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Biomedical subjects

M L Speck

Publications and source records attributed to M L Speck.

At least 19 recordsLinked to original sources
PubMed1980

Adherence as a method of differentiating virulent and avirulent strains of Vibrio parahaemolyticus.

Usually only Kanagawa-positive strains of Vibrio parahaemolyticus are considered virulent; yet, a significant portion of V. parahaemolyticus food poisonings appear to be caused by Kanagawa-negative strains. Therefore, additional and more accurate measurements of a strain's food-poisoning potential are needed. Adherence of V. parahaemolyticus to human fetal intestinal (HFI) cells in vitro seems to offer this information. All strains of V. parahaemolyticus adhered to the HFI cells, but the degree of adherence was related to a number of factors. These included the age of the culture, the strain's Kanagawa reaction and source, the length of time the bacteria were exposed to the HFI cells, and the composition of the growth medium. Cells harvested during the late log phase of growth adhered more intensely than those harvested from the late stationary phase. Virulent strains, i.e., those involved in food poisoning, were observed to have a high adherence ability regardless of their Kanagawa reaction, whereas Kanagawa-negative strains isolated from seafood exhibited weak adherence intensities. Kanagawa-positive strains isolated from seafood adhered strongly to the HFI cells. The difference between the virulent and avirulent strains was quantitative in nature, and the greatest differences in adherence intensities were observed after short (10 to 15 min) exposure times. The presence of ferric iron in the growth medium was found to increase the adherence intensities of the virulent strains.

Bacteriological Techniques↗
PubMed1979

Repair detection procedure for enumeration of fecal coliforms and enterococci from seafoods and marine environments.

The repair detection procedure of Speck et al. (Appl. Microbiol. 29:549-550, 1975) was adapted for the enumeration of coliforms, fecal coliforms, and enterococci in seafood and environmental samples. Samples were pour plated with Trypticase soy agar, followed by a 1- to 2-h incubation to effect repair; the plates were then overlaid with the selective medium and incubated. Violet red bile agar and an incubation temperature of 45 degrees C were used as the selective conditions for fecal coliforms, and KF streptococcal agar was used for the enumeration of enterococci. The method was more efficient than the standard most-probable-number method for fecal coliform enumeration and also allowed enumeration of the injured cells, which might have remained undetected when selective medium in the most-probable-number method was used. The repair detection method effectively recovered the injured portion of the population of enterococci capable of growing on KF streptococcal agar. The repair enumeration method was not suitable for coliforms in marine samples because associative marine bacteria mimicked coliforms in violet red bile agar plates incubated at 35 degrees C. The marine bacteria did not grow at 45 degrees C and therefore did not interfere with fecal coliform enumeration.

Escherichia coli↗
PubMed1978

Plating procedure for the enumeration of coliforms from dairy products.

A "repair-detection" procedure consisting of pour plating of food samples with Trypticase soy agar, followed by 1-h repair incubation at room temperature and subsequent overlay with violet red bile agar, was found to be an effective method for the detection of injuried and uninjuried coliforms from dairy products. This method was relatively less effective for the detection of coliforms in many semipreserved foods as compared with dairy products, but more effective than the most-probable-number method.

Bacteriological Techniques↗
PubMed1977

Deconjugation of bile acids by intestinal lactobacilli.

Lactobacillus species normally found in the intestinal tract of humans varied in the ability to deconjugate bile acids, whereas laboratory strains of Lactobacillus acidophilus deconjugated both glycocholate and taurocholate. All isolates of L. acidophilus from human feces deconjugated taurocholate, whereas only one of six deconjugated glycocholate. None of 13 isolates identified as L. casei deconjugated taurocholate, whereas 9 deconjugated glycocholate. The deconjugating system of L. acidophilus appeared to be constitutive, required low oxidation-reduction potential, and was most active at pH 6. No degradation beyond deconjugation was detected.

Cholic Acids↗
PubMed1977

Use of the Minitek system for characterizing lactobacilli.

Incubation of inoculated substrates of the Minitek system in anaerobic GasPak jars provided a method that produced results comparable to those of conventional tubed media for characterizing species of Lactobacillus. The use of sterile mineral oil to overlay inoculated substrate disks was responsible for erroneous results.

Anaerobiosis↗
PubMed1976

Stabilization of a psychrotrophic Pseudomonas protease by calcium against thermal inactivation in milk at ultrahigh temperature.

