Protection of probiotic bacteria in a synbiotic matrix following aerobic storage at 4 °C.

The survival of single strains of Bifidobacterium breve, Bifidobacterium longum, Lactobacillus acidophilus, and Lactobacillus reuteri was investigated in synbiotics that included 10 mg/ml of fructo-oligosaccharides, inulin and pectic-oligosaccharides in an alginate matrix under refrigerated (4 °C) aerobic storage conditions. When the matrices were cross-linked with calcium (45 mM), 102-103 cfu/ml of L. acidophilus and L. reuteri, and 0-103 cfu/ml of B. breve and B. longum survived refrigerated aerobic storage for 28 days. Following refrigerated storage, acetic (3-9 mM), butyric (0-2 mM), propionic (5-16 mM) and lactic acids (1-48 mM) were produced during the growth of probiotics in BHI broth at 37 °C, suggesting their metabolic activity after storage was stressed. When calcium cross-linking was not used in synbiotics, the matrix remained more gel-like after inoculation when compared to the calcium cross-linked matrix. At least 107 cfu/ml of probiotic bacteria survived after 21 days of storage within these gel-like alginate matrices. Significantly higher levels of B. breve, L. acidophilus and L. reuteri were obtained from the synbiotic matrices supplemented with fructo-oligosaccharides, inulin and pectic-oligosaccharides compared to alginate alone. B. longum survival was the same (~7 logs) in all gel-like synbiotic matrices. These results show that synbiotics protected probiotic bacteria and extended their shelf-life under refrigerated aerobic conditions. Synbiotics represent a viable delivery vehicle for health-promoting bacteria.

Pilot-scale crossflow-microfiltration and pasteurization to remove spores of Bacillus anthracis (Sterne) from milk.

High-temperature, short-time pasteurization of milk is ineffective against spore-forming bacteria such as Bacillus anthracis (BA), but is lethal to its vegetative cells. Crossflow microfiltration (MF) using ceramic membranes with a pore size of 1.4 µm has been shown to reject most microorganisms from skim milk; and, in combination with pasteurization, has been shown to extend its shelf life. The objectives of this study were to evaluate MF for its efficiency in removing spores of the attenuated Sterne strain of BA from milk; to evaluate the combined efficiency of MF using a 0.8-µm ceramic membrane, followed by pasteurization (72°C, 18.6s); and to monitor any residual BA in the permeates when stored at temperatures of 4, 10, and 25°C for up to 28 d. In each trial, 95 L of raw skim milk was inoculated with about 6.5 log(10) BA spores/mL of milk. It was then microfiltered in total recycle mode at 50°C using ceramic membranes with pore sizes of either 0.8 µm or 1.4 µm, at crossflow velocity of 6.2 m/s and transmembrane pressure of 127.6 kPa, conditions selected to exploit the selectivity of the membrane. Microfiltration using the 0.8-µm membrane removed 5.91±0.05 log(10) BA spores/mL of milk and the 1.4-µm membrane removed 4.50±0.35 log(10) BA spores/mL of milk. The 0.8-µm membrane showed efficient removal of the native microflora and both membranes showed near complete transmission of the casein proteins. Spore germination was evident in the permeates obtained at 10, 30, and 120 min of MF time (0.8-µm membrane) but when stored at 4 or 10°C, spore levels were decreased to below detection levels (≤0.3 log(10) spores/mL) by d 7 or 3 of storage, respectively. Permeates stored at 25°C showed coagulation and were not evaluated further. Pasteurization of the permeate samples immediately after MF resulted in additional spore germination that was related to the length of MF time. Pasteurized permeates obtained at 10 min of MF and stored at 4 or 10°C showed no growth of BA by d 7 and 3, respectively. Pasteurization of permeates obtained at 30 and 120 min of MF resulted in spore germination of up to 2.42 log(10) BA spores/mL. Spore levels decreased over the length of the storage period at 4 or 10°C for the samples obtained at 30 min of MF but not for the samples obtained at 120 min of MF. This study confirms that MF using a 0.8-µm membrane before high-temperature, short-time pasteurization may improve the safety and quality of the fluid milk supply; however, the duration of MF should be limited to prevent spore germination following pasteurization.

Validation of food-grade salts of organic acids as ingredients to control Listeria monocytogenes on pork scrapple during extended refrigerated storage.

