Fate of Listeria monocytogenes during freezing, thawing and home storage of frankfurters.

Little information is available regarding the fate of Listeria monocytogenes during freezing, thawing and home storage of frankfurters even though recent surveys show that consumers regularly store unopened packages in home freezers. This study examined the effects of antimicrobials, refrigerated storage, freezing, thawing method, and post-thawing storage (7 degrees C) on L. monocytogenes on frankfurters. Inoculated (2.1 log CFU/cm(2)) frankfurters formulated without (control) or with antimicrobials (1.5% potassium lactate plus 0.1% sodium diacetate) were vacuum-packaged, stored at 4 degrees C for 6 or 30 d and then frozen (-15 degrees C) for 10, 30, or 50 d. Packages were thawed under refrigeration (7 degrees C, 24 h), on a countertop (23 +/- 2 degrees C, 8 h), or in a microwave oven (2450 MHz, 1100 watts, 220 s followed by 120 s holding), and then stored aerobically (7 degrees C) for 14 d. Bacterial populations were enumerated on PALCAM agar and tryptic soy agar plus 0.6% yeast extract. Antimicrobials completely inhibited (p < 0.05) growth of L. monocytogenes at 4 degrees C for 30 d under vacuum-packaged conditions, and during post-thawing aerobic storage at 7 degrees C for 14 d. Different intervals between inoculation and freezing (6 or 30 d) resulted in different pathogen levels on control frankfurters (2.1 or 3.9 log CFU/cm(2), respectively), while freezing reduced counts by <1.0 log CFU/cm(2). Thawing treatments had little effect on L. monocytogenes populations (<0.5 log CFU/cm(2)), and post-thawing fate of L. monocytogenes was not influenced by freezing or by thawing method. Pathogen counts on control samples increased by 1.5 log CFU/cm(2) at d-7 of aerobic storage, and reached 5.6 log CFU/cm(2) at d-14. As indicated by these results, consumers should freeze frankfurters immediately after purchase, and discard frankfurters formulated without antimicrobials within 3 d of thawing and/or opening.

Modeling the effect of inoculum size and acid adaptation on growth/no growth interface of Escherichia coli O157:H7.

The objective of this study was to model with logistic regression the growth/no growth interface of different initial inoculation levels (10(1), 10(3) and 10(5) CFU/ml; study 1), or nonadapted vs acid-adapted (study 2) Escherichia coli O157:H7 as influenced by pH, NaCl concentration and incubation temperature. Study 1 was conducted with a mixture of four E. coli O157:H7 strains grown (35 degrees C, 24 h) in tryptic soy broth (TSB). Study 2 was conducted with the same mixture of four E. coli O157:H7 strains grown (35 degrees C, 24 h) in glucose-free TSB with 1% added glucose (final pH 4.83), or in diluted lactic acid meat decontamination runoff fluids (washings; final pH 4.92), or nonadapted cultures prepared in glucose-free TSB (final pH 6.45), or in water washings (final pH 6.87). Parameters included incubation temperature (10-35 degrees C), pH (3.52-7.32), and NaCl concentration (0-10% w/v). Growth responses were evaluated for 60 days turbidimetrically (610 nm) every 5 days in 160 (study 1) and 360 (study 2) combinations in quadruplicate samples, with a microplate reader. The lower the initial inoculum the higher were the minimum pH and a(w) values permitting growth. Differences in the pH and a(w) growth limits among inoculum concentrations increased at 15 and 10 degrees C. Acid-adapted cultures were able to grow at lower pH than nonadapted cultures, while at temperatures below 25 degrees C, growth initiation of nonadapted cultures stopped at higher a(w) compared to acid-adapted cultures for the whole pH range of 3.52 to 7.32. A comparison with available data indicated that our model for acid-adapted E. coli O157:H7 in different environments may provide representative growth probabilities covering both nonadapted and stress-adapted contaminants.

Effects of stage of the cycle and estradiol-17 beta on oxytocin synthesis by ovine granulosa and luteal cells.

