Effect of Product Dimensions and Surface Browning Method on Salmonella Contamination in Frozen, Surface-Browned, Breaded Chicken Products Treated with Antimicrobials.

Not-ready-to-eat breaded chicken products formulated with antimicrobial ingredients were tested for the effect of sample dimensions, surface browning method and final internal sample temperature on inoculated Salmonella populations. Fresh chicken breast meat portions (5 × 5 × 5 cm), inoculated with Salmonella (7-strain mixture; 5 log CFU/g), were mixed with (5% v/w total moisture enhancement) (i) distilled water (control), (ii) caprylic acid (CAA; 0.0625%) and carvacrol (CAR; 0.075%), (iii) CAA (0.25%) and ε-polylysine (POL; 0.5%), (iv) CAR (0.15%) and POL (0.5%), or (v) CAA (0.0625%), CAR (0.075%) and POL (0.5%). Sodium chloride (1.2%) and sodium tripolyphosphate (0.3%) were added to all treatments. The mixtures were then ground and formed into 9 × 5 × 3 cm (150 g) or 9 × 2.5 × 2 cm (50 g) portions. The products were breaded, browned in (i) an oven (208 °C, 15 min) or (ii) deep fryer (190 °C, 15 s), packaged, and stored at -20 °C (8 d). Overall, maximum internal temperatures of 62.4 ± 4.0 °C (9 × 2.5 × 2 cm) and 46.0 ± 3.0 °C (9 × 5 × 3 cm) were reached in oven-browned samples, and 35.0 ± 1.1 °C (9 × 2.5 × 2 cm) and 31.7 ± 2.6 °C (9 × 5 × 3 cm) in fryer-browned samples. Irrespective of formulation treatment, total (after frozen storage) reductions of Salmonella were greater (P < 0.05) for 9 × 2.5 × 2 cm oven-browned samples (3.8 to at least 4.6 log CFU/g) than for 9 × 5 × 3 cm oven-browned samples (0.7 to 2.5 log CFU/g). Product dimensions did not (P ≥ 0.05) affect Salmonella reductions (0.6 to 2.8 log CFU/g) in fryer-browned samples. All antimicrobial treatments reduced Salmonella to undetectable levels (<0.3 log CFU/g) in oven-browned 9 × 2.5 × 2 cm samples. Overall, the data may be useful for the selection of antimicrobials, product dimensions, and surface browning methods for reducing Salmonella contamination.

Activity of caprylic acid, carvacrol, ε-polylysine and their combinations against Salmonella in not-ready-to-eat surface-browned, frozen, breaded chicken products.

UNLABELLED: Caprylic acid (CAA), carvacrol (CAR), ε-polylysine (POL), and their combinations were evaluated for reduction of Salmonella contamination in not-ready-to-eat surface-browned, frozen, breaded chicken products. Fresh chicken breast meat pieces (5 × 5 × 5 cm) were inoculated with Salmonella (7-strain mixture; 4-5 log CFU/g) and mixed with distilled water (control) or with CAA, CAR, and POL as single or combination treatments of 2 or 3 ingredients. Sodium chloride (1.2%) and sodium tripolyphosphate (0.3%) were added to all formulations, followed by grinding of the mixtures and forming into 9 × 5 × 3 cm portions. Sample surfaces were brushed with egg whites, coated with breadcrumbs, surface-browned in an oven (208 °C, 15 min), packaged, and stored at -20 °C (7 d). Total reductions of inoculated Salmonella in untreated (control) surface-browned, breaded products after frozen storage were 0.8 to 1.4 log CFU/g. In comparison, single treatments of CAA (0.25% to 1.0%), CAR (0.3% to 0.5%), and POL (0.125% to 1.0%) reduced counts by 2.9 to at least 4.5, 3.4 to at least 4.4, and 1.4 to 2.3 log CFU/g, respectively, depending on concentration. Pathogen counts of products treated with 2- or 3-ingredient combination treatments (0.03125% to 0.25% CAA, 0.0375% to 0.3% CAR, and/or 0.5% POL) were 0.4 to at least 3.3 log CFU/g lower (depending on treatment) than those of the untreated controls. The antimicrobial activity of 2-ingredient combinations comprised of 0.125% CAA, 0.15% CAR, or 0.5% POL was enhanced (P < 0.05) when applied as a 3-ingredient combination (that is, 0.125% CAA + 0.15% CAR + 0.5% POL). These data may be useful for the selection of antimicrobial treatments to reduce Salmonella contamination in not-ready-to-eat processed chicken products. PRACTICAL APPLICATION: Findings from the study may be useful for the selection of suitable antimicrobials, concentrations, and combinations to reduce Salmonella contamination in not-ready-to-eat surface-browned, frozen, breaded chicken products.