This study was conducted to investigate control of Listeria monocytogenes on pork scrapple during storage at 4°C. In phase I, scrapple was formulated, with or without citrate-diacetate (0.64%), by a commercial processor to contain various solutions or blends of the following antimicrobials: (i) lactate-diacetate (3.0 or 4.0%), (ii) lactate-diacetate-propionate (2.0 or 2.5%), and (iii) levulinate (2.0 or 2.5%). Regardless of whether citrate-diacetate was included in the formulation, without the subsequent addition of the targeted antimicrobials pathogen levels increased ca. 6.4 log CFU/g within the 50-day storage period. In the absence of citrate-diacetate but when the targeted antimicrobials were included in the formulation, pathogen numbers increased by ca. 1.3 to 5.2 log CFU/g, whereas when citrate-diacetate was included with these antimicrobials, pathogen numbers increased only by ca. 0.7 to 2.3 log CFU/g. In phase II, in the absence of citrate-diacetate, when the pH of the lactate-diacetate-propionate blend (2.5%) was adjusted to pH 5.0 or 5.5 pathogen numbers remained unchanged (≤0.5 log CFU/g increase) over 50 days, whereas when citrate-diacetate was included with the lactate-diacetate-propionate blend adjusted to pH 5.0 or 5.5, pathogen numbers decreased by 0.3 to 0.8 log CFU/g. In phase III, when lower concentrations of the lactate-diacetate-propionate blend (1.5 or 1.94%) were adjusted to pH 5.5, pathogen numbers increased by ca. 6.0 and 4.7 log CFU/g, respectively, whereas when the mixture was adjusted to pH 5.0, pathogen numbers increased by ≤0.62 log CFU/g. Thus, scrapple formulated with lactate-diacetate-propionate (1.5 and 1.94% at pH 5.0) is an unfavorable environment for outgrowth of L. monocytogenes.

Control of Listeria monocytogenes on commercially-produced frankfurters prepared with and without potassium lactate and sodium diacetate and surface treated with lauric arginate using the Sprayed Lethality in Container (SLIC(R)) delivery method.

Viability of Listeriamonocytogenes was monitored on frankfurters formulated with or without potassium lactate and sodium diacetate at a ratio of ca. 7:1 and treated with lauric arginate (LAE; 22 or 44ppm) using the Sprayed Lethality in Container (SLIC(R)) delivery method. Without antimicrobials, pathogen numbers remained relatively constant at ca. 3.3logCFU/package for ca. 30d, but then increased to ca. 8.4logCFU/package over 120d. Regardless of whether or not lactate and diacetate were included, when treated with LAE, pathogen numbers decreased from ca. 3.3logCFU/package to ca. 1.5logCFU/package within 2h, but then increased to 7.3 and 6.7logCFU/package, respectively, after 120d. When frankfurters were formulated with lactate and diacetate and treated with LAE, pathogen numbers decreased by ca. 2.0logCFU/package within 2h and remained relatively unchanged over the 120d. These data confirm that LAE provides an initial lethality towards L. monocytogenes and when used in combination with reduced levels/ratio of lactate and diacetate as an ingredient for frankfurters provides inhibition throughout shelf life.

Effect of storage and subsequent reheating on viability of Listeria monocytogenes on pork scrapple.

We evaluated the fate of Listeria monocytogenes on commercial pork scrapple, a regionally popular, ready-to-eat (RTE) meat. We also conducted an informal survey to address consumer practices for storing and reheating scrapple. Of the 129 consumers who responded to at least one of the eight questions posed in the survey, about half (46.4%; 52 of 112) considered scrapple RTE, the majority (69.7%; 76 of 109) stored it in the refrigerator, and all (100%; 112 of 112) preferred to reheat it prior to consumption. Most respondents (83.9%; 94 of 112) reheated the scrapple by pan frying for 1 to 10 min at medium to high temperature. To study pathogen behavior, slices of pork scrapple were surface inoculated with a five-strain cocktail of L. monocytogenes (ca. 2.0 log CFU/g), vacuum sealed, and stored for up to 60 days. Pathogen levels increased to 8.9, 9.5, and 9.9 log CFU/g after 44 (4 degrees C), 21 (10 degrees C), and 5 (21 degrees C) days, respectively. When slices 1.3 cm (ca. 55 g) and 1.9 cm (ca. 85 g) thick were surface inoculated with L. monocytogenes (ca. 7.0 log CFU/g) and then reheated in a skillet (191 degrees C) for 0.5 to 4 min per side or to target instantaneous internal temperatures of 48.9 to 71.1 degrees C, it was possible to achieve pathogen reductions ranging from ca. 2.2 to 6.5 log CFU/g. These data confirm that in the unlikely event of postprocessing contamination of pork scrapple by L. monocytogenes, proper reheating can appreciably reduce levels of the pathogen before consumption.