Individual ovine follicles or corpora lutea (CL) were obtained at different stages of the estrous cycle to compare the pattern of oxytocin synthesis with time in vitro. Granulosa cells from follicles in the early follicular phase produced minimal amounts of oxytocin whereas output from preovulatory (post LH surge) follicles increased to a peak of 540 pg/10(4) cells.24 h on days 4-7 in vitro declining to 180 pg/10(4) cells.24 h by day 11. Production from day 1 CL was also high, peaking at 1639 pg/10(4) cells.24 h. In contrast the capacity for oxytocin synthesis by day 2 CL had already declined, with peak output reaching only 185 pg/10(4) cells.24 h on days 3-4. Day 9 CL produced small amounts of oxytocin (50 pg/10(4) cells in the first 24 h) followed by a low output thereafter. The effect of estradiol-17 beta (E2 beta) on oxytocin synthesis was examined. The results were dependent on the stage of the cycle at which the cells were obtained. Oxytocin production was significantly stimulated in three and inhibited in four out of nine preovulatory follicles by the addition of 50 or 500 ng/ml E2 beta, whereas in days 1 and 2 CL E2 beta consistently inhibited oxytocin synthesis and in day 9 CL no response was found. These data indicate that the ovarian capacity to synthesize oxytocin varies markedly at different stages of the cycle, and that cells obtained close to ovulation do not experience the rapid down-regulation in oxytocin synthesis which occurs in vivo in the early luteal phase. E2 beta may switch from having a stimulatory to an inhibitory action on oxytocin synthesis shortly before ovulation.

Localization of messenger ribonucleic acids for insulin-like growth factor I (IGF-I), IGF-II, and the type 1 IGF receptor in the ovine ovary throughout the estrous cycle.

The distribution pattern of messenger RNAs (mRNAs) for insulin-like growth factor I (IGF-I), IGF-II, and the type 1 IGF receptor and the detection of IGF-binding sites in sections of ovine ovary were demonstrated using in situ hybridization and autoradiography. Ovaries were collected from 30 ewes at time points throughout the estrous cycle. Luteal IGF-II mRNA and IGF-binding site concentrations altered significantly during the cycle, peaking on day 8 (midluteal phase; P < 0.01) and day 15 (late luteal phase; P < 0.001), respectively. In contrast, mRNA expression for IGF-I and the type 1 IGF receptor in the corpus luteum was low and did not vary. IGF-binding sites and mRNAs for IGF-II and the type 1 IGF receptor were also present at low and constant concentrations in ovarian stroma. There was no detectable follicular expression of IGF-I mRNA, although there were high concentrations of IGF-II and the type 1 IGF receptor mRNAs, which both varied significantly with follicular size (P < 0.001 and 0.01, respectively), with the highest concentrations in small follicles (< 2 mm in diameter). Follicular IGF-II expression was confined to the theca, whereas the type 1 IGF receptor was present in both theca and granulosa. IGF-binding site concentrations were significantly higher (P < 0.01) in atretic than healthy follicles, but were uninfluenced by follicular size. These results suggest that IGF-II, in contrast to IGF-I, appears to be the most significant IGF in luteal and, particularly, follicular development in the ewe.

A comparison of nutrient-based and exchange-group methods of diet instruction for patients with noninsulin-dependent diabetes.

This study compared effectiveness of nutrient-based (Diet Guide) vs food-group (Exchange Lists) methods of diabetic diet evaluation in improving dietary compliance, glycemic control, and biochemical indicators of heart disease risk. Eighty-three persons with noninsulin-dependent diabetes were taught one of two diet-planning methods in a 3-session workshop. Both methods led to reductions in energy intake and percent of calories from fat and saturated fatty acids in 6 mo postworkshop. Reductions in fat intake were greater and more long lasting for persons using Diet Guide than using Exchange Lists method of diet planning. Despite dietary changes, neither diet-planning method led to significant decreases in weight or skinfold thickness. Few differences were seen in clinical measurements pre- and 6 mo postworkshop. Total and LDL cholesterol values were lower than preworkshop values for men in both groups. Suggestions are given for improving effectiveness of both diet-planning methods.

