Development of a risk-ranking framework to evaluate potential high-threat microorganisms, toxins, and chemicals in food

Through a cooperative agreement with the U.S. Food and Drug Administration, the Institute of Food Technologists developed a risk-ranking framework prototype to enable comparison of microbiological and chemical hazards in foods and to assist policy makers, risk managers, risk analysts, and others in determining the relative public health impact of specific hazard-food combinations. The prototype is a bottom-up system based on assumptions that incorporate expert opinion/insight with a number of exposure and hazard-related risk criteria variables, which are propagated forward with food intake data to produce risk-ranking determinations. The prototype produces a semi-quantitative comparative assessment of food safety hazards and the impacts of hazard control measures. For a specific hazard-food combination the prototype can produce a single metric: a final risk value expressed as annual pseudo-disability adjusted life years (pDALY). The pDALY is a harmonization of the very different dose-response relationships observed for chemicals and microbes. The prototype was developed on 2 platforms, a web-based user interface and an Analytica(R) model (Lumina Decision Systems, Los Gatos, Calif., U.S.A.). Comprising visual basic language, the web-based platform facilitates data input and allows use concurrently from multiple locations. The Analytica model facilitates visualization of the logic flow, interrelationship of input and output variables, and calculations/algorithms comprising the prototype. A variety of sortable risk-ranking reports and summary information can be generated for hazard-food pairs, showing hazard and dose-response assumptions and data, per capita consumption by population group, and annual p-DALY.

Standardization of a method to determine the efficacy of sanitizers in inactivating human pathogenic microorganisms on raw fruits and vegetables

The efficacy of sanitizers in killing human pathogenic microorganisms on a wide range of whole and fresh-cut fruits and vegetables has been studied extensively. Numerous challenge studies to determine the effects of storage conditions on survival and growth of pathogens on raw produce have also been reported. Results of these studies are often difficult to assess because of the lack of sufficient reporting of methods or, comparatively, because of variations in procedures for preparing and applying inocula to produce, conditions for treatment and storage, and procedures for enumerating pathogens. There is a need for a standard method to accurately determine the presence and populations of pathogenic microorganisms on produce. The adoption of standard, well-characterized reference strains would benefit a comparative assessment of a basic method among laboratories. A single protocol will not be suitable for all fruits and vegetables. Modifications of a basic method will be necessary to achieve maximum recovery of pathogens on various types of produce subjected to different sanitizer or storage treatments. This article discusses parameters that must be considered in the course of developing a basic standard method against which these modifications could be made.

Sublethal sanitizer stress and adaptive response of Escherichia coli O157:H7

The effect of sublethal exposure to peroxyacetic acid (PAA) sanitizer on adaptation to peroxidative stress and development of thermal cross-resistance was investigated in Escherichia coli O157:H7. Acute sublethal PAA sanitizer exposure was used to represent a contact scenario. Cultures were grown in Trypticase soy-yeast extract broth. Acute treatment cultures were pretreated with 0.1% PAA, then all cultures were challenged at either 80 mM H202 or 54 degrees C. Acute and peroxide control cultures showed substantially increased peroxidative tolerance (D80mM > 2 h) versus negative control cultures not exposed to sanitizer (D80mM = 0.19+/-0.03 h). The inactivation rate of the acetic acid control (D80mM = 0.21+/-0.05 h) was similar to the negative control rate. Acute (D54 degrees C = 0.55+/-0.07 h) cultures did not exhibit increased thermal resistance versus the control (D54 degrees C = 0.54+/-0.07 h). Thermal injury was determined as difference in D54 degrees C value (deltaD54 degrees c) obtained on pyruvate and deoxycholate media. Thermal-induced injury was not observed in either control (deltaD54 degrees C = 0.04 h) or acute (deltaD54 degrees C = 0.05 h) cultures.

The role of probiotic cultures in the prevention of colon cancer

Risk factors for colon cancer include both hereditary and environmental factors. Dietary patterns represent controllable risk factors for the development of colon cancer. Much attention has focused on decreasing colon cancer risk through increasing intake of dietary fiber; recently, this has included interest in the consumption of prebiotics and probiotics. Because factors involved in the initiation and promotion of colon cancer might be separated in time from actual tumor development, it is difficult to choose "outcomes" or "end points" that are definitive indicators of efficacy of probiotics or prebiotics. Studies that have explored the cause-effect relationship directly have used animal models. In this review, we have confined our discussion to animal studies from the last 10 years that have examined most directly the relationship between prebiotic and probiotic consumption and colon cancer development. To present the consensus of these studies first, it appears that probiotics with or without prebiotics have an inhibitory effect on the development of aberrant crypts (precancerous lesions) and tumors in animal models. The effect is not completely consistent and is small in some studies, but this may represent a dose or time effect.

Consumption of exogenous bifidobacteria does not alter fecal bifidobacteria and breath hydrogen excretion in humans

The hypothesis that consumption of bifidobacteria by humans would increase colonic bifidobacteria and decrease breath hydrogen excretion was examined. A commercially available strain of bifidobacteria was tracked through the gastrointestinal tract. We determined that a 12-d feeding period of 10(10) cells of exogenous bifidobacteria daily was adequate to achieve a stable number of exogenous bifidobacteria in the colon. A 12-d washout period was chosen because the exogenous bifidobacteria could no longer be detected at that time. A double-blind crossover study used both male and female subjects. The order of treatment with skim milk alone or skim milk + bifidobacteria was randomized. Breath hydrogen excretion (micromol/L) and fecal counts of total bifidobacteria [log colony forming units (CFU)/g feces] were not significantly different between males and females and were not affected by consumption of exogenous bifidobacteria. Calculations based on the numbers of exogenous bifidobacteria consumed and the fecal numbers of exogenous bifidobacteria excreted suggested that numbers of the exogenous strain increased within the gastrointestinal tract. These data suggest that it is difficult to permanently alter total colonic bifidobacteria and affect physiologic function (net hydrogen in the colon as reflected by breath hydrogen) by feeding bifidobacteria, although the percentage of the total bifidobacteria represented by the exogenous strain can be affected.

