Biomedical subjects

L R Beuchat

Publications and source records attributed to L R Beuchat.

At least 55 records · Page 3Linked to original sources

PubMed2001

Survival of salmonellae in pasteurized, refrigerated calcium-fortified orange juice.

Studies were done to determine the survival of salmonellae in orange juice as affected by fortification with calcium. Four brands of commercially pasteurized orange juice fortified with calcium (350 mg/240-ml serving) and nonfortified juice were inoculated separately with three types of inocula: strains of Salmonella Muenchen (inoculum 1), serotypes of human and animal origin (inoculum 2), and isolates from raw produce- and juice-associated outbreaks (inoculum 3). Juice inoculated with populations of 6.6 to 7.0 log10 CFU of Salmonella per ml was held at 4 degrees C for up to 32 days. The number of cells of inoculum 1 that survived in juice fortified with calcium lactate/tricalcium phosphate (CaL/TCP) was significantly lower (P < or = 0.05) (2.80 log10 CFU/ml) than in nonfortified juice (3.50 log10 CFU/ml) after 32 days' storage. Death of salmonellae in inocula 1 and 2 was less in juice fortified with TCP (3.21 and 3.33 log10 CFU/ml, respectively) than in the nonfortified juice (3.75 and 4.15 log10 CFU/ml, respectively). During the 32-day storage period, populations in inocula 1 and 3 showed significantly less inactivation (2.62 and 3.12 log10 CFU/ml, respectively) in juice fortified with calcium citrate (CC) than in nonfortified juice (3.14 and 3.60 log10 CFU/ml, respectively). There were no significant differences in the survival of Salmonella in juice fortified with calcium citrate malate (CCM) and nonfortified juice. Polymerase chain reaction (PCR) typing of randomly selected Salmonella colonies revealed that Salmonella Heidelberg in inoculum 2 and Salmonella Baildon and Salmonella Poona in inoculum 3 were the most prevalent at the end of the 32-day storage period at 4 degrees C, suggesting that serotypes selected for use in inocula differed in tolerance to acidic environments. This study reveals that the form of calcium used to fortify orange juice may affect the survival of Salmonella.

Animals↗

PubMed2001

Location of Escherichia coli O157:H7 on and in apples as affected by bruising, washing, and rubbing.

Confocal scanning laser microscopy (CSLM) was used to determine the location of Escherichia coli O157:H7 cells on the surface and in tissue of bruised Red Delicious cv. apples. Undamaged and bruised apples were inoculated by immersing in a suspension of E. coli O157:H7 cells transformed with a plasmid that encodes for the production of a green fluorescent protein. Apples were then washed in 0.1% (wt/vol) peptone water and/or rubbed with a polyester cloth and examined to determine if these treatments removed or introduced cells into lenticels, cutin, and cracks on the skin surface. Optical slices of the apples obtained using CSLM were examined to determine the depth at which colonization or attachment of cells occurred. Populations of E. coli O157:H7 on the surface of apples were determined to assess the effectiveness of washing and rubbing in physically removing cells. The location of cells on or in undamaged and bruised areas of apples that were not washed or rubbed did not differ significantly. However, washing apples resulted in an approximate 2-log reduction in CFU of E. coli O157:H7 per cm2 of apple surface. On unwashed apples, cells were detected at depths up to 30 microm below the surface. No E. coli O157:H7 cells were detected at locations more than 6 microm below the surface of washed apples. Cells that remained on the surface of rubbed apples appeared to be sealed within naturally occurring cracks and crevices in waxy cutin platelets. These cells may be protected from disinfection and subsequently released when apples are eaten or pressed for cider production.

Bacterial Adhesion↗

PubMed2000

Presence and changes in populations of yeasts on raw and processed poultry products stored at refrigeration temperature.

