Growth Of Clostridium Perfringens Research Articles

Inhibition of Clostridium perfringens Growth by Potassium Lactate during an Extended Cooling of Cooked Uncured Ground Turkey Breasts

The U.S. Department of Agriculture's Food Safety and Inspection Service compliance guideline known as Appendix B specifies chilling time and temperature limits for cured and uncured meat products to inhibit growth of spore-forming bacteria, particularly Clostridium perfringens. Sodium lactate and potassium lactate inhibit toxigenic growth of Clostridium botulinum, and inhibition of C. perfringens has been reported. In this study, a cocktail of spores of three C. perfringens strains (ATCC 13124, ATCC 12915, and ATCC 12916) were inoculated into 100-g samples of ground skinless, boneless turkey breast formulated to represent deli-style turkey breast. Three treatment groups were supplemented with 0 (control), 1, or 2% potassium lactate (pure basis), cooked to 71 °C, and assayed for C. perfringens growth during 10 or 12 h of linear cooling to 4 °C. In control samples, populations of C. perfringens increased 3.8 to 4.7 log CFU/g during the two chilling protocols. The 1% potassium lactate treatment supported only a 2.5- to 2.7-log increase, and the 2% potassium lactate treatment limited growth to a 0.56- to 0.70-log increase. When compared with the control, 2% potassium lactate retarded growth by 2.65 and 4.21 log CFU/g for the 10- and 12-h cooling protocols, respectively. These results confirm that the addition of 2% potassium lactate inhibits growth of C. perfringens and that potassium lactate can be used as an alternative to sodium nitrite for safe extended cooling of uncured meats.

Evaluation of a new mathematical model to describe Clostridium perfringens growth during the cooling of cooked ground beef

A mathematical model previously developed to study microbial growth in food products under an isothermal environment was adapted to a time-varying temperature regime. The resulting model was applied to study the growth of Clostridium perfringens in meat products. This micro-organism is of particular relevance to public health and economy due to the loss of productivity caused by it. Results showed a similar performance of the model used compared to the Baranyi model under an isothermal situation and a slightly better performance under a non-isothermal temperature profile.

Prevalence and characterization of Clostridium perfringens from the faecal microbiota of elderly Irish subjects

The aim of this study was to investigate the diversity and composition of the intestinal microbiota of elderly subjects using a combination of culture-dependent techniques and 16S rRNA gene amplicon sequencing. The study was performed as part of the ELDERMET project, in which 368 faecal samples were assessed for viable numbers of Bifidobacterium spp., Lactobacillus spp. and Enterobacteriaceae on selective agar. However, the Bifidobacterium selective medium used also supported the growth of Clostridium perfringens, which appeared as distinct colonies and were subsequently characterized phenotypically and genotypically. All the isolates were confirmed as toxin biotype A producers. In addition, three isolates tested also had the genetic determinants for the β2 toxin. Of the 368 faecal samples assessed, C. perfringens was detected in 28 samples (7.6%). Moreover, C. perfringens was observed in samples from subjects in all the residence locations assessed but was most prevalent in subjects from long-stay residential care, with 71.4% of the samples (63.2% of the subjects) being from this residence location, and with a shedding level in excess of 10(6) c.f.u. (g faeces)(-1). Microbiota profiling revealed some significant compositional changes across both the family and genus taxonomic levels between the C. perfringens-positive and -negative datasets. Levels of culturable Bifidobacterium spp. and Lactobacillus spp. were significantly (P<0.05) lower in the C. perfringens-positive samples. Sequence-based methods also confirmed a significant difference in the Bifidobacterium spp. level (P<0.05) between both datasets. Taken together, these data suggest that a high viable count [>10(6) c.f.u. (g faeces)(-1)] of C. perfringens in stool samples may be indicative of a less healthy microbiota in the intestine of elderly people in long-stay residential care.