The heat-stable extracellular protease of Pseudomonas sp. (isolate MC60) was investigated. Heat resistance of the enzyme in milk at sterilization temperature was dependent on the presence of Ca2+. The half-life of the enzyme at ultrahigh temperature (149 C) in skim milk or milk-salts buffer with Ca2+ was approximately 7.0 s. Treatment of milk with chelators completely removed the heatstabilizing effect of milk. The enzyme was partially purified by ammonium sulfate precipitation and column chromatography on Sephadex G-100. At 21 C the enzyme retained greater than 85% activity after exposure to pH values between 5 and 10. Enzyme activity was reduced by metal chelating agents. Both Ca2+ and Zn2+ were required for optimal enzyme activity. Molecular weight was estimated at 48,000 by gel filtration.

Acrylic Resins↗
PubMed1976

Interactions among lactobacilli and man.

Lactobacilli and other lactic acid bacteria have been involved intimately with man for centuries. The associations have involved manufacture of various human foods as well as performance of various beneficial interactions in different parts of the human body. Renewed interests in the role of the intestinal microflora again have focused on the intestinal lactobacilli, particularly Lactobacillus acidophilus.

Animals↗
PubMed1976

Effect of psychrotrophic bacteria from raw milk on milk proteins and stability of milk proteins to ultrahigh temperature treatment.

The effects of psychrotroph growth in raw milk on proteins of mils and on the response of milk proteins to heat treatments with ultrahigh temperature were studied. Ten gram-negative psychrotrophs isolated from raw milk readily attacked raw milk proteins. Kappa- and beta-casein were most susceptible although some of the isolates also attacked the whey proteins. Detectable proteolysis did not require large psychrotroph populations. A 10 to 20% decrease in kappa-casein during 2 days at 5 C accompanied growth of one isolate to a population of only 10,000/ml. Growth of psychrotrophs in raw milk predisposed the proteins to deleterious effects of ultrahigh temperature treatments. Ultrahigh temperature treatment by direct steam injection had little effect on raw milk caseins and decreased alpha-lactalbumin and beta-lactoglobulin by 21% and 34%, respectively. Milk that had undergone proteolysis exhibited decreased detectable kappa-, beta-, and alphas-caseins and increased loss of beta-lactoglobulin as a result of ultrahigh temperature treatment. Milk suffering extensive kappa-casein degradation coagulated during ultrahigh temperature treatment. Coagulation during or shortly after heating increased with severity of heat treatment and size of psychrotroph population.

Animals↗
PubMed1975

Detection of Lactobacillus acidophilus in feces of humans, pigs, and chickens.

Lactobacilli in fecal material from humans, pigs, and chickens were enumerated on lactobacillus selective agar (LBS). In all samples, higher numbers of lac-tobacilli were detected when plates were incubated in a system flushed with CO2 rather than in air. Much higher numbers of bacteria from human feces were detected when the LBS agar plates were incubated anaerobically in a hydrogen-carbon dioxide atmosphere (GasPak) than when incubated in CO2. The bacteria from human feces isolated on LBS agar incubated anaerobically were predominately bifidobacteria. Cultures from all three sources isolated on LBS agar incubated under CO2 were lactobacilli, including Lactobacillus acidophilus. Differences were observed in biochemical characteristics of some of the L. acidophilus isolated from all three sources. Guanine plus cytosine base ratios of deoxyribonucleic acid isolated from L. acidophilus cultures from humans were lower, in most cases, than those from pigs and chickens.

Agar↗
PubMed1975

Heat resistant proteases produced in milk by psychrotrophic bacteria of dairy origin.

Production of heat resistant proteases by psychrotrophs growing in milk, resistance of such proteases to ultrahigh temperature treatments and action of these enzymes on milk were studied. All of the psychrotrophs obtained from raw milk produced proteases that survived 149 C for 10s. Seventy to ninety percent of the raw milk samples contained psychrotrophs capable of producing heat resistant proteases. The protease chosen as a model was resistant to heat treatments at 110 to 150 C, and the inactivation parameters suggested that thermal destruction of heat resistant proteases would damage the milk severely. The casein content and pH of normal milk were suitable for protease action, and the protease was quite active at normal and elevated room temperatures. The protease rapidly spoiled sterile milk with the development of bitter flavor, clearing, or coagulation; and the susceptibility of sterile milk to protease increased during storage of the milk.

Animals↗
PubMed1974

Relationship of cellular fatty acid composition to survival of Lactobacillus bulgaricus in liquid nitrogen.