Antimicrobials for reduction of Salmonella contamination in uncooked, surface-browned breaded chicken products.

Surface-browned but uncooked frozen breaded chicken products have been associated with salmonellosis outbreaks due to inadequate or no cooking of the products before consumption. This study was conducted to evaluate the effect of three antimicrobials against Salmonella during manufacture of a surface-browned, uncooked frozen breaded chicken meat product. Fresh chicken breast meat portions (5 by 5 by 5 cm) were inoculated (4 to 5 log CFU/g) with Salmonella and mixed with caprylic acid (CAA; 0.5 and 1.0%), carvacrol (CAR; 0.3 and 0.5%), ε-polylysine (POL; 0.125 and 0.25%), or distilled water (control). Sodium chloride (1.2%) and sodium tripolyphosphate (0.3%) were added to all treatments, and the mixtures were ground (5% total moisture enhancement level) and formed into portions (9 by 5 by 3 cm). The products were breaded and surface browned by baking in an oven (208°C for 15 min) or deep frying in vegetable oil (190°C for 15 s), packaged in polyethylene bags, and stored at -20°C for 7 days. Total reductions of inoculated Salmonella in untreated control oven- or fryer-browned products after frozen storage were 1.2 and 0.8 log CFU/g, respectively. In comparison, treatment with CAA, CAR, or POL reduced initial pathogen counts by 3.3 to >4.5, 4.1 to >4.7, and 1.1 to 1.6 log CFU/g, respectively, regardless of the antimicrobial concentration and browning method. Treatment with 1.0% CAA (oven browned) or 0.5% CAR (oven or fryer browned) reduced Salmonella to nondetectable levels (<0.3 log CFU/g) in stored frozen products. These data may be useful for development of suitable antimicrobial treatments to reduce the risk of Salmonella contamination in surface-browned, uncooked frozen breaded chicken products.

Heat and acid tolerance responses of Listeria monocytogenes as affected by sequential exposure to hurdles during growth.

This study aimed to evaluate the effects of the level and sequence of hurdles, applied during growth, on the subsequent heat and acid tolerances of a 10-strain composite of Listeria monocytogenes. Individual strains were grown in glucose-free tryptic soy broth with 0.6% yeast extract (TSBYE-G). Then cultures were mixed and inoculated in fresh TSBYE-G (0.5% NaCl, pH 7.42; control), TSBYE-G that was supplemented with 3% NaCl (3.5% NaCl in total), or TSBYE-G with pH adjusted to 6.01 or 5.04 with lactic acid and incubated at 30 degrees C for 24 h. Furthermore, the culture composite was exposed to the following five combinations of double sequential hurdles (12 h in each at 30 degrees C): NaCl then pH 6.01, NaCl then pH 5.04, pH 7.42 then NaCl, pH 5.04 then NaCl, and pH 6.01 then NaCl. The heat and acid tolerances of the culture were assessed at 57 degrees C (for 2 h) and at pH 3.5 (for 7 h), respectively, in TSBYE-G. No significant (P > or = 0.05) differences in thermotolerance were observed among cultures exposed to various stresses. In contrast, the acid resistance followed the order: pH 6.01 = NaCl > NaCl then pH 5.04 > pH 6.01 then NaCl = pH 5.04 > pH 5.04 then NaCl > pH 7.42 then NaCl > control. The results suggest that exposure of L. monocytogenes to NaCl and low pH during growth may not affect its heat (57 degrees C) tolerance, but it may increase its acid (pH 3.5) resistance, depending on the sequence and intensity of the applied stresses.