Differentiation of ingested and endogenous bifidobacteria by DNA fingerprinting demonstrates the survival of an unmodified strain in the gastrointestinal tract of humans

Consumption of bifidobacteria as a dietary adjunct has received considerable attention for its possible role in the maintenance of gastrointestinal health. However, speculation exists about these presumed health benefits because of an inability to assess the fate and mechanism of action of ingested bifidobacteria. Thus, our objective was to examine the fate of ingested bifidobacteria through the gastrointestinal tract. Variations in the highly conserved 16S ribosomal DNA (rDNA) of bifidobacteria from six male subjects (18 to 35 y old) were assessed by restriction fragment length polymorphism (RFLP) analysis. During the 16-d study, 10(10) colony-forming units (CFU) of a commercially available bifidobacteria were delivered to subjects in fluid milk for each of 8 d. During the remaining 8 d, subjects consumed milk without bifidobacteria. Feces were collected at 4-d intervals and plated on selective media. For each subject, 10-15 colonies were randomly selected and used as template for PCR-amplification of 16S rDNA. 16S rDNA was restriction digested and resolved by electrophoresis. The 16S rDNA-RFLP of the ingested bifidobacteria was unique compared with bifidobacteria found in subjects prior to the feeding study. When subjects consumed bifidobacteria, a 16S rDNA-RFLP identical to that of the ingested bifidobacteria was observed in feces. The concentration of the ingested bifidobacteria in feces increased to 67.2 +/- 8.5% (mean +/- SEM) of total bifidobacteria. After feeding stopped, the ingested bifidobacteria diminished and became undetectable. Using this molecular approach to monitor ingested bifidobacteria, we demonstrate the kinetics of passage of this organism through the gastrointestinal tract of healthy humans.

Probiotics, cecal microflora, and aberrant crypts in the rat colon

Our hypothesis was that administration of bifidobacteria, Lactobacillus acidophilus or both to rats will minimize the numbers of aberrant crypts in the distal colon that develop in response to the carcinogen 1,2-dimethylhydrazine (DMH). A series of experiments was designed to test this hypothesis where the treatments used were as follows: skim milk controls (Skim-Basal), skim milk + bifidobacteria (Bifido-Basal), skim milk + fructooligosaccharide (Skim-FOS), and skim milk + bifidobacteria + fructooligosaccharide (Bifido-FOS). In two experiments, bifido-bacteria + FOS administration significantly decreased the number of aberrant crypts that developed, but there was no clear relationship of aberrant crypts to numbers of bifidobacteria or Clostridium perfringens. In the third experiment, the Bifido-FOS treatment led to significantly fewer aberrant crypts and aberrant crypt foci than the Bifido-Basal treatment. The Skim-FOS group had significantly more cecal bifidobacteria than the Skim-Basal group and significantly fewer C. perfringens than the Skim-Basal and Bifido-Basal. In a fourth experiment, L. acidophilus was added as an additional treatment. The number of aberrant crypts was not significantly different among the groups. However, the number of C. perfringens was significantly decreased by the addition of bifidobacteria, L. acidophilus or the combination of the two, whereas the numbers of bifidobacteria and L. acidophilus were not affected by treatment. A significant correlation (R2 = 0.84, P < 0.01) was noted between the body weight of rats at DMH administration and the magnitude of the difference in aberrant crypts between the Skim-Basal rats and the Bifido-FOS rats. The results suggest that there is variability in the effects of bifidobacteria and L. acidophilus administration on both aberrant crypt formation and C. perfringens.

Thermal inactivation kinetics of Bacillus subtilis spores suspended in buffer and in oils

The heat resistance of Bacillus subtilis 5230 and A spores freeze dried and suspended in buffer or oils was investigated. As expected, spores were more resistant to heat when suspended in oils than in buffer. This was ascribed to the low aw of oils and to their content of free fatty acids. Linear survivor curves were obtained for spores suspended in buffer at 105 degrees C or above and for B. subtilis A spores suspended in a vegetable oil. However, the survivor curves of the spores suspended in mineral oil (strain 5230) or olive oil (both strains) were concave upward with a characteristic tailing. The tailing could not be ascribed to spore clumping or to a specific heat injury that can be circumvented by Ca-dipicolinate. It is possibly due to another mechanism of injury or to the activation at high temperature of a normally dormant germination system.

Resistance of Neosartorya fischeri to wet and dry heat

Dry heat resistance parameters for Neosartorya fischeri ascospores were obtained at 90 degrees C and 95 degrees C under 30%, 40%, 50%, 60%, and 75% relative humidity (RH) conditions. The dry heat treated spores were exposed to saturated water vapor (for 20-24 h at 4 degrees C) prior to recovery in buffer held at two temperatures (0 degrees C and 80 degrees C). Approximately the same level of recovery was obtained at the two buffer temperatures except at the shortest heating times for the heat treatment carried at 30% and 40% RH, where the number of survivors was significantly higher for spores placed in the buffer held at 80 degrees C. The effect of this high temperature was attributed to heat activation of the ascospores that remained dormant during the dry heat treatment conditions mentioned above. The wet heat resistance of N. fischeri ascospores was also determined at temperatures ranging from 82.5 degrees C to 95 degrees C. The results indicate that as the RH decreased, the heat resistance of the ascospores increased. There were about four orders of magnitude difference in the heat resistance between wet heat (100% RH) and the lowest dry heat treatment condition (30% RH).

