Increased Detection of Acid-Injured Escherichia coli O157:H7 in Autoclaved Apple Cider by Using Nonselective Repair on Trypticase Soy Agar †

Recent Progress and Challenges on the Microfluidic Assay of Pathogenic Bacteria Using Biosensor Technology

Microfluidic technology is one of the new technologies that has been able to take advantage of the specific properties of micro and nanoliters, and by reducing the costs and duration of tests, it has been widely used in research and treatment in biology and medicine. Different materials are often processed into miniaturized chips containing channels and chambers within the microscale range. This review (containing 117 references) demonstrates the significance and application of nanofluidic biosensing of various pathogenic bacteria. The microfluidic application devices integrated with bioreceptors and advanced nanomaterials, including hyperbranched nano-polymers, carbon-based nanomaterials, hydrogels, and noble metal, was also investigated. In the present review, microfluid methods for the sensitive and selective recognition of photogenic bacteria in various biological matrices are surveyed. Further, the advantages and limitations of recognition methods on the performance and efficiency of microfluidic-based biosensing of photogenic bacteria are critically investigated. Finally, the future perspectives, research opportunities, potential, and prospects on the diagnosis of disease related to pathogenic bacteria based on microfluidic analysis of photogenic bacteria are provided.

A single-tube approach for in vitro diagnostics using diatomaceous earth and optical sensor

Versatile, simple and efficient sample preparation is desirable for point-of-care testing of emerging diseases such as zoonoses, but current sample preparation assays are insensitive, labour-intensive and time-consuming and require multiple instruments. We developed a single-tube sample preparation approach involving direct pathogen enrichment and extraction from human specimens using diatomaceous earth (DE). Amine-modified DE was used to directly enrich a zoonotic pathogen, Brucella, in a large sample volume. Next, a complex of amine-modified DE and dimethyl suberimidate was used for nucleic acid extraction from the enriched pathogen. Using our single-tube approach, the pathogen can be enriched and extracted within 60min at a level of 1 colony formation unit (CFU) from a 1ml sample volume in the same tube. The performance of this approach is 10-100 times better than that of a commercial kit (102 to 103CFU/ml) but does not require a large centrifuge. Finally, we combined the single-tube approach with a bio-optical sensor for rapid and accurate zoonotic pathogen detection in human urine samples. Using the combination system, Brucella in human urine can be efficiently enriched (~ 8-fold) and the detection limit is enhanced by up to 100 times (1CFU/ml bacteria in urine) compared with the commercial kit. This combined system is fast and highly sensitive and thus represents a promising approach for disease diagnosis in the clinical setting.

Detection Methodologies for Pathogen and Toxins: A Review

Pathogen and toxin-contaminated foods and beverages are a major source of illnesses, even death, and have a significant economic impact worldwide. Human health is always under a potential threat, including from biological warfare, due to these dangerous pathogens. The agricultural and food production chain consists of many steps such as harvesting, handling, processing, packaging, storage, distribution, preparation, and consumption. Each step is susceptible to threats of environmental contamination or failure to safeguard the processes. The production process can be controlled in the food and agricultural sector, where smart sensors can play a major role, ensuring greater food quality and safety by low cost, fast, reliable, and profitable methods of detection. Techniques for the detection of pathogens and toxins may vary in cost, size, and specificity, speed of response, sensitivity, and precision. Smart sensors can detect, analyse and quantify at molecular levels contents of different biological origin and ensure quality of foods against spiking with pesticides, fertilizers, dioxin, modified organisms, anti-nutrients, allergens, drugs and so on. This paper reviews different methodologies to detect pathogens and toxins in foods and beverages.

The survival of E. coli O157:H7, S. Typhimurium and L. monocytogenes in black carrot (Daucus carota) juice

In this study the survival and growth patterns of Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes in various concentrations of black carrot juice were investigated during incubation period at 4 °C and 37 °C for 7 days. Several parameters, such as juice concentration (%), pH, incubation temperature (°C) and time (days) were found effective on the survival of pathogens tested. Although L. monocytogenes has been found to be the less resistant microorganism to the variable conditions, there were only ca. 1 and 2 log reductions in the number of the cells in the juice samples incubated at 4 °C for 2 and 7 days, respectively. Incubating at low temperature (4 °C) enhanced the survival of test microorganisms.