Escherichia coli O157:H7 survival, biofilm formation and acid tolerance under simulated slaughter plant moist and dry conditions.

Microorganisms persisting in slaughter plant environments may develop acid resistance and be translocated to other environmental surfaces or products. The objective of this study was to evaluate the potential of Escherichia coli O157:H7 to form biofilms and maintain acid resistance, under different culture habituation scenarios, on stainless steel coupons (2 x 5 x 0.08 cm), in the presence of beef carcass decontamination runoff fluids (washings). Coupons were stored in test tubes with unsterilized water washings (WW; pH 6.94) or lactic acid washings (LAW; pH 4.98), which were inoculated with E. coli O157:H7 (10(3)-10(4)CFU/ml) and incubated at 15 (24 or 48 h) or 35 degrees C (7 or 24 h), simulating different habituation scenarios on sites of a slaughter plant, including sanitation and overnight drying, during consecutive operational shifts. Acid resistance (AR) of planktonic and detached E. coli O157:H7 cells was assessed in tryptic soy broth adjusted to pH 3.5 with lactic acid. The highest pre-drying attachment and AR of E. coli O157:H7 were observed after 24h at 35 degrees C and 48 h at 15 degrees C. Drying reduced (P<0.05) recovery of attached E. coli O157:H7 cells; however, exposure of dried coupons to uninoculated washings allowed recovery of attached E. coli O157:H7, which restored AR, especially under conditions that favored post-drying growth. Exposure of attached cells to 50 ppm PAA for 45 s before drying, as well as habituation in LAW, reduced the recovery and AR of E. coli O157:H7. Therefore, incomplete removal of biofilms may result in cells of increased AR, especially in sites within a slaughter plant, in which liquid meat wastes may remain for long periods of time.

Heat and acid tolerance of Listeria monocytogenes after exposure to single and multiple sublethal stresses.

The majority of published studies on the adaptive heat or acid tolerance response of Listeria monocytogenes have been performed with a single strain exposed to a single adaptation treatment; however, in food ecosystems, microorganisms commonly exist as multi-species communities and encounter multiple stresses, which may result in "stress hardening". Therefore, the present study evaluated the adaptive responses to heat (52, 57 and 63 degrees C) or lactic acid (pH 3.5) of a 10-strain composite of L. monocytogenes meat and human isolates at stationary phase, following exposure to combinations of osmotic (10% NaCl), acidic (pH 5.0 with HCl) and thermal (T; 46 degrees C) stresses, sequentially or simultaneously within 1.5h, in tryptic soy broth with 0.6% yeast extract (TSBYE). All treatments induced adaptive responses on L. monocytogenes at 57 degrees C, while no such cross-protection was observed at 52 and 63 degrees C. Survivor curves at 57 degrees C appeared convex with profound shoulders determined by a Weibull model. The highest thermotolerance was observed after combined exposure to acid and heat shock (pH-T), followed by exposure to osmotic shock, and by the combination of osmotic with heat shock (NaCl-T). Regarding acid tolerance, prior exposure to low pH, pH-T, or a combination of NaCl, pH and T resulted in a marked increase of resistance to pH 3.5, showing concave inactivation curves with tails at higher levels of survivors (log(10)CFU ml(-1)) than the control cultures. The sequence of exposure to sublethal stresses did not affect the thermotolerance of L. monocytogenes, whereas simultaneous exposure to most multiple stresses (e.g., NaCl-pH-T, NaCl-T and NaCl-pH) resulted in higher survivors of L. monocytogenes at pH 3.5 than exposure to the same stresses sequentially. The results indicate that combinations and sequences of sublethal hurdles may affect L. monocytogenes acid and heat tolerance, especially in acidic environments with mild heating or in low moisture environments.

Modeling the effect of storage atmosphere on growth-no growth interface of Listeria monocytogenes as a function of temperature, sodium lactate, sodium diacetate, and NaCl.