A study was undertaken to determine populations and profiles of yeast species on fresh and processed poultry products upon purchase from retail supermarkets and after storage at 5 degrees C until shelf life expiration, and to assess the potential role of these yeasts in product spoilage. Fifty samples representing 15 commercial raw, marinated, smoked, or roasted chicken and turkey products were analyzed. Yeast populations were determined by plating on dichloran rose bengal chloramphenicol (DRBC) agar and tryptone glucose yeast extract (TGY) agar. Proteolytic activity was determined using caseinate and gelatin agars and lipolytic activity was determined on plate count agar supplemented with tributyrin. Populations of aerobic microorganisms were also determined. Initial populations of yeasts (log10 cfu/g) ranged from less than 1 (detection limit) to 2.89, and increased by the expiration date to 0.37-5.06, indicating the presence of psychrotrophic species. Highest initial populations were detected in raw chicken breast, wings, and ground chicken, as well as in turkey necks and legs, whereas roasted chicken and turkey products contained less than 1 log10 cfu/g. During storage, yeast populations increased significantly (P < or = 0.05) in whole chicken, ground chicken, liver, heart and gizzard, and in ground turkey and turkey sausage. Isolates (152 strains) of yeasts from poultry products consisted of 12 species. Yarrowia lipolytica and Candida zeylanoides were predominant, making up 39 and 26% of the isolates, respectively. Six different species of basidiomycetous yeasts representing 24% of the isolates were identified. Most Y. lipolytica strains showed strong proteolytic and lipolytic activities, whereas C. zeylanoides was weakly lipolytic. Results suggest that yeasts, particularly Y. lipolytica, may play a more prominent role than previously recognized in the spoilage of fresh and processed poultry stored at 5 degrees C.

Animals↗

PubMed2000

Survival and growth of Salmonella baildon in shredded lettuce and diced tomatoes, and effectiveness of chlorinated water as a sanitizer.

An outbreak of salmonellosis associated with diced tomatoes occurred in the United States in 1999. Experiments were done to determine the efficacy of chlorine in killing Salmonella baildon, the causative serotype, inoculated onto shredded lettuce and diced tomatoes, and to determine survival characteristics of the organism on these produce items stored at 4 degrees C for up to 12 days and on tomatoes stored at 21 or 30 degrees C for up to 72 h. Populations of S. baildon in lettuce and tomatoes (pH 4.51 +/- 0.02) inoculated with 3.60 log10 and 3.86 log10 cfu/g, respectively, were reduced by less than 1 log when the produce was immersed for 40 s in a 120 or 200 microg/ml free chlorine solution. Produce inoculated with 0.60-0.86 log10 cfu/g was positive for the pathogen after treatment with 200 microg/ml chlorine. Initial populations of 3.28 and 3.40 log10 cfu/g of lettuce and tomatoes, respectively, decreased by about 2 log10 cfu/g during storage for 12 days at 4 degrees C. One of six samples of lettuce initially containing 0.28 log10 cfu of S. baildon per gram was positive after storage for 12 days, but the pathogen was not detected in tomatoes analyzed within 15 min of inoculation with 0.40 log10 cfu/g. While the number of viable cells decreased during storage at 4 degrees C, initial populations of 0.28 log10 cfu/g of shredded lettuce and 3.40 log10 cfu/g of diced tomatoes are not reduced to undetectable levels during storage at 4 degrees C for 12 days. Tolerance of S. baildon to an acidic pH (4.5) was not influenced by the pH (4.5, 5.8, or 7.2) of the medium in which it was grown, suggesting that this strain possesses unusual resistance to acid pH. The pathogen grew in diced tomatoes (pH 4.40 +/- 0.01) from an initial population of 0.79 log10 cfu/g to 5.32 and 7.00 log10 cfu/g within 24 h at 21 and 30 degrees C, respectively.

Chlorine↗

PubMed2000

Efficacy of allyl isothiocyanate in killing enterohemorrhagic Escherichia coli O157:H7 on alfalfa seeds.