Effectiveness of cross-flow microfiltration for removal of microorganisms associated with unpasteurized liquid egg white from process plant.

Thermal preservation is used by the egg industry to ensure the microbiological safety of liquid egg white (LEW); however, it does not eliminate all microorganisms and impairs some of the delicate functional properties of LEW. In this study, a pilot-scale cross-flow microfiltration (MF) process was designed to remove the natural microflora present in commercial LEW, obtained from a local egg-breaking plant, while maintaining the nutritional and functional properties of the LEW. LEW, containing approximately 10(6 +/- 1.7) colony forming units (CFU) per milliliter of total aerobic bacteria, was microfiltered using a ceramic membrane with a nominal pore size of 1.4 microm, at a cross-flow velocity of 6 m/s. To facilitate MF, LEW was screened, homogenized, and then diluted (1 : 2, w/w) with distilled water containing 0.5% sodium chloride. Homogenized LEW was found to have a threefold lower viscosity than unhomogenized LEW. Influence of MF temperature (25 and 40 degrees C) and pH (6 and 9) on permeate flux, transmission of egg white nutrients across the membrane, and microbial removal efficiency were evaluated. The pH had a significantly greater influence on permeate flux than temperature. Permeate flux increased by almost 148% when pH of LEW was adjusted from pH 9 to pH 6 at 40 degrees C. Influence of temperature on permeate flux, at a constant pH, however, was found to be inconclusive. Microbial removal efficiency was at least 5 log(10) CFU/mL. Total protein and SDS-PAGE analysis indicated that this MF process did not alter the protein composition of the permeate, compared to that of the feed LEW, and that the foaming properties of LEW were retained in the postfiltered samples.

Validation of commercial processes for inactivation of Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on the surface of whole-muscle turkey jerky.

Three strips of turkey breast meat were separately inoculated with multistrain mixtures of Escherichia coli O157:H7, Salmonella Typhimurium, or Listeria monocytogenes and placed on the top, middle, and bottom levels of a loading rack. The strips on the rack were then loaded into a smokehouse and cooked-dried for either 2.5 or 3.5 h at 73.8 degrees C (165 degrees F) or 1.5 or 2.5 h at 82.2 degrees C (180 degrees F) with constant hickory smoking and without addition of humidity. Cooking-drying marinated turkey jerky at 73.8 degrees C (165 degrees F) or 82.2 degrees C (180 degrees F) resulted in a >or= 7.1 log(10) cfu/strip reduction of all 3 pathogens. For nonmarinated jerky strips that were inoculated with E. coli O157:H7 or L. monocytogenes and cooked-dried at 82.2 degrees C (180 degrees F), a reduction of >or= 7.4 log(10) cfu/strip was observed, whereas for strips that were inoculated with Salmonella, a reduction of >or= 6.8 log(10) cfu/strip was observed. Cooking-drying nonmarinated turkey breast strips at 73.8 degrees C (165 degrees F) for 3.5 h resulted in a reduction of ca. 7.1 to 7.6 log(10) cfu/strip for all 3 pathogens, whereas for strips that were cooked-dried for 2.5 h, a reduction of ca. 5.4 to 6.2 log(10) cfu/strip was observed. Only marinated turkey jerky that was cooked-dried for 3.5 h at 73.8 degrees C (165 degrees F) satisfied the USDA-FSIS standard of identity (moisture: protein

Translocation of surface-inoculated Escherichia coli O157:H7 into beef subprimals following blade tenderization.