Factors affecting recovery of Neosartorya fischeri ascospores after exposure to dry heat

Recovery of Neosartorya fischeri ascospores subjected to a dry heat treatment (DHT) at 95 degrees C, 50% relative humidity (RH) for 60 minutes increased exponentially as the initial temperature of the recovery buffer increased. Different diluents were evaluated and the same recovery pattern was obtained when water or dilute buffers were used to recover the DHT spores. However, when glycerol was added to the buffer, the number of spores recovered in solutions held in ice water increased with increasing glycerol concentration. When the DHT spores were exposed to an atmosphere saturated with water vapor (100% RH) before being placed in the buffer, the recovery was independent of the initial temperature of the buffer. This occurred even if the spores were subsequently dried before being introduced into the buffer. It is hypothesized that the temperature-dependent recovery was due to injury of the DHT spores during the sudden rehydration in dilute solutions at low temperatures.

Evaluation of a Visual DNA Probe for Enterotoxigenic E. coli Detection in Foods and Wastewater by Colony Hybridization

A visual DNA probe for the detection of enterotoxigenic E. coli (LT EEC) by colony hybridization was evaluated to determine its efficacy as a more restrictive, routine indicator method for foods and wastewater. The E. coli heat labile enterotoxin (LT) gene was used as the DNA probe to detect LT EEC. In control experiments the reliability of the probe was demonstrated with food spiked with LT EEC. Raw oysters and wastewater examined for naturally occurring LT EEC showed significant levels of probe positive isolates. Despite some problems, for example background noise associated with food type, the DNA probe proved satisfactory as a method for indicating the presence of enterotoxigenic Enterobacteriaceae .

Effect of thermal treatments in oils on bacterial spore survival

The heat resistance of Bacillus cereus F4165/75, Clostridium sporogenes PA 3679 and Cl. botulinum 62A spores suspended in buffer (pH 7.2), olive oil and a commercial oil (a mixture of rapeseed oil and soy oil) was investigated. Linear survivor curves were obtained with B. cereus spores in the three menstrua and with 62A and PA 3679 spores suspended in buffer. However, the inactivation kinetics of the clostridial spores suspended in oils were concave upward with a characteristic tailing-off for 62A spores suspended in olive oil. These deviations from the semi-log model could not be ascribed to a heterogeneity in heat resistance of the spore population or to the variation of aw during heating. Spore resistance to heat increased in the order: buffer much less than commercial oil less than olive oil. The greater heat resistance of oil-suspended spores was ascribed to the low aw (0.479 and 0.492 for commercial oil and olive oil, respectively) and to the composition of the oils. The difference in z values (ca 28 degrees C in oils and 10 degrees-12 degrees C in buffer) suggested that the mechanism of inactivation differs for spores suspended in lipids and in aqueous systems. The thermodynamic data were consistent with this hypothesis.

Tailing of survivor curves of clostridial spores heated in edible oils

Tailing of survivor curves was observed for Clostridium sporogenes PA 3679 and Cl. botulinum 62A spores heated whilst suspended in edible oils, but not for the same spores suspended in buffer (pH 7.2) or mineral oil or for Bacillus cereus F4165/75 spores suspended in buffer or oils. The tailing cannot be ascribed to a genetic or developmental heterogeneity in the resistance of the spore population or to a heterogeneity of the treatment severity during heating. Heat adaptation due to the release of protective factor(s), to the selection for resistant spores or to the diffusion of oil constituents inside the spore protoplast to protect key molecules from heat denaturation was also ruled out. The tailing can be ascribed to spore clumping during the course of heating or to a heterogeneity in heat resistance of germination system(s) within spores, concurrently with the activation of a dormant germination system. It is probably caused by some oleic acid containing triglycerides.

Histamine Levels in Commercially Processed Fish in Morocco

Histamine levels were determined in 248 samples of fish commercially processed in Morocco. Concentrations ranging from <0.01 to 694 mg/100 g of fish (mg%) were observed. The mean value was 12.33 mg% (sardines, 9.75; mackerel, 13.74; tuna 9.86) and the standard deviation was 55.28 mg% (sardines, 43.21; mackerel, 71.99; tuna, 25.05). The bulk of the samples (85.5%) had low histamine levels (<10 mg%); 26 samples (10.5%) had levels within the range 10-50 mg% and should be classified as not from fresh fish or of low quality; 10 samples (4%) had toxicologically significant levels, above 50 mg%. Tuna fish was more susceptible to histamine development than were sardines or mackerel; 7% of tuna fish samples contained levels above 50 mg% as compared to 3.7% and 3.2% for sardines and mackerel, respectively. The percentage of samples containing levels above 50 mg% was somewhat higher for fish processed in the central region (7.1%) than the southern (4.3%) or northern (1.3%) regions; however, statistically the regional differences were not significantly different. Histamine development in sardines demonstrated first-order kinetics. Reaction rates ranged from 0.00200 to 0.000421 mn^-1. Refrigeration controlled histamine development. Fish held at 8°C showed a shelf life 12 h longer than fish held at 17°C. A combination of salting and refrigeration was more effective. Fish held at 8°C and salted at a level of 5 or 8% showed a shelf life 35 h longer than fish held at 17°C with no salt.

Association of [32P] with Clostridium botulinum 52A Vegetative Cells Following Growth in a Medium Containing Sodium Dihydrogen [32P]-Pyrophosphate

The association of [³²P] with Clostridium botulinum 52A vegetative cells following growth in a medium containing either sodium dihydrogen [³²P]-pyrophosphate ([³²P]-SAPP) or sodium dihydrogen [³²P]-orthophosphate ([³²P]-orthophosphate) was studied. Absorbency measurements at 630 nm were used in addition to [³²P] recovery in determining [³²P] association with cellular growth and metabolism. Radiolabeling experiments showed [³²P]-orthophosphate was associated with vegetative cells during logarithmic growth, yet was released once stationary phase was attained or upon lysis. [^3P]-SAPP was also associated with cells during growth, but was not released once stationary phase was attained. Results suggested [³²P]-SAPP continued to bind cells or other metabolic materials following attainment of the stationary phase of cells. Fractionation of 24 and 48 h-old cultures grown in the presence of [³²P]-SAPP showed a higher percentage of [³²P] associated with the RNA fraction (3.91 and 2.48%, respectively) compared to the DNA fraction (0.09 and 0.07%, respectively).