Volatile compounds occurring in the essential oil of plants were tested for their efficacy in killing Escherichia coli O157:H7. Experiments using an agar disk assay revealed that exposure of the pathogen to 50 microl of eugenol, carvacrol, linalool, or methyl jasmonate in a 950-cc jar at 20, 37 or 47 degrees C for up to 48 h failed to inhibit colony formation. However, exposure to 8 microl of allyl isothiocyanate (AIT) (equivalent to 8.4 ppm in the air within the jar, if completely volatilized) resulted in more than a 7-log10 reduction in population of E. coli O157:H7 at 37 degrees C within 48 h; significant (P < or = 0.05) reduction in populations also occurred in the presence of 4 microl of AIT compared to 2 microl, which had no lethal affect. At 20 degrees C, the lethality of AIT was substantially less, although significant reduction occurred when disks were exposed to 8 or 10 microl of AIT compared to 4 or 6 microl and when exposed to 4 or 6 microl compared to 2 microl. Treatment with 10 microl of AIT for 5 h at 47 degrees C resulted in death of 6 log10 of E. coli O157:H7. The efficacy of AIT in killing E. coli O157:H7 on dry and wet alfalfa seeds was investigated. The pathogen, at an initial population of 2.7 log10 cfu/g of seed, was not recovered by direct plating (< 0.7 log10 cfu/g) or enrichment of wet seeds exposed to 50 microl of AIT/950-cc jar for 24 h at 37 or 47 degrees C. Exposure of dry seeds containing 2.9 log10 cfu of E. coli O157:H7 per g to an atmosphere containing 100 microl of AIT/950-cc jar (ca. 105 ppm AIT if completely volatilized) for 24 h at 47 degrees C did not eliminate viable E. coli O157:H7 cells. Unfortunately, the enhanced effectiveness of AIT in killing the pathogen on wet alfalfa seeds is offset by a dramatic reduction in seed viability. Nevertheless, the use of AIT as an alternative to chlorine for the purpose of killing E. coli O157:H7 and perhaps other pathogens on alfalfa seed holds promise. Factors that may influence conditions rendering increased sensitivity of E. coli O157:H7 to AIT without compromising seed viability should be investigated.

Escherichia coli O157↗

PubMed2000

Human pathogens associated with raw produce and unpasteurized juices, and difficulties in decontamination.

The ability of public health agencies to identify, through enhanced epidemiologic and surveillance techniques, raw fruits, vegetables, and unpasteurized juices as probable sources of infectious microorganisms, has undoubtedly resulted in increased numbers of documented outbreaks. Changes in agronomic, harvesting, distribution, processing, and consumption patterns and practices have also likely contributed to this increase. The risk of illness associated with raw produce and unpasteurized produce products can be reduced by controlling or preventing contamination, or by removing or killing pathogenic microorganisms by washing or treating them with sanitizers. However, the hydrophobic cutin, diverse surface morphologies, and abrasions in the epidermis of fruits and vegetables limit the efficacy of these treatments.

Journal Article↗

PubMed2000

Survival of Salmonella in peanut butter and peanut butter spread.

In 1996, the first documented outbreak of salmonellosis associated with the consumption of peanut butter was reported. This study was undertaken to determine survival characteristics of high (5.68 log10 cfu g(-1)) and low (1.51 log10 cfu g(-1)) inocula of a five-serotype mixture of Salmonella in five commercial peanut butters and two commercial peanut butter spreads. Populations in samples inoculated with 5.68 log10 cfu g(-1) and stored for 24 weeks at 21 or 5 degrees C decreased 4.14-4.50 log10 cfu g(-1) and 2.86-4.28 log10 cfu g(-1), respectively, depending on the formulation. The order of retention of viability was: peanut butter spreads > traditional (regular) and reduced sugar, low-sodium peanut butters > natural peanut butter. Differences in rates of inactivation are attributed to variation in product composition as well as size and stability of water droplets in the colloidal matrix, which may influence nutrient availability. With the exception of natural peanut butter, products initially inoculated with 1.51 log10 cfu of Salmonella g(-1) (32 cfu g(-1)) were positive for the pathogen after storage for 24 weeks at 5 degrees C. At 21 degrees C, however, with the exception of one peanut butter spread, all products were negative for Salmonella after storage for 24 weeks. Post-process contamination of peanut butter and spreads with Salmonella may to result in survival in these products for the duration of their shelf life at 5 degrees C and possibly 21 degrees C, depending on the formulation.

Arachis↗

PubMed2000

Survival of Escherichia coli O157:H7 in potato starch as affected by water activity, pH and temperature.

A study was done to determine the survival characteristics of Escherichia coli O157:H7 in potato starch powder as affected by aw (0.24-0.26, 0.51-0.52 and 0.75-0.78), pH (4.1 and 6.7) and temperature (4, 20 and 37 degrees C) over a 33-week storage period. Survival was enhanced as the aw decreased. The rate of death was higher as the storage temperature increased. Survival did not appear to be affected by pH. Since the composition of foods greatly affects the viability of E. coli O157:H7 at reduced aw, development of models to predict patterns of inactivation in a given food should be carried out using data generated from that food or one with very similar composition, aw and pH.

Escherichia coli O157↗

PubMed2000

Molecular characterization of Yarrowia lipolytica and Candida zeylanoides isolated from poultry.