Predictive Model for Growth of Clostridium perfringens during Cooling of Cooked Beef Supplemented with NaCl, Sodium Nitrite and Sodium Pyrophosphate

This paper presents a model for predicting relative growth of Clostridium perfringens in ground beef products at different percentages of salt (0 to 3%), sodium pyrophosphate (0 to 0.3%), and nitrite (0 and 200 ppm). The results of the experiments indicates that salt was the primary variable affecting the amount of growth, and that growth in general, was significantly affected by the presence of nitrite. The inclusion of SPP did not significantly improve the model’s fit with observed results. The primary growth model, derived from growth experiments at constants temperatures, is based on a common form of Baranyi’s growth curves and the secondary model is based on cardinal temperatures, relating maximum specific growth rates as a function of temperature. When product is heated and then cooled, the model predicts an initial decline in the number of cells. The model’s predictions compared well with results obtained from dynamic temperatures experiments, for salt concentrations up to 1.5% and nitrite, to 200 ppm, when samples were initially heated and then cooled. The model can be used by processors to evaluate the risk of C. perfringens spore germination and outgrowth during cooling (stabilization) deviations or in custom cooling schedules in case the processors cannot follow the USDA FSIS Compliance Guidelines (Appendix A) for Cooling of Heat-Treated Meat and Poultry Products (Stabilization).

Growth of Clostridium perfringens during cooling of refried beans.

Outbreaks of Clostridium perfringens have been associated with dishes containing refried beans from food service establishments. However, growth of C. perfringens in refried beans has not been investigated, and predictive models have not been validated in this food matrix. We investigated the growth of C. perfringens during the cooling of refried beans. Refried beans (pinto and black, with and without salt added) were inoculated with 3 log CFU/g C. perfringens spores and incubated isothermally at 12, 23, 30, 35, 40, 45, and 50°C. The levels of C. perfringens were monitored 3, 5, 8, and 10 h after inoculation, and then fitted to the Baranyi primary model and the Rosso secondary model prior to solving the Baranyi differential equation. The final model was validated by dynamic cooling experiments carried out in stockpots, thus mimicking the worst possible food service conditions. All refried beans samples supported the growth of C. perfringens, and all models fit the data with pseudo-R(2) values of 0.95 or greater and mean square errors of 0.3 or lower. The estimated maximum specific growth rates were generally higher in pinto beans, with or without salt added (2.64 and 1.95 h(-1), respectively), when compared with black beans, with or without salt added (1.78 and 1.61 h(-1), respectively). After 10 h of incubation, maximum populations of C. perfringens were significantly higher in samples with no salt added (7.9 log CFU/g for both pinto and black beans) than in samples with salt added (7.3 and 7.2 log CFU/g for pinto and black beans, respectively). The dynamic model predicted the growth of C. perfringens during cooling, with an average root mean squared error of 0.44. The use of large stockpots to cool refried beans led to an observed 1.2-log increase (1.5-log increase predicted by model) in levels of C. perfringens during cooling. The use of shallower pans for cooling is recommended, because they cool faster, therefore limiting the growth of C. perfringens.

Impact of temperature sampling strategy on the risk of Clostridium growth: Application to rapid cooling of food in institutional food service facilities

In French institutional food services, cooked food must be cooled within 2 h of cooking and the temperature of the cooked food must then be lower than 10 °C to avoid significant growth of Clostridium perfringens. However, food placed on trolleys and put in a rapid cooling unit (a blast-chiller) shows great variation in temperature. What criterion should then be used to decide when the trolley can be removed from the blast-chiller? We studied four different strategies of when to remove the trolley by fitting 217 time–temperature profiles collected in a central hospital kitchen to mixed-effect models. We modelled the temperatures between and within containers holding meals on trolleys. We compared the strategies as to the probability that C. perfringens can proliferate to at least 1 log CFU g−1. For each strategy, this probability was plotted against the probability of the trolley leaving the blast-chiller. The probability of leaving the blast-chiller varied, depending on the number of measurements taken on the trolley and on the points where temperature was measured. The best strategy depends on the risk of C. perfringens growth exceeding 1 log10 CFU g−1 the food service operator accepts and the temperature monitoring protocol that is implemented.