In phase I, beef subprimals were inoculated on the lean side with ca. 0.5 to 3.5 log CFU/g of a rifampin-resistant (rifr) cocktail of Escherichia coli O157:H7 and passed once, lean side up, through a mechanical blade tenderizer. Inoculated subprimals that were not tenderized served as controls. Ten core samples were removed from each subprimal and cut into six consecutive segments: segments 1 to 4 comprised the top 4 cm and segments 5 and 6 the deepest 4 cm. Levels of E. coli O157:H7 recovered from segment 1 of control subprimals when inoculated with ca. 0.5, 1.5, 2.5, or 3.5 log CFU/g were 0.6, 1.46, 2.5, and 3.19 log CFU/g, respectively. Following tenderization, pathogen levels recovered from segment 1 inoculated with 0.5 to 3.5 log CFU/g were 0.22, 1.06, 2.04, and 2.7 log CFU/g, respectively. Levels recovered in segment 2 were 7- to 34-fold lower than levels recovered from segment 1. Next, in phase II, the translocation of ca. 4 log CFU of the pathogen per g was assessed for lean-side-inoculated subprimals passed either once (LS) or twice (LD) through the tenderizer and for fat-side-inoculated subprimals passed either once (FS) or twice (FD) through the tenderizer. Levels in segment 1 for LS, LD, FS, and FD tenderized subprimals were 3.63, 3.52, 2.85, and 3.55 log CFU/g, respectively. The levels recovered in segment 2 were 14- to 50-fold lower than levels recovered in segment 1 for LS, LD, FS, and FD subprimals. Thus, blade tenderization transfers E. coli O157:H7 primarily into the topmost 1 cm, but also into the deeper tissues of beef subprimals.

Viability of multi-strain mixtures of Listeria monocytogenes, Salmonella typhimurium, or Escherichia coli O157:H7 inoculated into the batter or onto the surface of a soudjouk-style fermented semi-dry sausage.

The fate of Listeria monocytogenes, Salmonella typhimurium, or Escherichia coli O157:H7 were separately monitored both in and on soudjouk. Fermentation and drying alone reduced numbers of L. monocytogenes by 0.07 and 0.74 log(10)CFU/g for sausages fermented to pH 5.3 and 4.8, respectively, whereas numbers of S. typhimurium and E. coli O157:H7 were reduced by 1.52 and 3.51 log(10)CFU/g and 0.03 and 1.11 log(10)CFU/g, respectively. When sausages fermented to pH 5.3 or 4.8 were stored at 4, 10, or 21 degrees C, numbers of L. monocytogenes, S. typhimurium, and E. coli O157:H7 decreased by an additional 0.08-1.80, 0.88-3.74, and 0.68-3.17 log(10)CFU/g, respectively, within 30 days. Storage for 90 days of commercially manufactured soudjouk that was sliced and then surface inoculated with L. monocytogenes, S. typhimurium, and E. coli O157:H7 generated average D-values of ca. 10.1, 7.6, and 5.9 days at 4 degrees C; 6.4, 4.3, and 2.9 days at 10 degrees C; 1.4, 0.9, and 1.6 days at 21 degrees C; and 0.9, 1.4, and 0.25 days at 30 degrees C. Overall, fermentation to pH 4.8 and storage at 21 degrees C was the most effective treatment for reducing numbers of L. monocytogenes (2.54 log(10)CFU/g reduction), S. typhimurium (> or =5.23 log(10)CFU/g reduction), and E. coli O157:H7 (3.48 log(10)CFU/g reduction). In summary, soudjouk-style sausage does not provide a favorable environment for outgrowth/survival of these three pathogens.

Prevalence, types, and geographical distribution of Listeria monocytogenes from a survey of retail Queso Fresco and associated cheese processing plants and dairy farms in Sonora, Mexico.

In the first part of this study, samples were collected from farms, cheese processing plants (CPPs), and retail markets located in various geographical areas of Sonora, Mexico, over a 12-month period during the summer of 2004 and winter of 2005. Four (all Queso Fresco [QF] from retail markets) of 349 total samples tested positive for Listeria monocytogenes (Lm). Of these four positive samples, three were collected in the northern region and one in the southern region of Sonora. Additionally, two were collected during the winter months, and two were collected during the summer months. For the second part of the study, a total of 39 samples from a farm, a CPP, and retail markets were collected and processed according to a combination of the Norma Oficial Mexicana NOM-143-SSA1-1995.10 method (NOM) and the U.S. Food and Drug Administration (FDA) Bacteriological Analytical Manual method, and 27 samples from these same locations were collected and processed according to the U.S. Department of Agriculture Food Safety and Inspection Service method (USDA-FSIS). The NOM-FDA method recovered the pathogen from 6 (15%) of 39 samples (one cheese and five product contact surfaces), while the USDA-FSIS method recovered the pathogen from 5 (18.5%) of 27 samples (all product contact surfaces). In addition, the 40 isolates recovered from the 15 total samples that tested positive for Lm grouped into five distinct pulsotypes that were ca. 60% related, as determined by pulsed-field gel electrophoresis analysis. The results of this study confirmed a 3.4% prevalence of Lm in QF collected from retail markets located in Sonora and no appreciable difference in the effectiveness of either the NOM-FDA or USDA-FSIS method to recover the pathogen from cheese or environmental samples.