Yeast isolates from raw and processed poultry products were characterized using PCR amplification of the internally transcribed spacer (ITS) 5.8S ribosomal DNA region (ITS-PCR), restriction analysis of amplified products, randomly amplified polymorphic DNA (RAPD) analysis, and pulsed-field gel electrophoresis (PFGE). ITS-PCR resulted in single fragments of 350 and 650 bp, respectively, from eight strains of Yarrowia lipolytica and seven strains of Candida zeylanoides. Digestion of amplicons with HinfI and HaeIII produced two fragments of 200 and 150 bp from Y. lipolytica and three fragments of 350, 150, and 100 bp from C. zeylanoides, respectively. Although these fragments showed species-specific patterns and confirmed species identification, characterization did not enable intraspecies typing. Contour-clamped heterogeneous electric field PFGE separated chromosomal DNA of Y. lipolytica into three to five bands, most larger than 2 Mbp, whereas six to eight bands in the range of 750 to 2,200 bp were obtained from C. zeylanoides. Karyotypes of both yeasts showed different polymorphic patterns among strains. RAPD analysis, using enterobacterial repetitive intergenic sequences as primers, discriminated between strains within the same species. Cluster analysis of patterns formed groups that correlated with the source of isolation. For ITS-PCR, extraction of DNA by boiling yeast cells was successfully used.

Animals↗

PubMed2000

Attachment of Escherichia coli O157:H7 to the surfaces and internal structures of apples as detected by confocal scanning laser microscopy.

Confocal scanning laser microscopy (CSLM) was used to demonstrate the attachment of Escherichia coli O157:H7 transformed with a plasmid encoding for green fluorescent protein (GFP) to the surface and within the internal structures of nonwaxed Red Delicious cv. apples. Apples at 2 or 25 degrees C were inoculated with an E. coli O157:H7 cell suspension at 2 or 25 degrees C. The effect of a negative temperature differential (cold inoculum, warm apple), a positive differential (warm inoculum, cold apple), and no differential (warm inoculum, warm apple), in combination with a pressure differential (atmospheric versus 10,130 Pa), on the attachment and infiltration of cells was determined. CSLM stereo images of external surfaces of apples subjected to all combinations of test parameters showed preferential cellular attachment to discontinuities in the waxy cuticle on the surface and to damaged tissue surrounding puncture wounds, where the pathogen was observed at depths up to 70 microm below the skin surface. Attachment to lenticels was sporadic but was occasionally observed at depths of up to 40 microm. Infiltration through the floral tube and attachment to seeds, cartilaginous pericarp, and internal trichomes were observed in all apples examined, regardless of temperature differential during inoculation. The pressure differential had no effect on infiltration or attachment of E. coli O157:H7. Image analysis to count cells at various depths within tissues was used to quantitatively compare the extent of infiltration into various apple structures as well as the effects of the temperature differential. Puncture wounds harbored greater numbers of the pathogen at greater depths than did other sites examined. Attachment or infiltration of cells was greater on the intact skin and in lenticels, russet areas, and the floral tube of apples inoculated under a negative temperature differential compared to those inoculated under no temperature differential. The results suggest that E. coli O157:H7 attached to internal core structures or within tissues of apples may evade decontamination treatments. Interventions designed to deliver disinfectants to these locations or to remove viable cells of E. coli O157:H7 and other pathogens from apples by other means need to be developed and validated.

Animals↗

PubMed2000

PCR detection of Salmonella enterica serotype Montevideo in and on raw tomatoes using primers derived from hilA.

Salmonellae have been some of the most frequently reported etiological agents in fresh-produce-associated outbreaks of human infections in recent years. PCR assays using four innovative pairs of primers derived from hilA and sirA, positive regulators of Salmonella invasive genes, were developed to identify Salmonella enterica serotype Montevideo on and in tomatoes. Based on examination of 83 Salmonella strains and 22 non-Salmonella strains, we concluded that a pair of hilA primers detects Salmonella specifically. The detection limits of the PCR assay were 10(1) and 10(0) CFU/ml after enrichment at 37 degrees C for 6 and 9 h, respectively. When the assay was validated by detecting S. enterica serotype Montevideo in and on artificially inoculated tomatoes, 10(2) and 10(1) CFU/g were detected, respectively, after enrichment for 6 h at 37 degrees C. Our results suggest that the hilA-based PCR assay is sensitive and specific, and can be used for rapid detection of Salmonellae in or on fresh produce.