Evaluation of impact of exposure of Sudan azo dyes and their metabolites on human intestinal bacteria

Sudan azo dyes are banned for food usage in most countries, but they are illegally used to maintain or enhance the color of food products due to low cost, bright staining, and wide availability of the dyes. In this report, we examined the toxic effects of these azo dyes and their potential reduction metabolites on 11 prevalent human intestinal bacterial strains. Among the tested bacteria, cell growth of 2, 3, 5, 5, and 1 strains was inhibited by Sudan I, II, III, IV, and Para Red, respectively. At the tested concentration of 100 μM, Sudan I and II inhibited growth of Clostridium perfringens and Lactobacillus rhamnosus with decrease of growth rates from 14 to 47%. Sudan II also affected growth of Enterococcus faecalis. Growth of Bifidobacterium catenulatum, C. perfringens, E. faecalis, Escherichia coli, and Peptostreptococcus magnus was affected by Sudan III and IV with decrease in growth rates from 11 to 67%. C. perfringens was the only strain in which growth was affected by Para Red with 47 and 26% growth decreases at 6 and 10 h, respectively. 1-Amino-2-naphthol, a common metabolite of the dyes, was capable of inhibiting growth of most of the tested bacteria with inhibition rates from 8 to 46%. However, the other metabolites of the dyes had no effect on growth of the bacterial strains. The dyes and their metabolites had less effect on cell viability than on cell growth of the tested bacterial strains. Clostridium indolis and Clostridium ramosum were the only two strains with about a 10 % decrease in cell viability in the presence of Sudan azo dyes. The present results suggested that Sudan azo dyes and their metabolites potentially affect the human intestinal bacterial ecology by selectively inhibiting some bacterial species, which may have an adverse effect on human health.

Impact of the method chosen for measuring temperatures on the efficacy of rapid cooling of foods in catering facilities

Cooked dishes must be cooled rapidly after cooking to avoid significant growth of Clostridium perfringens. French regulations require that produce be cooled from 63 °C to 10 °C in less than 2 h.Cooling is a critical phase for central cooking facilities that need to cool large quantities of food. The food is cooled in blast-chillers before being placed in cold storage. We observed that in France the blast-chiller is usually switched off by operators as soon as a measured temperature is equal to or below 10 °C. This temperature measurement may be taken at any place in the batch. We studied the consequences of this procedure on the distribution of temperatures at the time when cooling is stopped. We did this by monitoring the core temperatures of the foodstuffs during 52 cooling operations carried out in seven central cooking facilities for hospitals or schools. The data allowed us to estimate the characteristics of the distribution of temperatures within batches. Simulations suggest that, when the blast-chiller is switched off after cooling, there can be significant differences between random temperature readings in the batch and the highest temperatures. For 5% of simulations, the difference could be greater than 17 °C. We propose alternative rules to reduce this discrepancy. If such a single measurement was replaced by three measurements, with each of them taken at the centre of a container, this difference would be less than 3.8 °C in 95% of the simulations. The improvement of methods for measuring temperatures is necessary to achieve the cooling durations recommended by the official organizations.

Use of natural ingredients to control growth of Clostridium perfringens in naturally cured frankfurters and hams.

A major concern for processed meats marketed as natural/organic is that they do not contain nitrite in concentrations known to be most effective for inhibiting foodborne pathogens. Supplemental treatments to increase the level and consistency of antimicrobial protection in these products may be important to provide consumers with the degree of safety that they have come to expect from conventionally cured meats. Therefore, the objective of this study was to identify and test ingredients that might improve processed meat product safety without altering their natural/organic status. Eight treatments of hams and frankfurters were prepared: (A) uncured control (typical ingredients except nitrite and nitrate); (B) conventionally cured control (erythorbate, nitrite, and a lactate-diacetate blend); (C) natural nitrate cure (including starter culture containing Staphylococcus carnosus); (D) natural nitrate cure (culture and natural antimicrobial A containing a vinegar, lemon, and cherry powder blend); (E) natural nitrate cure (culture and antimicrobial B containing a cultured sugar and vinegar blend); (F) natural nitrite cure without additional antimicrobials; (G) natural nitrite cure with natural antimicrobial A; and (H) natural nitrite cure with antimicrobial B. For the hams, treatments C, D, E, and H impacted growth of Clostridium perfringens to the same extent (P < 0.05) as the conventionally cured control (approximately 2 log less growth over time than uncured control). For frankfurters, treatments D, G, and H had an effect (approximately 1 log) on growth equivalent to that of the conventionally cured control (P < 0.05). These results suggest that natural/organic cured meats have more potential for pathogen growth than conventionally cured products, but supplemental natural ingredients offer safety improvement.