Viability of Listeria monocytogenes on commercially-prepared hams surface treated with acidic calcium sulfate and lauric arginate and stored at 4°C.

We demonstrated the effectiveness of delivering an antimicrobial purge/fluid into shrink-wrap bags immediately prior to introducing the product and vacuum sealing, namely the "Sprayed Lethality In Container" (SLIC™) intervention delivery method. The pathogen was Listeria monocytogenes, the antimicrobials were acidic calcium sulfate (ACS; calcium sulfate plus lactic acid; 1:1 or 1:2 in dH(2)O) and lauric arginate (LAE; Ethyl-N-dodecanoyl-l-arginate hydrochloride; 5% or 10% in dH(2)O), and the product was commercially prepared "table brown" ham (ca. 3 pounds each). Hams were surface inoculated with a five-strain cocktail of L. monocytogenes (ca. 7.0 log(10) CFU per ham), added to shrink-wrap bags that already contained ACS or LAE, vacuum-sealed, and stored at 4°C for 24h. Pathogen levels decreased by 1.2, 1.6, 2.4, and 3.1 log(10) CFU/ham and 0.7, 1.6, 2.2, and 2.6 log(10) CFU/ham in samples treated with 2, 4, 6, and 8mL of a 1:1 and 1:2 solution of ACS, respectively. In samples treated with 2, 4, 6, and 8mL of a 5% solution of LAE, pathogen levels decreased by 3.3, 6.5, 5.6, and 6.5 log(10) CFU/ham, whereas when treated with a 10% solution of LAE pathogen levels decreased ca. 6.5 log(10) CFU/ham for all application volumes tested. The efficacy of ACS and LAE were further evaluated in shelf-life studies wherein hams were surface inoculated with either ca. 3.0 or 7.0 log(10) CFU of L. monocytogenes, added to shrink-wrap bags that contained 0, 4, 6, or 8mL of either a 1:2 solution of ACS or a 5% solution of LAE, vacuum-sealed, and stored at 4°C for 60 days. For hams inoculated with 7.0 log(10) CFU, L. monocytogenes levels decreased by ca.1.2, 1.5, and 2.0 log(10) CFU/ham and 5.1, 5.4, and 5.5 log(10) CFU/ham within 24h at 4°C in samples treated with 4, 6, and 8mL of a 1:2 solution of ACS and a 5% solution of LAE, respectively, compared to control hams that were not treated with either antimicrobial. Thereafter, pathogen levels remained relatively unchanged (±1.0 log(10) CFU/ham ) after 60 days at 4°C in hams treated with 4, 6, and 8mL of a 1:2 solution of ACS and increased by ca. 2.0-5.0 log(10) CFU/ham in samples treated with 4, 6, and 8mL of a 5% solution of LAE. For hams inoculated with 3.0 log(10) CFU, L. monocytogenes levels decreased by 1.3, 1.9, and 1.8 log(10) CFU/ham within 24h at 4°C in samples treated with 4, 6, and 8mL of a 1:2 solution of ACS, respectively, compared to control hams that were not treated. Likewise, levels of the pathogen were reduced to below the limit of detection (i.e., 1.48 log(10) CFU/ham) in the presence of 4, 6, and 8mL of a 5% solution of LAE within 24h at 4°C. After 60 days at 4°C, pathogen levels remained relatively unchanged (±0.3 log(10) CFU/ham) in hams treated with 4, 6, and 8mL of a 1:2 solution of ACS. However, levels of L. monocytogenes increased by ca. 2.0 log(10) CFU/ham in samples treated with 4 and 6mL of a 5% LAE solution within 60 days but remained below the detection limit on samples treated with 8mL of this antimicrobial. These data confirmed that application via SLIC™ of both ACS and LAE, at the concentrations and volumes used in this study, appreciably reduced levels of L. monocytogenes on the surface of hams within 24h at 4°C and showed potential for controlling outgrowth of the pathogen over 60 days of refrigerated storage.