Bacterial Proteins↗

PubMed2000

Factors influencing inactivation of Salmonella enteritidis in hard-cooked eggs.

The inside of a hen's egg, once considered sterile, is now known to occasionally harbor Salmonella Enteritidis. At least two recent outbreaks of salmonellosis in which Salmonella Enteritidis PT34 was involved have been associated with hard-cooked eggs. This study was undertaken to compare D56 degrees C values of Salmonella Senftenberg 775W and six strains of Salmonella Enteritidis isolated from outbreaks associated with eggs. D56 degrees C values for Salmonella Enteritidis in liquid egg yolk ranged from 5.14 to 7.39 min; the D56 degrees C value for Salmonella Senftenberg was 19.96 min. The two PT34 strains from outbreaks associated with hard-cooked eggs did not exhibit significantly higher resistance to heat compared with two PT4 strains and one strain each of PT8 and PT13a. A PT4 strain and a PT34 strain of Salmonella Enteritidis were separately inoculated (10(7) to 10(8) CFU) into the yolk of medium and extra large shell eggs at 10 and 21 degrees C, and survival was monitored using two cooking methods: (i) placing eggs in water at 23 degrees C, heating to 100 degrees C, removing from heat, and holding for 15 min (American Egg Board method) and (ii) placing eggs in water at 100 degrees C, then holding for 15 min at this temperature. Within the 15-min holding periods, inactivation was more rapid using the method recommended by the American Egg Board compared with method 2. Within each cooking method, inactivation was most rapid in medium eggs initially at 21 degrees C. The PT4 strain survived in yolk of extra large eggs initially at 10 degrees C when eggs were held in boiling water 9 min using method 2. The final temperature of the yolk in these eggs was 62.3 +/- 2 degrees C. Of the two methods evaluated for hard cooking eggs, the American Egg Board method is clearly most effective in killing Salmonella Enteritidis in the yolk.

Animals↗

PubMed2000

Comparison of aqueous chemical treatments to eliminate Salmonella on alfalfa seeds.

Several outbreaks of salmonellosis associated with alfalfa sprouts have been documented in the United States since 1995. This study was undertaken to evaluate various chemical treatments for their effectiveness in killing Salmonella on alfalfa seeds. Immersing inoculated seeds in solutions containing 20,000 ppm free chlorine (Ca[OCl]2), 5% Na3PO4, 8% H2O2, 1% Ca(OH)2, 1% calcinated calcium, 5% lactic acid, or 5% citric acid for 10 min resulted in reductions of 2.0 to 3.2 log10 CFU/ g. Treatment with 1,060 ppm Tsunami or Vortex, 1,200 ppm acidified NaClO2, or 5% acetic acid were less effective in reducing Salmonella populations. With the exceptions of 8% H2O2, 1% Ca(OH)2, and 1% calcinated calcium that reduced populations by 3.2, 2.8, and 2.9 log10 CFU/g, respectively, none of treatments reduced the number of Salmonella by more than 2.2 log10 CFU/g without significantly reducing the seed germination percentage. Treatment with 5% acetic, lactic, or citric acids substantially reduced the ability of seeds to germinate. Treatment with 1% Ca(OH)2 in combination with 1% Tween 80, a surfactant, enhanced inactivation by 1.3 log10 CFU/g compared to treatment with 1% Ca(OH)2 alone. Presoaking seeds in water, 0.1% EDTA, 1% Tween 80, or 1% Tween 80 plus 0.1% EDTA for 30 min before treatment with water, 2,000 ppm NaOCl, or 2% lactic acid had a minimal effect on reducing populations of Salmonella. Results indicate that, although several chemical treatments cause reductions in Salmonella populations of up to 3.2 log10 CFU/g initially on alfalfa seeds when analyzed by direct plating, no treatment eliminated the pathogen, as evidenced by detection in enriched samples.

Acetic Acid↗

PubMed2000

Detection of guaiacol produced by Alicyclobacillus acidoterrestris in apple juice by sensory and chromatographic analyses, and comparison with spore and vegetative cell populations.