Regional differences in catecholamine concentrations in bovine ovaries analysed by high-performance liquid chromatography.

Bovine corpora lutea and ovarian stroma were analysed by high-performance liquid chromatography for catecholamine content. High concentrations (up to 102 nmol/g wet weight) were found in both 'central' stroma, containing many blood vessels, and 'peripheral' stroma. Central stroma contained noradrenaline and some dopamine, whereas peripheral stroma contained a higher proportion of dopamine and also significant amounts of 3,4-dihydroxyphenylacetic acid (DOPAC). Occasional samples of stroma had very high amounts of dopamine, suggesting that it is stored in specific regions. Corpora lutea, although devoid of direct innervation, contained dopamine (up to 5.3 nmol/g) and noradrenaline (up to 1.2 nmol/g). The average dopamine:noradrenaline molar ratio was 1.19:1 and the concentrations of dopamine and noradrenaline were highly correlated (P less than 0.002). The concentration of dopamine was significantly higher in the early luteal phase of the oestrous cycle than during the rest of the cycle or in pregnancy. The levels of noradrenaline and dopamine present in corpora lutea are sufficient to modulate the production of both oxytocin and progesterone by luteal cells in vitro.

Peptides derived from pro-opiocortin in the pituitary gland of the dogfish, Squalus acanthias.

Combined rostral, median and neurointermediate lobes from 650 pituitary glands of the dogfish Squalus acanthias were extracted in 0.1 M-HCl and subjected to filtration on Sephadex G-50. Fractions were monitored for ACTH, alpha-MSH, gamma-MSH and endorphin by heterologous radioimmunoassay, corticotrophin-like intermediate lobe peptide (CLIP) and gamma-MSH by homologous radioimmunoassay, and methionine enkephalin after enzymatic digestion. The majority (about 99%) of the immunoreactivity detected was present as small peptides, with alpha-MSH, CLIP and gamma-MSH predominant. The single peaks of ACTH, alpha-MSH and CLIP contrasted with many distinct peaks of endorphin-like immunoreactivity. The gamma-MSH radioimmunoassays monitored different peptides; the heterologous assay revealed a single major peak, while the homologous assay detected a number of distinct small peptides. The results suggested that there may be more than three distinct forms of MSH in the dogfish pituitary gland. Small amounts of much larger proteins were detected by a number of the radioimmunoassays, suggesting that peptides related to ACTH, gamma-MSH and lipotrophin are derived from common pro-opiocortin-type precursor molecules in this phylogenetically ancient cartilaginous fish.

Two vasopressin-like peptides in the pig testis?

Vasopressin (VP)-like immunoreactivity (IR) has been located in the testes of several species of mammal. There is evidence that most of this IR in the rat does not represent authentic arginine vasopressin (AVP) and that a second AVP-like peptide may exist. We have studied testis samples from the pig, which produces lysine vasopressin (LVP) in its pituitary, and have found both LVP- and AVP-like IR. High-performance liquid chromatography (HPLC) of testis extracts showed two peaks of VP-IR. The first peak co-eluted with authentic LVP and was recognized only by antisera which cross-reacted with LVP. The second peak co-eluted with authentic AVP and was recognized by antisera raised against AVP. Both VP-like peptides bound to a neurophysin affinity column and the HPLC elution profiles of the bound peptides were similar to those of the authentic hormones. When the LVP-like material was oxidized with performic acid, a peak of IR running in the same position as oxidized authentic LVP on HPLC was produced. Similarly, the performic acid-oxidized AVP-like material co-eluted with oxidized authentic AVP. The presence of both LVP- and AVP-like peptides in the pig testis may mean that more than one gene is involved. A second VP-like gene could also explain the anomalies of VP-IR in other species.