Comparison of a Dry Medium Culture Plate (Petrifilm SM Plates) Method to the Aerobic Plate Count Method for Enumeration of Mesophilic Aerobic Colony-Forming Units in Fresh Ground Beef

Mesophilic aerobic microbial populations in fresh ground beef were enumerated with a new system, Petrifilm™ SM Plates (PSM), and with the conventional aerobic plate count (APC) method using standard methods agar (SMA). Total colony-forming units were determined in 119 fresh ground beef samples (29 extra-lean, 30 lean and 60 regular) purchased at nine different retail markets over a period of 6 wk. Linear regression analysis of PSM vs. APC counts gave a slope of 0.963, an intercept of -0.027, and a correlation coefficient of 0.951. Mean log₁₀ counts on PSM were 5.86 compared to 6.11 on SMA (P<0.01) or a mean log₁₀ difference of -0.25. These analyses indicate that the Petrifilm SM method would be a possible alternative for the aerobic plate count method.

Multiple modes of inhibition of spore germination and outgrowth by reduced pH and sorbate

Germination and outgrowth of three strains of Clostridium botulinum in PYEG medium were measured by phase contrast microscopy. Reduction in pH from 7 to 5.5 completely inhibited germination of strain 12885A, reduced the extent of germination of strain 62A and had no effect on the extent of germination of strain 53B. At pH 5.5, 225 mg/l of undissociated sorbic acid had no effect on the germination of strain 53B, while at pH 6.5, 225 mg/l of undissociated sorbic acid completely inhibited germination of strains 62A and 12885A. Outgrowth of germinated spores of strains 62A and 53B was not inhibited at pH 5.5, but the addition of sorbate (225 mg/l undissociated sorbic acid) completely inhibited outgrowth. Sorbate inhibited germination of Cl. botulinum and Bacillus cereus spores triggered to germinate by amino acids. Inhibition occurred after germinant binding, as measured by commitment to germinate.

Influence of a Minimal Change in pH on Germination of Clostridium botulinum 52A in Media Containing Sodium Acid Pyrophosphate and Potassium Sorbate

The influence of 0.4% sodium acid pyrophosphate (SAPP) or 0.26% potassium sorbate (PS) on Clostridium botulinum 52A growth and toxicity from spores was studied at two pH levels 5.55 and 5.85. Absorbancy measurements at 630 nm were used in combination with microscopic evaluations and toxin analysis to compare effects of additives on normal cell development. Treatment cultures containing 0.4% SAPP and 0.26% PS at a higher pH of 5.85 showed no increase in absorbancy and no sign of toxicity, but elongated vegetative cells (≥9 μm) were observed using phase contrast microscopy rather than scanning electron microscopy. The SAPP-PS treatment culture at a lower pH of 5.55 displayed no signs of growth spectrophometrically or microscopically, as well as no toxicity. These data suggest that a SAPP-PS combination in a laboratory medium at pH 5.85 does not halt germination and outgrowth, yet may prevent cell division; whereas, the same treatment at pH 5.55 inhibits normal spore germination.

Inhibition of germinant binding by bacterial spores in acidic environments

Commitment to germinate occurred in both Clostridium botulinum and Bacillus cereus spores during 0.5 min of exposure to 100 mM L-alanine or L-cysteine, measured by the inability of germination inhibitors (D form of amino acid) to inhibit germination. Spore germination at pH 4.5 was inhibited because the germinant did not bind to the trigger sites. C. botulinum spores exposed to 100 mM L-alanine or L-cysteine at pH 4.5 remained sensitive to D-amino acid inhibition at pH 7, indicating that no germinants had bound to the trigger site at pH 4.5. Inhibition of germinant binding at pH 4.5 was reversible but lagged in commitment to germinate upon transfer to pH 7. Spores sequentially exposed to pH 4.5 buffer and pH 7 buffer with the germinant also demonstrated a lag in commitment to germinate. The pH at which binding was inhibited was not significantly affected by composition of the buffer or by reduced germinant concentrations (10 mM). Nonspecific uptake of L-[3H]alanine by C. botulinum spores was not inhibited at pH 4.5. Inhibition of germinant binding in acidic environments appeared to be due to protonation of a functional group in or near the trigger site. This may represent a general mechanism for inhibition of spore germination in acidic environments.

Inhibitory Effects of Various Salts and/or Ionic Strengths on Growth from Clostridium botulinum 52A Spores or Vegetative Cells

Growth response from spores and vegetative cells of Clostridium botulinum strain 52A in peptone-yeast extract-glucose (PYEG) broth at two pH levels (5.55 or 5.85) containing sodium acid pyrophosphate (SAPP) (0, 0.2, 0.4%), NaCl (0, 1.25, 2.50%) and/or potassium sorbate (KS) (0, 0.13, 0.26%) was measured as the mean A₆₃₀ nm of 20 tubes at 37°C. Additional treatments contained KC1 and MgCl₂ (0, 1.25, 2.50%) without SAPP or KS. Growth ratios (GR = treatment/control) based on time to reach A₆₃₀ = 0.35 were calculated to compare effects of additives on strain 52A. Growth from spores was affected significantly (p≤0.01) by pH level. KS and KS/pH interactions were also significant factors in growth from both spores and vegetative cells; SAPP/pH interactions were significant for cell growth, only. Combinations of SAPP (0.2, 0.4%) NaCl (0%) and KS (0.26%) were the most favorable treatments for delaying growth from spores or vegetative cells. NaCl (1.25, 2.50%) decreased antibotulinal effects produced by combinations of SAPP and KS. Elimination of NaCl enhanced antibotulinal effects. Formulations containing KC1 or MgCl₂ (without SAPP and KS) at the same molarity as the NaCl in earlier treatments (0.21, 0.43) resulted in inhibition of growth from vegetative cells greater than growth from spores in the presence of MgCl₂ at M = 0.43 (ionic strength = 1.29). This inhibition was more evident at pH 5.55 than pH 5.85. This study in a model system suggests ionic strength and/or chloride salt may be important considerations when manipulating formulations of additives designed to control C. botulinum growth.