Survival and growth of Clostridium perfringens in commercial no-nitrate-or-nitrite-added (natural and organic) frankfurters, hams, and bacon.

The popularity of "preservative-free" foods among consumers has stimulated rapid growth of processed meats manufactured without sodium nitrite. The objective of this study was to quantify the potential for Clostridium perfringens growth in commercially available processed meats manufactured without the direct addition of nitrite or nitrate. Commercial brands of naturally cured, no-nitrate-or-nitrite-added frankfurters (10 samples), hams (7 samples), and bacon (9 samples) were obtained from retail stores and challenged with a three-strain inoculation (5 log CFU/g) of C. perfringens. Reduced inhibition (P < 0.05) was observed in seven brands of frankfurters, six brands of hams, and four brands of bacon when compared with each respective sodium nitrite-added control. In naturally cured and truly uncured commercial frankfurters, growth over time was approximately 4.7 log, while conventionally cured frankfurters exhibited growth at 1.7 log. Naturally cured ham and bacon products exhibited growth at 4.8 and 3.4 log, respectively, while their conventionally cured counterparts exhibited growth at 2.6 and 2.3 log, respectively. These products also demonstrated variation in growth response. The results indicate that commercially available natural/organic naturally cured meats have more potential for growth of this pathogen than do conventionally cured products. Natural and organic processed meats may require additional protective measures in order to consistently provide the level of safety from bacterial pathogens achieved by conventionally cured meat products, and which is expected by consumers.

Predictive model for growth of Clostridium perfringens during cooling of cooked uncured meat and poultry

Comparison of Clostridium perfringens spore germination and outgrowth in cooked uncured products during cooling for different meat species is presented. Cooked, uncured product was inoculated with C. perfringens spores and vacuum packaged. For the isothermal experiments, all samples were incubated in a water bath stabilized at selected temperatures between 10 and 51 °C and sampled periodically. For dynamic experiments, the samples were cooled from 54.4 to 27 °C and subsequently from 27 to 4 °C for different time periods, designated as x and y hours, respectively. The growth models used were based on a model developed by Baranyi and Roberts (1994. A dynamic approach to predicting bacterial growth in food. Int. J. Food Micro. 23, 277–294), which incorporates a constant, referred to as the physiological state constant, q 0. The value of this constant captures the cells’ history before the cooling begins. To estimate specific growth rates, data from isothermal experiments were used, from which a secondary model was developed, based on a form of Ratkowsky’s 4-parameter equation. The estimated growth kinetics associated with pork and chicken were similar, but growth appeared to be slightly greater in beef; for beef, the maximum specific growth rates estimated from the Ratkowsky curve was about 2.7 log 10 cfu/h, while for the other two species, chicken and pork, the estimate was about 2.2 log 10 cfu/h. Physiological state constants were estimated by minimizing the mean square error of predictions of the log 10 of the relative increase versus the corresponding observed quantities for the dynamic experiments: for beef the estimate was 0.007, while those for pork and chicken the estimates were about 0.014 and 0.011, respectively. For a hypothetical 1.5 h cooling from 54 °C to 27° and 5 h to 4 °C, corresponding to USDA-FSIS cooling compliance guidelines, the predicted growth (log 10 of the relative increase) for each species was: 1.29 for beef; 1.07 for chicken and 0.95 log 10 for pork. However, it was noticed that for pork in particular, the model using the derived q 0 had a tendency to over-predict relative growth when the observed amount of relative growth was small, and under-predict the relative growth when the observed amount of relative growth was large. To provide more fail-safe estimate, rather than using the derived value of q 0, a value of 0.04 is recommended for pork.