Is in vitro expansion of human cord blood cells clinically relevant?

Peripheral blood recovery after cord blood (CB) transplantation is delayed compared with marrow. Expansion of CB haemopoietic cells has been investigated with the aim of reducing cytopenia following transplantation. Mature cells, post-progenitors, progenitors and long-term culture-initiating cells (LTC-IC) from expansion products may contribute to peripheral blood recovery. We investigated the increase in total nucleated cells, colony-forming cells (CFC), CD34+ cells and LTC-IC by limiting dilution after a 14 day culture of CB CD34+ cells (5 x 10(3)/ml) with SCF, IL-3, IL-6, GM-CSF and G-CSF all at 10 ng/ml. On average, nucleated cells increased 2500-fold, CD34+ cells 39-fold and CFU-GM 49-fold with maintenance of BFU-E. The more primitive LTC-IC expanded on average 2.5-fold but effects on long-term marrow-repopulating cells (LTRC) during culture are unknown. A practical application of in vitro expansion of CB might be to expand a 20% aliquot of a CB donation and infuse the remainder unmanipulated. This could provide a 5- to 7-fold increase in progenitor cells, an estimated 1570-fold increase in post-progenitor cells and maintenance of LTC-IC compared to an untreated donation. Combined with in vivo post-transplant growth factor therapy this could prompt early peripheral blood recovery after CB transplantation, without significant loss of LTC-IC or donor lymphocytes.

Clinical application of in vitro expansion of cord blood.

Expansion of cord blood (CB) haemopoietic cells has been investigated with the aim of reducing cytopenia following transplantation. We investigated the increase in total nucleated cells, colony-forming cells (CFC), CD34+ cells and long-term culture-initiating cells (LTC-IC) by limiting dilution after a 14-day culture of CB CD34+ cells (5 x 10(3)/ml) with SCF, IL-3, IL-6, GM-CSF and G-CSF all at 10 ng/ml. On average nucleated cells increased 2500-fold, CD34+ cells 39-fold and CFU-GM 49-fold with maintenance of BFU-E. The more primitive LTC-IC expanded on average 2.5-fold. Expansion of a 20% aliquot of a CB donation could provide a 5-7-fold increase in progenitor cells, and a 1570-fold increase in post-progenitor cells compared to an untreated donation.

Optimal cryopreservation of human umbilical cord blood.

Cryopreservation techniques for umbilical cord blood (UCB) have been based on methods established for marrow (BM) and peripheral blood progenitor cells (PBPC) with varying degrees of success. The aim of this study was to optimise cryopreservation of UCB haemopoietic cells based on sound cryopreservation principles. UCB samples were cryopreserved with different combinations of DMSO and hydroxyethyl starch (HES) by a variety of freezing protocols. After cooling at 1 degree C/min in solutions containing 4% HES and various concentrations of DMSO there was a dramatic fall in CD34+ recovery from 85.4% (s.d. 28.4) to 12.2% (s.d. 10.0) as DMSO concentration was reduced from 5 to 2.5%. Varying HES concentration in solutions containing 5% DMSO did not have a significant effect on CD34+ cell recovery. Increasing cooling rate from 1 to 10 degrees C/min significantly reduced CD34+ recovery (P < 0.0001) while increasing DMSO concentration up to 10% had little effect (P = 0.8, two-way ANOVA). Good recovery of UCB CD34+ cells can be achieved with 5-10% DMSO at a controlled cooling rate of 1 degrees C/min. There was a significant difference (P < 0.0001) in the apparent recovery of CD34+ cells between paired aliquots thawed in the presence (recovery = 76.8%, s.d. 26.0) and absence (32.5%, s.d. 18.7) of DNase. In conclusion, conditions for cryopreserving UCB for clinical banking that yield optimal recovery of CD34+ cells have been established.

Educating patients with diabetes: comparison of nutrient-based and exchange group methods.