Evaluation of Dry Medium Film (Petrifilm VRB) for Coliform Enumeration

A new system, Petrifilm VRB, was compared to two commonly used methods for enumerating coliforms: (a) colony counts on violet red bile agar (VRBA) and (b) MPN determinations with lauryl sulfate tryptose broth (LST) and brilliant green lactose bile broth (BGLB). Petrifilm VRB consists of a bottom film coated with VRB nutrients and a top film coated with a cold-water-soluble gelling agent and a tetrazolium indicator dye. Gas bubbles from lactose fermentation produced around colonies differentiated coliforms from other gram-negative organisms. Coliforms from 120 raw milk samples were enumerated by the Petrifilm VRB, VRBA and MPN methodologies. Randomly selected colonies were chosen from each methodology for characterization. Counts determined with Petrifilm VRB were comparable to counts with VRBA, and both Petrifilm VRB and VRBA compared similarly to the MPN method. Data examined by plotting log₁₀ coliform counts from Petrifilm VRB vs. log₁₀ coliform counts from VRBA resulted in a regression line with a slope of 0.959 and an intercept of -0.076 which was close to the line of equality (slope of one and intercept of zero) for the two methods. No method selected or excluded any one type of microorganisms, and VRBA and Petrifilm VRB had equivalent repeatability.

Heat-induced temperature sensitivity of outgrowing Bacillus cereus spores

Inactivation of Bacillus cereus spores during cooling (10 degrees C/h) from 90 degrees C occurred in two phases. One phase occurred during cooling from 90 to 80 degrees C; the second occurred during cooling from 46 to 38 degrees C. In contrast, no inactivation occurred when spores were cooled from a maximum temperature of 80 degrees C. Inactivation of spores at a constant temperature of 45 degrees C was induced by initial heat treatments from 80 to 90 degrees C. The higher temperatures accelerated the rate of inactivation. Germination of spores was required for 45 degrees C inactivation to occur; however, faster germination was not the cause of accelerated inactivation of spores receiving higher initial heat treatments. Repair of possible injury was not observed in Trypticase soy broth (BBL Microbiology Systems), peptone, beef extract, starch, or L-alanine at 30 or 35 degrees C. Microscopic evaluation of spores outgrowing at 45 degrees C revealed that when inactivation occurred, outgrowth halted at the swelling stage. Inhibition of protein synthesis by chloramphenicol at the optimum temperature also stopped outgrowth at swelling; thus protein synthesis may play a role in the 45 degree C inactivation mechanism.

Effect of Carbon Dioxide, Nitrogen and Hydrogen Gases on Germination of Clostridium botulinum Spores

Germination of spores of Clostridium botulinum strains 62A, 213B and 12885A was monitored in modified peptone yeast extract broth flushed with CO₂, N₂, CO₂ + H₂ and N₂ + H₂. Carbon dioxide enhanced germination of spores of each of the strains. Hydrogen gas in combination with CO₂ or N₂ did not substantially alter germination compared to germination in CO₂ or N₂ alone, even though the oxidation-reduction potential of the system was lower in the systems flushed with H₂.

Effect of Polyphosphates in Combination with Nitrite-Sorbate or Sorbate on Clostridium botulinum Growth and Toxin Production in Chicken Frankfurter Emulsions

Sodium nitrite, sorbic acid, potassium sorbate and polyphosphates (sodium acid pyrophosphate, SAPP; sodium hexametaphosphate, SHMP; and sodium tripolyphosphate, STPP) were tested at similar preadjusted (before cooking) pH levels (in the range of pH 5.78 to 6.19 after cooking) to determine effective combinations capable of controlling Clostridium botulinum growth and toxin production in mechanically deboned chicken meat frankfurter emulsions incubated at 27°C. In combination with low levels of nitrite (40 ppm), potassium sorbate (0.26%, pH 6.06) was more effective than sorbic acid (0.20%, pH 6.03) in delaying toxin production (>27 d vs. 6 d) and in controlling growth. In formulations containing combinations of nitrite (40 ppm) and sorbic acid (0.20%) or nitrite (40 ppm) and potassium sorbate (0.26%), the addition of polyphosphates (0.4%) resulted in a greater delay of toxin production (8 to 25 d for nitrite-sorbic acid-SAPP vs. 28 d for nitrite-potassium sorbate-SAPP) at similar pH levels. Under these conditions, SAPP delayed production of detectable toxin longer (25 d) than did either SHMP (6 to 11 d) or STPP (4 to 14 d). The addition of polyphosphates to nitrite-free emulsions containing sorbic acid (0.20%) or potassium sorbate (0.26%) did not delay the development of botulinal toxin when the pH was essentially equivalent in the range of 5.78 to 6.07.

Proposed mechanism for sensitization by hypochlorite treatment of Clostridium botulinum spores

Hypochlorite-treated Clostridium botulinum 12885A spores, but not buffer-treated spores, could be germinated with lysozyme, indicating that their coats are made permeable to lysozyme by hypochlorite treatment so that the cortex is accessible. Hypochlorite-treated spores and spores extracted with 8 M urea-2-mercaptoethanol (pH 3.0) were sensitive to certain components of recovery media, but spores sensitized to lysozyme by other treatments were not. These data indicate that hypochlorite does more than increase coat permeability to lysozyme. Scanning electron microscopy revealed a more open-appearing surface of hypochlorite-treated spores, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that a greater amount of protein was removed from hypochlorite-treated and other lysozyme-sensitized spores than from buffer-treated spores. The data suggest that spore coat proteins may be removed by hypochlorite treatment, and this may be responsible for the sensitivity of spores and for their observed ability to germinate in lysozyme.