Prevalence of Campylobacter within a swine slaughter and processing facility.

In this work, the occurrence of Campylobacter in a swine slaughter and processing facility was studied. Thirty composite carcass samples, representing 360 swine carcasses, were taken immediately after exsanguination, immediately after polishing, after the final wash, and after overnight chilling at 2 degrees C. Thirty matching composite rectal samples were also taken immediately after exsanguination, and 60 nonmatching individual colon samples were collected from the same lot of swine during evisceration. Also, 72 environmental samples were collected from equipment used in the slaughter operation (42 samples) and the processing operation (30 samples). Campylobacter was isolated by direct plating on Campy-Line agar (CLA) or Campy-Cefex agar (CCA), as well as by Bolton broth enrichment and subsequent inoculation onto CLA or CCA. For all four recovery methods combined, Campylobacter was detected on 33% (10 of 30) of the composite carcasses immediately after exsanguination, 0% (0 of 30) after polishing, 7% (2 of 30) immediately before chilling, and 0% (0 of 30) after overnight chilling. The pathogen was recovered from 100% (30 of 30) of the composite rectal samples and 80% (48 of 60) of the individual colon samples. Campylobacter was detected in 4.8% (2 of 42) and 3.3% (1 of 30) of the slaughter and processing equipment samples, respectively. The recovery rate achieved with direct plating on CLA was significantly higher (P < 0.05) than those achieved with the other three recovery methods. For the 202 isolates recovered from all of the various samples tested, Campylobacter coli was the predominant species (75%) and was followed by Campylobacter spp. (24%) and Campylobacter jejuni (1%). These results indicate that although Campylobacter is highly prevalent in the intestinal tracts of swine arriving at the slaughter facility, this microorganism does not progress through the slaughtering operation and is not detectable on carcasses after overnight chilling.

Characterization of Escherichia coli O157:H7 from downer and healthy dairy cattle in the upper Midwest region of the United States.

While cattle in general have been identified as a reservoir of Escherichia coli O157:H7, there are limited data regarding the prevalence and clonality of this pathogen in downer dairy cattle and the potential impact to human health that may occur following consumption of meat derived from downer dairy cattle. In the present study, conducted at two slaughter facilities in Wisconsin between May and October of 2001, we established a higher prevalence of E. coli O157:H7 in fecal and/or tissue samples obtained aseptically from intact colons of downer dairy cattle (10 of 203, 4.9%) than in those from healthy dairy cattle (3 of 201, 1.5%). Analyses of 57 isolates, representing these 13 positive samples (one to five isolates per sample), by pulsed-field gel electrophoresis, revealed 13 distinct XbaI restriction endonuclease digestion profiles (REDP). Typically, isolates from different animals displayed distinct REDP and isolates from the same fecal or colon sample displayed indistinguishable REDP. However, in one sample, two different, but highly related, REDP were displayed by the isolates recovered. Antimicrobial susceptibility testing indicated that 10 of the 57 isolates, recovered from 2 (1 downer and 1 healthy animal) of the 13 positive samples, were resistant to at least 1 of 18 antimicrobials tested. However, there was no appreciable difference in the frequency of resistance of isolates recovered from downer and healthy dairy cattle, and not all isolates with the same REDP displayed the same antimicrobial susceptibility profile. Lastly, it was not possible to distinguish between isolates recovered from downer and healthy cattle based on their XbaI REDP or antimicrobial susceptibility. These results indicate that downer cattle had a 3.3-fold-higher prevalence of E. coli O157:H7 than healthy cattle within the time frame and geographic scope of this study.

Effect of pH on survival, thermotolerance, and verotoxin production of Escherichia coli O157:H7 during simulated fermentation and storage.