This study compared the effectiveness of a nutrient-based (diet guide) approach with that of a food-group (exchange lists) approach to menu planning for persons with noninsulin-dependent diabetes. Each method was presented to four groups in three-session workshops emphasizing meal planning to reduce risk of heart disease. The diet guide method evaluated menus specifically for calories, source of calories, cholesterol, fiber, sodium, and key vitamins and minerals. Of 105 subjects recruited, 97 completed the workshops and 83 the 6-month follow-up. Subjects responded positively to the diet guide method, finding it as easy to use as the exchange lists method. Menu planning and evaluation initially took longer using the diet guide than the exchange group method (25 vs. 16 minutes per day), but subjects indicated that time was well spent. Also, with practice, the time required to use the diet guide method decreased to 17 minutes per day. Both diet-education programs improved attitude and knowledge regarding diabetes, diet, and nutrition, with retention of knowledge gained for up to 6 months. Increases in applied nutrition knowledge scores were significantly greater, however, for diet guide than for exchange lists subjects both 3 months (24% vs. 15% increase) and 6 months postworkshop (15% vs. 8% increase). We conclude that the diet guide method can effectively serve as an alternative menu-planning system to exchange lists for patients with noninsulin-dependent diabetes who have at least a high school education.

College students with diabetes: using focus groups and interviews to determine psychosocial issues and barriers to control.

College students with diabetes are at risk for improvised diabetes care due to their age, newly acquired independence, and erratic schedules. The purpose of this study was to employ focus groups and interviews to identity factors that affect the ability of these students to engage in appropriate self-care behaviors. Focus group and interview questions were developed to address variables of the Expanded Health Belief Model. Two focus groups and fifteen interviews were conducted. Barriers to successful diabetes management were time management, stress hypoglycemic reactions, diet management constraints, and inadequate finances. Several psychosocial issues that affected successful management also were identified. These issues were grouped into three categories: (1) inconveniences of diabetes management, (2) motivators to managing diabetes, and (3) social support issues. The findings show the value of formative evaluation that can then be used to design diabetes education programs to meet clients' perceived needs.

Development and evaluation of an intervention program: "Control on Campus".

PURPOSE: This study was designed to develop and test an intervention for college students with type 1 diabetes. METHODS: A diabetes program, "Control on Campus," and guide were developed based on the Expanded Health Belief Model and Social Learning Theory. Diabetes knowledge, attitudes, and behaviors were assessed preprogram, postprogram, and at follow-up for 3 intervention cohorts and a control group. RESULTS: Reporting of HbA1c values and diabetes knowledge improved significantly as a result of the intervention compared with no increase in the control group. Furthermore, participants reported feeling more support on campus after the intervention, appeared to have overcome their fears associated with testing their blood glucose, reported an increased frequency of blood glucose testing, and were more likely to test when they felt their blood glucose level was low. CONCLUSIONS: Overall, this research yielded substantial insight into the characteristics of college students with diabetes and was successful in designing and evaluating an intervention trial for this population.

Ascorbic acid enhances destruction of Escherichia coli O157:H7 during home-type drying of apple slices.