The effect of aerobic and anaerobic conditions on growth initiation by a 10-strain composite of Listeria monocytogenes (10(4) CFU/ml) was evaluated in tryptic soy broth with 0.6% yeast extract (TSBYE) as a function of 220 combinations of pH (3.82 to 7.42), sodium lactate (SL) (0 to 10%, vol/vol), and sodium diacetate (SD) (0 to 0.5%, wt/vol) at 10 or 30 degrees C (a slightly abusive and the optimal growth temperature, both above the growth limiting range of 0 to 3 degrees C for L. monocytogenes) in 96-well microplates. In addition, four probability-of-growth models were developed to quantify the effect of 346 aerobic and 346 anaerobic combinations of temperature (4 to 30 degrees C), SL (0 to 6%, vol/vol), and SD (0 to 0.5%, wt/vol) in the presence of NaCl (0.5 or 2.5%, wt/vol) on the growth-no growth responses of the same L. monocytogenes strain composite, with a microplate reader. Growth responses were evaluated turbidimetrically (620 nm) every 5 days for a total of 40 days. Data were modeled with logistic regression to determine the growth-no growth interfaces. The minimum pH values at which growth of L. monocytogenes occurred were higher under anaerobic than under aerobic conditions, and this difference was more evident at 10 degrees C or at higher SL and SD concentrations. The MIC of SD decreased with increasing SL levels. Anaerobic storage reduced the levels of SL-SD, allowing the growth of L. monocytogenes compared with aerobic storage, especially at low temperatures. In the presence of 2.5% NaCl, the MICs for SD were lower than those obtained with 0.5% NaCl, especially at 4 and 10 degrees C, or in the presence of 5 to 6% SL. The developed models for anaerobic incubation showed good performance (80% successful predictions; i.e., in 40 of 50 comparisons) with independent data from studies on survival-growth of L. monocytogenes on meat products. The study provides quantitative data on the antimicrobial activity of SL (0 to 10%) and SD (0 to 0.5%), temperature (4 to 30 degrees C), and pH (3.82 to 7.42) and on the probability of growth of L. monocytogenes under anaerobic or aerobic conditions in the presence of 0.5 or 2.5% NaCl, and hence, addresses important needs for risk assessment activities.

Acid tolerance of acid-adapted and nonacid-adapted Escherichia coli O157:H7 strains in beef decontamination runoff fluids or on beef tissue.

This study assessed the acid tolerance response (ATR) of stationary phase, acid-adapted (tryptic soy broth [TSB]+1% glucose) or nonacid-adapted (glucose-free TSB) Escherichia coli O157:H7 strains (ATCC43889, ATCC43895, ATCC51658 and EO139), grown individually or in a mixed culture, prior to inoculation of beef or meat decontamination runoff (washings) fluids (acidic [pH 4.95] or nonacidic [pH 7.01]). The inoculated beef was left untreated or treated by dipping for 30s in hot water (75 degrees C) followed by 2% lactic acid (55 degrees C). Inoculated beef samples and washings were stored aerobically at 4 or 15 degrees C for 6d, and at set intervals (0, 2, and 6d) were exposed (for 0, 60, 120, and 180min) to pH 3.5 (adjusted with lactic acid) TSB plus 0.6% yeast extract. Overall, there were no significant (P0.05) differences in responses of cultures prepared as individual or mixed strains. Decontamination of meat did not affect the subsequent ATR of E. coli O157:H7 other than resulting in lower initial pathogen levels exposed to acidic conditions. In this study, E. coli O157:H7 appeared to become more tolerant to acid following incubation in acidic washings of sublethal pH (4.89-5.22) compared to nonacidic washings (pH 6.97-7.41) at 4 degrees C or in both types of washings incubated at 15 degrees C. The ATR of the pathogen inoculated into washings was enhanced when cells were previously acid-adapted and incubated at 4 degrees C. Similarly, the ATR on meat was increased by previous acid-adaptation of the inoculum in broth and enhanced by storage at 4 degrees C. Populations on treated meat were consistently lower than those on untreated meat during storage and following exposure to acid. Although on day-0 there were no significant (P0.05) differences in ATR between acid-adapted and nonacid-adapted populations on meat, acid-adapted cells displayed consistently higher resistance through day-6. This suggests that acid-adapted E. coli O157:H7 introduced on meat may become resistant to subsequent lactic acid exposure following storage at 4 degrees C.