Culture-free detection and enumeration of STEC in water

Shiga toxin-producing Escherichia coli (STEC) causes worldwide outbreaks of food and waterborne diseases. Rapid identification of causative agents is critical for early intervention in the case of widespread diarrheal epidemics to prevent mortality. In this study, a Molecular-Beacon targeting stx2 gene (highly associated with human illness) was designed to develop a culture-independent real-time PCR assay for detection and quantification of STEC in water samples. The assay could detect lowest 10 genomic equivalent (GE) of the reference strain (E. coli I.T.R.C.-18) per PCR or 100 GE/mL. The presence of 10(6)CFU/mL of non-pathogenic E. coli DH5α has no impact on sensitivity of the assay. The assay could successfully enumerate STEC in surface water (collected from a sewage impacted river) and potable water samples collected from Lucknow city without prior enrichment. The assay will be useful in pre-emptive monitoring of surface/potable waters to prevent waterborne outbreaks caused by STEC.

A QCM-D-based biosensor for E. coli O157:H7 highlighting the relevance of the dissipation slope as a transduction signal

A biosensor for detection of viable Escherichia coli (E. coli) O157:H7 is developed using a quartz crystal microbalance with dissipation monitoring (QCM-D). The detection platform is based on the immobilization of affinity purified polyclonal antibodies onto gold-coated QCM-D quartz crystals via a cysteamine self-assembled monolayer. QCM-D measurements conducted over a broad range of bacterial cell concentrations show that the optimal biosensor response is the initial slope of the dissipation shift as a function of elapsed time (D(slope)). A highly log-log linear response in the initial D(slope) is obtained for detection of E. coli O157:H7 over a wide range of cell concentrations from 3 x 10(5) to 1 x 10(9)cells/mL. The prepared biosensor also exhibits a log-log linear working range from 10(7) to 10(9)cells/mL for E. coli K12 D21, a non-pathogenic model organism and further shows satisfactory selectivity using Bacillus subtilis. To our knowledge, this is the first study demonstrating the use of the initial D(slope) as a sensor response when using QCM-D technology.

Evaluation of Escherichia coli O157:H7 in apple juice with Cornus fruit (Cornus officinalis Sieb. et Zucc.) extract by conventional media and thin agar layer method

Escherichia coli O157:H7 survival in apple juice supplemented with Cornus fruit (Cornus officinalis Sieb. et Zucc.) extract was studied. Inoculated samples with or without Cornus fruit extract were kept at 21 and 7 degrees C. Microbial analysis was conducted on days 0, 1, 3, 5, and 7. MacConkey sorbitol agar (MSA), tryptic soy agar (TSA), and thin agar layer (TAL) medium were used to compare the recovery of bacteria stressed under combination treatment. Influence of temperature, storage time, and Cornus fruit on survival of cells was evaluated. The most dramatic reduction of E. coli O157:H7 was observed in apple juice with Cornus fruit extract at 21 degrees C. At 7 degrees C, E. coli O157:H7 was reduced by 2.3logcfu/ml in the apple juice with Cornus fruit extract compared to the control sample on day 7. TAL and TSA were more efficient than MSA. Cornus fruit extract can be used in combination with temperature and storage time controls to inactivate E. coli O157:H7 in apple juice. This study has shown that TAL is a viable method of recovering and differentiating injured microorganisms and apple juice supplemented with Cornus fruit has potential as a value-added beverage with antimicrobial effects and potential health benefits.

Survival of Escherichia coli O157:H7 and Salmonella in apple cider and orange juice as affected by ozone and treatment temperature

Inactivation of Escherichia coli O157:H7 and Salmonella in apple cider and orange juice treated with ozone was evaluated. A five-strain mixture of E. coli O157:H7 or a five-serovar mixture of Salmonella was inoculated (7 log CFU/ml) into apple cider and orange juice. Ozone (0.9 g/h) was pumped into juices maintained at 4 degrees C, ambient temperature (approximately 20 degrees C), and 50 degrees C for up to 240 min, depending on organism, juice, and treatment temperature. Samples were withdrawn, diluted in 0.1% peptone water, and surface plated onto recovery media. Recovery of E. coli O157:H7 was compared on tryptic soy agar (TSA), sorbitol MacConkey agar, hemorrhagic coli agar, and modified eosin methylene blue agar; recovery of Salmonella was compared on TSA, bismuth sulfite agar, and xylose lysine tergitol 4 (XLT4) agar. After treatment at 50 degrees C, E. coli O157:H7 populations were undetectable (limit of 1.0 log CFU/ml; a minimum 6.0-log CFU/ml reduction) after 45 min in apple cider and 75 min in orange juice. At 50 degrees C, Salmonella was reduced by 4.8 log CFU/ml (apple cider) and was undetectable in orange juice after 15 min. E. coli O157:H7 at 4 degrees C was reduced by 4.8 log CFU/ml in apple cider and by 5.4 log CFU/ml in orange juice. Salmonella was reduced by 4.5 log CFU/ml (apple cider) and 4.2 log CFU/ml (orange juice) at 4 degrees C. Treatment at ambient temperature resulted in population reductions of less than 5.0 log CFU/ml. Recovery of E. coli O157:H7 and Salmonella on selective media was substantially lower than recovery on TSA, indicating development of sublethal injury. Ozone treatment of apple cider and orange juice at 4 degrees C or in combination with mild heating (50 degrees C) may provide an alternative to thermal pasteurization for reduction of E. coli O157:H7 and Salmonella in apple cider and orange juice.