Spoilage of fruit juice by Alicyclobacillus acidoterrestris is characterized by a distinct medicinal or antiseptic off odor attributed to guaiacol, a metabolic by product of the bacterium. Detection of low populations of A. acidoterrestris that would precede sensory detection of guaiacol would enable juice processors to select appropriate processing and storage conditions that would minimize or eliminate spoilage. The objective of this study was to determine the recognition threshold of guaiacol in apple juice by sensory analysis and the population of A. acidoterrestris and incubation time at 21 and 37 degrees C necessary for chemical detection of guaiacol. Commercially sterilized apple juice (pH 3.54 +/- 0.04, 11.3 +/- 0.3 degrees Brix) was inoculated with a five-strain mixture of A. acidoterrestris spores (2.98 log10 CFU/ml) and stored at 21 or 37 degrees C for up to 61 days. Using an experienced sensory panel and the forced-choice ascending concentration method of limits, the best estimate threshold (BET) for recognition of guaiacol added to uninoculated apple juice was 2.23 ppb. Numbers of A. acidoterrestris spores and cells in inoculated juice remained constant during the 61-day storage period; however, the panel detected (P < or = 0.01) guaiacol in juice stored at 37 degrees C within 8 days. At three of four sampling times ranging from 13 to 61 days at which the sensory panel detected (P < or = 0.001) guaiacol, concentrations of 8.1 to 11.4 ppb were detected by chromatographic analysis. The panel detected (P < or = 0.1 to P < or = 0.01) guaiacol in five samples stored at 21 to 37 degrees C for 8 to 61 days in which the compound was not detected by chromatographic analyses. It appears that guaiacol content in apple juice inoculated with A. acidoterrestris is not always correlated with numbers of cells, and the limit of sensitivity of chromatographic quantitation of the compound is higher than the BET.

Bacillus↗

PubMed2000

Fate of Shigella sonnei on parsley and methods of disinfection.

Outbreaks of shigellosis associated with chopped parsley used as a garnish for foods occurred in four states in the United States and in two Canadian provinces in 1998. This prompted a study to determine survival and growth characteristics of Shigella sonnei inoculated onto raw parsley. Two inoculum levels (approximately 10(3) and 10(6) CFU/g) were applied to parsley leaves, portions of which were then chopped. Inoculated whole and chopped parsley leaves were held at 4 degrees C or 21 degrees C for up to 14 days. Initial populations of the organism on chopped parsley receiving high or low levels of inoculum increased by approximately 3 log10 CFU/g, within 1 day at 21 degrees C. Populations of S. sonnei on inoculated chopped or whole parsley leaves held at 4 degrees C decreased by 2.5 to 3.0 log10 CFU/g during a 14-day storage period. The pathogen multiplied, without a lag phase, on inoculated (2.72 log10 CFU/g) chopped parsley held at 21 degrees C, exceeding 6 log10 CFU/g within 24 h. Treatment of inoculated whole parsley leaves with vinegar containing 5.2% (vol/vol) acetic acid or 200 ppm free chlorine for 5 min at 21 degrees C reduced the population of S. sonnei by more than 6 log10 CFU/g, whereas treatment with vinegar containing 7.6% acetic acid or 250 ppm free chlorine reduced initial populations of 7.07 and 7.26 log10 CFU/g, respectively, to undetectable levels (<0.6 log10 CFU/g). These studies revealed that S. sonnei can grow rapidly on chopped parsley held at ambient temperature and remain viable for at least 14 days at 4 degrees C. Treatment of contaminated parsley with vinegar or chlorinated water offers a simple method to reduce markedly or eliminate the pathogen in food-service or home settings.

Acetic Acid↗

PubMed2000

Efficacy of disinfectants in killing spores of Alicyclobacillus acidoterrestris and performance of media for supporting colony development by survivors.

Alicyclobacillus has recently emerged as a spoilage microorganism of concern in a wide range of pasteurized fruit products. The focus of this study was to determine the efficacy of chemical disinfectants in killing Alicyclobacillus acidoterrestris spores. Direct plating media were evaluated for their suitability to support germination and outgrowth of spores surviving exposure to these disinfectants. Significant (P < or = 0.05) reductions of about 2.2, 0.4, and 0.1 logs in the number of viable A. acidoterrestris spores in a five-strain mixture were achieved when spores were suspended in 200 ppm chlorine, 500 ppm acidified sodium chlorite, or 0.2% H2O2 solutions, respectively, for 10 min at 23 degrees C. When treated with either 1,000 ppm chlorine or 4% H2O2, the number of spores was reduced by more than 5 logs. Treatment with 8% trisodium phosphate or 80 ppm Tsunami did not significantly reduce numbers of viable spores. Spores of individual strains of A. acidoterrestris varied little in resistance to the same chemical treatment. K agar (pH 3.7) was judged best for recovering chemically treated spores, compared to orange serum agar (pH 5.0) and potato dextrose agar (pH 3.5). Experiments were done to determine the effectiveness of chemical treatments in killing a mixed-strain inoculum of A. acidoterrestris spores on the surface of apples. Treatment with 500 ppm chlorine or 1,200 ppm acidified sodium chlorite for 1 min significantly (P < or = 0.05) reduced the number of viable spores, but reductions were less than 1 log. Hydrogen peroxide (2%) was ineffective in killing spores remaining on the apple skin after treatment.

