons. Serum did not effect survival of Salmonella or Yersinia on stainless steel, acetal resin, or FRP.

Effects of Applying Safe2 O Poultry Wash to Broiler Wings on Shelf Life, Listeria Monocytogenes, Pseudomonads, Staphylococcus Species, and Psychrotrophic Bacteria Levels After Three, Seven, and Ten Days of Storage

Bacterial contamination of raw processed poultry continues to be of concern to consumers as well as regulatory and health officials. For many years wings were considered a low-value product; therefore, shelf life of wings was not a major concern. Due to changes in consumer attitudes and increases in the fast-food market, wings are now a valuable commodity. Because wings have a shorter shelf life than most other raw poultry products, acceptable intervention to decrease the population of associated spoilage organisms and human enteropathogens are needed. Safe2 O Poultry Wash was evaluated as a postchill treatment to reduce microbial contamination and increase shelf life. Ninety-six carcasses were obtained from a local processor prior to final wash. On arrival at the research facility all carcasses were inoculated with 1 mL of a culture with 103 cfu/mL Listeria monocytogenes. After a 30-min attachment time, carcasses were subjected to a 4-s in-out final wash, hung for 3 min, and chilled in ice-water for 45 min. After the chilling, wings were removed by hand with a knife, pooled together, and subjected to a hand spray (4 mL/wing) with deionized water or Safe2 O Poultry Wash. Two wings were then placed in each of 96 ziplock type storage bags, and wings were held at 5 ± 1°C for 3, 7, 10, and 14 d. On the day of sample, weep was decanted, and 100 mL of Butterfield's phosphate buffer was added to each bag. Three sets of wings were shaken by hand for 1 min, and total aerobes, Pseudomonads, Staphylococcus sp., psychrotrophic bacteria, and L. monocytogenes in the rinsates were enumerated. By using 7 log10 recovery of total aerobes from rinsates as a spoilage baseline, all wings were spoiled by d 10, but the wings treated with water were approaching spoilage counts on d 7, (log10 6.8), whereas only log10 5.5 bacteria were recovered from the wings sprayed with Safe2 O Poultry Wash. Fewer Pseudomonads, Staphylcoccus sp., L. monocytogenes, and psychrotrophic bacteria were recovered from wings treated with Safe2 O Poultry Wash and stored for 10 d. Log10 counts for the organisms were Pseudomonas sp., 8.2 and 6.9; Staphylcoccus sp., 5.5 and 4.9; L. monocytogenes, 5.2 and 4.6; and psychrotrophs, 8.2 and 6.9 for the water and Safe2 O Poultry Wash treatments, respectively. Use of the Safe2 O Poultry Wash as a postchill treatment on wings could increase the shelf life of wings by up to 3 d.

Loss of crystal violet binding activity in stationary phase Yersinia enterocolitica following gamma irradiation

Ionizing radiation can eliminate virulent Yersinia enterocolitica from meat. It is possible, however unlikely, that a small number of Y. enterocolitica could survive the pasteurization process. The virulence ofY. enterocolitica is dependent upon the presence of a 70 kb plasmid. The effect of low-dose ionizing radiation on the plasmid-associated virulence trait of crystal violet binding was investigated. Y. enterocolitica strains which carried the virulence plasmid were suspended in Butterfield's Phosphate Buffer or raw ground pork and irradiated to a dose of 1·0 or 1·25 kGy, respectively. Loss of crystal violet binding increased 10-fold following exposure to ionizing radiation, regardless of the suspending medium. Polymerase chain reaction analysis of Y. enterocolitica isolates that did not bind crystal violet following irradiation indicated that loss of the virulence plasmid, as opposed to mutation of a single plasmid-encoded gene, was the major mechanism for elimination of the crystal violet binding trait.

Heat resistance of Desulfotomaculum nigrificans spores in soy protein infant formula preparations.

The heat resistance of Desulfotomaculum nigrificans spores was determined in soy protein infant formula preparations. Methods of sporulation were developed and evaluated. D. nigrificans spores of highest heat resistance were produced in a 40% infusion of spent mushroom compost. Fraction-negative D121 degrees C-values obtained in modified soy formula were 25.8 min for spores of ATCC 7946 produced at 55 degrees C and 54.4 min for an isolate designated RGI 1, which was sporulated at 66 degrees C. From the fraction-negative D-values, z-values were obtained of 6.7 degrees C for ATCC 7946 and 9.5 degrees C for RGI 1. Survivor-curve D121 degrees C-values were 5.6 min for ATCC 7946 and 2.7 min for RGI 1 sporulated at 55 degrees C and heated in modified soy formula. Corresponding D121 degrees C-values in Butterfield phosphate buffer (pH 7.2) were 3.3 min (ATCC 7946) and 1.1 min (RGI 1). The z-values generated from survivor-curve D-values were similar to those obtained by using fraction-negative procedures. In all instances the inactivation kinetics appeared to be linear. The isolate designated RGI 1, when sporulated at 66 degrees C and heated in a modified infant soy formula, exhibited an extraordinary heat resistance far in excess of previous reports.

COMPARISON OF TWO PROCEDURES FOR ENUMERATION OF MICROORGANISMS FROM FROZEN FOODS

Microbial counts of frozen raw shrimp, frozen processed shrimp, and frozen mixed vegetables were obtained by various combinations of recovery media, diluents, spread or pourplating, and incubation temperatures of 27 C and 35 C.Greater numbers of microorganisms were recovered after incubation at 27 than at 35 C. Spread-plating yielded higher counts than the pour-plating. The addition of 0.5% NaCl and peptone to the agar medium resulted in a greater recovery of microorganisms from frozen raw shrimp, but had no effect on frozen processed shrimp or frozen mixed vegetables. Butterfield's phosphate buffer was slightly superior to 0.2% peptone as a diluent.