GC-MS analysis of fennel essential oil and its effect on microbiology growth in rats intestine

The compositions of the essential oil of fennel have been analyzed by ion-trap GC-MS. The main components identified were: Benzene, 1-methoxy-4-(1-propenyl) - (82%), D-Limonene (6.55%), Estragole (3.53%), 3-Carene (1.12%) and 1,6-Octadien-3-ol, 3,7-dimethyl - (1.12%). The effect of the fennel on Enterococcus,Clostridium perfringens and Bacillus bifidus were tested. Fennel essential oils inhibited Enterococcus and Clostridium perfringens growth in rat’s intestine. By contrast, the essential oil promoted Bacillus bifidus growth. The results of this study confirmed the possibility of using the fennel essential oils in maintaining useful bacteria colony on rat’s intestine. Key words: Enterococcus, Clostridium perfringens, Bacillus bifidus, fennel, essential oil, GC-MS.

Bayesian modeling of Clostridium perfringens growth in beef-in-sauce products

Models on Clostridium perfringens growth which have been published to date have all been deterministic. A probabilistic model describing growth under non-isothermal conditions was thus proposed for predicting C. perfringens growth in beef-in-sauce products cooked and distributed in a French hospital. Model parameters were estimated from different types of data from various studies. A Bayesian approach was proposed to model the overall uncertainty regarding parameters and potential variability on the ‘work to be done’ ( h 0) during the germination, outgrowth and lag phase. Three models which differed according to their description of this parameter h 0 were tested. The model with inter-curve variability on h 0 was found to be the best one, on the basis of goodness-of-fit assessment and validation with literature data on results obtained under non-isothermal conditions. This model was used in two-dimensional Monte Carlo simulations to predict C. perfringens growth throughout the preparation of beef-in-sauce products, using temperature profiles recorded in a hospital kitchen. The median predicted growth was 7.8.10 −2 log 10 cfuċg −1 (95% credibility interval [2.4.10 −2,0.8]) despite the fact that for more than 50% of the registered temperature profiles cooling steps were longer than those required by French regulations.

Effect of tannins on the in vitro growth of Clostridium perfringens

Vegetable tannins are water-soluble polyphenolic compounds of varying molecular weights that occur abundantly in nature. The diet of many free-ranging wild animals contains significant amounts of tannins. Also, commercial tannins are used in animal industry as food additives to improve animal performance. In order to further determine the capacity of tannins to inhibit the development of intestinal diseases produced by Clostridium pefringens, we evaluated here the effect of tannins from quebracho, chestnut or combinations of both on C. perfringens and their toxins. The C. perfringens (types A, B, C, D and E) growth obtained from the intestine of healthy and diseased animals was reduced in a dose-dependent manner in the presence of quebracho tannins, chestnut tannins, combinations of both or a commercial formula based in these tannins. Although the minimal inhibitory concentration of both tannins varied between isolates, no statistically significant differences were observed between isolates from healthy or sick animals. Comparative analysis showed that the concentrations of quebracho tannin inhibiting the growth of C. perfringens were higher than chestnut tannin. In fact, antibacterial effect of quebracho tannin was increased up to 20 times with the addition of 25% of chestnut tannin and 85 times with 75% of chestnut tannin. Antibacterial activity of the commercial product was up to ∼50 times higher than quebracho tannin alone. Quebracho tannin showed partial bactericidal activity, whereas chestnut tannin activity was stronger. Both tannins were able to reduce the alpha toxin lecithinase activity and epsilon toxin cytotoxicity in MDCK cells. These results suggest that tannin-supplemented diet could be useful to prevent some clostridial diseases.

Control of Clostridium perfringens-induced necrotic enteritis in broilers by target-released butyric acid, fatty acids and essential oils

The efficacy of target-released butyric acid, medium-chain fatty acids (C6 to C12 but mainly lauric acid) and essential oils (thymol, cinnamaldehyde, essential oil of eucalyptus) micro-encapsulated in a poly-sugar matrix to control necrotic enteritis was investigated. The minimal inhibitory concentrations of the different additives were determined in vitro, showing that lauric acid, thymol, and cinnamaldehyde are very effective in inhibiting the growth of Clostridium perfringens. The in vivo effects were studied in two trials in an experimental necrotic enteritis model in broiler chickens. In the first trial, four groups of chickens were fed a diet supplemented with butyric acid, with essential oils, with butyric acid in combination with medium-chain fatty acids, or with butyric acid in combination with medium-chain fatty acids and essential oils. In all groups except for the group receiving only butyric acid, a significant decrease in the number of birds with necrotic lesions was found compared with the infected, untreated control group. In the second trial the same products were tested but at a higher concentration. An additional group was fed a diet supplemented with only medium-chain fatty acids. In all groups except for that receiving butyric acid in combination with medium-chain fatty acids and essential oils, a significant decrease in the number of birds with necrotic lesions was found compared with the infected, untreated control group. These results suggest that butyric acid, medium-chain fatty acids and/or essential oils may contribute to the prevention of necrotic enteritis in broilers.