Independent effects of acetic acid and pH on survival of Escherichia coli in simulated acidified pickle products

Our objective was to determine the effects of organic acids and pH on the rate at which selected strains of Escherichia coli O157:H7 die in acid solutions representative of acidified pickle products (pH < 4.6). We used gluconic acid/sodium gluconate (pKa = 3.7) as a noninhibitory buffer to maintain pH at selected values in the absence of other organic acids. This was possible because we found that the inhibitory effects of this acid on E. coli strains at pH 3.1 were independent of acid concentration over a range of 2 to 200 mM. By this method, the lethal effects of acetic acid solutions (100 to 400 mM) at selected pH values between 3.1 and 4.1 were compared with the effects of pH alone (as determined using gluconate buffer). We found D-values were two- to fourfold lower with acetic acid compared with the effect of pH alone for simulated pickle brines in this pH range. Glutamic acid, an amino acid that is known to enhance acid resistance in E. coli and is a component of pickle brines, protected the E. coli strains from the specific effects of acetic acid.

Antimicrobial performance of alkaline ionic fluid (GC-100X) and its ability to remove Escherichia coli O157:H7 from the surface of tomatoes

An efficacy test of GC-100X, a noncorrosive alkaline ionic fluid (pH 12) composed of free radicals and supplemented with xylitol, was carried out against six major foodborne pathogens-Staphylococcus aureus FRI 913, Salmonella enterica serovar Enteritidis ATCC 13076, S. enterica serovar Typhimurium DT104 Korean isolate, Vibrio parahaemolyticus ATCC 17803, Escherichia coli O157:H7 ATCC 43894, and Pseudomonas aeruginosa KCTC 1637-at three different temperatures (4, 25, and 36 degrees C) with or without organic load (2% yeast extract). Results revealed a more than 4-log10 (CFU/ml) reduction (1.0 x 10(4) CFU/ml reduction) against all pathogens reacted at 37 degrees C for 3 h in the absence of organic material. GC-100X solution diluted with an equal volume of distilled or standard hard water (300 ppm CaCO3) showed effective bactericidal activity, particularly against gram-negative bacteria. Washing efficacy of GC-100X solution was compared against E. coli O157:H7 on cherry tomato surfaces with those of a commercially used detergent and chlorine water (100 ppm). Viable cell counts of E. coli O157:H7 that had penetrated to the cores of tomatoes after sanitizing treatment revealed that GC-100X stock and its 5% diluted solutions had similar washing effects to 100-ppm chlorine water and were more effective than the other kitchen detergent. These results indicate that GC-100X has good bactericidal and sanitizing activities and is useful as a new sanitizer for food safety and kitchen hygiene.

Survival of Salmonella spp. and Escherichia coli O157:H7 on fresh and frozen strawberries

For maximum shelf life, fresh strawberries are harvested directly without washing into retail containers. Frozen berries are usually hulled in the field and washed prior to freezing, sometimes with the addition of sucrose. To determine survival of potential bacterial contaminants, cut or intact surfaces of fresh strawberries were spot inoculated with five- or six-strain cocktails of Salmonella or Escherichia coli O157:H7 (log 7.0 CFU/sample). Inoculated strawberries were dried for 1 h at 24 degrees C and were stored in closed containers at 5 or 24 degrees C. Sliced strawberries with or without added 20% sucrose were inoculated with one of two strains of E. coli O157:H7 and frozen at -20 degrees C. An initial population reduction of approximately 0.5-log cycles was observed on intact but not cut berries after the 1-h drying period. During storage at 24 degrees C for up to 48 h, populations of Salmonella and E. coli O157:H7 did not decline further. When strawberries were stored at 5 degrees C for up to 7 days, populations of both pathogens remained constant on cut surfaces but decreased by 1 - to 2-log cycles on intact surfaces. After 30 days of frozen storage, the population of E. coli O157:H7 had declined by 0.7- to 2.2-log cycles (with and without sucrose, respectively). Results of this study indicate that E. coli O157:H7 and Salmonella are capable of survival but not growth on the surface of fresh strawberries throughout the expected shelf life of the fruit and can survive in frozen strawberries for periods of greater than 1 month.