Hypochlorite injury of Clostridium botulinum spores alters germination responses

Clostridium botulinum spores were sublethally damaged by exposure to 12 or 28 micrograms of available chlorine per ml for 2 min at 25 degrees C and pH 7.0. The damaging dose was 2.7 x 10(-6) to 3.1 x 10(-6) micrograms of available chlorine per spore. Damage was manifested by a consistent 1.6 to 2.4 log difference between the most probable number enumeration of spores (modified peptone colloid medium) and the colony count (modified peptone yeast extract glucose agar); this did not occur with control spores. Damaged spores could be enumerated by the colony count procedure. Germination responses were measured in several defined and nondefined media. Hypochlorite treatment altered the rate and extent of germination in some of the media. Calcium lactate (9 mM) permitted L-alanine (4.5 mM) germination of hypochlorite-treated spores in a medium containing 12 or 55 mM sodium bicarbonate, 0.8 mM sodium thiosulfate, and 100 mM Tris-hydrochloride (pH 7.0) buffer. Tryptose inhibited L-alanine germination of the spores. Treatments with hypochlorite and with hydrogen peroxide (7%, 25 degrees C, 2 min) caused similar enumeration and germination responses, indicating that the effect was due to a general oxidation phenomenon.

Differing L-alanine germination requirements of hypochlorite-treated Clostridium botulinum spores from two crops

Similar populations of hypochlorite-treated spores were enumerated from two crops of Clostridium botulinum 12885A produced by the same procedure; however, germination required different L-alanine concentrations. Lactate permitted the germination of spores from both crops with suboptimal L-alanine concentrations. The data suggest that the spores differ slightly in chemical or structural composition.

Proposed role of lactate in germination of hypochlorite-treated Clostridium botulinum spores

Clostridium botulinum 12885A spores treated with hypochlorite required added DL-calcium lactate for L-alanine germination. Lactate was the active component of calcium lactate. Equimolar concentrations of L-malate, but not of DL-propionate, could replace lactate, suggesting that the alpha-hydroxy acid structure is important. Neither lactate nor malate was an effective germinant for buffer-treated or hypochlorite-treated spores. If the L-alanine concentration was increased 100-fold (to 450 mM), the lactate germination requirement was overcome. The data suggest that the L-alanine germination sites were modified by hypochlorite so that a higher concentration of alanine was required for activity. Lactate appeared to be an activator of modified or non-hypochlorite-modified L-alanine germination sites.

Characterization of Germination of Desulfotomaculum nigrificans Spores 1

Germination of spores of Desulfotomaculum nigrificans was studied by measuring reduction in numbers of heat-resistant units. Complete (>99.9%) germination was observed with heat-activated spores suspended in a combination of 1% soytone, 0.1% ferric citrate, 0.1% sodium metabisulfite (Na₂S₂O₅), and distilled water. In this medium spores germinated most rapidly at pH 6.0 - 8.0 when incubated at 55°C after the spores were exposed to a 15 - 20 min heat-shock at 100°C. Twelve amino acids triggered germination either together or individually only in the presence of ferric citrate and Na₂S₂O₅. No one amino acid as a germinant was superior to the others evaluated. Of nine carbohydrates examined (at 1% levels), fructose, ribose, and arabinose initiated germination individually in distilled water. Ferrous ion initiated germination whereas the ferric ion did not. Cu⁺⁺ (10mM) initiated germation whereas Zn⁺⁺ (10mM) inhibited germination. Phosphate buffer (67mM) and EDTA (10mM) inhibited cation-initiated germination. Reducing agents such as Na₂S₂O₅ may provide ferrous ions needed for spore germination. Ferrous ions as germinants indicate a possible significant role for an iron source when enumerating D. nigrificans spores or when evaluating food spoilage caused by D. nigrificans .

Bacterial Spore Injury - An Update 1

Injury has long been recognized in bacterial spores, especially in evaluation of apparent survival after administration of treatments to control these resistant entities. Compared to vegetative cells, the complexity of the germination and outgrowth processes has retarded research activity on injury and resuscitation. Heat-injury has been observed and studied to the greatest extent, but irradiation and chemical treatments also damage spores from anaerobic or aerobic bacteria. Injury has been associated with germination or specific steps in outgrowth or both. Damage of enzymes, DNA, RNA, membranes or other systems may be implied by resuscitation studies. Injury has been manifested by increased sensitivity to selective or antimicrobial agents or by increased requirements for germination and growth. The need for extensive fundamental research on bacterial spore injury continues to exist, especially to aid in explaining unique spore resistance.

Antimicrobial Activity of Sorbate

During the last 30 years sorbate has been tested and used widely in the preservation of various food products throughout the world. Currently it has received increased attention as a potential replacer of nitrite for botulism control in processed meat products. Previous reports, however, had suggested sorbate as a selective agent for clostridia in laboratory media. Recent developments as well as the need for safe, practical and effective food preservatives in current and future food processing have generated intense interest in preservatives such as sorbate. This paper reviews the significant developments relating to use of sorbate as a food preservative - its antimicrobial effects, applications, advantages and limitations. A summary of the current status as well as unanswered questions relevant to the mechanism(s) through which the compound exerts its antimicrobial activity also is presented.

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.

Effect of Rising Temperatures on Growth and Survival of Clostridium perfringens Indigenous to Raw Beef 1

Growth and survival of Clostridium perfringens indigenous to raw beef were compared to that of a composite of eight strains of C. perfringens inoculated into raw ground beef round, beef-round strips, and beef-round cores. A constantly rising temperature rate of 6 C/h and a dynamic rising temperature rate, predetermined from long time-low temperature (LTLT) oven beef cookery processes, were used to evaluate growth and survival. Survivors of C. perfringens were observed in raw ground beef and autoclaved ground beef at temperatures between 59 and 63 C. Growth in raw ground beef was more rapid than in raw beef-round strips. Raw ground beef supported growth of the indigenous flora to a greater extent than did autoclaved ground beef inoculated with the composite. The populations in raw, domestic frozen beef rounds used in commercial cooking processes were low, ranging from < 70/g to 1000/g, and varied among lots.