Characterization of Acp, a Peptidoglycan Hydrolase of Clostridium perfringens with N -Acetylglucosaminidase Activity That Is Implicated in Cell Separation and Stress-Induced Autolysis

This work reports the characterization of the first known peptidoglycan hydrolase (Acp) produced mainly during vegetative growth of Clostridium perfringens. Acp has a modular structure with three domains: a signal peptide domain, an N-terminal domain with repeated sequences, and a C-terminal catalytic domain. The purified recombinant catalytic domain of Acp displayed lytic activity on the cell walls of several Gram-positive bacterial species. Its hydrolytic specificity was established by analyzing the Bacillus subtilis peptidoglycan digestion products by coupling reverse phase-high-pressure liquid chromatography (RP-HPLC) and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) analysis, which displayed an N-acetylglucosaminidase activity. The study of acp expression showed a constant expression during growth, which suggested an important role of Acp in growth of C. perfringens. Furthermore, cell fractionation and indirect immunofluorescence staining using anti-Acp antibodies revealed that Acp is located at the septal peptidoglycan of vegetative cells during exponential growth phase, indicating a role in cell separation or division of C. perfringens. A knockout acp mutant strain was obtained by using the insertion of mobile group II intron strategy (ClosTron). The microscopic examination indicated a lack of vegetative cell separation in the acp mutant strain, as well as the wild-type strain incubated with anti-Acp antibodies, demonstrating the critical role of Acp in cell separation. The comparative responses of wild-type and acp mutant strains to stresses induced by Triton X-100, bile salts, and vancomycin revealed an implication of Acp in autolysis induced by these stresses. Overall, Acp appears as a major cell wall N-acetylglucosaminidase implicated in both vegetative growth and stress-induced autolysis.

Clostridium Perfringens Growth from Spore Inocula in Sous‐Vide Processed Pork‐Based Mexican Entrée

The combined effect of Citricidal wih irradiation on Clostridium perfringens growth from spores in a sous-vide processed marinated pork meat Mexican entrée was investigated. Citricidal was added at 200 or 800 ppm after mixing pork meat with tomatillo sauce and inoculated with 3 log(10) CFU/g of C. perfringens spores. Samples were irradiated at either 0 or 2 kGy, heated to an internal temperature of 71 degrees C, and stored at 4 degrees C for 28 d, 15 degrees C for 45 d, and 25 degrees C for 26 h. To simulate the conditions that may occur during transportation, distribution, storage, or handling in supermarkets or by consumers, the effect of static temperature abuse on C. perfringens growth was assessed by transferring samples stored at 4 to 25 degrees C for 13 and 15 h. Total C. perfringens populations were determined by plating diluted samples on tryptose-sulfite-cycloserine agar. Growth was not observed up to 45 d of storage at 15 degrees C in samples supplemented with 800 ppm of Citricidal. At 25 degrees C, no significant differences (P > 0.05) on the lag phase duration due to antimicrobial treatments was observed. The temperature abuse of refrigerated products for up to 15 h did not lead to C. perfringens growth to high infective dose levels of 1 million cells required to cause food poisoning. The results suggest that 800 ppm Citricidal can have significant bacteriostatic activity against C. perfringens and may provide a degree of protection against this pathogen in sous-vide processed marinated pork meat Mexican entrée, under mild temperature abuse (<or= 15 degrees C) conditions.