Validation of methods used to recover Escherichia coli O157:H7 and Salmonella spp. subjected to stress conditionst

Escherichia coli O157:H7, Salmonella spp., and Salmonella Typhimurium DT104 were stressed with lactic acid and cell-free supernatants from lactic acid bacteria and plated on three different media to determine if injured cells were recovered. A comparison of the susceptibility and recovery of antibiotic-resistant strains of the pathogens and nonresistant strains was also made. Acid stress conditions were created by adjusting the pH of a cocktail mixture (two to four strains) of the pathogen to 3.50 with lactic acid and holding for 18 h. The pathogen cocktail was also stressed with a cell-free supernatant of Lactobacillus lactis (pH 3.90) in a 4:6 ratio. Both nonstressed and stressed cocktail cultures were plated on Trypticase soy agar (TSA) and violet red bile agar (VRBA) for E. coli and xylose lysine tergitol4 (XLT4) for Salmonella. Repair of injured cells was evaluated by pour plating the stressed cells on a 5-ml thin layer of TSA and allowing a 2-h room temperature incubation followed by overlaying with VRBA or XLT4. There were significant reductions in the populations of both pathogens under both stress conditions when plating was done on nonselective media. Injured E. coli O157:H7 was not recovered on recovery or selective media compared with TSA. Numbers of cells of supernatant-stressed Salmonella spp. plated on selective and recovery media were similar to those on TSA. Acid-stressed cells for all Salmonella spp. were not recovered on TSA, selective, or recovery media at levels comparable to recovery on TSA. Antibiotic-resistant strains showed similar recovery patterns on all media evaluated. However, the antibiotic-resistant strains were less sensitive to both stress conditions. The use of antibiotic-resistant strains resulted in a greater recovery of stressed pathogens than the use of recovery media.

Phosphate buffer increases recovery of Escherichia coli O157:H7 from frozen apple juice

It is common practice to dilute food products in 0.1% peptone before microbiological analysis. However, this diluent may not be appropriate for detection of injured organisms present in acidic foods. Shelf-stable unclarified apple juice (pH 3.6) was inoculated with approximately 1 x 10(7) CFU/ml of Escherichia coli O157:H7 and held at 23 +/- 2 degrees C (control) or frozen to -20 +/- 2 degrees C for 24 h to induce injury before sampling. Unfrozen or frozen and thawed juice was diluted 1:1 or 1:10 in 0.1% (wt/vol) peptone (pH 6.1) or 0.1 M phosphate buffer (pH 7.2). Juice samples were plated onto tryptic soy agar with 0.1% (wt/vol) sodium pyruvate (TSAP) to measure survival or onto sorbitol MacConkey agar (SMA) to indicate injury. Counts on TSAP or SMA were the same for control samples held in peptone or phosphate buffer for up to 45 min. However, populations of E. coli in frozen and thawed samples declined rapidly upon dilution in 0.1% peptone. Within 20 min, E. coli underwent a >1-log10 CFU/ml reduction in viability as measured on TSAP and a >2-log10 CFU/ml reduction to below the limit of detection (1.6 or 2.3 log10 CFU/ml) on SMA. In contrast, populations of E. coli in frozen and thawed samples diluted in phosphate buffer did not decrease significantly on TSAP and decreased by <0.6 log CFU/ml on SMA during a 45-min holding period. The acidity of apple juice appears to interfere with the recovery of freeze-thaw-injured E. coli O157:H7 during sampling. Using 0.1 M phosphate buffer (pH 7.2) as a diluent results in superior recovery of these organisms on both selective and nonselective plating media.