Destruction of Escherichia coli O157:H7 was evaluated on inoculated apple slices dehydrated at two temperatures with and without application of predrying treatments. Half-ring slices (0.6 cm thick) of peeled and cored Gala apples were inoculated by immersion for 30 min in a four-strain composite inoculum of E. coli O157:H7. The inoculated slices (8.7 to 9.4 log CFU/g) either received no predrying treatment (control), were soaked for 15 min in a 3.4% ascorbic acid solution, or were steam blanched for 3 min at 88 degrees C immediately prior to drying at 57.2 or 62.8 degrees C for up to 6 h. Samples were plated on tryptic soy (TSA) and sorbitol MacConkey (SMAC) agar media for direct enumeration of surviving bacterial populations. Steam blanching changed initial inoculation levels by +0.3 to -0.7 log CFU/g, while immersion in the ascorbic acid solution reduced the inoculation levels by 1.4 to 1.6 log CFU/g. Dehydration of control samples for 6 h reduced mean bacterial populations by 2.9 log CFU/g (TSA or SMAC) at 57.2 degrees C and by 3.3 (SMAC) and 3.5 (TSA) log CFU/g at 62.8 degrees C. Mean decreases from initial inoculum levels for steam-blanched slices after 6 h of drying were 2.1 (SMAC) and 2.0 (TSA) log CFU/g at 57.2 degrees C, and 3.6 (TSA or SMAC) log CFU/g at 62.8 degrees C. In contrast, initial bacterial populations on ascorbic acid-pretreated apple slices declined by 5.0 (SMAC) and 5.1 (TSA) log CFU/g after 3 h of dehydration at 57.2 degrees C, and by 7.3 (SMAC) and 6.9 (TSA) log CFU/g after 3 h at 62.8 degrees C. Reductions on slices treated with ascorbic acid were in the range of 8.0 to 8.3 log CFU/g after 6 h of drying, irrespective of drying temperature or agar medium used. The results of immersing apple slices in a 3.4% ascorbic acid solution for 15 min prior to drying indicate that a predrying treatment enhances the destruction of E. coli O157:H7 on home-dried apple products.

Fate of Escherichia coli O157:H7, Salmonella typhimurium DT 104, and Listeria monocytogenes in fresh meat decontamination fluids at 4 and 10 degrees C.

Bacterial pathogens may colonize meat plants and increase food safety risks following survival, stress hardening, or proliferation in meat decontamination fluids (washings). The objective of this study was to evaluate the ability of Escherichia coli O157:H7, Salmonella Typhimurium DT 104, and Listeria monocytogenes to survive or grow in spray-washing fluids from fresh beef top rounds sprayed with water (10 or 85 degrees C) or acid solutions (2% lactic or acetic acid, 55 degrees C) during storage of the washings at 4 or 10 degrees C in air to simulate plant conditions. Inoculated Salmonella Typhimurium DT 104 (5.4 +/- 0.1 log CFU/ml) died off in lactate (pH 2.4 +/- 0.1) and acetate (pH 3.1 +/- 0.2) washings by 2 days at either storage temperature. In contrast, inoculated E. coli O157:H7 (5.2 +/- 0.1 log CFU/ml) and L. monocytogenes (5.4 +/- 0.1 log CFU/ml) survived in lactate washings for at least 2 days and in acetate washings for at least 7 and 4 days, respectively; their survival was better in acidic washings stored at 4 degrees C than at 10 degrees C. All inoculated pathogens survived in nonacid (pH > 6.0) washings, but their fate was different. E. coli O157:H7 did not grow at either temperature in water washings, whereas Salmonella Typhimurium DT 104 failed to multiply at 4 degrees C but increased by approximately 2 logs at 10 degrees C. L. monocytogenes multiplied (0.6 to 1.3 logs) at both temperatures in water washings. These results indicated that bacterial pathogens may survive for several days in acidic, and proliferate in water, washings of meat, serving as potential cross-contamination sources, if pathogen niches are established in the plant. The responses of surviving pathogens in meat decontamination waste fluids to acid or other stresses need to be addressed to better evaluate potential food safety risks.

Acid adaptation does not promote survival or growth of Listeria monocytogenes on fresh beef following acid and nonacid decontamination treatments.