Concentrated cultures of Lactobacillus bulgaricus were prepared by resuspending cells grown in semisynthetic media in sterile 10% non-fat milk solids. The concentrated cultures were frozen in liquid nitrogen for 24 h. The cell suspensions exhibited decreased viability after storage, and the amount of death varied among the different strains tested. Storage stability of all strains examined was improved by supplementing the growth medium with sodium oleate. Radioisotopes were used to study the fate of sodium oleate with L. bulgaricus NCS1. [1-(14)C]sodium oleate was incorporated solely into the lipid portion of the cells, including both neutral and polar lipids. The fatty acid composition of L. bulgaricus NCS1, NCS2, NCS3, and NCS4 grown with and without sodium oleate was studied. The major fatty acids of strains NCS1, NCS2, and NCS3 grown without sodium oleate were dodecanoic, tetradecanoic, hexadecanoic, hexadecenoic, and octadecenoic acids. In addition to these, strain NCS4 contained C(19) cyclopropane fatty acid. The major fatty acids of all strains grown with sodium oleate were tetradecanoic, hexadecanoic, hexadecenoic, octadecenoic, and C(19) cyclopropane fatty acids. All strains grown in broth containing sodium oleate contained larger amounts of octadecenoic and C(19) cyclopropane fatty acid, and less saturated fatty acids than when grown without sodium oleate. Statistical analyses indicated that C(19) cyclopropane fatty acid was most closely related to stability of the lactobacilli in liquid nitrogen. A negative regression line that was significant at P < 0.001 was obtained when the cellular content of this fatty acid was plotted against death.

Carbon Radioisotopes↗
PubMed1974

Relationship of cellular components to the stability of concentrated lactic streptococcus cultures at -17 C.

Concentrated cultures of lactic streptococci varied with respect to survival at -17 C. Cells of each strain grown at pH 6.0 were more stable to freezing than were those grown statically. The lipid fraction of the cells from static cultures was important in preventing death during freezing. As the percentage of octadecenoic acid in the cellular lipids from different cultures increased, the percentage of survivors decreased. Capsular material associated with cells from cultures grown both statically and at pH 6.0 was also important in protecting the cells at -17 C. The amount of capsular material, measured as percentage of cellular glucose, varied among the cultures tested. Cultures containing larger amounts of the capsular material were more resistant to the stress of freezing than those containing low levels.

Cell Survival↗
PubMed1974

Recovery of heated Clostridium perfringens type A spores on selective media.

The enumeration of Clostridium perfringens spores on sulfite-polymyxin-sulfadiazine agar (SPS), tryptone-sulfite-neomycin agar (TSN), Shahidi-Ferguson-perfringens agar (SFP), tryptone-sulfite-cycloserine agar (TSC), and TSN lacking antibiotics (BASE) was studied. The spores were heated at 105 to 120 C by the capillary-tube method. The media were about equally efficient for the enumeration of heat-activated spores. Efficiency of the media for the recovery of spores surviving heat treatments at ultrahigh temperatures varied as follows: TSC >/= SFP > BASE > SPS > TSN. Greater recovery when survivors were enumerated on TSC or SFP was attributed to germination of injured spores by the lysozyme present in the egg yolk emulsion used in these media. Low recovery of survivors on TSN and SPS was due to both the absence of lysozyme and inhibition of injured spores by the selective agents of these media. Recovery of heated spores was reduced greatly by polymyxin, neomycin, and kanamycin, and slightly by sulfadiazine and D-cycloserine. The addition of lysozyme to SPS or TSN did not improve the percentage of heat-injured spores recovered because the selective agents of these media interfered with the action of lysozyme. The suitability of the selective media for the enumeration of survivors was greatly affected by the presence of certain foods.

Agar↗
PubMed1974

Antagonism of lactic streptococci toward Staphylococcus aureus in associative milk cutures.

The inhibition of growth of Staphylococcus aureus by lactic streptococci in associative cultures in milk was not due to hydrogen peroxide produced by the streptococci. Dialyzed whey from the milk culture of lactic streptococci was more inhibitory than dialyzed whey from milk acidified with lactic acid, indicating that material other than lactate was also involved. Analyses of cation and anion exchange fractions from the dialyzed whey showed that only the neutral fraction was inhibitory.

Animals↗
PubMed1973

Discrepancies in the enumeration of Escherichia coli.

Stationary-phase cells of Escherichia coli were enumerated by the pour plate method on Trypticase soy agar containing 0.3% yeast extract (TSYA), violet red-bile agar, and desoxycholate-lactose agar, and by the most-probable-number method in Brilliant Green-bile broth and lauryl sulfate broth. Maximum counts were assumed to be those on TSYA. In general, numbers detected were lower with the selective solid media and higher with the selective liquid media. Inhibitory effects, especially on selective solid media varied with the strains of E. coli. The lower detection on selective solid media was partly due to the stress induced in some cells by the temperature of the melted media used in the pour plate method. These cells apparently failed to repair and form colonies in the selective media. Improved detection on the selective solid media was achieved by using 1% nonfat milk solids, 1% peptone, or 1% MgSO(4).7H(2)O in the dilution blanks. Higher detection on selective agar media was effected by surface plating or by surface-overlay plating of the cells. The surface-overlay method appeared to be superior for the direct enumeration of E. coli in foods.

Agar↗