Modeling the survival of Escherichia coli O157:H7 in apple cider using probability distribution functions for quantitative risk assessment

Outbreaks of foodborne illness from apple cider have prompted research on the survival of Escherichia coli O157:H7 in this food. Published results vary widely, potentially due to differences in E. coli O157:H7 strains, enumeration media, and other experimental considerations. We developed probability distribution functions for the change in concentration of E. coli O157:H7 (log CFU/day) in cider using data from scientific publications for use in a quantitative risk assessment. Six storage conditions (refrigeration [4 to 5 degrees C]; temperature abuse [6 to 10 degrees C]; room temperature [20 to 25 degrees C]; refrigerated with 0.1% sodium benzoate, 0.1% potassium sorbate, or both) were modeled. E. coli survival rate data for all three unpreserved cider storage conditions were highly peaked, and these data were fit to logistic distributions: ideal refrigeration, logistic (-0.061, 0.13); temperature abuse, logistic (-0.0982, 0.23); room temperature, logistic (-0.1, 0.29) and uniform (-4.3, -1.8), to model the very small chance of extremely high log CFU reductions. There were fewer published studies on refrigerated, preserved cider, and these smaller data sets were modeled with beta (4.27, 2.37) x 2.2 - 1.6, normal (-0.2, 0.13), and gamma (1.45, 0.6) distributions, respectively. Simulations were run to show the effect of storage on E. coli O157:H7 during the shelf life of apple cider. Under every storage condition, with and without preservatives, there was an overall decline in E. coli O157:H7 populations in cider, although a small fraction of the time a slight increase was seen.

A New Semi-Selective Medium for Xanthomonas campestris pv. vitians, the Causal Agent of Bacterial Leaf Spot of Lettuce

A semi-selective medium containing maltose, methyl green, and antibiotics (MMG) was developed for the isolation of Xanthomonas campestris pv. vitians. The semi-selective medium was evaluated based on plating efficiency of X. campestris pv. vitians in cell suspensions of pure cultures from leaves and soil. MMG medium allowed recovery of 5.7 to 30.6% of the X. campestris pv. vitians colonies recovered on nutrient agar and 0.1 to 8.4% of those recovered on 1/10-strength tryptic soy agar. MMG inhibited growth of most background bacteria and allowed reliable identification of X. campestris pv. vitians. The semi-selective medium contained (per liter) maltose (10 g), tryptone (5 g), K₂HPO₄ (3.5 g), KH₂PO₄ (2.75 g), trace elements (0.02 to 1.0 mg), methyl green (2 ml of a 1% aqueous solution), amoxicillin (32 mg), cephalothin (32 mg), cycloheximide (50 mg), and agar (15 g).

Growth and survival of E. coli O157:H7 during the manufacture and ripening of a smear-ripened cheese produced from raw milk

AIMS

The behaviour of Escherichia coli O157:H7 was studied during the manufacture and ripening of a smear-ripened cheese produced from raw milk.

METHODS AND RESULTS

Cheese was manufactured on a laboratory scale using milk (20 l) inoculated with E. coli O157:H7, and enumeration was carried out using CT-SMAC. From an initial level of 1.52 +/- 0.03 log cfu ml-1 in the milk (34 +/- 2 cfu ml-1), the numbers increased to 3.4 +/- 0.05 log cfu g-1 in the cheese at day 1. During ripening, the numbers decreased to <1 cfu g-1 and <10 cfu g-1 in the rind and core, respectively, after 21 days, although viable cells were detected by enrichment after 90 days. The presence of E. coli O157:H7 in the cheese was confirmed by latex agglutination and by multiplex PCR.

CONCLUSION

The results indicate that the manufacturing procedure encouraged substantial growth of E. coli O157:H7 to levels that permitted survival during ripening and extended storage.

SIGNIFICANCE AND IMPACT OF THE STUDY

The presence of low numbers of E. coli O157:H7 in milk, destined for raw milk cheese manufacture, could constitute a threat to the consumer.

Modeling of combined processing steps for reducing Escherichia coli O157:H7 populations in apple cider