Production of Phospholipase C by Nine Strains of Clostridium perfringens at 37 C and at a Constantly Rising Temperature 1

Nine strains of Clostridium perfringens were compared for phospholipase C production in autoclaved ground beef (AGB) at 37 C. Enzyme production is reported as units per colony forming unit (CFU). Phospholipase C concentrations were determined by the hemolysin indicator method and colonies were observed on Tryptose Sulfite Cycloserine agar. Enzyme production by each of the nine strains was significantly different. The increase and decrease of viable cells of C. perfringens in AGB exposed to temperatures rising constantly at a rate of 4.1 C/h was accompanied by the appearance and disappearance of phospholipase C. This demonstrated that C. perfringens can produce detectable levels of phospholipase C when grown during dynamic increasing temperatures.

Botulism Control by Nitrite and Sorbate in Cured Meats: A Review 1

Nitrite plays a major role in the botulinal safety of cured meat products. When used at appropriate levels, it retards Clostridium botulinum growth and delays production of its deadly neurotoxin. Even though the incidence of botulinal spores in meat is very low, factors such as the tonnage of cured meats consumed, the potential for mishandling such products, and the nature of the disease necessitate the use of nitrite or other equally effective compound(s) for extra safety. Residual nitrite and nitrosamine levels in cured meat products have been decreasing in recent years through control and research conducted by the meat industry and related institutions. Such levels are minimal compared to total nitrate and nitrite amounts ingested or formed in the human body. Sorbate, especially in combination with nitrite at concentrations adequate only for cured meat color and flavor development, is at least as effective as currently used nitrite levels in delaying C. botulinum growth and toxin production. The mechanism(s) through which nitrite and/or sorbate perform their actions upon C. botulinum remains to be found. A review of the pertinent research completed to date should be helpful in the search for the mechanism(s).

Food Protection for the 80's 1

New social, economic and political demands for conservation of energy, water and consumable products coupled with changes in lifestyle including more meals eaten away from home will require new approaches to food handling. These modifications may increase or uncover new hazards and potential opportunities for food borne illness. Microbial hazards will remain a major problem but will be only one of the many concerns of the consumer about food. Increases in awareness of newly identified pathogens, carcinogens, mutagens and the like will demand greater efforts but will also increase cost of foods. Acute sensitivity to escalating costs will in turn bring about more objective evaluations of benefit/risk ratios on all programs. Education of producers, handlers, processors and consumers will be required so that they may monitor and serve as protectors of the food system thus minimizing regulatory costs and placing responsibility at the point of action. This process will be successful only with appropriate educational and research support to evaluate and implement modified programs.

Sodium nitrite and sorbic acid effects on Clostridium botulinum spore germination and total microbial growth in chicken frankfurter emulsions during temperature abuse

Samples of (i) a control or of (ii) sodium nitrite-containing or (iii) sorbic acid-containing, mechanically deboned chicken meat frankfurter-type emulsions inoculated with Clostridium botulinum spores, or a combination of ii and iii, were temperature abuse at 27 degrees C. Spore germination and total microbial growth were followed and examined at specified times and until toxic samples were detected. The spores germinated within 3 days in both control and nitrite (20, 40 and 156 micrograms/g) treatments. Sorbic acid (0.2%) alone or in combination with nitrite (20, 40, and 156 micrograms/g) significantly (P less than 0.05) inhibited spore germinations. No significant germination was recorded until toxic samples were detected. A much longer incubation period was necessary for toxin to be formed in nitrite-sorbic acid combination treatments as contrasted with controls or nitrite and sorbic acid used individually. Total growth was not affected by the presence of nitrite, whereas sorbic acid appeared to depress it. Possible mechanisms explaining the effects of nitrite and sorbic acid on spore germination and growth are postulated.

Inactivation of Salmonellae in Autoclaved Ground Beef Exposed to Constantly Rising Temperatures 1

Inactivation of a composite of five serotypes of salmonellae was monitored in autoclaved ground beef exposed to constantly rising temperatures increased at rates similar to those used in beef cookery. Rising temperature rates of 6.0 C/h, 8.5 C/h and 12.5 C/h and constant temperatures of 55, 57, 61 and 63 C were examined. Survival of Salmonella typhimurium TM-1 was compared to survival of the composite. D and z values were compared for constant and rising temperature rates. The D₅₀ C for constant temperature data was 30.2 min, and the D₅₀ C for changing temperature data was 78.6 min (6.0 C/h), 82.4 min (8.5 C/h), and 49.8 min (12.5 C/h). Neither serotype nor heat treatment of ground beef had a major influence on apparent heat resistance of salmonellae. A comparison of these results to previous rising temperature work with Clostridium perfringens suggested that controlling C. perfringens will result in control of salmonellae. On the basis of these results, the July 18, 1978, USDA processing ruling appears adequate to control salmonellae in precooked beef roasts.

Growth of Clostridium perfringens in Three Different Beef Media and Fluid Thioglycollate Medium at Static and Constantly Rising Temperatures 1

Growth of an eight-strain composite of Clostridium perfringens was compared using rolled raw beef strips, raw and autoclaved ground beef and Fluid Thioglycollate medium. The inoculated media were exposed to either static or dynamic temperatures increasing at linear rates. The most rapid growth and shortest lag times were observed in autoclaved ground beef. Generation times in the beef media were directly related to oxidation-reduction potential. Fluid Thioglycollate medium supported the slowest growth even though it presented a favorable E_h.