Predictive model for growth of Clostridium perfringens during cooling of cooked ground chicken

Traditional methodologies for development of microbial growth models under dynamic temperature conditions do not take into account the organism's history. Such models have been shown to be inadequate in predicting growth of the organisms under dynamic conditions commonly encountered in the food industry. The objective of the current research was to develop a predictive model for Clostridium perfringens spore germination and outgrowth in cooked chicken products during cooling by incorporating a function to describe the prior history of the microbial cell in the secondary model. Incorporating an assumption that growth kinetics depends in an explicit way on the cells' history could provide accurate estimates of growth or inactivation. Cooked, ground uncured chicken was inoculated with C. perfringens spores, and from this chicken, samples were formed and vacuum packaged. For the isothermal experiments, all samples were incubated in a constant temperature water baths stabilized at selected temperatures between 10 and 51 °C and sampled periodically. The samples were cooled from 54.4 to 27 °C and subsequently from 27 to 4 °C at different time periods (cooling rates) for dynamic cooling experiments. The standard model provided predictions that varied from the observed mean log10 growth values by magnitudes up to about 0.65 log10. However, for a selected memory model, estimates of log10 relative growth provided predictions within 0.3 log10 of the mean observed log10 growth values. These findings point to an improvement of predictions obtained by memory models over those obtained by the standard model. More study though is needed to validate the selected model. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.

Antimicrobial activity of leptospermone and its derivatives against human intestinal bacteria

Abstract The anaerobic growth inhibiting activity of the essential oil of Leptospermum scoparium seeds against intestinal bacteria was evaluated in vitro . The essential oil at 5.0 mg/disc strongly (+++) inhibited the growth of Clostridium difficile and Clostridium perfringens , but did not inhibit the growth of Bifidobacterium breve , Bifidobacterium longum , Escherichia coli , or Lactobacillus casei . Spectroscopic analyses revealed that the active component of the essential oil was leptospermone. Leptospermone strongly inhibited the growth of C. difficile and C. perfringens at 1.0 mg/disc and moderately inhibited their growth at 0.5 mg/disc. However, leptospermone did not inhibit the growth of B. breve , B. longum , and L. casei . When compared with the leptospermone derivatives, 1,2,3-cyclohexanetrione-1,3-dioxime exerted strong inhibition against C. perfringens and moderate inhibition against C. difficile at 0.5 mg/disc, whereas the other derivatives exerted weak or no growth inhibition against all bacteria tested. Taken together, these results indicate that cyclohexanetrione is required for triketone derivatives to inhibit the growth of C. difficile and C. perfringens . These findings indicate that L. scoparium seed-derived materials and 1,2,3-cyclohexanetrione-1,3-dioxime are naturally occurring antimicrobial agents that could be useful in the development of new agents for the specific control of C. difficile and C. perfringens .

Predictive model for growth of Clostridium perfringens during cooling of cooked ground pork

Abstract A predictive dynamic model for Clostridium perfringens spore germination and outgrowth in cooked pork products during cooling is presented. Cooked, ground pork was inoculated with C. perfringens spores and vacuum packaged. For the isothermal experiments, all samples were incubated in a water bath stabilized at selected temperatures between 10 and 51 °C and sampled periodically. For dynamic experiments, the samples were cooled from 54.4 to 27 °C and subsequently from 27 to 4 °C for different time periods, designated as x and y hours, respectively. The growth models used were based on a model developed by Baranyi and Roberts (1994), which incorporates a constant, referred to as the physiological state constant, q 0 . The value of this constant captures the cells' history before the cooling begins. To estimate specific growth rates, data from isothermal experiments were used, from which a secondary model was developed, based on a particular form of Ratkowsky's 4-parameter equation. Using the data from dynamic experiments and the Ratkowsky model, an optimal value of q 0 (=0.01375) was derived minimizing the mean square error of predictions. However, using this estimate, the model had a tendency to over-predict relative growth when there was observed small amounts of relative growth, and under-predict relative growth when there was observed large relative growth. To provide more fail-safe estimates, rather than using the derived value of q 0 , a value of 0.04 is recommended. The predictive model with this value of q 0 would provide more fail-safe estimates of relative growth and could aid producers and regulatory agencies with determining disposition of products that were subjected to cooling deviations. Industrial relevance Safe time/temperature for cooling of cooked pork is very important to guard against the pathogen in cooked products. Predictive model will assist industry to determine compliance with regulatory performance standards and to ensure microbiological safety of cooked products.