The objective of this study was to evaluate the survival and growth of acid-adapted and nonadapted Listeria monocytogenes inoculated onto fresh beef subsequently treated with acid or nonacid solutions. Beef slices (2.5 by 5 by 1 cm) from top rounds were inoculated with acid-adapted or nonadapted L. monocytogenes (4.6 to 5.0 log CFU/cm2) and either left untreated (control) or dipped for 30 s in water at 55 degrees C, water at 75 degrees C, 2% lactic acid at 55 degrees C, or 2% acetic acid at 55 degrees C. The beef slices were vacuum packaged and stored at 4 or 10 degrees C and were analyzed after 0, 7, 14, 21, and 28 days of storage. Dipping in 75 degrees C water, lactic acid, and acetic acid resulted in immediate pathogen reductions of 1.4 to 2.0, 1.8 to 2.6, and 1.4 to 2.4 log CFU/cm2, respectively. After storage at 10 degrees C for 28 days, populations of L. monocytogenes on meat treated with 55 degrees C water increased by ca. 1.6 to 1.8 log CFU/cm2. The pathogen remained at low population levels (1.6 to 2.8 log CFU/cm2) on acid-treated meat, whereas populations on meat treated with 75 degrees C water increased rapidly, reaching levels of 3.6 to 4.6 log CFU/cm2 by day 14. During storage at 4 degrees C, there was no growth of the pathogen for at least 21 days in samples treated with 55 and 75 degrees C water, and periods of no growth were longer for acid-treated samples. There were no differences between acid-adapted and nonadapted organisms across treatments with respect to survival or growth. In conclusion, the dipping of meat inoculated with L. monocytogenes into acid solutions reduced and then inhibited the growth of the pathogen during storage at 4 and 10 degrees C, while dipping in hot water allowed growth despite initial reductions in pathogen contamination. The results of this study indicate a residual activity of acid-based decontamination treatments compared with water-based treatments for refrigerated (4 degrees C) or temperature-abused (10 degrees C) lean beef tissue in vacuum packages, and these results also indicate that this activity may not be counteracted by prior acid adaptation of L. monocytogenes.

Comparative analysis of acid resistance between susceptible and multi-antimicrobial-resistant Salmonella strains cultured under stationary-phase acid tolerance-inducing and noninducing conditions.

This study compared acid resistance levels among five antimicrobial-susceptible strains of Salmonella and five strains that were simultaneously resistant to a minimum of six antimicrobial agents. The induction of a stationary-phase acid tolerance response (ATR) was attempted by both transient low-pH acid shock and acid adaptation. For acid shock induction, strains were grown for 18 h in minimal E medium containing 0.4% glucose (EG medium) and exposed to sublethal acid stress (pH 4.3) for 2 h, and subsequently, both shocked and nonshocked cultures were acid challenged (pH 3.0) for 4 h. Acid adaptation was achieved by growing strains for 18 h in tryptic soy broth containing 1.0% glucose (TSB+G), while nonadapted cultures were grown for 18 h in glucose-free tryptic soy broth (TSB-G). Acid-adapted and nonadapted inocula were acid challenged (pH 2.3) for 4 h. Initial (0 h) mean populations of nonchallenged Salmonella were 8.5 to 8.7, 8.4 to 8.8, and 8.2 to 8.3 log CFU/ml for strains grown in EG medium, TSB-G, and TSB+G, respectively. After 4 h of acid challenge, mean populations were 3.0 to 4.8 and 2.5 to 3.7 log CFU/ml for previously acid-shocked susceptible and resistant strains, respectively, while corresponding counts for nonshocked strains were 4.3 to 5.5 log CFU/ml and 3.9 to 4.9 log CFU/ml. Following 4 h of acid exposure, acid-adapted cultures of susceptible and resistant strains had mean populations of 6.1 to 6.4 log CFU/ml and 6.4 to 6.6 log CFU/ml, respectively, while corresponding counts for nonadapted cultures were 1.9 to 2.1 log CFU/ml and 1.8 to 2.0 log CFU/ml, respectively. A low-pH-inducible ATR was not achieved through transient acid shock, while an ATR was evident following acid adaptation, as adapted populations were 4.2 to 4.8 log units larger than nonadapted populations following acid exposure. Although some strain-dependent variations in acid resistance were observed, results from this study suggest no association between susceptibility to antimicrobial agents and the ability of the Salmonella strains evaluated to survive low-pH stress.

Biofilm formation by acid-adapted and nonadapted Listeria monocytogenes in fresh beef decontamination washings and its subsequent inactivation with sanitizers.