Microbial Harboring Characteristics of Dishmachine-Filmed Glassware

Alkaline-earth type films, produced by detergent-water interactions, are frequently deposited on eating utensils during mechanical dishwashing. These films are aesthetically unacceptable but their public health significance and food spoilage potential have not been established. Sterile glass petri dishes were washed in an institutional-type dishmachine containing Bacillus subtilis spores in the washwater. A film-producing model system was developed to examine film formation in conjunction with spore deposition. The influence of three distinct detergent formulations on this association was also determined. Detergent formulations contained 6.75% phosphorus (P), as sodium tripolyphosphate (STP), 3.0% P as STP, a proprietary phosphate substitute, and the film-producing model formulation devoid of both STP and substitute water conditioning agents. Film deposition was quantified as μg Ca⁺⁺ per cm² by an acid rinse-atomic absorption spectrophotometric method. The quantity of B. subtilis spores recovered from washed petri dishes in the model system was related to film deposition. The relationship was dependent on the number of consecutive dishmachine cycles and the hardness of the water supply. Above a threshold value of 3 μg Ca⁺⁺ per cm², Ca⁺⁺ deposition and B. subtilis spore harborage were directly correlated. Both of these conditions were inhibited to varying degrees by the three detergent formulations. These data suggest that dishware filming may be cause for public health and food spoilage concerns.

Osmotically induced increase in thermal resistance of heat-sensitive, dipicolinic acid-less spores of Bacillus cereus Ht-8

Thermal resistance in heat-sensitive, dipicolinic acid (DPA)-less spores of Bacillus cereus Ht-8 heated in sucrose solutions increased at and above a concentration of 2 M sucrose. The decimal reduction times at 75 degrees C for spores heated in 0.0, 1.8, 2.2, and 2.6 M sucrose were 2.0, 2.8, 4.5, and 12 min, respectively. Maltose, fructose, and glucose increased heat resistance above that observed in water but did not elevate resistance to the level observed with sucrose at the same osmolality. Cation-induced loss of thermal resistance in chemically sensitized spores was reversed in the presence of sucrose. Spores germinated in brain heart infusion were resistant when heated in sucrose. In the presence of sucrose, spores exhibited an increase in optical density at 700 nm. Electron micrographs of the DPA-less spores suspended in 2.2 M sucrose revealed a shrinkage of outer coats and exosporium membranes. The results suggested that the osmotic property of sugars increased thermal resistance in DPA-less spores. The osmotic pressure exerted by sugars may be similar to the pressure that usually exists within the cortex of normal spores containing DPA and may cause the dehydration of the protoplast and the consequent thermal resistance. The role of dehydration and the nonessential nature of DPA for thermal resistance in spores were confirmed.

Dialysis technique for containment of microbial populations inoculated into food systems

A technique utilizing dialysis tubing was developed for the containment of microbial populations introduced into a food system. The entrapment of the inoculum was accomplished while reducing interference with interactions between the sample and the surrounding environment.

Heat-induced requirements for sucrose or magnesium for expression of heat resistance in Bacillus cereus forespores

The addition of 0.6 M sucrose of 0.016 M Mg2+ to the enumeration medium was required for early expression of heat resistance (10 min at 70 degrees C) in stage V Bacillus cereus forspores. The addition of Mg2+ to the sporulation medium did not remove this requirment for sucrose of Mg2+. The heat damage did not affect forespore germination or outgrowth, but injured cells in the absence of sucrose or Mg2+ were not capable of cell division. The heat-induced sublethal damage apparently affected the forspore component(s) that could be repaired or was capable of normal function in the presence of added Mg2+ or sucrose.

GLUCOSE INHIBITS GROWTH OF CLOSTRIDIUM PERFRINGENS IN FOOD PROTEINS1

A study of the effects of food components on Clostridium perfringens growth indicated that the addition of D-glucose to sodium caseinate or to isolated soy protein greatly extended the lag phase of growth. A final concentration of 10 g glucose per liter in a sodium caseinate medium containing NaCl, K2HPO4, Na2SO4, and sodium thioglycollate increased the lag time of C. perfringens strain S40 to 3.5 h compared to 2 h for the control with no glucose, Growth was determined by colony count or absorbance (650 nm) measurement, or both. Addition of Trypticase (2 g/1) or Fe++, Ca++, or Mg++ cations (1 mM) relieved the glucose inhibition. Similar inhibition by glucose was also observed when amino acids replaced sodium caseinate and the amount of cations was controlled by adding low levels or by adding EDTA. Other sugars tested did not give this inhibitory effect. The extent of the lag time varied with glucose concentration or with level of the cell inoculum. There was a direct linear relationship between the molecules of added glucose per cell and the lag time. The mechanism appears to involve competition by food proteins for cations that affect the glucose transport system (s). These data indicate a potential control or at least delay for initial growth of C. perfringens in certain fabricated protein foods.

INCIDENCE OF POTENTIALLY PATHOGENIC MICROORGANISMS IN FURTHER-PROCESSED TURKEY PRODUCTS1

Numbers of certain pathogenic microorganisms associated with turkey and turkey products were determined at three Minnesota turkey eviscerating and processing plants. The influence of processing and freezing was investigated. Using a predetermined sampling plan, skin and meat samples were obtained from 96 turkeys. Numbers of Clostridium perfringens, Staphylococcus aureus, salmonellae, and coliform organisms in each sample were determined. All types of organisms studied were found in 10 to 1000-fold higher levels in the skin than in meat samples. Clostridium perfringens and S. aureus organisms were recovered from samples obtained during each stage in the processing of the birds. Salmonellae were not found as frequently. Of 85 fresh skin and meat samples, 53 (62%) yielded C. perfringens and 46 (54%) yielded S. aureus. Salmonellae were recovered from 11 of 74 (15%) fresh samples and coliform organisms from 74 of 85 (85%) fresh samples, Frozen storage (31 days at −20 F) reduced recovery of the organisms to 56, 53, 9, and 67% respectively.