Growth and stress resistance variation in culture broth among Listeria monocytogenes strains of various serotypes and origins.

Twenty-five Listeria monocytogenes strains of various serotypes and sources, including clinical and food isolates associated with the same outbreaks, were characterized and compared based on growth rates and heat and acid death rates. Growth was monitored in tryptic soy broth supplemented with 0.6% yeast extract (TSBYE) at 4 and 30 degrees C for 32 days and 20 h, respectively. Heat and acid stress responses in TSBYE heated to 55 degrees C or acidified to pH 3.0 with lactic acid were evaluated for 240 or 120 min, respectively. Extensive variation in growth and stress resistance was observed among the tested strains. Growth rate differences were less evident at 30 than at 4 degrees C, where growth rates (log CFU per milliliter per day) ranged from 0.28 to 0.43. Thermal and acid death rates (log CFU per milliliter per minute) ranged from -0.023 to -0.052 and from -0.012 to -0.134, respectively. Serotype appeared to play a significant role (P < 0.05) only with respect to the heat resistance of the organism. Serotype 4b isolates as a group had lower heat resistance than did isolates representing all other serotypes combined. Although no clear origin-related (food versus clinical) trends were observed under the tested conditions, outbreak-related isolates of serotype 4b had lower acid death rates (higher acid resistance) (P < 0.05) than did the rest of the strains belonging to this serotype. Strain Scott A exhibited slow growth at 4 degrees C and low acid resistance, behavior that was distinct among both clinical and serotype 4b isolates. The results of this study highlight the risks associated with extrapolation to other strains of findings obtained with only one strain of L. monocytogenes. This information should be useful when test strains are to be selected for the evaluation of antimicrobial alternatives in ready-to-eat meat and other food products and when risk assessments are to be conducted.

Fate of inoculated Escherichia coli O157:H7, cultured under different conditions, on fresh and decontaminated beef transitioned from vacuum to aerobic packaging.

This study evaluated the behavior of Escherichia coli O157:H7 during aerobic storage, after storage in vacuum packages, on beef inoculated with cultures prepared (35 degrees C, 24 h) in tryptic soy broth without dextrose (TSB), nonacid hot water carcass decontamination runoff fluids (washings; pH 6.0; WASH), cells from biofilms formed on stainless steel coupons in WASH (WETB), or WETB dried (25 degrees C, 12 h) before harvesting of cells (DRYB). These inocula were applied to fresh beef pieces (40 cm2), which were then left untreated or treated by immersion in hot water (75 degrees C) followed by 2% lactic acid (55 degrees C; hot water/lactic acid [HW/LA]), for 30 s each. Inoculated samples were vacuum packaged and stored at 0 (30, 60, or 90 days), 4 (7 or 14 days), or 12 degrees C (4 or 8 days) and subsequently transferred to retail packages for aerobic storage at 7 degrees C for 5 days. Populations of E. coli O157:H117, regardless of inoculum type, remained generally unchanged (P > 0.05) after aerobic storage (7 degrees C, 5 days) of untreated or HW/LA-treated beef samples previously stored in vacuum packages at 0 or 4 degrees C. However, reductions in E. coli O157:H7 levels were generally obtained when vacuum packaged, untreated beef samples previously stored at 12 degrees C were transitioned to aerobic conditions. Additionally, despite similar (P > 0.05) levels of E. coli O157:H7 cells of TSB, WASH, WETB, and DRYB origin on vacuum-packaged, untreated samples after 8 days of storage at 12 degrees C, subsequent aerobic storage resulted in larger (P < 0.05) reductions of cells of WETB and DRYB origin than for cells of TSB and WASH origin. For HW/LA-treated beef previously stored at 12 degrees C in vacuum packages, populations of E. coli O157:H7 remained largely unchanged after aerobic storage in retail packages. Results thus indicated that aerobic storage of beef (7 degees C, 5 days) previously stored in vacuum packages at 0 or 4 degrees C did not lead to E. coli O157:H7 population changes, whereas transition from vacuum packages stored under mildly abusive temperature (12 degrees C) to aerobic storage may have caused injury and death to the pathogen.