Heat treatment is increasingly being introduced to fermented meat processing, since the acid tolerance properties of Escherichia coli O157:H7 can permit this organism to survive traditional processing procedures. This study investigated the effect of growth pH and fermentation on the thermotolerance at 55 degrees C of E. coli O157:H7 in a model fermented meat system. E. coli O157:H7 (strain 380-94) was grown at pH 5.6 or 7.4 (18 h at 37 degrees C), fermented to pH 4.8 or 4.4 in brain heart infusion broth, and stored for 96 h. Cells grown at pH 5.6 had higher D values at 55 degrees C (D55 degrees C) than cells grown at pH 7.4 (P < 0.001). Cells fermented to pH 4.8 had higher D55 degrees C than those fermented to pH 4.4 (P < 0.001). Cells fermented to pH 4.8 demonstrated an increase in D55 degrees C during storage (P < 0.001), whereas cells fermented to pH 4.4 showed a decrease in D55 degrees C during the same period (P < 0.001). The effect of growth pH on verotoxin production by E. coli O157:H7 was assessed using the verotoxin assay. Cells grown at pH 5.6 had lower verotoxin production then cells grown at pH 7.4. This effect was not sustained over storage. These results indicate that a lower growth pH can confer cross-protection against heat. This has implications for the production of acidic foods, such as fermented meat, during which a heating step may be used to improve product safety.

Fate of gram-positive bacteria in reconditioned, pork-processing plant water.

This study investigated the responses of Enterococcus faecium (ATCC 19433), Staphylococcus aureus (196E), and Listeria monocytogenes Scott A in water from a local meat-processing plant. Each bacterium was added to a starting count of 3 log10 CFU/ml and held from 5 to 28 degrees C. At intervals (0, 2, 7, 14, and 21 days), aliquots were plated on appropriate selective agars. In contrast to the gram-negative bacteria studied previously and which grew, the three gram-positive bacteria survived with some slight increase in number in only nonchlorinated, reconditioned water, either filtered (0.22 microm pore size) or nonfiltered. The presence of chlorine in either potable or reconditioned water contributed to the rapid decline in viable counts for all three bacteria. These results further emphasize the importance of residual chlorine in preventing the growth of these gram-positive bacteria in potable and reconditioned waters.

In situ characterization of Clostridium botulinum neurotoxin synthesis and export.

A monoclonal antitoxin/colloidal gold probe and sequential centrifugation were used to study synthesis, translocation and export of Clostridium botulinum strain 62A neurotoxin (NT). Exponential growth occurred after 5 h of anaerobic incubation of spores and continued for 15-16 h. NT was detected at 15 h using the probe and transmission electron microscopy (TEM), 2 h earlier than the first detection by the mouse bioassay. During exponential growth, the probe localized NT primarily in the cytoplasm, on the inner side of the cytoplasmic membrane and in the cell wall. During stationary and death phases, the NT was located within the cytoplasm, cell wall and extracellularly. NT was released from the cell during cell wall exfoliation. Cells retained NT after repeated gelatin-phosphate washes and sequential centrifugations, consistent with the TEM observation that the NT is bound to the cell wall. These observations indicate that the process of Cl. botulinum type A NT production follows a sequence of synthesis, translocation across the cytoplasmic membrane and export through the cell wall.

Stereotactic breast biopsy: initial experience and recommendations for improvement.

The results of 54 stereotactic core breast biopsies performed at Bishop Clarkson Memorial Hospital were reviewed. In 47 biopsies (87% of the total), a definitive diagnosis of either benign or malignant was made. Two biopsies (4% of the total) were classified as missed, and 5 biopsies (9% of the total) were deemed indeterminate. To improve both the success of the procedure and patient management, six recommendations were made: Patients judged to be potentially uncooperative and inclined to move during the procedure should receive sedation. A post-biopsy, non-stereo film should be taken to determine whether additional stereotactic biopsies will be required to adequately sample the lesion. Lesions containing microcalcifications should have a specimen radiograph prior to completing the biopsy procedure. A history sheet including clinical and mammographic findings should be given to pathology along with the biopsy specimen to assist in the histologic interpretation. The radiologist should review the pathology results in order to determine if a miss has occurred and additional biopsy is indicated. Six-month follow-up mammograms are to be required following a benign stereotactic biopsy diagnosis.

Permanent percutaneous antegrade ureteral stent placement without transurethral assistance.

A simple, one-step, permanent, percutaneous, antegrade insertion of a ureteral stent is described, utilizing a double, pigtail catheter. No transurethral assistance is necessary. The advantages of this simplified technique are presented, and the necessary prerequisites for its application are discussed.