Agar↗

PubMed1999

Survival of multidrug-resistant Salmonella typhimurium DT104 in egg powders as affected by water activity and temperature.

A study was done to determine if a four-strain mixture of multidrug-resistant Salmonella typhimurium definitive type 104 (DT104) cells and a four-strain mixture of S. typhimurium non-DT104 cells differed in ability to survive in whole egg powder, whole egg powder supplemented with corn syrup solids (38%) and salt (1.9%), egg yolk powder, and egg white powder as affected by a(w)(0.29-0.37 and 0.51-0.61) during storage at 13 or 37 degrees C for 8 weeks. Rates of inactivation of S. typhimurium DT104 and non-DT104 cells were similar within each set of test parameters. With the exception of whole egg powder supplemented with corn syrup solids and salt, death was enhanced at a(w) 0.29-0.37 compared to a(w) 0.51-0.61 when powders were stored at 13 degrees C. Survival of cells in whole egg powder supplemented with corn syrup solids and salt was significantly (P < or = 0.05) higher compared to survival in other egg powders stored at 13 degrees C. The opposite trend occurred in powders at a(w) 0.5-0.61 stored at 37 degrees C. Survival of S. typhimurium DT104 and non-DT104 cells at initial populations of 5.01-5.39 log10 cfu/g of egg white powder containing 4.9, 6.1, or 8.2% moisture at 54 or 82 degrees C for 7 days or 8 h, respectively, was determined. Rates of inactivation of DT104 and non-DT104 cells did not differ. Both cell types were detected in egg white powder containing 4.9% moisture but not in powder containing 8.2% moisture when held at 54 degrees C for 7 days. Heating at 82 degrees C for 8 h failed to eliminate 5 log10 S. typhimurium per g of egg white powder, regardless of the moisture content.

Drug Resistance, Multiple↗

PubMed1999

Fermentation of low-salt miso as affected by supplementation with ethanol.

Steam-cooked soybeans and rice koji were combined (1:1, w/w), mixed with 5% (w/w) NaCl and ground into a fine paste. Samples (30 g) were deposited in nylon/polyethylene plastic bags and supplemented with 10 ml of aqueous ethanol solutions to give concentrations of 0, 2.5, 5, 7.5, 10, 15, 20, and 25% ethanol. Mixtures were homogenized, sealed, and incubated at 28 degrees C for eight weeks. Mold populations were less than 3 log10 CFU/g in all miso products after four weeks of fermentation. Yeast populations increased to 6.1 log10 CFU/g in the control (0% added ethanol) during the first week of fermentation and remained stable throughout the eight-week fermentation period. Yeasts were not detected in products containing 5-25% ethanol. Populations of lactic acid bacteria (LAB) increased to 6 log10 CFU/g after one week of fermentation in products containing 0 and 2.5% ethanol. However, after eight weeks of fermentation, LAB populations in all products were less than 4 log10 CFU/g. Rapid decreases in pH occurred only in products supplemented with 0 or 2.5% ethanol. Percentages of soluble protein in miso products containing various ethanol concentrations during the eight-week fermentation period revealed that protease activity was still active or not greatly inhibited in products supplemented with less than 10% ethanol. In comparison, koji enzymes were comparatively less affected by ethanol than were populations of molds, yeasts, and LAB. Total soluble carbohydrate and glucose contents were higher in products supplemented with 5, 7.5 and 10% ethanol than in other products. Discoloration (browning) during fermentation occurred most rapidly in products supplemented with 5 or 7.5% ethanol. Sensory evaluation of the low-salt (5%) product supplemented with 7.5% ethanol and fermented for eight weeks revealed normal or enhanced flavor ratings compared to ratings for a commercial product.

Aspergillus oryzae↗