Impact of inoculum preparation and storage conditions on the response of Escherichia coli O157:H7 populations to undercooking and simulated exposure to gastric fluid.

This study evaluated the impact of inoculum preparation and storage conditions on the response of Escherichia coli O157:H7 exposed to consumer-induced stresses simulating undercooking and digestion. Lean beef tissue samples were inoculated with E. coli O157:H7 cultures prepared in tryptic soy broth or meat decontamination runoff fluids (WASH) or detached from moist biofilms or dried biofilms formed on stainless steel coupons immersed in inoculated WASH. After inoculation, the samples were left untreated or dipped for 30 s each in hot (75 degrees C) water followed by lactic acid (2%, 55 degrees C), vacuum packaged, stored at 4 (28 days) or 12 degrees C (16 days), and periodically transferred to aerobic storage (7 degrees C for 5 days). During storage, samples were exposed to sequential heat (55 degrees C; 20 min) and simulated gastric fluid (adjusted to pH 1.0 with HCl; 90 min) stresses simulating consumption of undercooked beef. Under the conditions of this study, cells originating from inocula of planktonic cells were, in general, more resistant to heat and acid than cells from cultures grown as biofilms and detached prior to meat inoculation. Heat and acid tolerance of cells on meat stored at 4 degrees C was lower than that of cells on nondecontaminated meat stored at 12 degrees C, where growth occurred during storage. Decontamination of fresh beef resulted in injury that inhibited subsequent growth of surviving cells at 12 degrees C, as well as in decreases in resistance to subsequent heat and acid stresses. The shift of pathogen cells on beef stored under vacuum at 4 degrees C to aerobic storage did not affect cell populations or subsequent survival after sequential exposure to heat and simulated gastric fluid. However, the transfer of meat stored under vacuum at 12 degrees C to aerobic storage resulted in reduction in pathogen counts during aerobic storage and sensitization of survivors to the effects of sequential heat and acid exposure.

Inactivation of Salmonella during drying and storage of Roma tomatoes exposed to predrying treatments including peeling, blanching, and dipping in organic acid solutions.

The objective of this study was to evaluate the influence of predrying treatments, i.e., peeling, blanching prior to inoculation, and dipping in organic acid solutions, on inactivation of Salmonella during drying (60 degrees C for 14 h) and aerobic storage (25 degrees C for 28 days) of inoculated (five-strain composite, 7.1 to 7.4 log CFU/g) Roma tomato halves. Four predrying treatments groups were established. One group received no treatment (C). In the other three groups, unpeeled-unblanched, unpeeled-blanched (steam blanched at 88 degrees C for 3 min), peeled-unblanched, and peeled-blanched tomato halves were immersed for 10 min in water (W), ascorbic acid solution (AA; 3.40%, pH 2.48), or citric acid solution (CA; 0.21%, pH 2.51). Appropriate dilutions of homogenized tomato samples were spread plated on tryptic soy agar with 0.1% pyruvate and XLT4 agar for bacterial enumeration during drying and storage. Ten minutes of immersion in W, AA, or CA reduced bacterial populations by 0.7 to 1.6 log CFU/g. After 14 h of dehydration, total log reductions in the populations of bacteria were 3.2 to 4.5 (C), 3.7 to 4.9 (W), > 5.6 to > 6.1 (AA), and 4.5 to 5.5 (CA) log CFU/g, depending on type of agar used and condition of tomato samples. During drying and storage, the order of pathogen inactivation for predrying dipping treatments was AA > CA > W > C, with AA and CA rendering bacterial populations below detectable levels ( < 1.3 log CFU/g) prior to storage and between 7 and 14 days of storage, respectively. The results also indicated that peeling and blanching of tomatoes prior to inoculation may not necessarily affect destruction of Salmonella during the drying process. Use of predrying acid dipping treatments of tomatoes, especially in AA, may improve destruction of Salmonella during the dehydration process.