The antimicrobial effects of sodium hypochlorite (SH, 200 ppm, at an adjusted pH of 6.80 +/- 0.20 and at an unadjusted pH of 10.35 +/- 0.25), quaternary ammonium compound (pH 10.20 +/- 0.12, 200 ppm), and peroxyacetic acid (PAA, pH 3.45 +/- 0.20, 150 ppm) on previously acid-adapted or nonadapted Listeria monocytogenes inoculated (10(5) CFU/ml) into beef decontamination water washings were evaluated. The effects of the sanitizers on suspended cells (planktonic or deattached) and on cells attached to stainless steel coupons obtained from inoculated washings stored at 15 degrees C for up to 14 days were studied. Cells were exposed to sanitizers on days 2, 7, and 14. The pathogen had formed a biofilm of 5.3 log CFU/cm2 by day 2 of storage (which was reduced to 4.6 log CFU/cm2 by day 14), while the total microbial populations showed more extensive attachment (6.1 to 6.6 log CFU/cm2). The sanitizers were more effective in reducing populations of cells in suspension than in reducing populations of attached cells. Overall, there were no differences between previously acid-adapted and nonadapted L monocytogenes with regard to sensitivity to sanitizers. The total microbial biofilms were the most sensitive to all of the sanitizers on day 2, but their resistance increased during storage, and they were at their most resistant on day 14. Listeria monocytogenes displayed stronger resistance to the effects of the sanitizers on day 7 than on day 2 but had become sensitized to all sanitizers by day 14. SH at the adjusted pH (6.80) (ASH) was generally more effective in reducing bacterial populations than was SH at the unadjusted pH. PAA generally killed attached cells faster at 30 to 300 s of exposure than did the other sanitizers, except for ASH on day 2. PAA was more effective in killing attached cells than in killing cells treated in suspension, in contrast to the other sanitizers.

Control of Listeria monocytogenes on frankfurters with antimicrobials in the formulation and by dipping in organic acid solutions.

The antilisterial activity of sodium lactate (SL) and sodium diacetate (SD) was evaluated in a frankfurter formulation and in combination with a dipping treatment into solutions of lactic acid or acetic acid after processing and inoculation. Pork frankfurters were formulated with 1.8% SL or 0.25% SD or combinations of 1.8% SL with 0.25 or 0.125% SD. After processing, frankfurters were inoculated (2 to 3 log CFU/cm2) with a 10-strain composite of Listeria monocytogenes and left undipped or were dipped (2 min) in 2.5% solutions of lactic acid or acetic acid (23 +/- 2 degrees C) before vacuum packaging and storage at 10 degrees C for 40 days. Total microbial populations and L. monocytogenes, lactic acid bacteria, and yeasts and molds were enumerated during storage. Sensory evaluations also were carried out on frankfurters treated and/or formulated with effective antimicrobials. The combination of 1.8% SL with 0.25% SD provided complete inhibition of L. monocytogenes growth throughout storage. Dipping in lactic acid or acetic acid reduced initial populations by 0.7 to 2.1 log CFU/cm2, but during storage (12 to 20 days), populations on dipped samples without antimicrobials in the formulation reached 5.5 to 7.9 log CFU/cm2. For samples containing single antimicrobials and dipped in lactic acid or acetic acid, L. monocytogenes growth was completely inhibited or reduced over 12 and 28 days, respectively, whereas final populations were lower (P < 0.05) than those in undipped samples of the same formulations. Bactericidal effects during storage (reductions of 0.6 to 1.0 log CFU/ cm2 over 28 to 40 days) were observed in frankfurters containing combinations of SL and SD that were dipped in organic acid solutions. Inclusion of antimicrobials in the formulation and/or dipping the product into organic acid solutions did not affect (P > 0.05) the flavor and overall acceptability of products compared with controls. The results of this study may be valuable to meat processors as they seek approaches for meeting new regulatory requirements in the United States.