Probabilistic models were used as a systematic approach to describe the response of Escherichia coli O157:H7 populations to combinations of commonly used preservation methods in unpasteurized apple cider. Using a complete factorial experimental design, the effect of pH (3. 1 to 4.3), storage temperature and time (5 to 35 degrees C for 0 to 6 h or 12 h), preservatives (0, 0.05, or 0.1% potassium sorbate or sodium benzoate), and freeze-thaw (F-T; -20 degrees C, 48 h and 4 degrees C, 4 h) treatment combinations (a total of 1,600 treatments) on the probability of achieving a 5-log(10)-unit reduction in a three-strain E. coli O157:H7 mixture in cider was determined. Using logistic regression techniques, pH, temperature, time, and concentration were modeled in separate segments of the data set, resulting in prediction equations for: (i) no preservatives, before F-T; (ii) no preservatives, after F-T; (iii) sorbate, before F-T; (iv) sorbate, after F-T; (v) benzoate, before F-T; and (vi) benzoate, after F-T. Statistical analysis revealed a highly significant (P < 0.0001) effect of all four variables, with cider pH being the most important, followed by temperature and time, and finally by preservative concentration. All models predicted 92 to 99% of the responses correctly. To ensure safety, use of the models is most appropriate at a 0.9 probability level, where the percentage of false positives, i.e., falsely predicting a 5-log(10)-unit reduction, is the lowest (0 to 4.4%). The present study demonstrates the applicability of logistic regression approaches to describing the effectiveness of multiple treatment combinations in pathogen control in cider making. The resulting models can serve as valuable tools in designing safe apple cider processes.

Detection of freeze-injured Escherichia coli O157:H7 cells from foods by resuscitation prior to selective enrichment

We tried to detect Escherichia coli O157:H7 in food samples artificially contaminated with freeze-injured E. coli O157:H7 using an enrichment method with modified EC broth supplemented with novobiocin (mEC + n). When the samples were cultured for enrichment immediately after inoculation of freeze-injured cells, E. coli O157:H7 was not detected in 13 out of 18 samples. However, allowing the food samples to stand for 3 h at room temperature prior to enrichment in mEC + n remarkably improved recovery of E. coli O157:H7 except for some acidic foods. E. coli O157:H7 was detected in the acidic foods by introducing a resuscitation step of 3-h of incubation in a non-selective broth at room temperature prior to enrichment with mEC + n.

Molecular beacon polymerase chain reaction detection of Escherichia coli O157:H7 in milk

A fluorescently labeled oligonucleotide probe (molecular beacon) was applied to detect Escherichia coli O157:H7 in artificially contaminated skim milk during polymerase chain reaction (PCR) amplification of extracted DNA. The probe was designed to hybridize with a region of the slt-II gene coding for the A subunit and to fluoresce when the hairpin-stem conformation was linearized upon hybridization to the target sequence. The molecular beacon was incorporated into PCR reactions containing DNA extracted from artificially contaminated skim milk. The degree of fluorescence was monitored in PCR reactions containing 10(3), 10(5), and 10(7) CFU of E. coli O157:H7 per ml and was found to correlate with the amount of template in each reaction. Fluorescence significantly increased above background levels by cycle 8, 14, or 14 in reactions containing DNA from the 10(7)-, 10(5)-, or 10(3)-CFU/ml template, respectively (P < 0.05). Molecular beacon PCR demonstrated positive results more rapidly than traditional agarose gel electrophoresis analysis of PCR products. Use of molecular beacons allows real-time monitoring of PCR reactions, and the closed-tube format allows simultaneous detection and confirmation of target amplicons without the need for agarose gel electrophoresis and/or Southern blotting. This is the first report of a stem-and-loop molecular beacon being applied for direct detection of a pathogen in food.

Survival of Escherichia coli O157:H7 in buttermilk as affected by contamination point and storage temperature

The effects of contamination point (during fermentation versus postfermentation) and storage temperature (5 and 12 degrees C) were determined for survival of Escherichia coli O157:H7 in fermented buttermilk. E. coli O157:H7 was recovered from buttermilk inoculated during fermentation for 22 days and in buttermilk inoculated postfermentation for 32 days. For storage temperatures of 5 and 12 degrees C, D-values were lower for E. coli O157:H7 inoculated during fermentation (2.5, 2.2 days) than postfermentation (5.6, 4.8 days) (P < 0.05). Developed acidity in inoculated buttermilks was not different from controls (P > 0.05). The extended recovery of viable enterohemorrhagic E. coli O157:H7 from both processing scenarios indicates that the presence of E. coli O157:H7 in buttermilk is not limited to postprocessing contamination.

Effects of acid adaptation, product pH, and heating on survival of Escherichia coli O157:H7 in pepperoni

The thermotolerance of E. coli O157:H7 cells (strain 380-94) heated in pepperoni is reported. Information on the pattern of thermal inactivation of E. coli O157:H7 in pepperoni was applied in the development of heating processes designed to reduce E. coli O157:H7 numbers therein by 5 log(10) units.