Survival of acid-adapted or nonadapted Escherichia coli O157:H7 in apple wounds and surrounding tissue following chemical treatments and storage.

This study evaluated survival/growth of acid-adapted or nonadapted Escherichia coli O157:H7 inoculated (4 log CFU/wound) in wounds (10 mm deepx6 mm diameter) of apples. Wounds were inoculated with a green fluorescent protein (GFP)-expressing derivative of a rifampicin-resistant strain of E. coli O157:H7 ATCC 43895 and allowed to attach (1 h). Apples were dipped (2 min) in solutions (approximately 25 degrees C) of water (W), 5% acetic acid (AA), 5% hydrogen peroxide (HP), 0.02% sodium hypochlorite (SH), or not treated (NT), and stored at 25 degrees C. Survivors were determined in cores (10-mm deep) of the apple wounds (12 mm from center of wound; inner core) and surrounding tissue (18 mm from center of wound; outer core) after homogenizing the samples in Dey-Engley (D/E) neutralizing broth and plating on tryptic soy agar (TSA) and TSA supplemented with 100 microg/ml rifampicin (35 degrees C, 48 h) after 0, 2 and 5 days. Average bacterial populations at day-0 were 4.0 and 2.0 logs in the inner and outer core, respectively. In the inner core of the untreated apples populations increased to 7.0 logs at day-2, while counts did not exceed 3.0 logs in the outer core during storage of all treatments. Previous acid-adaptation of the cultures did not affect survival of the pathogen. Dipping in W, AA and SH did not reduce initial bacterial populations, while at day-2 of storage inner core counts from W, AA and SH reached 7.1, 5.5 and 6.9 logs, respectively. In contrast, HP reduced initial counts in the inner core by approximately 1.5 logs, but they increased to 7.0 logs by day-2. Populations of all treatments reached 6.6-7.2 logs in the inner core by day-5. Thus, sanitizer treatment did not effectively reduce nor inhibit growth of E. coli O157:H7 contamination in apple wounds and surrounding tissue.

Influence of extended acid stressing in fresh beef decontamination runoff fluids on sanitizer resistance of acid-adapted Escherichia coli O157:H7 in biofilms.

This study evaluated resistance to sanitizing solutions of Escherichia coli O157:H7 cells forming biofilms on stainless steel coupons exposed to inoculated meat decontamination runoff fluids (washings). A previously acid-adapted culture of a rifampicin-resistant derivative of E. coli O157:H7 strain ATCC 43895 was inoculated in unsterilized or sterilized combined hot-water (85 degrees C) and cold-water (10 degrees C) (50/50 [vol/vol]) composite water (W) washings (pH 6.29 to 6.47) and in W washings mixed with 2% acetic acid (pH 4.60 to 4.71) or in 2% lactic acid W washings (pH 4.33 to 4.48) at a ratio of 1/99 (vol/vol). Stainless steel coupons (2 by 5 by 0.08 cm) were submerged in the inoculated washings and stored for up to 14 days at 15 degrees C. Survival of E. coli O157:H7 was determined after exposure (0 to 60 s for cells in suspension and 0 to 300 s for attached cells) to two commercial sanitizers (150 ppm peroxyacetic acid and 200 ppm quaternary ammonium compound) at 2, 7, and 14 days. E. coli O157:H7 attached more rapidly to coupons submerged in washings containing the natural flora than to those without. The attached cells were more resistant to the effects of the sanitizers than were the cells in suspension, and survival was highest in the presence of the natural flora. Attached cells in the presence of dilute acid washings were more sensitive to subsequent sanitizer treatments than were cells generated in the presence of W washings. Under the conditions of this study, cells of E. coli O157:H7 in W washings were more sensitive to acidic (peroxyacetic acid) than to alkaline (quaternary ammonium) sanitizers during storage. These results suggest that meat processing plants that apply no decontamination or that use only water washings of meat should consider using acidic sanitizers to enhance biofilm removal. Plants that apply both water and acidic washings may create a sublethal acid-stressing environment in the runoff fluids, sensitizing biofilm cells to subsequent sanitizing treatments.